Information

15.6.1.4: Hormones of the Pituitary - Biology

15.6.1.4: Hormones of the Pituitary - Biology


We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

The pituitary gland is pea-sized structure located at the base of the brain. In humans, it consists of two lobes: the Anterior Lobe and the Posterior Lobe.

Hormones of the Anterior Lobe

The anterior lobe contains six types of secretory cells, all but one of which are specialized to secrete only one of the anterior lobe hormones. All of them secrete their hormone in response to hormones reaching them from the hypothalamus of the brain.

Thyroid Stimulating Hormone (TSH)

TSH (also known as thyrotropin) is a glycoprotein consisting of a beta chain of 118 amino acids and an alpha chain of 92 amino acids. The alpha chain is identical to that found in two other pituitary hormones, FSH and LH as well as in the hormone chorionic gonadotropin. Thus it is its beta chain that gives TSH its unique properties. The secretion of TSH is stimulated by the arrival of thyrotropin releasing hormone (TRH) from the hypothalamus and is inhibited by the arrival of somatostatin from the hypothalamus.

As its name suggests, TSH stimulates the thyroid gland to secrete its hormone thyroxine (T4). It does this by binding to transmembrane G-protein-coupled receptors (GPCRs) on the surface of the cells of the thyroid. Some people develop antibodies against their own TSH receptors. When these bind the receptors, they "fool" the cell into making more T4 causing hyperthyroidism. The condition is called thyrotoxicosis or Graves' disease.

Hormone deficiencies

A deficiency of TSH causes hypothyroidism: inadequate levels of T4 (and thus of T3). Physicians occasionally encounter patients who are homozygous for mutant TSH receptors or mutant TRH receptors. In either case, they suffer from hypothyroidism. A deficiency of TSH, or mutant TSH receptors, have also been implicated as a cause of osteoporosis. Mice, whose TSH receptors have been knocked out, develop increased numbers of bone-reabsorbing osteoclasts.

Follicle-Stimulating Hormone (FSH)

FSH is a heterodimeric glycoprotein consisting of the same alpha chain found in TSH (and LH) and a beta chain of 118 amino acids, which gives it its unique properties. Synthesis and release of FSH is triggered by the arrival from the hypothalamus of gonadotropin-releasing hormone (GnRH). The effect of FSH depends on one's sex. In sexually-mature females, FSH (assisted by LH) acts on the follicle to stimulate it to release estrogens. FSH produced by recombinant DNA technology (Gonal-f®) is available to promote ovulation in women planning to undergo in vitro fertilization (IVF) and other forms of assisted reproductive technology. In sexually-mature males, FSH acts on spermatogonia stimulating (with the aid of testosterone) the production of sperm.

Luteinizing Hormone (LH)

LH is synthesized within the same pituitary cells as FSH and under the same stimulus (GnRH). It is also a heterodimeric glycoprotein consisting of the same 92-amino acid alpha subunit found in FSH and TSH (as well as in chorionic gonadotropin) and a beta chain of 121 amino acids that is responsible for its properties.

The effects of LH also depend on sex. In sexually-mature females, a surge of LH triggers the completion of meiosis I of the egg and its release (ovulation) in the middle of the menstrual cycle; LH also stimulates the now-empty follicle to develop into the corpus luteum, which secretes progesterone during the latter half of the menstrual cycle. Women with a severe LH deficiency can now be treated with human LH (Luveris®) produced by recombinant DNA technology. LH in males acts on the interstitial cells (also known as Leydig cells) of the testes stimulating them to synthesize and secrete the male sex hormone, testosterone. LH in males is also known as interstitial cell stimulating hormone (ICSH).

Prolactin (PRL)

Prolactin is a protein of 198 amino acids. During pregnancy it helps in the preparation of the breasts for future milk production. After birth, prolactin promotes the synthesis of milk. Prolactin secretion is stimulated by TRH and repressed by estrogens and dopamine. In pregnant mice, prolactin stimulates the growth of new neurons in the olfactory center of the brain.

Growth Hormone (GH)

Human growth hormone (HGH; also called somatotropin) is a protein of 191 amino acids. The GH-secreting cells are stimulated to synthesize and release GH by the intermittent arrival of growth hormone releasing hormone (GHRH) from the hypothalamus. GH promotes body growth by:

  • binding to receptors on the surface of liver cells.
  • This stimulates them to release insulin-like growth factor-1 (IGF-1; also known as somatomedin)
  • IGF-1 acts directly on the ends of the long bones promoting their growth

Things that can go wrong:

  • In childhood,
    • hyposecretion of GH produces a short but normally-proportioned body.
    • Growth retardation can also result from an inability to respond to GH. This can be caused by inheriting two mutant genes encoding the receptors for
      • GHRH or
      • GH (causing Laron syndrome, a form of dwarfism) or
      • homozygosity for a disabling mutation in STAT5b, which is part of the "downstream" signaling process after GH binds its receptor.
    • hypersecretion leads to gigantism
  • In adults, a hypersecretion of GH or GHRH leads to acromegaly.

Hormone-replacement therapy

GH from domestic mammals like cows and pigs does not work in humans. So for many years, the only source of GH for therapy was that extracted from the glands of human cadavers. But this supply was shut off when several patients died from a rare neurological disease attributed to contaminated glands. Now, thanks to recombinant DNA technology, recombinant human GH (rHGH) is available. While a benefit to patients suffering from GH deficiency or the short stature associated with Turner syndrome, there has also been pressure to use it to stimulate growth in youngsters who have no deficiency but whose parents want them to grow up tall. So, in the summer of 2003, the U.S. FDA approved the use of human growth hormone (HGH) for boys predicted to grow no taller than 5′3″ and for girls, 4′11″ even though otherwise perfectly healthy.

ACTH — the adrenocorticotropic hormone

ACTH is a peptide of 39 amino acids. It is cut from a larger precursor proopiomelanocortin (POMC). ACTH acts on the cells of the adrenal cortex, stimulating them to produce

  • glucocorticoids, like cortisol
  • mineralocorticoids, like aldosterone
  • androgens (male sex hormones, like testosterone)
  • In the fetus, ACTH stimulates the adrenal cortex to synthesize a precursor of estrogen called dehydroepiandrosterone sulfate (DHEA-S) which helps prepare the mother for giving birth.

Production of ACTH depends on the intermittent arrival of corticotropin-releasing hormone (CRH) from the hypothalamus. Hypersecretion of ACTH is a frequent cause of Cushing's syndrome.

Alpha Melanocyte-Stimulating Hormone (α-MSH )

Alpha MSH is also a cleavage product of proopiomelanocortin (POMC). In fact, α-MSH is identical to the first 13 amino acids at the amino terminal of ACTH. MSH is discussed in a separate page.

Hormones of the Posterior Lobe

The posterior lobe of the pituitary releases two hormones — both synthesized in the hypothalamus — vasopressin and oxytocin into the circulation.

Vasopressin

Vasopressin is a peptide of 9 amino acids (Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly). It is also known as arginine vasopressin (AVP) and the antidiuretic hormone (ADH). Vasopressin acts on the collecting ducts of the kidney to facilitate the reabsorption of water into the blood. Thus it acts to reduce the volume of urine formed (giving it its name of antidiuretic hormone). A deficiency of vasopressin or inheritance of mutant genes for its receptor (called V2) leads to excessive loss of urine, a condition known as diabetes insipidus. The most severely-afflicted patients may urinate as much as 30 liters (almost 8 gallons!) of urine each day. The disease is accompanied by terrible thirst, and patients must continually drink water to avoid dangerous dehydration.

Another type of receptor for vasopressin (designated V1a) is found in the brain, e.g., in voles and mice (rodents) and in primates like monkeys and humans.

  • Male prairie voles (Microtus pinetorum) and marmoset monkeys have high levels of the V1a receptor in their brains, tend to be monogamous, and help with care of their young.
  • Male meadow voles (Microtus montanus) and rhesus monkeys have lower levels of the V1a receptor in their brains, are promiscuous, and give little or no help with the care of their young.

Meadow voles whose brains have been injected with a vector causing increased expression of the V1a receptor become more like prairie voles in their behavior. (See Lim, M. M. et al., Nature, 17 June 2004.)

The level of expression of the V1a receptor gene is controlled by a "microsatellite" region upstream (5') of the ORF. This region contains from 178 to 190 copies of a repeated tetranucleotide (e.g., CAGA). Prairie voles have more copies of the repeat than meadow voles, and they express higher levels of the receptor in the parts of the brain associated with these behaviors. A similar microsatellite region is present in the pygmy chimpanzee or bonobo (Pan paniscus) but is much shorter in the less-affectionate common chimpanzee (Pan troglodytes).

Vasopressin and the Circadian Clock

Mice are nocturnal and become active at the start of the night. This is a circadian rhythm that persists for a time even after the lights in the lab are turned off each day 8 hours sooner (like arriving in London after a flight from Los Angeles, California). Only after 8–10 days do the mice overcome their "jet lag", adjusting to the new dark-light schedule. (It also takes us about one day to reset our circadian rhythms for each hour that our day-night schedule is shifted.)

It turns out that arginine vasopressin, acting on the suprachiasmatic nucleus (SCN), plays a role in this resistance to resetting their circadian clock. Mice with their genes for the V1a and V1b receptors knocked out adjust much more quickly (2–4 days) to the change. What evolutionary advantage this resistance to resetting the circadian clock confers is not clear, but understanding the mechanism raises the possibility of using drugs to speed getting over jet lag and also to help those whose work shifts are periodically altered. (Read about this work in Yamaguchi, Y., et al. in the 4 October 2013 issue of Science.).

Oxytocin

Oxytocin is a peptide of 9 amino acids (Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly). It acts on certain smooth muscles by stimulating contractions of the uterus at the time of birth and stimulating release of milk when the baby begins to suckle. Oxytocin is often given to prospective mothers to hasten birth.

In rodents, oxytocin also acts on the nucleus accumbens and amygdala in the brain where it enhances bonding between males and females after they have mated and bonding between a mother and her newborn. In mice, oxytocin acts on striated muscle stem cells to promote repair after they have been injured. In humans, oxytocin increases the level of one's trust in other people.


The Anterior Lobe

Some people develop antibodies against their own TSH receptors. When these bind the receptors, they "fool" the cell into making more T4 causing hyperthyroidism. The condition is called thyrotoxicosis or Graves' disease.

Hormone deficiencies

A deficiency of TSH causes hypothyroidism: inadequate levels of T4 (and thus of T3 [Link]).

Physicians occasionally encounter patients who are homozygous for mutant TSH receptors or mutant TRH receptors. In either case, they suffer from hypothyroidism.

A deficiency of TSH, or mutant TSH receptors, have also been implicated as a cause of osteoporosis. Mice, whose TSH receptors have been knocked out, develop increased numbers of bone-reabsorbing osteoclasts.


Pituitary Gland

The pituitary gland is a tiny organ, the size of a pea, found at the base of the brain. As the &ldquomaster gland&rdquo of the body, it produces many hormones that travel throughout the body, directing certain processes or stimulating other glands to produce other hormones.The pituitary gland makes or stores many different hormones. The following hormones are made in the anterior (front part) of the pituitary gland:

PROLACTIN

This hormone stimulates breast milk production after childbirth. When prolactin is high, it affects the hormones that control the ovaries in women and testes in men. As a result, high prolactin can affect menstrual periods, sexual function and fertility.

GROWTH HORMONE (GH)

This hormone stimulates growth in childhood and plays a role in maintaining healthy muscles and bone and well-being in adults. It also affects fat distribution in the body. Too much growth hormone causes a disease that is called acromegaly. In children, too much growth hormone causes excessive growth, called gigantism.

ADRENOCORTICOTROPIN (ACTH)

This hormone stimulates the production of cortisol by the adrenal glands&mdashsmall glands that sit on top of the kidneys. Cortisol, a "stress hormone," is needed for our survival. It helps maintain blood pressure and blood glucose (sugar) levels, and is produced in larger amounts when we&rsquore under stress, especially during illness, surgery, or after injury. Too much ACTH will result in too much cortisol production this is called Cushing&rsquos syndrome or Cushing&rsquos disease. Low ACTH will result in low cortisol, called adrenal insufficiency.

THYROID-STIMULATING HORMONE (TSH)

This hormones stimulates the thyroid gland to produce thyroid hormones, which regulate the body's metabolism, energy balance, growth, and nervous system activity. Too much TSH is rare and will cause hyperthyroidism (too much thyroid hormone). Lack of TSH results in hypothyroidism (not enough thyroid hormone).

LUTEINIZING HORMONE (LH)

This hormone stimulates testosterone production in men and egg release (ovulation) in women

FOLLICLE-STIMULATING HORMONE (FSH)

This hormone promotes sperm production in men and stimulates the ovaries to produce estrogen and develop eggs in women. LH and FSH work together to enable normal function of the ovaries and testes. Problems with these hormones affects menstrual periods in women and fertility and sexual function in both women and men.

The following hormones are stored in the posterior (back part) of the pituitary gland:
ANTIDIURETIC HORMONE (ADH)

This hormone is also called vasopressin, it regulates water balance in the body and sodium levels in the blood. It conserves body water by reducing the amount of water lost in urine. Lack of ADH causes increased urination and thirst, a condition that is called diabetes insipidus .

OXYTOCIN

This hormone causes milk to flow from the breasts in breastfeeding women, and may also help labor to progress. Oxytocin may also play an important role in human behavior and social interaction and may promote bonding between a mother and her child.

When the pituitary gland doesn't operate in a healthy manner, this can lead to pituitary disorders.


Pituitary Gland Location

The pituitary gland lies roughly in the center of the human skull. It rests below the hypothalamus of the brain and behind the bridge of our noses. This location actually makes sense, in light of the hypothalamus’s role in fine-tuning the activity of the pituitary gland. This is made possible by the nerve fibers that span these two structures and allow for easy communication.

Likewise, a thin vascular connection that is forged within the pituitary stalk, or infundibulum, facilitates the hypothalamus’s control. Further, the pituitary gland itself is supplied by branches off of the internal carotid artery. Its regulation is fine-tuned by a negative feedback relationship between the pituitary and hypothalamus.

The concept map illustrates the complex regulatory relationship between the superseding hypothalamus and the pituitary gland. The relationship follows a negative feedback loop.


Hormones produced by other glands in the body

In total more than 200 hormones or hormone-like substances have been discovered. In addition to the hormones listed in the table above, five of these hormones are controlled by hormones released by the pituitary.

Hormone Organ Function
Cortisol Adrenals Cortisol has a number of functions. It promotes normal metabolism, maintains blood sugar levels and blood pressure, provides resistance to stress and acts as an anti-inflammatory agent. It also plays a part in regulation of fluid balance in the body.
Thyroxine Thyroid Thyroxine controls many body functions, including heart rate, temperature and metabolism. It also plays a role in the metabolism of calcium in the body.
Oestrogen Ovaries Oestrogen facilitates growth of the tissues of the sex organs and other tissues related to reproduction. Oestrogen also acts to strengthen bones and has a protective effect on the heart.
Progesterone Ovaries Progesterone promotes the changes in the uterus that occur in preparation for the implantation of a fertilised ovum and prepares the breasts for milk production.
Testosterone Testes Testosterone is responsible for the characteristics of the masculine body, including hair growth on the face and body and muscle development. Testosterone is essential for the production of sperm and also acts to strengthen bones.

For more information about glands and hormones, as well as educational resources, visit the Society for Endocrinology's 'You and Your Hormones' website


15.6.1.4: Hormones of the Pituitary - Biology

The official publication of the Pituitary Society and the Growth Hormone Research Society

Pituitary is an international publication devoted to basic and clinical aspects of the pituitary gland. It is designed to publish original, high quality research in both basic and pituitary function as well as clinical pituitary disease.

Biology of Pituitary Tumors
Mechanisms of Pituitary Hormone Secretion
Regulation of Pituitary Function
Prospective Clinical Studies of Pituitary Disease
Critical Basic and Clinical Reviews

Pituitary is directed at basic investigators, physiologists, clinical adult and pediatric endocrinologists, neurosurgeons and reproductive endocrinologists interested in the broad field of the pituitary and its disorders. The Editorial Board has been drawn from international experts in basic and clinical endocrinology. The journal offers a rapid turnaround time for review of manuscripts, and the high standard of the journal is maintained by a selective peer-review process which aims to publish only the highest quality manuscripts. Pituitary will foster the publication of creative scholarship as it pertains to the pituitary and will provide a forum for basic scientists and clinicians to publish their high quality pituitary-related work.


Disorders of Pituitary Hormones

This disease is caused by hyper secretion of STH in child. It is char­acterized by morphological, physiologi­cal, psychological and sexological fea­tures (Fig. 12.1).

(i) Morphological features:

1. Abnormal body height (7 to 8 ft.)

2. Unusual elongation of limbs and hands.

3. Thickening of skin of eyelids and nose.

6. Visceral organs enlarged.

7. Face looks like young individual,

(ii) Physiological features:

(iii) Psychological features:

Individual becomes intelligent.

(iv) Sexological features:

1. The primary and secondary sex characters are not well devel­oped.

2. The sexual activity may be de­creased.

This disease is caused by the hyper secretion of STH in adult con­dition due to tumors of somatotrophs. It is characterized by

(i) Morphological features (Fig. 12.2)

1. There is overgrowth of the mem­branous bones like skull, upper jaw, lower jaw.

2. Protrusion of lower jaw (Prog­nathism).

3. The acral parts like small bones of hands and feet become grossly enlarged and become spade like.

4. Irregular enlargement of hands and feet.

5. Abnormal increase of facial length.

6. Thickening of skin of fingers, hands, feet, nose, lips etc.

7. Body bends in form due to abnor­mal growth of vertebral column.

8. Eye brow ridges become promi­nent.

9. Increase of visceral organs like heart, liver and lung.

10. The size of thyroid and adrenal glands become enlarged.

11. The tongue is enlarged.

(ii) Physiological features:

1. May cause hyper-glycaemia.

4. Increased secretion of sweat.

(iii) Psychological features:

(iv) Sexological features:

1. Sexual function in both become depressed.

2. Gonads become reduced in size.

3. In male, there is loss of libido ef­fect.

4. In female, menstrual distur­bances and ill developed breast takes place.

(B) Due to Hypo-secretion of STH:

It is caused due to hypo-activity of STH cells in pre-pubertal life.

It shows following features:

(i) Morphological features (Fig. 12.3)

1. Very abnormal short height (about 3 ft.)

2. Abnormal skeletal growth.

3. The body proportions and facial features of an adult looks like a normal child.

5. Primary teeth appear at the ex­pected age but the eruption of secondary teeth is delayed.

(ii) Physiological features:

4. The insulin response to glucose in usually subnormal.

5. Accumulation of nitrogen prod­uct is increased.

(iii) Psychological features:

1. Normal intelligence is developed in proportion to age.

2. Psychological adjustment be­comes difficult when they enter into adult stage.

(iv) Sexological features:

1. Gonads are underdeveloped.

2. Secondary sex characters are less developed.

3. Loss of sexual desire in adult.

(a) GH-deficiency dwarfism:

It is characterised by failure of STH se­cretion and a consequent decline in IGF-I (insulin like growth factor-l) for­mation.

It is charac­terised by the deficiency on defect of hepatic STH receptors so that plasma IGF-I is low in-spite of a high plasma level of STH.

(c) Pigmy type dwarfism:

It is charac­terised by the defect in synthesis of IGF-I.

(d) Forlich’s type dwarfism:

It is caused due to damage of tissues of adenohypophysis.

It is caused due to hypo-secretion in adult. It is characterized by fol­lowing features.

(i) Morphological features:

1. Retarded development of bones, feet and face.

2. Some ridge formation takes place on the bones of face.

4. Skin is wrinkle and dry.

5. Adiposity is fairly common.

(ii) Physiological features:

2. Less Ca ++ level in blood.

3. Accumulation of nitrogenous products.

(iii) Psychological features:

(iv) Sexological features:

2. Sexual functions are reduced.

(C) Due to Hypo Secretion of Vasopressin/ADH:

This disease is caused by severe depression or suppression of neu­rohypophysial hormone vasopressin (ADH) secretion. It is of two types—(i) neurogenic and (ii) nephrogenic.

Due to damage of hypathalamo-hypophysial system, or de­velopment of hypothalamic tumour, or damage of nervous system, or infections etc.

Due to unresponsive­ness of renal tissue to vasopressin or re­nal infections, or renal defects.

(i) Polyuria (production of large volume of urine)

(ii) Poly dypsia (severe thirst)

(iii) Hypokalemia (electrolyte disorder)

(iv) Physical and mental retardation.

(v) Dilation of urinary bladder.

It is caused by the hypo-function of anterior pituitary. The main etiology of this is formation of tumor, pi­tuitary apoplexy, head trauma, radiation therapy, surgery problems etc. (Figs. 12.4 and 12.5).

Hyperactivity of adenohypophysis occurs due to formation of neoplastic pituitary tumour, hypertro­phy or enhanced hypothalamic stimula­tion.

(C) Pan hypopituitarism:

It involves total loss of hypophysial hormone secretion which could be due to a congenital dysfunc­tion, i.e., failure of the pituitary to de­velop, or to destruction of the pituitary at a later stage in life. It is also possible that the pars distalis might fail to secrete only one of its many hormones.

This disease is formed by hyper secretion of prolactin (LTH). Hyper secretion takes place due to pituitary adenomas or defect in hypothalamohypophysial system. In case of pituitary adenoma, lateral growth of adenohypophysis takes place.


Pituitary Gland Hormones

The mammalian endocrine system consists of the following endocrine glands.
(1) Hypothalamus, pituitary and pineal glands, which are associated with the brain.
(2) Thyroids, parathyroid and thymus, associated with the pharynx and bronchial pouches.
(3) Pancreas, adrenals and gonads, which lie in the coelom.

Pituitary Gland

Pituitary gland is one of the most important endocrine glands. It produces several hormones, some of which profusely influence the activities of other endocrine tissues are known as pituitary gland hormones. Its own activity is influenced by hypothalamus and pineal body.
The pituitary is a small ovoid gland of pea size and weighs 0.5 - 1.0 g in man and slightly more in a woman during pregnancy. It remains suspended from the floor of the third ventricle of the brain by a narrow funnel shaped stalk called infundibulum that lies in a depression on the upper surface of the sphenoid bone. Pituitary gland is divisible into two major parts: (i) the anterior pituitary or the pars anterior and (ii) the posterior pituitary or the pars posterior.

The anterior pituitary gland hormones

The six hormones synthesized by the anterior pituitary are as follows: -
i) Growth hormone (GH) or somatotropic hormone (STH)
ii) Adrenocorticotropic hormone (ACTH) or corticotrophin
iii) Prolactin or lactogenic hormone or mammotropin (LTH)
iv) Thyrotrophic hormone or thyroid stimulating hormone (TSH) or thyrotropin
v) Follicle stimulating hormone (FSH)
vi) Luteinizing hormone (LH) or interstitial cell stimulating hormone (ICSH)
Note that, two of these hormones, FSH and LH, are collectively known as gonadotropic hormones.

Growth hormone

The pituitary gland hormones GH or STH or somatotropin produced by somatotrophs (acidophil cells). Functionally, somatotropin is the most important hormone for normal growth of the body. It does so I stimulating retention of proteins and calcium in the body, synthesis and disposition of proteins in the tissues, growth and elongation of long bones, and proportionate growth of the muscles and visceral organs. It affects
carbohydrate and fat metabolism. It also increases blood sugar level and lipolysis of the adipose tissue. Normal growth pattern is disturbed by the secretion of abnormal levels of GH. Its deficiency leads to warfism, while excessive secretion produces gigantism and acromegaly. Deficiency of GH in childhood produces profound impairment of growth. Children with deficiency of GH grow less than half of the normal rate, leading to dwarfism Secretion of GH in excess amounts in childhood or puberty causes gigantism.

Adrenocorticotropic hormone (ACTH)

The pituitary gland hormones ACTH is produced by corticotrophs (basophil cells), located chiefly in the central part of the anterior pituitary. Corticotropin releasing factor (CRH) of hypothalamus has a very strong influence on ACTH secretion. Cortisol level of plasma affects the hypothalamus, thereby exerting a feedback control on the hypothalamic CRH. Both, mental and physical stresses cause stimulation of ACTH secretion.
ACTH is necessary for normal growth, development and maintenance of the adrenal cortex. It stimulates the secretion of cortisol and adrenal androgens of the adrenal cortex. It also acts on melanocytes. Thus hypersecretion of ACTH is the cause of pigmentation in Addison's disease. It stimulates lipolysis in the adipose tissue. Moreover, ACTH, along with cortisol and CRH, forms an axis which is the main weapon against various forms of stresses.

Lactogenic hormone or mammotropin (LTH)

Prolactin, one of the anterior pituitary gland hormones is secreted by lactotrophs (mammotrophs), which are acidophil cells. There is a considerable increase in the number of lactotrophs during pregnancy. Prolactin inhibitory factor (PIF) released from the hypothalamus inhibits the secretion of prolactin.
However, mammary teats sucking by baby generate afferent impulses which reflex to stimulate the secretion of prolactin through hypothalamus. Prolactin is responsible for the maintenance of corpus luteum and continued production of progesterone in female mammals. It also supplements the actions of gonadal hormones in stimulating the growth and activity of the female mammary gland during pregnancy and lactation.

Thyroid stimulating hormone(TSH)

Another of the anterior pituitary gland hormones is thyrotropin, synthesized by thyrotrophs, which are basophilic cells. Secretion of thyrotropin is controlled by hypothalamus and the level of circulating thyroxine. Thyrotropin releasing factor (TRF) of hypothalamus causes stimulation of thyiotrophs and thus increases TSH level. TSH secretion is also under the feedback control of thyroxine. The major action of TSH is to stimulate the thyroid gland to produce thyroid hormones.

Follicle stimulating hormone (FSH)

FSH is secreted by gonadotrophs, which are basophilic in nature. Gonadotropin, one of the anterior pituitary gland hormones releasing hormone of hypothalamus. The concentration of sex hormones in the blood also determines the FSH secretion. In females, FSH causes growth and maturation of Graafian follicles the growing follicle in turn secretes estrogen. However, in males, FSH helps in spermatogenesis and normal functioning of seminal vesicles.

Luteinizing hormone (LH)

LH is also secreted by gonadotrophs and is glycoprotein in nature. In females, LH is chiefly responsible for ovulation, formation and maintenance of corpus luteum and secretion of progesterone. However, in males, it is responsible for the stimulation of interstitial cells which in turn produce the male sex hormone, testosterone.


The Pituitary

The pituitary, albeit a small gland, is known as the "master gland" of the endocrine system and contributes to a wide spectrum of disorders, diseases, and syndromes. Since the publication of the second edition of The Pituitary, in 2002, there have been major advances in the molecular biology research of pituitary hormone production and action and there is now a better understanding of the pathogenesis of pituitary tumors and clinical syndromes resulting in perturbation of pituitary function. There have also been major advances in the clinical management of pituitary disorders. Medical researchers and practitioners now better understand the morbidity and mortality associated with pituitary hormone hyposecretion and hypersecretion. Newly developed drugs, and improved methods of delivering established drugs, are allowing better medical management of acromegaly and prolactinoma. These developments have improved the worldwide consensus around the definition of a "cure" for pituitary disease, especially hormone hypersecretion, and hence will improve the success or lack of success of various forms of therapy. It is therefore time for a new edition of The Pituitary.

The third edition will continue to be divided into sections that summarize normal hypothalamic-pituitary development and function, hypothalamic-pituitary failure, and pituitary tumors additional sections will describe pituitary disease in systemic disorders and diagnostic procedures, including imaging, assessment of the eyes, and biochemical testing.

The first chapter will be completely new – placing a much greater emphasis on physiology and pathogenesis. Two new chapters will be added on the Radiation and Non-surgical Management of the Pituitary and Other Pituitary Lesions. Other chapters will be completely updated and many new author teams will be invited. The second edition published in 2002 and there have been incredible changes in both the research and clinical aspects of the pituitary over the past 8 years – from new advances in growth hormones to pituitary tumor therapy.

The pituitary, albeit a small gland, is known as the "master gland" of the endocrine system and contributes to a wide spectrum of disorders, diseases, and syndromes. Since the publication of the second edition of The Pituitary, in 2002, there have been major advances in the molecular biology research of pituitary hormone production and action and there is now a better understanding of the pathogenesis of pituitary tumors and clinical syndromes resulting in perturbation of pituitary function. There have also been major advances in the clinical management of pituitary disorders. Medical researchers and practitioners now better understand the morbidity and mortality associated with pituitary hormone hyposecretion and hypersecretion. Newly developed drugs, and improved methods of delivering established drugs, are allowing better medical management of acromegaly and prolactinoma. These developments have improved the worldwide consensus around the definition of a "cure" for pituitary disease, especially hormone hypersecretion, and hence will improve the success or lack of success of various forms of therapy. It is therefore time for a new edition of The Pituitary.

The third edition will continue to be divided into sections that summarize normal hypothalamic-pituitary development and function, hypothalamic-pituitary failure, and pituitary tumors additional sections will describe pituitary disease in systemic disorders and diagnostic procedures, including imaging, assessment of the eyes, and biochemical testing.

The first chapter will be completely new – placing a much greater emphasis on physiology and pathogenesis. Two new chapters will be added on the Radiation and Non-surgical Management of the Pituitary and Other Pituitary Lesions. Other chapters will be completely updated and many new author teams will be invited. The second edition published in 2002 and there have been incredible changes in both the research and clinical aspects of the pituitary over the past 8 years – from new advances in growth hormones to pituitary tumor therapy.


Section Summary

The male and female reproductive cycles are controlled by hormones released from the hypothalamus and anterior pituitary as well as hormones from reproductive tissues and organs. The hypothalamus monitors the need for the FSH and LH hormones made and released from the anterior pituitary. FSH and LH affect reproductive structures to cause the formation of sperm and the preparation of eggs for release and possible fertilization. In the male, FSH and LH stimulate Sertoli cells and interstitial cells of Leydig in the testes to facilitate sperm production. The Leydig cells produce testosterone, which also is responsible for the secondary sexual characteristics of males. In females, FSH and LH cause estrogen and progesterone to be produced. They regulate the female reproductive system which is divided into the ovarian cycle and the menstrual cycle. Menopause occurs when the ovaries lose their sensitivity to FSH and LH and the female reproductive cycles slow to a stop.


Clinical and Pathological Aspects of Silent Pituitary Adenomas

Context: Silent pituitary adenomas are anterior pituitary tumors with hormone synthesis but without signs or symptoms of hormone hypersecretion. They have been increasingly recognized and represent challenging diagnostic issues.

Evidence acquisition: A comprehensive literature search was performed using MEDLINE and EMBASE databases from January 2000 to March 2018 with the following key words: (i) pituitary adenoma/tumor and nonfunctioning or (ii) pituitary adenoma/tumor and silent. All titles and abstracts of the retrieved articles were reviewed, and recent advances in the field of silent pituitary adenomas were summarized.

Evidence synthesis: The clinical and biochemical picture of pituitary adenomas reflects a continuum between functional and silent adenomas. Although some adenomas are truly silent, others will show some evidence of biochemical hypersecretion or could have subtle clinical signs and, therefore, can be referred to as clinically silent or "whispering" adenomas. Silent tumors seem to be more aggressive than their secreting counterparts, with a greater recurrence rate. Transcription factors for pituitary cell lineages have been introduced into the 2017 World Health Organization guidelines: steroidogenic factor 1 staining for gonadotroph lineage PIT1 (pituitary-specific positive transcription factor 1) for growth hormone, prolactin, and TSH lineage, and TPIT for the corticotroph lineage. Prospective studies applying these criteria will establish the value of the new classification.

Conclusions: A concise review of the clinical and pathological aspects of silent pituitary adenomas was conducted in view of the new World Health Organization classification of pituitary adenomas. New classifications, novel prognostics markers, and emerging imaging and therapeutic approaches need to be evaluated to better serve this unique group of patients.


Watch the video: Endocrine System 4 Hypothalamus, Pituitary Gland u0026 Hormones Secreted (December 2022).