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Why does liver wrap around inferior vena cava?

Why does liver wrap around inferior vena cava?


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As shown in the image, the liver wraps around inferior vena cava, which takes blood from liver via hepatic veins. Is there an advantage of having the inferior vena cava closer to the liver rather than abdominal aorta? I am guessing it has to do with lower blood pressure in the veins, but I want to check.

It could also be evolutionary thing that has no reason for such structure, but that wrapping around structure seems to have a purpose.


Lesson Explainer: The Liver Biology

In this explainer, we will learn how to describe the structure of the liver and its role in excretion.

The liver is an organ found in the human body. Did you know that your liver is the only organ in your body that can regenerate itself? This means that up to

of it can be removed and donated to someone else, in a process known as living-donor liver transplantation. Following transplantation, the liver immediately starts to regenerate, both in the donor’s body and in the body of the person who received the transplant. Within only

weeks , both livers should have almost completely regenerated.

The liver is a large organ made up of two lobes. It is found in your abdomen, and you can see in Figure 1 from its position in the human body that it is part of the digestive system. It is one of the accessory organs of the digestive system. This means that food does not directly pass through it, but it rather assists in the digestion of food by producing bile. Although the liver has many functions, in this explainer, we are going to focus on its role in detoxification and excretion.

Key Term: Liver

The liver is a large lobed organ in the abdomen of vertebrates that is responsible for various functions, including bile production, detoxification, and excretion.

Excretion is a process that occurs in the cells, in which the waste products of their metabolic reactions are removed. These waste products may, for example, be carbon dioxide produced during respiration in muscle cells. A common misconception is that excretion and egestion are the same thing. While excretion removes metabolic waste formed by the cells, egestion refers to the final removal of undigested waste products as feces.

Many metabolic waste products removed from the cells by excretion are broken down by the liver, before being egested or removed from the body. These waste products are excreted from other body cells and transported via the bloodstream to the liver. As some of these substances can be toxic, the liver then breaks down and neutralizes them. This process is called detoxification.

Definition: Excretion

Excretion is the removal of the waste products of metabolism from the body.

Definition: Detoxification

Detoxification is a process in which harmful or toxic substances in the body are broken down or neutralized.

Example 1: Explaining Excretion

The liver is vital for excretion in humans. Which of the following best explains excretion?

  1. Excretion is the removal of excess water and food from the body.
  2. Excretion is the production of sweat from the sweat glands in the skin.
  3. Excretion is the removal of the waste products of metabolism from the body.
  4. Excretion is the process by which waste products are converted into useful compounds for the body.

Answer

We need to take care when answering questions asking for the best explanation. This is because although they are multiple-choice questions, they are not easy as more than one answer may technically be correct.

Excretion is a process in which the waste products of metabolic reactions in the cells are removed. Metabolic reactions include the synthesis of proteins or the breakdown of glucose during respiration. These waste products may, for example, be carbon dioxide produced during respiration in muscle cells. The correct definition of excretion must, therefore, include the waste products of metabolic reactions.

A common misconception is that excretion and egestion are the same thing. While excretion refers to the removal of metabolic waste formed by the cells, egestion refers to the final removal of undigested waste products as feces. Excess water is expelled from the body as urine, and excess food is either stored as fats or egested from the body as feces. Therefore, this does not describe what excretion is, as food is not a metabolic product and can only be egested.

Sweat, which consists of water and dissolved salts, is an example product of metabolism, which is excreted from the body cells as a way to lower the body’s temperature. However, as it is not the only substance excreted, this is not our best explanation.

The liver, an organ of excretion, does store useful substances, such as vitamins and minerals, and also converts some toxic compounds into less toxic ones. These are different functions, however, and converting waste products into other useful substances is not considered as excretion.

Therefore, the best explanation of excretion is that excretion is the removal of the waste products of metabolism from the body.

Let’s look at the macroscopic structures, which are those visible to the naked eye, of the liver and its associated blood vessels. These are shown in Figure 2.

The liver plays a role in the digestive system by producing bile. Bile is used in the small intestine to emulsify the many lipids that we ingest in our food. Emulsification increases the surface area of lipids, which lipase enzymes can act on, to increase the rate of lipid digestion. After being produced by the liver, bile is transported to the gallbladder, which, as you can see in Figure 2, is connected to the liver by bile ducts. Bile is stored in the gallbladder until food containing lipids is eaten and bile is needed in the small intestine.

The prefix hepato- comes from the Greek word meaning “liver.” For this reason, structures in the liver contain the word hepatic. For example, the three major blood vessels in the liver are called the hepatic artery, the hepatic vein, and the hepatic portal vein, and the cells of the liver are called hepatocytes.

Key Term: Hepatocyte

A hepatocyte is the specific term used to refer to a liver cell.

Hepatocytes have many functions and are, therefore, very active cells, using up to

of the total energy in the body. They require lots of oxygen to carry out aerobic respiration to release the energy needed for these functions.

Arteries always carry blood away from the heart. The hepatic artery carries oxygen-rich blood from the heart to the liver, where it then diffuses into the hepatocytes. The hepatic artery delivers oxygen not only to the hepatocytes in the liver, but also to adjacent organs, such as the stomach, duodenum of the small intestine, pancreas, and gallbladder.

Key Term: Hepatic Artery

The hepatic artery carries oxygenated blood to the liver and its adjacent organs from the heart.

Veins always carry blood to the heart. There are two different veins associated with the liver: the hepatic vein and the hepatic portal vein.

The hepatic vein carries deoxygenated blood from the liver to the heart, traveling via a larger blood vessel called the inferior vena cava. Hepatocytes produce carbon dioxide during aerobic respiration, which moves into the blood. The blood, which is now deoxygenated, is carried by the hepatic vein back to the heart. From the heart, this blood travels to the lungs to be oxygenated, before cycling around the body once more.

Key Term: Hepatic Vein

The hepatic vein carries deoxygenated blood from the liver via the inferior vena cava to the heart.

The liver receives two blood supplies: one rich in oxygen from the hepatic artery and the other rich in nutrients and waste products from the hepatic portal vein.

The hepatic portal vein travels from the intestines, spleen, pancreas, and gallbladder to the liver. It carries blood that is rich in not only nutrients but also metabolic waste products and toxins to the hepatocytes. This is because the liver is the main organ of detoxification in the body. The volume of blood that the hepatic portal vein carries to the liver is three times the volume arriving via the hepatic artery, as it is carrying so many nutrients and toxins.

The blood in the hepatic portal vein carries lots of the products of digestion. For example, especially following a meal, the blood in the hepatic portal vein becomes rich in glucose, amino acids, cholesterol, vitamins, and minerals. Useful substances, such as vitamins and minerals, are stored by the hepatocytes until they are needed. At this point, they are released into the bloodstream to travel to the body cells as required.

The hepatic portal vein also transports substances that need to be detoxified, neutralized, and excreted, such as excess proteins and carbon dioxide. Furthermore, the hepatic portal vein transports hormones, such as insulin and glucagon, from the pancreas to the hepatocytes.

Example 2: Identifying the Key Blood Vessels of the Liver

The diagram provided is a basic outline of the human liver, with the names of some key blood vessels removed.

  1. What blood vessel is indicated by X?
  2. What blood vessel is indicated by Y?
  3. What blood vessel is indicated by Z?

Answer

The hepatic artery carries oxygenated blood from the heart to the liver, where it then diffuses into the hepatocytes (liver cells). Hepatocytes require a lot of oxygen to carry out aerobic respiration to release the energy needed for their many functions. The hepatic artery delivers oxygen not only to the hepatocytes in the liver, but also to adjacent organs, such as the stomach, duodenum of the small intestine, pancreas, and gallbladder.

The hepatic vein carries deoxygenated blood from the liver to the heart, traveling via a larger blood vessel called the inferior vena cava. Hepatocytes produce carbon dioxide during aerobic respiration, which moves into the blood to be carried by the hepatic vein back to the heart. From the heart, this blood travels to the lungs to be oxygenated, before cycling around the body once more.

The hepatic portal vein travels from the intestines, spleen, pancreas, and gallbladder to the liver. It carries blood rich in nutrients, metabolic waste products, and toxins to the hepatocytes. The blood in the hepatic portal vein carries many products of digestion. For example, especially following a meal, the blood in the hepatic portal vein becomes rich in glucose, amino acids, cholesterol, vitamins, and minerals. The hepatic portal vein also transports substances that need to be detoxified, neutralized, and excreted, such as excess proteins and carbon dioxide. Furthermore, the hepatic portal vein transports hormones, such as insulin and glucagon, from the pancreas to the hepatocytes.

Blood vessel X is traveling from the gastrointestinal tract into the liver. Therefore, it will be rich in digestive products and is, therefore, the hepatic portal vein. As blood vessel Y is leaving the liver toward the inferior vena cava, it is the hepatic vein. Blood vessel Z branches off the aorta, which is a major blood vessel carrying oxygenated blood from the heart to the body cells. Z is, therefore, the hepatic artery.

So, our correct answers are as follows:

Key Term: Hepatic Portal Vein

The hepatic portal vein carries blood rich in nutrients, waste products, and toxins from the intestines, spleen, pancreas, and gallbladder to the liver.

Each lobe of the liver is made up of around 100‎ ‎000 hexagonal lobules. A lobule is a small lobe, one of which you can see magnified in Figure 3 . Each of these lobules contains a branch of the bile duct and each of the blood vessels discussed above. You can see the branches of the bile ducts delivering bile from the liver, where it is synthesized, to the gallbladder to be stored. Branches of the hepatic portal vein that bring waste and products of digestion to the liver, as well as the hepatic artery that supplies hepatocytes with oxygenated blood, are also visible, along with a central hepatic vein that transports the deoxygenated blood from the liver back to the heart.

Each of these hexagonal lobules contains many hepatocytes. Hepatocytes make up about

of the mass of the liver. The contents of the hepatic artery and hepatic portal vein mix in an area called a sinusoid, shown in Figure 4. The hepatocytes surround the sinusoids so that the contents of the blood can be transported into them. The blood leaves the sinusoid via the hepatic vein. You can also see branches of the bile duct and Kupffer cells in Figure 4. These are specialized phagocytes that are unique to the liver and function to engulf and digest pathogens.

Let’s have a closer look at the hepatocytes themselves. Most hepatocytes have a large nucleus, a prominent endoplasmic reticulum, and many mitochondria.

Key Term: Nucleus

The nucleus is an organelle surrounded by a double membrane that contains genetic information in the form of DNA molecules.

Key Term: Mitochondria

Mitochondria (singular: mitochondrion) are membrane-bound organelles in eukaryotes that act as the site of cellular respiration and so release energy in the form of ATP.

Their nuclei, which contain their genetic material, are mostly round. A remarkable feature of the liver is that about

of the hepatocytes (in a normal liver) have more than two sets of homologous chromosomes. Sometimes they even have more than one nucleus, as you can see in some hepatocytes in the micrograph below.

The reason why hepatocytes tend to have large or multiple nuclei continues to inspire scientific research. This feature is believed to make more gene copies available for protein synthesis, as these cells are very active. It would also offer more protection against DNA damage and cell death, especially when the cells are exposed to toxic substances, for example.

Hepatocytes have a prominent endoplasmic reticulum, as they are active in synthesizing proteins and lipids to be exported to other body cells. Hepatocytes are highly metabolically active, so they have many mitochondria to carry out respiration and release a sufficient amount of energy.

Example 3: Describing the Characteristics of Hepatocytes

Liver cells are also called hepatocytes. Which of the following best describes the characteristics of normal hepatocytes?

  1. Normal hepatocytes have multiple nuclei and a thick cell membrane.
  2. Normal hepatocytes have a large reserve of fat within the cell and many ribosomes.
  3. Normal hepatocytes are long and cylindrical and contain many chloroplasts.
  4. Normal hepatocytes have a large nucleus, a prominent endoplasmic reticulum, and many mitochondria.

Answer

Most hepatocytes have a large round nucleus, and some hepatocytes even have two nuclei. They are believed to require large or multiple nuclei to make more gene copies available for protein synthesis, as these cells are very active. This would also offer more protection against DNA damage and cell death, especially when the cells are exposed to toxic substances, for example.

Hepatocytes have a prominent endoplasmic reticulum, as they are active in synthesizing proteins and lipids to be exported to other cells in the body. Hepatocytes are highly metabolically active, so they also have many mitochondria to carry out respiration and release a sufficient amount of energy.

The cell membrane of hepatocytes does not differ significantly from any other cell in eukaryotes. In particular, it does not differ in its thickness, as the phospholipid bilayer is almost always the same diameter regardless of the function of the cell.

Although hepatocytes do store fat and contain ribosomes, these are not the distinguishing characteristics of the cells.

Hepatocytes are animal cells, meaning that they do not photosynthesize. Therefore, they do not contain any chloroplasts, which are the site of photosynthesis in plants and some protists and bacteria.

Therefore, the best description of the characteristics of hepatocytes is that normal hepatocytes have a large nucleus, a prominent endoplasmic reticulum, and many mitochondria.

The liver plays an essential role in breaking down harmful or excess metabolic waste products.

Some substances that are produced or ingested by the body are toxic and need to be removed. For example, alcoholic drinks contain ethanol, which is toxic because it dissolves the phospholipids in the cell membranes, causing them to break down. If ethanol is ingested, the liver works hard to convert it into a less toxic form to be excreted.

The liver sustains the majority of the damage caused by this toxin. Excessive alcohol consumption can damage the hepatocytes to the extent of irreversible liver cirrhosis, which is scarring of the liver. An illustration outlining the difference between the appearance of a healthy liver and that of a liver with cirrhosis is shown in Figure 6.

Let’s look at another function of the liver: deamination. Not all of the amino acids that are formed during the digestion of proteins can be stored by the human body. Excess amino acids are delivered to the hepatocytes via the hepatic portal vein. The amino group is removed from the amino acid, which converts it into an organic acid that can be used by the cells, releasing ammonia as a by-product.

Key Term: Deamination

Deamination is the process in which the amino group is removed from amino acids by the liver:


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BIO 140 - Human Biology I - Textbook

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Chapter 27

Heart Anatomy

  • Describe the location and position of the heart within the body cavity
  • Describe the internal and external anatomy of the heart
  • Identify the tissue layers of the heart
  • Relate the structure of the heart to its function as a pump
  • Compare systemic circulation to pulmonary circulation
  • Identify the veins and arteries of the coronary circulation system
  • Trace the pathway of oxygenated and deoxygenated blood thorough the chambers of the heart

The vital importance of the heart is obvious. If one assumes an average rate of contraction of 75 contractions per minute, a human heart would contract approximately 108,000 times in one day, more than 39 million times in one year, and nearly 3 billion times during a 75-year lifespan. Each of the major pumping chambers of the heart ejects approximately 70 mL blood per contraction in a resting adult. This would be equal to 5.25 liters of fluid per minute and approximately 14,000 liters per day. Over one year, that would equal 10,000,000 liters or 2.6 million gallons of blood sent through roughly 60,000 miles of vessels. In order to understand how that happens, it is necessary to understand the anatomy and physiology of the heart.

Location of the Heart

The human heart is located within the thoracic cavity, medially between the lungs in the space known as the mediastinum. Figure 1 shows the position of the heart within the thoracic cavity. Within the mediastinum, the heart is separated from the other mediastinal structures by a tough membrane known as the pericardium, or pericardial sac, and sits in its own space called the pericardial cavity . The dorsal surface of the heart lies near the bodies of the vertebrae, and its anterior surface sits deep to the sternum and costal cartilages. The great veins, the superior and inferior venae cavae, and the great arteries, the aorta and pulmonary trunk, are attached to the superior surface of the heart, called the base. The base of the heart is located at the level of the third costal cartilage, as seen in Figure . The inferior tip of the heart, the apex, lies just to the left of the sternum between the junction of the fourth and fifth ribs near their articulation with the costal cartilages. The right side of the heart is deflected anteriorly, and the left side is deflected posteriorly. It is important to remember the position and orientation of the heart when placing a stethoscope on the chest of a patient and listening for heart sounds, and also when looking at images taken from a midsagittal perspective. The slight deviation of the apex to the left is reflected in a depression in the medial surface of the inferior lobe of the left lung, called the cardiac notch .

Figure 1: The heart is located within the thoracic cavity, medially between the lungs in the mediastinum. It is about the size of a fist, is broad at the top, and tapers toward the base.

Everyday Connection

CPR

The position of the heart in the torso between the vertebrae and sternum (see Figure for the position of the heart within the thorax) allows for individuals to apply an emergency technique known as cardiopulmonary resuscitation (CPR) if the heart of a patient should stop. By applying pressure with the flat portion of one hand on the sternum in the area between the line at T4 and T9 (Figure 2 ), it is possible to manually compress the blood within the heart enough to push some of the blood within it into the pulmonary and systemic circuits. This is particularly critical for the brain, as irreversible damage and death of neurons occur within minutes of loss of blood flow. Current standards call for compression of the chest at least 5 cm deep and at a rate of 100 compressions per minute, a rate equal to the beat in &ldquoStaying Alive,&rdquo recorded in 1977 by the Bee Gees. If you are unfamiliar with this song, a version is available on www.youtube.com. At this stage, the emphasis is on performing high-quality chest compressions, rather than providing artificial respiration. CPR is generally performed until the patient regains spontaneous contraction or is declared dead by an experienced healthcare professional.

When performed by untrained or overzealous individuals, CPR can result in broken ribs or a broken sternum, and can inflict additional severe damage on the patient. It is also possible, if the hands are placed too low on the sternum, to manually drive the xiphoid process into the liver, a consequence that may prove fatal for the patient. Proper training is essential. This proven life-sustaining technique is so valuable that virtually all medical personnel as well as concerned members of the public should be certified and routinely recertified in its application. CPR courses are offered at a variety of locations, including colleges, hospitals, the American Red Cross, and some commercial companies. They normally include practice of the compression technique on a mannequin.

Figure 2: If the heart should stop, CPR can maintain the flow of blood until the heart resumes beating. By applying pressure to the sternum, the blood within the heart will be squeezed out of the heart and into the circulation. Proper positioning of the hands on the sternum to perform CPR would be between the lines at T4 and T9.

Visit the American Heart Association website linked to below to help locate a course near your home in the United States. There are also many other national and regional heart associations that offer the same service, depending upon the location.

Shape and Size of the Heart

The shape of the heart is similar to a pinecone, rather broad at the superior surface and tapering to the apex (see Figure ). A typical heart is approximately the size of your fist: 12 cm (5 in) in length, 8 cm (3.5 in) wide, and 6 cm (2.5 in) in thickness. Given the size difference between most members of the sexes, the weight of a female heart is approximately 250&ndash300 grams (9 to 11 ounces), and the weight of a male heart is approximately 300&ndash350 grams (11 to 12 ounces). The heart of a well-trained athlete, especially one specializing in aerobic sports, can be considerably larger than this. Cardiac muscle responds to exercise in a manner similar to that of skeletal muscle. That is, exercise results in the addition of protein myofilaments that increase the size of the individual cells without increasing their numbers, a concept called hypertrophy. Hearts of athletes can pump blood more effectively at lower rates than those of nonathletes. Enlarged hearts are not always a result of exercise they can result from pathologies, such as hypertrophic cardiomyopathy . The cause of an abnormally enlarged heart muscle is unknown, but the condition is often undiagnosed and can cause sudden death in apparently otherwise healthy young people.

Chambers and Circulation through the Heart

The human heart consists of four chambers: The left side and the right side each have one atrium and one ventricle . Each of the upper chambers, the right atrium (plural = atria) and the left atrium, acts as a receiving chamber and contracts to push blood into the lower chambers, the right ventricle and the left ventricle. The ventricles serve as the primary pumping chambers of the heart, propelling blood to the lungs or to the rest of the body.

There are two distinct but linked circuits in the human circulation called the pulmonary and systemic circuits. Although both circuits transport blood and everything it carries, we can initially view the circuits from the point of view of gases. The pulmonary circuit transports blood to and from the lungs, where it picks up oxygen and delivers carbon dioxide for exhalation. The systemic circuit transports oxygenated blood to virtually all of the tissues of the body and returns relatively deoxygenated blood and carbon dioxide to the heart to be sent back to the pulmonary circulation.

The right ventricle pumps deoxygenated blood into the pulmonary trunk , which leads toward the lungs and bifurcates into the left and right pulmonary arteries . These vessels in turn branch many times before reaching the pulmonary capillaries , where gas exchange occurs: Carbon dioxide exits the blood and oxygen enters. The pulmonary trunk arteries and their branches are the only arteries in the post-natal body that carry relatively deoxygenated blood. Highly oxygenated blood returning from the pulmonary capillaries in the lungs passes through a series of vessels that join together to form the pulmonary veins &mdashthe only post-natal veins in the body that carry highly oxygenated blood. The pulmonary veins conduct blood into the left atrium, which pumps the blood into the left ventricle, which in turn pumps oxygenated blood into the aorta and on to the many branches of the systemic circuit. Eventually, these vessels will lead to the systemic capillaries, where exchange with the tissue fluid and cells of the body occurs. In this case, oxygen and nutrients exit the systemic capillaries to be used by the cells in their metabolic processes, and carbon dioxide and waste products will enter the blood.

The blood exiting the systemic capillaries is lower in oxygen concentration than when it entered. The capillaries will ultimately unite to form venules, joining to form ever-larger veins, eventually flowing into the two major systemic veins, the superior vena cava and the inferior vena cava , which return blood to the right atrium. The blood in the superior and inferior venae cavae flows into the right atrium, which pumps blood into the right ventricle. This process of blood circulation continues as long as the individual remains alive. Understanding the flow of blood through the pulmonary and systemic circuits is critical to all health professions (Figure 3).

Figure 3: Blood flows from the right atrium to the right ventricle, where it is pumped into the pulmonary circuit. The blood in the pulmonary artery branches is low in oxygen but relatively high in carbon dioxide. Gas exchange occurs in the pulmonary capillaries (oxygen into the blood, carbon dioxide out), and blood high in oxygen and low in carbon dioxide is returned to the left atrium. From here, blood enters the left ventricle, which pumps it into the systemic circuit. Following exchange in the systemic capillaries (oxygen and nutrients out of the capillaries and carbon dioxide and wastes in), blood returns to the right atrium and the cycle is repeated.

Membranes, Surface Features, and Layers

Our exploration of more in-depth heart structures begins by examining the membrane that surrounds the heart, the prominent surface features of the heart, and the layers that form the wall of the heart. Each of these components plays its own unique role in terms of function.

Membranes

The membrane that directly surrounds the heart and defines the pericardial cavity is called the pericardium or pericardial sac . It also surrounds the &ldquoroots&rdquo of the major vessels, or the areas of closest proximity to the heart. The pericardium, which literally translates as &ldquoaround the heart,&rdquo consists of two distinct sublayers: the sturdy outer fibrous pericardium and the inner serous pericardium. The fibrous pericardium is made of tough, dense connective tissue that protects the heart and maintains its position in the thorax. The more delicate serous pericardium consists of two layers: the parietal pericardium, which is fused to the fibrous pericardium, and an inner visceral pericardium, or epicardium , which is fused to the heart and is part of the heart wall. The pericardial cavity, filled with lubricating serous fluid, lies between the epicardium and the pericardium.

In most organs within the body, visceral serous membranes such as the epicardium are microscopic. However, in the case of the heart, it is not a microscopic layer but rather a macroscopic layer, consisting of a simple squamous epithelium called a mesothelium , reinforced with loose, irregular, or areolar connective tissue that attaches to the pericardium. This mesothelium secretes the lubricating serous fluid that fills the pericardial cavity and reduces friction as the heart contracts. Figure 4 illustrates the pericardial membrane and the layers of the heart.

Figure 4: The pericardial membrane that surrounds the heart consists of three layers and the pericardial cavity. The heart wall also consists of three layers. The pericardial membrane and the heart wall share the epicardium.

Disorders of the.

Heart: Cardiac Tamponade

If excess fluid builds within the pericardial space, it can lead to a condition called cardiac tamponade, or pericardial tamponade. With each contraction of the heart, more fluid&mdashin most instances, blood&mdashaccumulates within the pericardial cavity. In order to fill with blood for the next contraction, the heart must relax. However, the excess fluid in the pericardial cavity puts pressure on the heart and prevents full relaxation, so the chambers within the heart contain slightly less blood as they begin each heart cycle. Over time, less and less blood is ejected from the heart. If the fluid builds up slowly, as in hypothyroidism, the pericardial cavity may be able to expand gradually to accommodate this extra volume. Some cases of fluid in excess of one liter within the pericardial cavity have been reported. Rapid accumulation of as little as 100 mL of fluid following trauma may trigger cardiac tamponade. Other common causes include myocardial rupture, pericarditis, cancer, or even cardiac surgery. Removal of this excess fluid requires insertion of drainage tubes into the pericardial cavity. Premature removal of these drainage tubes, for example, following cardiac surgery, or clot formation within these tubes are causes of this condition. Untreated, cardiac tamponade can lead to death.

Surface Features of the Heart

Inside the pericardium, the surface features of the heart are visible, including the four chambers. There is a superficial leaf-like extension of the atria near the superior surface of the heart, one on each side, called an auricle &mdasha name that means &ldquoear like&rdquo&mdashbecause its shape resembles the external ear of a human (Figure 5). Auricles are relatively thin-walled structures that can fill with blood and empty into the atria or upper chambers of the heart. You may also hear them referred to as atrial appendages. Also prominent is a series of fat-filled grooves, each of which is known as a sulcus (plural = sulci), along the superior surfaces of the heart. Major coronary blood vessels are located in these sulci. The deep coronary sulcus is located between the atria and ventricles. Located between the left and right ventricles are two additional sulci that are not as deep as the coronary sulcus. The anterior interventricular sulcus is visible on the anterior surface of the heart, whereas the posterior interventricular sulcus is visible on the posterior surface of the heart. Figure 5 illustrates anterior and posterior views of the surface of the heart.

Figure 5: Inside the pericardium, the surface features of the heart are visible.

Layers

The wall of the heart is composed of three layers of unequal thickness. From superficial to deep, these are the epicardium, the myocardium, and the endocardium (see Figure 4). The outermost layer of the wall of the heart is also the innermost layer of the pericardium, the epicardium, or the visceral pericardium discussed earlier.

The middle and thickest layer is the myocardium , made largely of cardiac muscle cells. It is built upon a framework of collagenous fibers, plus the blood vessels that supply the myocardium and the nerve fibers that help regulate the heart. It is the contraction of the myocardium that pumps blood through the heart and into the major arteries. The muscle pattern is elegant and complex, as the muscle cells swirl and spiral around the chambers of the heart. They form a figure 8 pattern around the atria and around the bases of the great vessels. Deeper ventricular muscles also form a figure 8 around the two ventricles and proceed toward the apex. More superficial layers of ventricular muscle wrap around both ventricles. This complex swirling pattern allows the heart to pump blood more effectively than a simple linear pattern would. Figure 6 illustrates the arrangement of muscle cells.

Figure 6: The swirling pattern of cardiac muscle tissue contributes significantly to the heart&rsquos ability to pump blood effectively.

Although the ventricles on the right and left sides pump the same amount of blood per contraction, the muscle of the left ventricle is much thicker and better developed than that of the right ventricle. In order to overcome the high resistance required to pump blood into the long systemic circuit, the left ventricle must generate a great amount of pressure. The right ventricle does not need to generate as much pressure, since the pulmonary circuit is shorter and provides less resistance. Figure 7 illustrates the differences in muscular thickness needed for each of the ventricles.

Figure 7: The myocardium in the left ventricle is significantly thicker than that of the right ventricle. Both ventricles pump the same amount of blood, but the left ventricle must generate a much greater pressure to overcome greater resistance in the systemic circuit. The ventricles are shown in both relaxed and contracting states. Note the differences in the relative size of the lumens, the region inside each ventricle where the blood is contained.

The innermost layer of the heart wall, the endocardium , is joined to the myocardium with a thin layer of connective tissue. The endocardium lines the chambers where the blood circulates and covers the heart valves. It is made of simple squamous epithelium called endothelium , which is continuous with the endothelial lining of the blood vessels (see Figure 4).

Once regarded as a simple lining layer, recent evidence indicates that the endothelium of the endocardium and the coronary capillaries may play active roles in regulating the contraction of the muscle within the myocardium. The endothelium may also regulate the growth patterns of the cardiac muscle cells throughout life, and the endothelins it secretes create an environment in the surrounding tissue fluids that regulates ionic concentrations and states of contractility. Endothelins are potent vasoconstrictors and, in a normal individual, establish a homeostatic balance with other vasoconstrictors and vasodilators.

Internal Structure of the Heart

Recall that the heart&rsquos contraction cycle follows a dual pattern of circulation&mdashthe pulmonary and systemic circuits&mdashbecause of the pairs of chambers that pump blood into the circulation. In order to develop a more precise understanding of cardiac function, it is first necessary to explore the internal anatomical structures in more detail.

Septa of the Heart

The word septum is derived from the Latin for &ldquosomething that encloses&rdquo in this case, a septum (plural = septa) refers to a wall or partition that divides the heart into chambers. The septa are physical extensions of the myocardium lined with endocardium. Located between the two atria is the interatrial septum . Normally in an adult heart, the interatrial septum bears an oval-shaped depression known as the fossa ovalis , a remnant of an opening in the fetal heart known as the foramen ovale . The foramen ovale allowed blood in the fetal heart to pass directly from the right atrium to the left atrium, allowing some blood to bypass the pulmonary circuit. Within seconds after birth, a flap of tissue known as the septum primum that previously acted as a valve closes the foramen ovale and establishes the typical cardiac circulation pattern.

Between the two ventricles is a second septum known as the interventricular septum . Unlike the interatrial septum, the interventricular septum is normally intact after its formation during fetal development. It is substantially thicker than the interatrial septum, since the ventricles generate far greater pressure when they contract.

The septum between the atria and ventricles is known as the atrioventricular septum . It is marked by the presence of four openings that allow blood to move from the atria into the ventricles and from the ventricles into the pulmonary trunk and aorta. Located in each of these openings between the atria and ventricles is a valve , a specialized structure that ensures one-way flow of blood. The valves between the atria and ventricles are known generically as atrioventricular valves . The valves at the openings that lead to the pulmonary trunk and aorta are known generically as semilunar valves . The interventricular septum is visible in Figure 8. In this figure, the atrioventricular septum has been removed to better show the bicupid and tricuspid valves the interatrial septum is not visible, since its location is covered by the aorta and pulmonary trunk. Since these openings and valves structurally weaken the atrioventricular septum, the remaining tissue is heavily reinforced with dense connective tissue called the cardiac skeleton , or skeleton of the heart. It includes four rings that surround the openings between the atria and ventricles, and the openings to the pulmonary trunk and aorta, and serve as the point of attachment for the heart valves. The cardiac skeleton also provides an important boundary in the heart electrical conduction system.

Figure 8: This anterior view of the heart shows the four chambers, the major vessels and their early branches, as well as the valves. The presence of the pulmonary trunk and aorta covers the interatrial septum, and the atrioventricular septum is cut away to show the atrioventricular valves.

Disorders of the.

Heart: Heart Defects

One very common form of interatrial septum pathology is patent foramen ovale, which occurs when the septum primum does not close at birth, and the fossa ovalis is unable to fuse. The word patent is from the Latin root patens for &ldquoopen.&rdquo It may be benign or asymptomatic, perhaps never being diagnosed, or in extreme cases, it may require surgical repair to close the opening permanently. As much as 20&ndash25 percent of the general population may have a patent foramen ovale, but fortunately, most have the benign, asymptomatic version. Patent foramen ovale is normally detected by auscultation of a heart murmur (an abnormal heart sound) and confirmed by imaging with an echocardiogram. Despite its prevalence in the general population, the causes of patent ovale are unknown, and there are no known risk factors. In nonlife-threatening cases, it is better to monitor the condition than to risk heart surgery to repair and seal the opening.

Coarctation of the aorta is a congenital abnormal narrowing of the aorta that is normally located at the insertion of the ligamentum arteriosum, the remnant of the fetal shunt called the ductus arteriosus. If severe, this condition drastically restricts blood flow through the primary systemic artery, which is life threatening. In some individuals, the condition may be fairly benign and not detected until later in life. Detectable symptoms in an infant include difficulty breathing, poor appetite, trouble feeding, or failure to thrive. In older individuals, symptoms include dizziness, fainting, shortness of breath, chest pain, fatigue, headache, and nosebleeds. Treatment involves surgery to resect (remove) the affected region or angioplasty to open the abnormally narrow passageway. Studies have shown that the earlier the surgery is performed, the better the chance of survival.

A patent ductus arteriosus is a congenital condition in which the ductus arteriosus fails to close. The condition may range from severe to benign. Failure of the ductus arteriosus to close results in blood flowing from the higher pressure aorta into the lower pressure pulmonary trunk. This additional fluid moving toward the lungs increases pulmonary pressure and makes respiration difficult. Symptoms include shortness of breath (dyspnea), tachycardia, enlarged heart, a widened pulse pressure, and poor weight gain in infants. Treatments include surgical closure (ligation), manual closure using platinum coils or specialized mesh inserted via the femoral artery or vein, or nonsteroidal anti-inflammatory drugs to block the synthesis of prostaglandin E2, which maintains the vessel in an open position. If untreated, the condition can result in congestive heart failure.

Septal defects are not uncommon in individuals and may be congenital or caused by various disease processes. Tetralogy of Fallot is a congenital condition that may also occur from exposure to unknown environmental factors it occurs when there is an opening in the interventricular septum caused by blockage of the pulmonary trunk, normally at the pulmonary semilunar valve. This allows blood that is relatively low in oxygen from the right ventricle to flow into the left ventricle and mix with the blood that is relatively high in oxygen. Symptoms include a distinct heart murmur, low blood oxygen percent saturation, dyspnea or difficulty in breathing, polycythemia, broadening (clubbing) of the fingers and toes, and in children, difficulty in feeding or failure to grow and develop. It is the most common cause of cyanosis following birth. The term &ldquotetralogy&rdquo is derived from the four components of the condition, although only three may be present in an individual patient: pulmonary infundibular stenosis (rigidity of the pulmonary valve), overriding aorta (the aorta is shifted above both ventricles), ventricular septal defect (opening), and right ventricular hypertrophy (enlargement of the right ventricle). Other heart defects may also accompany this condition, which is typically confirmed by echocardiography imaging. Tetralogy of Fallot occurs in approximately 400 out of one million live births. Normal treatment involves extensive surgical repair, including the use of stents to redirect blood flow and replacement of valves and patches to repair the septal defect, but the condition has a relatively high mortality. Survival rates are currently 75 percent during the first year of life 60 percent by 4 years of age 30 percent by 10 years and 5 percent by 40 years.

In the case of severe septal defects, including both tetralogy of Fallot and patent foramen ovale, failure of the heart to develop properly can lead to a condition commonly known as a &ldquoblue baby.&rdquo Regardless of normal skin pigmentation, individuals with this condition have an insufficient supply of oxygenated blood, which leads to cyanosis, a blue or purple coloration of the skin, especially when active.

Septal defects are commonly first detected through auscultation, listening to the chest using a stethoscope. In this case, instead of hearing normal heart sounds attributed to the flow of blood and closing of heart valves, unusual heart sounds may be detected. This is often followed by medical imaging to confirm or rule out a diagnosis. In many cases, treatment may not be needed. Some common congenital heart defects are illustrated in Figure 9.

Figure 9: (a) A patent foramen ovale defect is an abnormal opening in the interatrial septum, or more commonly, a failure of the foramen ovale to close. (b) Coarctation of the aorta is an abnormal narrowing of the aorta. (c) A patent ductus arteriosus is the failure of the ductus arteriosus to close. (d) Tetralogy of Fallot includes an abnormal opening in the interventricular septum.

Right Atrium

The right atrium serves as the receiving chamber for blood returning to the heart from the systemic circulation. The two major systemic veins, the superior and inferior venae cavae, and the large coronary vein called the coronary sinus that drains the heart myocardium empty into the right atrium. The superior vena cava drains blood from regions superior to the diaphragm: the head, neck, upper limbs, and the thoracic region. It empties into the superior and posterior portions of the right atrium. The inferior vena cava drains blood from areas inferior to the diaphragm: the lower limbs and abdominopelvic region of the body. It, too, empties into the posterior portion of the atria, but inferior to the opening of the superior vena cava. Immediately superior and slightly medial to the opening of the inferior vena cava on the posterior surface of the atrium is the opening of the coronary sinus. This thin-walled vessel drains most of the coronary veins that return systemic blood from the heart. The majority of the internal heart structures discussed in this and subsequent sections are illustrated in Figure 8.

While the bulk of the internal surface of the right atrium is smooth, the depression of the fossa ovalis is medial, and the anterior surface demonstrates prominent ridges of muscle called the pectinate muscles . The right auricle also has pectinate muscles. The left atrium does not have pectinate muscles except in the auricle.

The atria receive venous blood on a nearly continuous basis, preventing venous flow from stopping while the ventricles are contracting. While most ventricular filling occurs while the atria are relaxed, they do demonstrate a contractile phase and actively pump blood into the ventricles just prior to ventricular contraction. The opening between the atrium and ventricle is guarded by the tricuspid valve.

Right Ventricle

The right ventricle receives blood from the right atrium through the tricuspid valve. Each flap of the valve is attached to strong strands of connective tissue, the chordae tendineae , literally &ldquotendinous cords,&rdquo or sometimes more poetically referred to as &ldquoheart strings.&rdquo There are several chordae tendineae associated with each of the flaps. They are composed of approximately 80 percent collagenous fibers with the remainder consisting of elastic fibers and endothelium. They connect each of the flaps to a papillary muscle that extends from the inferior ventricular surface. There are three papillary muscles in the right ventricle, called the anterior, posterior, and septal muscles, which correspond to the three sections of the valves.

When the myocardium of the ventricle contracts, pressure within the ventricular chamber rises. Blood, like any fluid, flows from higher pressure to lower pressure areas, in this case, toward the pulmonary trunk and the atrium. To prevent any potential backflow, the papillary muscles also contract, generating tension on the chordae tendineae. This prevents the flaps of the valves from being forced into the atria and regurgitation of the blood back into the atria during ventricular contraction. Figure 10 shows papillary muscles and chordae tendineae attached to the tricuspid valve.

Figure 10: In this frontal section, you can see papillary muscles attached to the tricuspid valve on the right as well as the mitral valve on the left via chordae tendineae. (credit: modification of work by &ldquoPV KS&rdquo/flickr.com)

The walls of the ventricle are lined with trabeculae carneae , ridges of cardiac muscle covered by endocardium. In addition to these muscular ridges, a band of cardiac muscle, also covered by endocardium, known as the moderator band (see Figure 8) reinforces the thin walls of the right ventricle and plays a crucial role in cardiac conduction. It arises from the inferior portion of the interventricular septum and crosses the interior space of the right ventricle to connect with the inferior papillary muscle.

When the right ventricle contracts, it ejects blood into the pulmonary trunk, which branches into the left and right pulmonary arteries that carry it to each lung. The superior surface of the right ventricle begins to taper as it approaches the pulmonary trunk. At the base of the pulmonary trunk is the pulmonary semilunar valve that prevents backflow from the pulmonary trunk.

Left Atrium

After exchange of gases in the pulmonary capillaries, blood returns to the left atrium high in oxygen via one of the four pulmonary veins. While the left atrium does not contain pectinate muscles, it does have an auricle that includes these pectinate ridges. Blood flows nearly continuously from the pulmonary veins back into the atrium, which acts as the receiving chamber, and from here through an opening into the left ventricle. Most blood flows passively into the heart while both the atria and ventricles are relaxed, but toward the end of the ventricular relaxation period, the left atrium will contract, pumping blood into the ventricle. This atrial contraction accounts for approximately 20 percent of ventricular filling. The opening between the left atrium and ventricle is guarded by the mitral valve.

Left Ventricle

Recall that, although both sides of the heart will pump the same amount of blood, the muscular layer is much thicker in the left ventricle compared to the right (see Figure 7). Like the right ventricle, the left also has trabeculae carneae, but there is no moderator band. The mitral valve is connected to papillary muscles via chordae tendineae. There are two papillary muscles on the left&mdashthe anterior and posterior&mdashas opposed to three on the right.

The left ventricle is the major pumping chamber for the systemic circuit it ejects blood into the aorta through the aortic semilunar valve.

Heart Valve Structure and Function

A transverse section through the heart slightly above the level of the atrioventricular septum reveals all four heart valves along the same plane (Figure 11). The valves ensure unidirectional blood flow through the heart. Between the right atrium and the right ventricle is the right atrioventricular valve , or tricuspid valve . It typically consists of three flaps, or leaflets, made of endocardium reinforced with additional connective tissue. The flaps are connected by chordae tendineae to the papillary muscles, which control the opening and closing of the valves.

Figure 11: With the atria and major vessels removed, all four valves are clearly visible, although it is difficult to distinguish the three separate cusps of the tricuspid valve.

Emerging from the right ventricle at the base of the pulmonary trunk is the pulmonary semilunar valve, or the pulmonary valve it is also known as the pulmonic valve or the right semilunar valve. The pulmonary valve is comprised of three small flaps of endothelium reinforced with connective tissue. When the ventricle relaxes, the pressure differential causes blood to flow back into the ventricle from the pulmonary trunk. This flow of blood fills the pocket-like flaps of the pulmonary valve, causing the valve to close and producing an audible sound. Unlike the atrioventricular valves, there are no papillary muscles or chordae tendineae associated with the pulmonary valve.

Located at the opening between the left atrium and left ventricle is the mitral valve , also called the bicuspid valve or the left atrioventricular valve . Structurally, this valve consists of two cusps, known as the anterior medial cusp and the posterior medial cusp, compared to the three cusps of the tricuspid valve. In a clinical setting, the valve is referred to as the mitral valve, rather than the bicuspid valve. The two cusps of the mitral valve are attached by chordae tendineae to two papillary muscles that project from the wall of the ventricle.

At the base of the aorta is the aortic semilunar valve, or the aortic valve , which prevents backflow from the aorta. It normally is composed of three flaps. When the ventricle relaxes and blood attempts to flow back into the ventricle from the aorta, blood will fill the cusps of the valve, causing it to close and producing an audible sound.

In Figure 12a, the two atrioventricular valves are open and the two semilunar valves are closed. This occurs when both atria and ventricles are relaxed and when the atria contract to pump blood into the ventricles. Figure 12b shows a frontal view. Although only the left side of the heart is illustrated, the process is virtually identical on the right.

Figure 12: (a) A transverse section through the heart illustrates the four heart valves. The two atrioventricular valves are open the two semilunar valves are closed. The atria and vessels have been removed. (b) A frontal section through the heart illustrates blood flow through the mitral valve. When the mitral valve is open, it allows blood to move from the left atrium to the left ventricle. The aortic semilunar valve is closed to prevent backflow of blood from the aorta to the left ventricle.

Figure 13a shows the atrioventricular valves closed while the two semilunar valves are open. This occurs when the ventricles contract to eject blood into the pulmonary trunk and aorta. Closure of the two atrioventricular valves prevents blood from being forced back into the atria. This stage can be seen from a frontal view in Figure 13b.

Figure 13: (a) A transverse section through the heart illustrates the four heart valves during ventricular contraction. The two atrioventricular valves are closed, but the two semilunar valves are open. The atria and vessels have been removed. (b) A frontal view shows the closed mitral (bicuspid) valve that prevents backflow of blood into the left atrium. The aortic semilunar valve is open to allow blood to be ejected into the aorta.

When the ventricles begin to contract, pressure within the ventricles rises and blood flows toward the area of lowest pressure, which is initially in the atria. This backflow causes the cusps of the tricuspid and mitral (bicuspid) valves to close. These valves are tied down to the papillary muscles by chordae tendineae. During the relaxation phase of the cardiac cycle, the papillary muscles are also relaxed and the tension on the chordae tendineae is slight (see Figure 12b). However, as the myocardium of the ventricle contracts, so do the papillary muscles. This creates tension on the chordae tendineae (see Figure 13b), helping to hold the cusps of the atrioventricular valves in place and preventing them from being blown back into the atria.

The aortic and pulmonary semilunar valves lack the chordae tendineae and papillary muscles associated with the atrioventricular valves. Instead, they consist of pocket-like folds of endocardium reinforced with additional connective tissue. When the ventricles relax and the change in pressure forces the blood toward the ventricles, the blood presses against these cusps and seals the openings.

Visit the site linked to below to observe an echocardiogram of actual heart valves opening and closing. Although much of the heart has been &ldquoremoved&rdquo from this gif loop so the chordae tendineae are not visible, why is their presence more critical for the atrioventricular valves (tricuspid and mitral) than the semilunar (aortic and pulmonary) valves?

Disorders of the.

Heart Valves

Valvular disorders are often caused by carditis, or inflammation of the heart. One common trigger for this inflammation is rheumatic fever, or scarlet fever, an autoimmune response to the presence of a bacterium, Streptococcus pyogenes, normally a disease of childhood.

While any of the heart valves may be involved in valve disorders, mitral regurgitation is the most common, detected in approximately 2 percent of the population, and the pulmonary semilunar valve is the least frequently involved. When a valve malfunctions, the flow of blood to a region will often be disrupted. The resulting inadequate flow of blood to this region will be described in general terms as an insufficiency. The specific type of insufficiency is named for the valve involved: aortic insufficiency, mitral insufficiency, tricuspid insufficiency, or pulmonary insufficiency.

If one of the cusps of the valve is forced backward by the force of the blood, the condition is referred to as a prolapsed valve. Prolapse may occur if the chordae tendineae are damaged or broken, causing the closure mechanism to fail. The failure of the valve to close properly disrupts the normal one-way flow of blood and results in regurgitation, when the blood flows backward from its normal path. Using a stethoscope, the disruption to the normal flow of blood produces a heart murmur.

Stenosis is a condition in which the heart valves become rigid and may calcify over time. The loss of flexibility of the valve interferes with normal function and may cause the heart to work harder to propel blood through the valve, which eventually weakens the heart. Aortic stenosis affects approximately 2 percent of the population over 65 years of age, and the percentage increases to approximately 4 percent in individuals over 85 years. Occasionally, one or more of the chordae tendineae will tear or the papillary muscle itself may die as a component of a myocardial infarction (heart attack). In this case, the patient&rsquos condition will deteriorate dramatically and rapidly, and immediate surgical intervention may be required.

Auscultation, or listening to a patient&rsquos heart sounds, is one of the most useful diagnostic tools, since it is proven, safe, and inexpensive. The term auscultation is derived from the Latin for &ldquoto listen,&rdquo and the technique has been used for diagnostic purposes as far back as the ancient Egyptians. Valve and septal disorders will trigger abnormal heart sounds. If a valvular disorder is detected or suspected, a test called an echocardiogram, or simply an &ldquoecho,&rdquo may be ordered. Echocardiograms are sonograms of the heart and can help in the diagnosis of valve disorders as well as a wide variety of heart pathologies.

Visit the site linked to below for a free download, including excellent animations and audio of heart sounds.

Career Connection

Cardiologist

Visit the site linked to below to learn more about cardiologists.

Career Connection

Cardiovascular Technologist/Technician

Cardiovascular technologists/technicians are trained professionals who perform a variety of imaging techniques, such as sonograms or echocardiograms, used by physicians to diagnose and treat diseases of the heart. Nearly all of these positions require an associate degree, and these technicians earn a median salary of $49,410 as of May 2010, according to the U.S. Bureau of Labor Statistics. Growth within the field is fast, projected at 29 percent from 2010 to 2020.

There is a considerable overlap and complementary skills between cardiac technicians and vascular technicians, and so the term cardiovascular technician is often used. Special certifications within the field require documenting appropriate experience and completing additional and often expensive certification examinations. These subspecialties include Certified Rhythm Analysis Technician (CRAT), Certified Cardiographic Technician (CCT), Registered Congenital Cardiac Sonographer (RCCS), Registered Cardiac Electrophysiology Specialist (RCES), Registered Cardiovascular Invasive Specialist (RCIS), Registered Cardiac Sonographer (RCS), Registered Vascular Specialist (RVS), and Registered Phlebology Sonographer (RPhS).

Visit the site linked to below to learn more about cardio vascular technologists/technicians .

Coronary Circulation

You will recall that the heart is a remarkable pump composed largely of cardiac muscle cells that are incredibly active throughout life. Like all other cells, a cardiomyocyte requires a reliable supply of oxygen and nutrients, and a way to remove wastes, so it needs a dedicated, complex, and extensive coronary circulation. And because of the critical and nearly ceaseless activity of the heart throughout life, this need for a blood supply is even greater than for a typical cell. However, coronary circulation is not continuous rather, it cycles, reaching a peak when the heart muscle is relaxed and nearly ceasing while it is contracting.

Coronary Arteries

Coronary arteries supply blood to the myocardium and other components of the heart. The first portion of the aorta after it arises from the left ventricle gives rise to the coronary arteries. There are three dilations in the wall of the aorta just superior to the aortic semilunar valve. Two of these, the left posterior aortic sinus and anterior aortic sinus, give rise to the left and right coronary arteries, respectively. The third sinus, the right posterior aortic sinus, typically does not give rise to a vessel. Coronary vessel branches that remain on the surface of the artery and follow the sulci are called epicardial coronary arteries .

The left coronary artery distributes blood to the left side of the heart, the left atrium and ventricle, and the interventricular septum. The circumflex artery arises from the left coronary artery and follows the coronary sulcus to the left. Eventually, it will fuse with the small branches of the right coronary artery. The larger anterior interventricular artery , also known as the left anterior descending artery (LAD), is the second major branch arising from the left coronary artery. It follows the anterior interventricular sulcus around the pulmonary trunk. Along the way it gives rise to numerous smaller branches that interconnect with the branches of the posterior interventricular artery, forming anastomoses. An anastomosis is an area where vessels unite to form interconnections that normally allow blood to circulate to a region even if there may be partial blockage in another branch. The anastomoses in the heart are very small. Therefore, this ability is somewhat restricted in the heart so a coronary artery blockage often results in death of the cells (myocardial infarction) supplied by the particular vessel.

The right coronary artery proceeds along the coronary sulcus and distributes blood to the right atrium, portions of both ventricles, and the heart conduction system. Normally, one or more marginal arteries arise from the right coronary artery inferior to the right atrium. The marginal arteries supply blood to the superficial portions of the right ventricle. On the posterior surface of the heart, the right coronary artery gives rise to the posterior interventricular artery , also known as the posterior descending artery. It runs along the posterior portion of the interventricular sulcus toward the apex of the heart, giving rise to branches that supply the interventricular septum and portions of both ventricles. Figure 14 presents views of the coronary circulation from both the anterior and posterior views.

Figure 14: The anterior view of the heart shows the prominent coronary surface vessels. The posterior view of the heart shows the prominent coronary surface vessels.

Diseases of the.

Heart: Myocardial Infarction

In the case of acute MI, there is often sudden pain beneath the sternum (retrosternal pain) called angina pectoris, often radiating down the left arm in males but not in female patients. Until this anomaly between the sexes was discovered, many female patients suffering MIs were misdiagnosed and sent home. In addition, patients typically present with difficulty breathing and shortness of breath (dyspnea), irregular heartbeat (palpations), nausea and vomiting, sweating (diaphoresis), anxiety, and fainting (syncope), although not all of these symptoms may be present. Many of the symptoms are shared with other medical conditions, including anxiety attacks and simple indigestion, so differential diagnosis is critical. It is estimated that between 22 and 64 percent of MIs present without any symptoms.

An MI can be confirmed by examining the patient&rsquos ECG, which frequently reveals alterations in the ST and Q components. Some classification schemes of MI are referred to as ST-elevated MI (STEMI) and non-elevated MI (non-STEMI). In addition, echocardiography or cardiac magnetic resonance imaging may be employed. Common blood tests indicating an MI include elevated levels of creatine kinase MB (an enzyme that catalyzes the conversion of creatine to phosphocreatine, consuming ATP) and cardiac troponin (the regulatory protein for muscle contraction), both of which are released by damaged cardiac muscle cells.

Immediate treatments for MI are essential and include administering supplemental oxygen, aspirin that helps to break up clots, and nitroglycerine administered sublingually (under the tongue) to facilitate its absorption. Despite its unquestioned success in treatments and use since the 1880s, the mechanism of nitroglycerine is still incompletely understood but is believed to involve the release of nitric oxide, a known vasodilator, and endothelium-derived releasing factor, which also relaxes the smooth muscle in the tunica media of coronary vessels. Longer-term treatments include injections of thrombolytic agents such as streptokinase that dissolve the clot, the anticoagulant heparin, balloon angioplasty and stents to open blocked vessels, and bypass surgery to allow blood to pass around the site of blockage. If the damage is extensive, coronary replacement with a donor heart or coronary assist device, a sophisticated mechanical device that supplements the pumping activity of the heart, may be employed. Despite the attention, development of artificial hearts to augment the severely limited supply of heart donors has proven less than satisfactory but will likely improve in the future.

MIs may trigger cardiac arrest, but the two are not synonymous. Important risk factors for MI include cardiovascular disease, age, smoking, high blood levels of the low-density lipoprotein (LDL, often referred to as &ldquobad&rdquo cholesterol), low levels of high-density lipoprotein (HDL, or &ldquogood&rdquo cholesterol), hypertension, diabetes mellitus, obesity, lack of physical exercise, chronic kidney disease, excessive alcohol consumption, and use of illegal drugs.

Coronary Veins

Coronary veins drain the heart and generally parallel the large surface arteries (see Figure 14). The great cardiac vein can be seen initially on the surface of the heart following the interventricular sulcus, but it eventually flows along the coronary sulcus into the coronary sinus on the posterior surface. The great cardiac vein initially parallels the anterior interventricular artery and drains the areas supplied by this vessel. It receives several major branches, including the posterior cardiac vein, the middle cardiac vein, and the small cardiac vein. The posterior cardiac vein parallels and drains the areas supplied by the marginal artery branch of the circumflex artery. The middle cardiac vein parallels and drains the areas supplied by the posterior interventricular artery. The small cardiac vein parallels the right coronary artery and drains the blood from the posterior surfaces of the right atrium and ventricle. The coronary sinus is a large, thin-walled vein on the posterior surface of the heart lying within the atrioventricular sulcus and emptying directly into the right atrium. The anterior cardiac veins parallel the small cardiac arteries and drain the anterior surface of the right ventricle. Unlike these other cardiac veins, it bypasses the coronary sinus and drains directly into the right atrium.

Diseases of the.

Heart: Coronary Artery Disease

Coronary artery disease is the leading cause of death worldwide. It occurs when the buildup of plaque&mdasha fatty material including cholesterol, connective tissue, white blood cells, and some smooth muscle cells&mdashwithin the walls of the arteries obstructs the flow of blood and decreases the flexibility or compliance of the vessels. This condition is called atherosclerosis, a hardening of the arteries that involves the accumulation of plaque. As the coronary blood vessels become occluded, the flow of blood to the tissues will be restricted, a condition called ischemia that causes the cells to receive insufficient amounts of oxygen, called hypoxia. Figure 15 shows the blockage of coronary arteries highlighted by the injection of dye. Some individuals with coronary artery disease report pain radiating from the chest called angina pectoris, but others remain asymptomatic. If untreated, coronary artery disease can lead to MI or a heart attack.

Figure 15: In this coronary angiogram (X-ray), the dye makes visible two occluded coronary arteries. Such blockages can lead to decreased blood flow (ischemia) and insufficient oxygen (hypoxia) delivered to the cardiac tissues. If uncorrected, this can lead to cardiac muscle death (myocardial infarction).

The disease progresses slowly and often begins in children and can be seen as fatty &ldquostreaks&rdquo in the vessels. It then gradually progresses throughout life. Well-documented risk factors include smoking, family history, hypertension, obesity, diabetes, high alcohol consumption, lack of exercise, stress, and hyperlipidemia or high circulating levels of lipids in the blood. Treatments may include medication, changes to diet and exercise, angioplasty with a balloon catheter, insertion of a stent, or coronary bypass procedure.

Angioplasty is a procedure in which the occlusion is mechanically widened with a balloon. A specialized catheter with an expandable tip is inserted into a superficial vessel, normally in the leg, and then directed to the site of the occlusion. At this point, the balloon is inflated to compress the plaque material and to open the vessel to increase blood flow. Then, the balloon is deflated and retracted. A stent consisting of a specialized mesh is typically inserted at the site of occlusion to reinforce the weakened and damaged walls. Stent insertions have been routine in cardiology for more than 40 years.

Coronary bypass surgery may also be performed. This surgical procedure grafts a replacement vessel obtained from another, less vital portion of the body to bypass the occluded area. This procedure is clearly effective in treating patients experiencing a MI, but overall does not increase longevity. Nor does it seem advisable in patients with stable although diminished cardiac capacity since frequently loss of mental acuity occurs following the procedure. Long-term changes to behavior, emphasizing diet and exercise plus a medicine regime tailored to lower blood pressure, lower cholesterol and lipids, and reduce clotting are equally as effective.

Chapter Review

The heart resides within the pericardial sac and is located in the mediastinal space within the thoracic cavity. The pericardial sac consists of two fused layers: an outer fibrous capsule and an inner parietal pericardium lined with a serous membrane. Between the pericardial sac and the heart is the pericardial cavity, which is filled with lubricating serous fluid. The walls of the heart are composed of an outer epicardium, a thick myocardium, and an inner lining layer of endocardium. The human heart consists of a pair of atria, which receive blood and pump it into a pair of ventricles, which pump blood into the vessels. The right atrium receives systemic blood relatively low in oxygen and pumps it into the right ventricle, which pumps it into the pulmonary circuit. Exchange of oxygen and carbon dioxide occurs in the lungs, and blood high in oxygen returns to the left atrium, which pumps blood into the left ventricle, which in turn pumps blood into the aorta and the remainder of the systemic circuit. The septa are the partitions that separate the chambers of the heart. They include the interatrial septum, the interventricular septum, and the atrioventricular septum. Two of these openings are guarded by the atrioventricular valves, the right tricuspid valve and the left mitral valve, which prevent the backflow of blood. Each is attached to chordae tendineae that extend to the papillary muscles, which are extensions of the myocardium, to prevent the valves from being blown back into the atria. The pulmonary valve is located at the base of the pulmonary trunk, and the left semilunar valve is located at the base of the aorta. The right and left coronary arteries are the first to branch off the aorta and arise from two of the three sinuses located near the base of the aorta and are generally located in the sulci. Cardiac veins parallel the small cardiac arteries and generally drain into the coronary sinus.


What Is the Function of the Vena Cava? (with pictures)

The venae cavae are two major veins found in all vertebrates that breathe air. Like all veins, the function of the vena cava is to transfer blood that has been deoxygenated from the body back into the heart. These veins are essential components of the circulatory system, and each one is responsible for returning the blood from half of the body. Blood from the upper half travels through the superior vena cava, while blood from the lower half runs through the inferior vena cava.

Other major veins feed into each vena cava, and reveal which portions of the body they are responsible for. The function of the vena cava can be seen from their tributary veins. The superior vena cava, located just above the heart, is formed from the junction of the left and right brachiocephalic veins. These veins return blood from the head, neck, and arms, as well as the upper spine and chest. Another vein, the azygos, collects blood from the chest wall and lungs, and empties into the superior vena cava, just above the heart.

The function of the vena cava that collects blood from the lower body determines its different structure. The inferior vena cava begins near the small of the back, where the iliac veins join. The iliac veins return blood which has been deoxygenated back from the legs. Many smaller tributaries feed into it as it runs near the backbone, crosses the diaphragm, and connects to the heart. These tributaries feed blood from the genitals, abdomen, kidneys, and liver.

Ultimately, the vena cava's function is to ensure the proper operation of the circulatory system. By returning blood that has been depleted of its oxygen to the heart's right atrium, the heart can then pump this blood to the lungs. In the lungs, the blood receives oxygen, which is vital for survival, and returns it to the heart. The heart can then pump the oxygenated blood throughout the body. These important veins help to return this blood for re-use after the body has utilized it.

To assist in the function of the vena cava, contractions from the heart time the delivery of blood and supply pressure. There are no valves that separate the venae cavae from the right atrium. Instead, contractions of the heart are relayed through other veins and muscles. These contractions provide pressure necessary to push deoxygenated blood to the heart. This process is crucial to ensuring continuous blood flow back to the heart.


Anatomy of the Liver

Gross Anatomy

The liver is a roughly triangular organ that extends across the entire abdominal cavity just inferior to the diaphragm. Most of the liver’s mass is located on the right side of the body where it descends inferiorly toward the right kidney. The liver is made of very soft, pinkish-brown tissues encapsulated by a connective tissue capsule. This capsule is further covered and reinforced by the peritoneum of the abdominal cavity, which protects the liver and holds it in place within the abdomen.

The peritoneum connects the liver in 4 locations: the coronary ligament, the left and right triangular ligaments, and the falciform ligament. These connections are not true ligaments in the anatomical sense rather, they are condensed regions of peritoneal membrane that support the liver.

  • The wide coronary ligament connects the central superior portion of the liver to the diaphragm.
  • Located on the lateral borders of the left and right lobes, respectively, the left and righttriangular ligaments connect the superior ends of the liver to the diaphragm.
  • The falciform ligament runs inferiorly from the diaphragm across the anterior edge of the liver to its inferior border. At the inferior end of the liver, the falciform ligament forms the round ligament (ligamentum teres) of the liver and connects the liver to the umbilicus. The round ligament is a remnant of the umbilical vein that carries blood into the body during fetal development.

The liver consists of 4 distinct lobes — the left, right, caudate, and quadrate lobes.

  • The left and right lobes are the largest lobes and are separated by the falciform ligament. The right lobe is about 5 to 6 times larger than the tapered left lobe.
  • The small caudate lobe extends from the posterior side of the right lobe and wraps around the inferior vena cava.
  • The small quadrate lobe is inferior to the caudate lobe and extends from the posterior side of the right lobe and wraps around the gallbladder.

Bile Ducts

The tubes that carry bile through the liver and gallbladder are known as bile ducts and form a branched structure known as the biliary tree. Bile produced by liver cells drains into microscopic canals known as bile canaliculi. The countless bile canaliculi join together into many larger bile ducts found throughout the liver.

These bile ducts next join to form the larger left and right hepatic ducts, which carry bile from the left and right lobes of the liver. Those two hepatic ducts join to form the common hepatic duct that drains all bile away from the liver. The common hepatic duct finally joins with the cystic duct from the gallbladder to form the common bile duct, carrying bile to the duodenum of the small intestine. Most of the bile produced by the liver is pushed back up the cystic duct by peristalsis to arrive in the gallbladder for storage, until it is needed for digestion.

Blood Vessels

The blood supply of the liver is unique among all organs of the body due to the hepatic portal vein system. Blood traveling to the spleen, stomach, pancreas, gallbladder, and intestines passes through capillaries in these organs and is collected into the hepatic portal vein. The hepatic portal vein then delivers this blood to the tissues of the liver where the contents of the blood are divided up into smaller vessels and processed before being passed on to the rest of the body. Blood leaving the tissues of the liver collects into the hepatic veins that lead to the vena cava and return to the heart. The liver also has its own system of arteries and arterioles that provide oxygenated blood to its tissues just like any other organ.

Lobules

The internal structure of the liver is made of around 100,000 small hexagonal functional units known as lobules. Each lobule consists of a central vein surrounded by 6 hepatic portal veins and 6 hepatic arteries. These blood vessels are connected by many capillary-like tubes called sinusoids, which extend from the portal veins and arteries to meet the central vein like spokes on a wheel.

Each sinusoid passes through liver tissue containing 2 main cell types: Kupffer cells and hepatocytes.

  • Kupffer cells are a type of macrophage that capture and break down old, worn out red blood cells passing through the sinusoids.
  • Hepatocytes are cuboidal epithelial cells that line the sinusoids and make up the majority of cells in the liver. Hepatocytes perform most of the liver’s functions — metabolism, storage, digestion, and bile production. Tiny bile collection vessels known as bile canaliculi run parallel to the sinusoids on the other side of the hepatocytes and drain into the bile ducts of the liver.

BIO 140 - Human Biology I - Textbook

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Chapter 19

Accessory Organs in Digestion: The Liver, Pancreas, and Gallbladder

  • State the main digestive roles of the liver, pancreas, and gallbladder
  • Identify three main features of liver histology that are critical to its function
  • Discuss the composition and function of bile
  • Identify the major types of enzymes and buffers present in pancreatic juice

Chemical digestion in the small intestine relies on the activities of three accessory digestive organs: the liver, pancreas, and gallbladder (Figure 1). The digestive role of the liver is to produce bile and export it to the duodenum. The gallbladder primarily stores, concentrates, and releases bile. The pancreas produces pancreatic juice, which contains digestive enzymes and bicarbonate ions, and delivers it to the duodenum.

Figure 1: The liver, pancreas, and gallbladder are considered accessory digestive organs, but their roles in the digestive system are vital.

The Liver

The liver is the largest gland in the body, weighing about three pounds in an adult. It is also one of the most important organs. In addition to being an accessory digestive organ, it plays a number of roles in metabolism and regulation. The liver lies inferior to the diaphragm in the right upper quadrant of the abdominal cavity and receives protection from the surrounding ribs.

The liver is divided into two primary lobes: a large right lobe and a much smaller left lobe. In the right lobe, some anatomists also identify an inferior quadrate lobe and a posterior caudate lobe, which are defined by internal features. The liver is connected to the abdominal wall and diaphragm by five peritoneal folds referred to as ligaments. These are the falciform ligament, the coronary ligament, two lateral ligaments, and the ligamentum teres hepatis. The falciform ligament and ligamentum teres hepatis are actually remnants of the umbilical vein, and separate the right and left lobes anteriorly. The lesser omentum tethers the liver to the lesser curvature of the stomach.

The porta hepatis (&ldquogate to the liver&rdquo) is where the hepatic artery and hepatic portal vein enter the liver. These two vessels, along with the common hepatic duct, run behind the lateral border of the lesser omentum on the way to their destinations. As shown in Figure 2, the hepatic artery delivers oxygenated blood from the heart to the liver. The hepatic portal vein delivers partially deoxygenated blood containing nutrients absorbed from the small intestine and actually supplies more oxygen to the liver than do the much smaller hepatic arteries. In addition to nutrients, drugs and toxins are also absorbed. After processing the bloodborne nutrients and toxins, the liver releases nutrients needed by other cells back into the blood, which drains into the central vein and then through the hepatic vein to the inferior vena cava. With this hepatic portal circulation, all blood from the alimentary canal passes through the liver. This largely explains why the liver is the most common site for the metastasis of cancers that originate in the alimentary canal.

Figure 2: The liver receives oxygenated blood from the hepatic artery and nutrient-rich deoxygenated blood from the hepatic portal vein.

Histology

The liver has three main components: hepatocytes, bile canaliculi, and hepatic sinusoids. A hepatocyte is the liver&rsquos main cell type, accounting for around 80 percent of the liver's volume. These cells play a role in a wide variety of secretory, metabolic, and endocrine functions. Plates of hepatocytes called hepatic laminae radiate outward from the portal vein in each hepatic lobule .

Between adjacent hepatocytes, grooves in the cell membranes provide room for each bile canaliculus (plural = canaliculi). These small ducts accumulate the bile produced by hepatocytes. From here, bile flows first into bile ductules and then into bile ducts. The bile ducts unite to form the larger right and left hepatic ducts, which themselves merge and exit the liver as the common hepatic duct . This duct then joins with the cystic duct from the gallbladder, forming the common bile duct through which bile flows into the small intestine.

A hepatic sinusoid is an open, porous blood space formed by fenestrated capillaries from nutrient-rich hepatic portal veins and oxygen-rich hepatic arteries. Hepatocytes are tightly packed around the fenestrated endothelium of these spaces, giving them easy access to the blood. From their central position, hepatocytes process the nutrients, toxins, and waste materials carried by the blood. Materials such as bilirubin are processed and excreted into the bile canaliculi. Other materials including proteins, lipids, and carbohydrates are processed and secreted into the sinusoids or just stored in the cells until called upon. The hepatic sinusoids combine and send blood to a central vein . Blood then flows through a hepatic vein into the inferior vena cava. This means that blood and bile flow in opposite directions. The hepatic sinusoids also contain star-shaped reticuloendothelial cells (Kupffer cells), phagocytes that remove dead red and white blood cells, bacteria, and other foreign material that enter the sinusoids. The portal triad is a distinctive arrangement around the perimeter of hepatic lobules, consisting of three basic structures: a bile duct, a hepatic artery branch, and a hepatic portal vein branch.

Bile

Recall that lipids are hydrophobic, that is, they do not dissolve in water. Thus, before they can be digested in the watery environment of the small intestine, large lipid globules must be broken down into smaller lipid globules, a process called emulsification. Bile is a mixture secreted by the liver to accomplish the emulsification of lipids in the small intestine.

Hepatocytes secrete about one liter of bile each day. A yellow-brown or yellow-green alkaline solution (pH 7.6 to 8.6), bile is a mixture of water, bile salts, bile pigments, phospholipids (such as lecithin), electrolytes, cholesterol, and triglycerides. The components most critical to emulsification are bile salts and phospholipids, which have a nonpolar (hydrophobic) region as well as a polar (hydrophilic) region. The hydrophobic region interacts with the large lipid molecules, whereas the hydrophilic region interacts with the watery chyme in the intestine. This results in the large lipid globules being pulled apart into many tiny lipid fragments of about 1 µm in diameter. This change dramatically increases the surface area available for lipid-digesting enzyme activity. This is the same way dish soap works on fats mixed with water.

Bile salts act as emulsifying agents, so they are also important for the absorption of digested lipids. While most constituents of bile are eliminated in feces, bile salts are reclaimed by the enterohepatic circulation . Once bile salts reach the ileum, they are absorbed and returned to the liver in the hepatic portal blood. The hepatocytes then excrete the bile salts into newly formed bile. Thus, this precious resource is recycled.

Bilirubin , the main bile pigment, is a waste product produced when the spleen removes old or damaged red blood cells from the circulation. These breakdown products, including proteins, iron, and toxic bilirubin, are transported to the liver via the splenic vein of the hepatic portal system. In the liver, proteins and iron are recycled, whereas bilirubin is excreted in the bile. It accounts for the green color of bile. Bilirubin is eventually transformed by intestinal bacteria into stercobilin, a brown pigment that gives your stool its characteristic color! In some disease states, bile does not enter the intestine, resulting in white (&lsquoacholic&rsquo) stool with a high fat content, since virtually no fats are broken down or absorbed.

Hepatocytes work non-stop, but bile production increases when fatty chyme enters the duodenum and stimulates the secretion of the gut hormone secretin. Between meals, bile is produced but conserved. The valve-like hepatopancreatic ampulla closes, allowing bile to divert to the gallbladder, where it is concentrated and stored until the next meal.

Watch the video linked below to to see the structure of the liver and how this structure supports the functions of the liver, including the processing of nutrients, toxins, and wastes. At rest, about 1500 mL of blood per minute flow through the liver. What percentage of this blood flow comes from the hepatic portal system?

The Pancreas

The soft, oblong, glandular pancreas lies transversely in the retroperitoneum behind the stomach. Its head is nestled into the &ldquoc-shaped&rdquo curvature of the duodenum with the body extending to the left about 15.2 cm (6 in) and ending as a tapering tail in the hilum of the spleen. It is a curious mix of exocrine (secreting digestive enzymes) and endocrine (releasing hormones into the blood) functions (Figure 3).

Figure 3: The pancreas has a head, a body, and a tail. It delivers pancreatic juice to the duodenum through the pancreatic duct.

The exocrine part of the pancreas arises as little grape-like cell clusters, each called an acinus (plural = acini), located at the terminal ends of pancreatic ducts. These acinar cells secrete enzyme-rich pancreatic juice into tiny merging ducts that form two dominant ducts. The larger duct fuses with the common bile duct (carrying bile from the liver and gallbladder) just before entering the duodenum via a common opening (the hepatopancreatic ampulla). The smooth muscle sphincter of the hepatopancreatic ampulla controls the release of pancreatic juice and bile into the small intestine. The second and smaller pancreatic duct, the accessory duct (duct of Santorini), runs from the pancreas directly into the duodenum, approximately 1 inch above the hepatopancreatic ampulla. When present, it is a persistent remnant of pancreatic development.

Scattered through the sea of exocrine acini are small islands of endocrine cells, the islets of Langerhans. These vital cells produce the hormones pancreatic polypeptide, insulin, glucagon, and somatostatin.

Pancreatic Juice

The pancreas produces over a liter of pancreatic juice each day. Unlike bile, it is clear and composed mostly of water along with some salts, sodium bicarbonate, and several digestive enzymes. Sodium bicarbonate is responsible for the slight alkalinity of pancreatic juice (pH 7.1 to 8.2), which serves to buffer the acidic gastric juice in chyme, inactivate pepsin from the stomach, and create an optimal environment for the activity of pH-sensitive digestive enzymes in the small intestine. Pancreatic enzymes are active in the digestion of sugars, proteins, and fats.

The pancreas produces protein-digesting enzymes in their inactive forms. These enzymes are activated in the duodenum. If produced in an active form, they would digest the pancreas (which is exactly what occurs in the disease, pancreatitis). The intestinal brush border enzyme enteropeptidase stimulates the activation of trypsin from trypsinogen of the pancreas, which in turn changes the pancreatic enzymes procarboxypeptidase and chymotrypsinogen into their active forms, carboxypeptidase and chymotrypsin.

The enzymes that digest starch (amylase), fat (lipase), and nucleic acids (nuclease) are secreted in their active forms, since they do not attack the pancreas as do the protein-digesting enzymes.

Pancreatic Secretion

Regulation of pancreatic secretion is the job of hormones and the parasympathetic nervous system. The entry of acidic chyme into the duodenum stimulates the release of secretin, which in turn causes the duct cells to release bicarbonate-rich pancreatic juice. The presence of proteins and fats in the duodenum stimulates the secretion of CCK, which then stimulates the acini to secrete enzyme-rich pancreatic juice and enhances the activity of secretin. Parasympathetic regulation occurs mainly during the cephalic and gastric phases of gastric secretion, when vagal stimulation prompts the secretion of pancreatic juice.

Usually, the pancreas secretes just enough bicarbonate to counterbalance the amount of HCl produced in the stomach. Hydrogen ions enter the blood when bicarbonate is secreted by the pancreas. Thus, the acidic blood draining from the pancreas neutralizes the alkaline blood draining from the stomach, maintaining the pH of the venous blood that flows to the liver.

The Gallbladder

The gallbladder is 8&ndash10 cm (

3&ndash4 in) long and is nested in a shallow area on the posterior aspect of the right lobe of the liver. This muscular sac stores, concentrates, and, when stimulated, propels the bile into the duodenum via the common bile duct. It is divided into three regions. The fundus is the widest portion and tapers medially into the body, which in turn narrows to become the neck. The neck angles slightly superiorly as it approaches the hepatic duct. The cystic duct is 1&ndash2 cm (less than 1 in) long and turns inferiorly as it bridges the neck and hepatic duct.

The simple columnar epithelium of the gallbladder mucosa is organized in rugae, similar to those of the stomach. There is no submucosa in the gallbladder wall. The wall&rsquos middle, muscular coat is made of smooth muscle fibers. When these fibers contract, the gallbladder&rsquos contents are ejected through the cystic duct and into the bile duct (Figure 4). Visceral peritoneum reflected from the liver capsule holds the gallbladder against the liver and forms the outer coat of the gallbladder. The gallbladder's mucosa absorbs water and ions from bile, concentrating it by up to 10-fold.

Figure 4: The gallbladder stores and concentrates bile, and releases it into the two-way cystic duct when it is needed by the small intestine.

Chapter Review

Chemical digestion in the small intestine cannot occur without the help of the liver and pancreas. The liver produces bile and delivers it to the common hepatic duct. Bile contains bile salts and phospholipids, which emulsify large lipid globules into tiny lipid droplets, a necessary step in lipid digestion and absorption. The gallbladder stores and concentrates bile, releasing it when it is needed by the small intestine.

The pancreas produces the enzyme- and bicarbonate-rich pancreatic juice and delivers it to the small intestine through ducts. Pancreatic juice buffers the acidic gastric juice in chyme, inactivates pepsin from the stomach, and enables the optimal functioning of digestive enzymes in the small intestine.


Inferior Vena Cava

The inferior vena cava is the largest vein in the human body. It collects blood from veins serving the tissues inferior to the heart and returns this blood to the right atrium of the heart. Although the vena cava is very large in diameter, its walls are incredibly thin due to the low pressure exerted by venous blood.

The inferior vena cava forms at the superior end of the pelvic cavity when the common iliac veins unite to form a larger vein. From the pelvis, the inferior vena cava ascends through the posterior abdominal body wall just to the right of the vertebral column. Continue Scrolling To Read More Below.

Anatomy Explorer

Anatomy Term

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The inferior vena cava and its tributaries drain blood from the feet, legs, thighs, pelvis and abdomen and deliver this blood to the heart. Many one-way venous valves help to move blood through the veins of the lower extremities against the pull of gravity. Blood passing through the veins is under very little pressure and so must be pumped toward the heart by the contraction of skeletal muscles in the legs and by pressure in the abdomen caused by breathing. Venous valves help to trap blood between muscle contractions or breaths and prevent it from being pulled back down towards the feet by gravity.

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The Pathology of the LIVER

Welcome back! So today we are going to be looking at what the liver does inside our body and the functions of it!

First of all let&aposs get a little gross anatomy lecture on the liver first, so the liver is a triangular organ that extends across the entire abdominal cavity just inferior to the diaphragm. Most of the liver’s mass is located on the right side of the body where it descends inferiorly toward the right kidney.The liver is made of very soft, pinkish-brown tissues encapsulated by a connective tissue capsule. This capsule is further covered and reinforced by the peritoneum of the abdominal cavity, which protects the liver and holds it in place within the abdomen. The liver consists of 4 distinct lobes – the left, right, caudate, and quadrate lobes. The left and right lobes are the largest lobes and are separated by the falciform ligament. The RL (Right Lobe) is about 5 to 6 times larger than the tapered left lobe. The small caudate lobe extends from the posterior side of the right lobe and wraps around the inferior vena cava.

So now lets take a closer look at the Bile ducts - The tubes that carry bile through the liver and gallbladder are known as bile ducts and form a branched structure known as the biliary tree. Bile produced by liver cells drains into microscopic canals known as bile canaliculi. Just a quick glance as to what biles are (it pretty much is a dark green to yellowish brown fluid, produced by the liver of most vertebrates , that aids the digestion of lipids in the small intestine.)

The blood vessels - The blood supply of the liver is unique among all organs of the body due to the hepatic portal vein system. Blood traveling to the spleen, stomach, gallbladder, and of course the intestines passes through capillaries in these organs and is collected into the HPV (Hepatic Portal Vein). It delivers this blood to the tissues of the liver where the contents of the blood are divided up into smaller vessels and processed before being passed on to the rest of the body. Now the interesting part is that leaving the tissues of the liver collects into the hepatic vein that lead to the vena cava and return to the great organ - the heart.

As we all know the liver is good at detoxification, that&aposs why we make all those smoothies and juice for detoxing our liver. Well did you know that as blood from the digestive organs passes through the hepatic portal circulation, the hepatocytes of the liver monitor the contents of the blood and remove many potentially toxic substances before they can reach the rest of the body? Not only that but in order to keep hormone levels within homeostatic limits, the liver also metabolizes and removes from circulation hormones produced by the body’s own glands. Speaking of detox- let me tell you about the best way to detoxify your liver. First of all BEETJUICE. yes that&aposs right beet juice is such a powerful vegetable, it has the great ability to improve blood flow and according to Dr. Oz they are richest dietary sources of antioxidants and naturally occurring nitrates. Nitrates are compounds which improve blood flow throughout the body – including the brain, heart, and muscles. All you have to do is take 1 beet, 3 carrots, juice them al together and what you are going to do is take 1/2 of a lemon and squeeze it in there giving you a tangy flavor. Drinking this 1-2 times a month will help to get rid of any harmful toxins in the body and cleanse out your liver.

Storage - So your liver is pretty much like a storage room, it stores vitamins, and minerals obtained from blood passing through the hepatic portal system. Glucose is transported into hepatocytes under the influence of the hormone insulin and stored as the polysaccharide glycogen. The liver also stores vitamins such as A, D, E, K, and B12, and the minerals iron and copper - in order to provide a constant supply of these essential substances to the tissues of the body.

Alright, so now let&aposs talk about how alcohol puts a big affect on the liver. Has anyone ever told you that drinking too much will affect your liver and kidneys? Well they are right. Let&aposs explore more as to why that is the case. So here&aposs the deal, the liver can only handle a certain amount of alcohol at any given time, so if you drink more than the liver can deal with by drinking too quickly, or drinking too much, your liver cells struggle to process it. So when the alcohol reaches your liver it produces a toxic enzyme called acetaldehyde which can damage liver cells and cause permanent scarring, as well as harm to the brain and stomach lining. But then that&aposs not all that alcohol does. When alcohol enters the body it acts as a diuretic and as such dehydrates you and forces the liver to find water from other sources. The severe dehydration has such a bad affect on the liver. Which is why it is recommended that you consume anywhere from 4-7 cups of water everyday, of course to cleanse out your liver and the harmful toxins.

So yes alcohol can be so bad for your liver, but there&aposs another thing. Too much fat can build up in your liver if you drink more than the liver can handle. This can cause inflammation and fatty liver disease. You can also develop fatty liver disease without even drinking alcohol. A poor diet, being an unhealthy weight, lack of exercise, high cholesterol, diabetes and heart disease can put you at risk of getting liver disease. So a condition called hepatitis is caused by inflammation of the liver associated with long term, excessive drinking. The condition causes the liver to become swollen and tender. (Ohhhh and that can be painful). If you continue to drink heavily, alcoholic hepatitis will most likely persist and develop into cirrhosis. THAT WOULD NOT BE PRETTY!

Ok what is Cirrhosis? Cirrhosis occurs when the liver cells are damaged and replaced by scar tissue because of chronic inflammation. The inflammation can develop because of chronic viral hepatitis, fatty liver disease, unsafe consumption of alcohol, some drugs and harmful substances. The scar tissue affects the flow of blood and other fluids through the liver.

Most recommendations from MDs suggest cutting out drinking completely or at least keeping alcohol intake to a minimum. But you have to know that everyone’s body is different and alcohol may cause abdominal pain and fatigue the day after drinking in some people. By bringing your consumption down you are reducing your risk of liver failure or disease.

If you do have any kind of pain around or close to the liver, visit your MD for more information. If you are consuming too much alcohol and may think you have cirrhosis you can call your doctor to schedule a visit.


The Pathology of the LIVER

Welcome back! So today we are going to be looking at what the liver does inside our body and the functions of it!

First of all let&aposs get a little gross anatomy lecture on the liver first, so the liver is a triangular organ that extends across the entire abdominal cavity just inferior to the diaphragm. Most of the liver’s mass is located on the right side of the body where it descends inferiorly toward the right kidney.The liver is made of very soft, pinkish-brown tissues encapsulated by a connective tissue capsule. This capsule is further covered and reinforced by the peritoneum of the abdominal cavity, which protects the liver and holds it in place within the abdomen. The liver consists of 4 distinct lobes – the left, right, caudate, and quadrate lobes. The left and right lobes are the largest lobes and are separated by the falciform ligament. The RL (Right Lobe) is about 5 to 6 times larger than the tapered left lobe. The small caudate lobe extends from the posterior side of the right lobe and wraps around the inferior vena cava.

So now lets take a closer look at the Bile ducts - The tubes that carry bile through the liver and gallbladder are known as bile ducts and form a branched structure known as the biliary tree. Bile produced by liver cells drains into microscopic canals known as bile canaliculi. Just a quick glance as to what biles are (it pretty much is a dark green to yellowish brown fluid, produced by the liver of most vertebrates , that aids the digestion of lipids in the small intestine.)

The blood vessels - The blood supply of the liver is unique among all organs of the body due to the hepatic portal vein system. Blood traveling to the spleen, stomach, gallbladder, and of course the intestines passes through capillaries in these organs and is collected into the HPV (Hepatic Portal Vein). It delivers this blood to the tissues of the liver where the contents of the blood are divided up into smaller vessels and processed before being passed on to the rest of the body. Now the interesting part is that leaving the tissues of the liver collects into the hepatic vein that lead to the vena cava and return to the great organ - the heart.

As we all know the liver is good at detoxification, that&aposs why we make all those smoothies and juice for detoxing our liver. Well did you know that as blood from the digestive organs passes through the hepatic portal circulation, the hepatocytes of the liver monitor the contents of the blood and remove many potentially toxic substances before they can reach the rest of the body? Not only that but in order to keep hormone levels within homeostatic limits, the liver also metabolizes and removes from circulation hormones produced by the body’s own glands. Speaking of detox- let me tell you about the best way to detoxify your liver. First of all BEETJUICE. yes that&aposs right beet juice is such a powerful vegetable, it has the great ability to improve blood flow and according to Dr. Oz they are richest dietary sources of antioxidants and naturally occurring nitrates. Nitrates are compounds which improve blood flow throughout the body – including the brain, heart, and muscles. All you have to do is take 1 beet, 3 carrots, juice them al together and what you are going to do is take 1/2 of a lemon and squeeze it in there giving you a tangy flavor. Drinking this 1-2 times a month will help to get rid of any harmful toxins in the body and cleanse out your liver.

Storage - So your liver is pretty much like a storage room, it stores vitamins, and minerals obtained from blood passing through the hepatic portal system. Glucose is transported into hepatocytes under the influence of the hormone insulin and stored as the polysaccharide glycogen. The liver also stores vitamins such as A, D, E, K, and B12, and the minerals iron and copper - in order to provide a constant supply of these essential substances to the tissues of the body.

Alright, so now let&aposs talk about how alcohol puts a big affect on the liver. Has anyone ever told you that drinking too much will affect your liver and kidneys? Well they are right. Let&aposs explore more as to why that is the case. So here&aposs the deal, the liver can only handle a certain amount of alcohol at any given time, so if you drink more than the liver can deal with by drinking too quickly, or drinking too much, your liver cells struggle to process it. So when the alcohol reaches your liver it produces a toxic enzyme called acetaldehyde which can damage liver cells and cause permanent scarring, as well as harm to the brain and stomach lining. But then that&aposs not all that alcohol does. When alcohol enters the body it acts as a diuretic and as such dehydrates you and forces the liver to find water from other sources. The severe dehydration has such a bad affect on the liver. Which is why it is recommended that you consume anywhere from 4-7 cups of water everyday, of course to cleanse out your liver and the harmful toxins.

So yes alcohol can be so bad for your liver, but there&aposs another thing. Too much fat can build up in your liver if you drink more than the liver can handle. This can cause inflammation and fatty liver disease. You can also develop fatty liver disease without even drinking alcohol. A poor diet, being an unhealthy weight, lack of exercise, high cholesterol, diabetes and heart disease can put you at risk of getting liver disease. So a condition called hepatitis is caused by inflammation of the liver associated with long term, excessive drinking. The condition causes the liver to become swollen and tender. (Ohhhh and that can be painful). If you continue to drink heavily, alcoholic hepatitis will most likely persist and develop into cirrhosis. THAT WOULD NOT BE PRETTY!

Ok what is Cirrhosis? Cirrhosis occurs when the liver cells are damaged and replaced by scar tissue because of chronic inflammation. The inflammation can develop because of chronic viral hepatitis, fatty liver disease, unsafe consumption of alcohol, some drugs and harmful substances. The scar tissue affects the flow of blood and other fluids through the liver.

Most recommendations from MDs suggest cutting out drinking completely or at least keeping alcohol intake to a minimum. But you have to know that everyone’s body is different and alcohol may cause abdominal pain and fatigue the day after drinking in some people. By bringing your consumption down you are reducing your risk of liver failure or disease.

If you do have any kind of pain around or close to the liver, visit your MD for more information. If you are consuming too much alcohol and may think you have cirrhosis you can call your doctor to schedule a visit.


Glossary

accessory duct: (also, duct of Santorini) duct that runs from the pancreas into the duodenum

acinus: cluster of glandular epithelial cells in the pancreas that secretes pancreatic juice in the pancreas

bile: alkaline solution produced by the liver and important for the emulsification of lipids

bile canaliculus: small duct between hepatocytes that collects bile

bilirubin: main bile pigment, which is responsible for the brown color of feces

central vein: vein that receives blood from hepatic sinusoids

common bile duct: structure formed by the union of the common hepatic duct and the gallbladder&rsquos cystic duct

common hepatic duct: duct formed by the merger of the two hepatic ducts

cystic duct: duct through which bile drains and enters the gallbladder

enterohepatic circulation: recycling mechanism that conserves bile salts

enteropeptidase: intestinal brush-border enzyme that activates trypsinogen to trypsin

gallbladder: accessory digestive organ that stores and concentrates bile

hepatic artery: artery that supplies oxygenated blood to the liver

hepatic lobule: hexagonal-shaped structure composed of hepatocytes that radiate outward from a central vein

hepatic portal vein: vein that supplies deoxygenated nutrient-rich blood to the liver

hepatic sinusoid: blood capillaries between rows of hepatocytes that receive blood from the hepatic portal vein and the branches of the hepatic artery

hepatic vein: vein that drains into the inferior vena cava

hepatocytes: major functional cells of the liver

liver: largest gland in the body whose main digestive function is the production of bile

pancreas: accessory digestive organ that secretes pancreatic juice

pancreatic juice: secretion of the pancreas containing digestive enzymes and bicarbonate

porta hepatis: &ldquogateway to the liver&rdquo where the hepatic artery and hepatic portal vein enter the liver

portal triad: bile duct, hepatic artery branch, and hepatic portal vein branch

reticuloendothelial cell: (also, Kupffer cell) phagocyte in hepatic sinusoids that filters out material from venous blood from the alimentary canal


Watch the video: How to obtain: Inferior Vena Cava Ultrasound View- Training and Techniques - ICU (January 2023).