Pituitary Gland and its Secretions

The human pituitary gland is reddish – Grey, oval structure about 10mm in diameter located in the brain just behind the optic chiasma as an extension from the field the hypothalamus. Average weight of the gland in females is 0.5 – 0.6gm and in males is 0.6 to 0.7 gm. The pituitary gland is made of 3 lobes namely,

Anterior pituitary gland lobe (largest of all) [70%]

  1. Pituitary gland Middle lobe (5%)
  2. Posterior pituitary gland lobe (25%)

Pituitary Gland and its Secretions

I) Anterior Pituitary Gland lobe:

Andreas vasalius” described the pituitary body in 1543. The anterior pituitary hormones are tropic (trophikosG =nourishing) or tropins (troposG =turning) in nature, stimulating the secretion of all these hormones from target organs. Hormones secreted by anterior pituitary are,

  • Growth Hormone (GH)
  • Adrenocorticotrophic hormone (ACTH)
  • Leutinizing Hormone (LH)
  • Follicular Stimulating Hormone (FSH)
  • Thyroid stimulating Hormone (TSH)

    Pituitary Gland and its Secretions

II) Middle lobe:

  • Melanocyte stimulating Hormone (MSH)

III) Posterior Pituitary Gland lobe:

The Posterior pituitary gland contains two hormones.

  • Vasopressin
  • Oxytocin (or) Ocytocin

I) Anterior Pituitary gland lobe:

Growth Hormone (GH):

Chemistry:

  • GH is a single polypeptide, with a molecular weight of about 22,000 in all mammalian species.
  • GH is synthesized in “Somatotropes”, a subclass of most abundant cell in the gland.
  • It consists of 191 amino acids.

Functions:

  • GH stimulates overall protein synthesis with an associated retention of phosphorous probably by increasing tubular reabsorption.Pituitary Gland and its Secretions
  • GH increases DNA & RNA synthesis
  • It increases the synthesis of collagen
  • GH brings about “Lipolysis” in a mild way by mobilizing fatty acids from adipose tissue by activating the hormone sensitive “triacylglycerol lipase”.
  • Hypersecretion of GH can result in hyperglycemia, poor sugar tolerance and glycosuria.

Abnormality:

  1. Panhypopitutarism: It is due to decreased secretion of all the anterior pituitary gland hormones. It may be congenital (or) ii may occur suddenly during the life of the individual.
  2. Dwarfism: It is due to deficiency of anterior pituitary gland secretion during childhood.
  3. Levi-lorain dwarfism: It is due to hereditary inability to form somatomedin C, but the rate of GH secretion.
  4. Acromegalay: It is due to increased secretion of GH.

More Details:

Kids and teens grow and go through puberty at different times. For girls, puberty usually begins between ages 8 and 13. For guys it often begins a bit later – between 10 and 15. You must have observed some teens develop a lot earlier, whereas others develop much later than other people of the same age. There’s a medical reason why some people grow more slowly than usual.

Reasons of slow growth:

  • Genetic Reason: If you’re short, you may just have familial (genetic) short stature. Like short parents tend to have short children.
  • Lack of Nutrition: Not getting adequate amounts of protein, calories, and other nutrients in your diet can also cause growth to slow, as well as a number of other chronic medical conditions such as kidney, heart, lung, and intestinal diseases.
  • Sickle cell anemia: People with sickle cell anemia may also grow and develop more slowly. Sickle cell anemia is a blood disorder that affects hemoglobin the protein found in red blood cells (RBCs) that help to carry oxygen throughout the body. Sickle cell anemia occurs when a person inherits two abnormal genes (one from each parent) that cause their RBCs to change shape.
  • Constitutional growth delay: These teens grow at a normal rate when they are younger kids, but they lag behind and don’t start their pubertal development and their growth spurt until after most of their peers.
  • Dwarfism: Dwarfism results from abnormal growth of the bones and cartilage in the body. In many forms of dwarfism the person has abnormal body proportions, such as noticeably short limbs.
  • Hormones: Many diseases of the endocrine system, which is made up of the glands that produce hormones, can affect growth. Hormones are secreted by the endocrine glands and carried throughout the body in the bloodstream. The hypothalamus (part of the brain) controls the pituitary gland, which in turn releases some of the hormones that control growth and sexual development. Estrogen and testosterone are important hormones that drive sexual development and function and also play a role in growth.
  • Hypothyroidism: This can cause slow growth because the thyroid gland isn’t producing enough thyroid hormone which is responsible for proper growth.
  • Turner syndrome: This is a genetic condition (due to a problem with a person’s genes) that occurs in girls. It is caused by a missing or abnormal X chromosome. Girls with Turner syndrome tend to be short and don’t usually undergo normal sexual development because their ovaries don’t mature and function normally.

  • Growth Hormone Deficiency (GHD): One growth disorder that is specific to the hormones that govern growth is called growth hormone deficiency. This condition involves the pituitary gland, the small gland located at the base of the brain that produces growth hormone and other hormones. If the pituitary gland doesn’t produce enough hormones for normal growth, growth slows down or stops.

Important Facts of Growth Hormone Deficiency:

  • This occurs at any age.
  • The most common sign in kids and teens is a slowing of growth to less than 2 inches (5 centimetres) a year.
  • Kids with this disorder usually have normal body proportions.
  • Growth hormone deficiency does not affect intelligence or brain function.
  • Growth hormone deficiency usually affects only one person in a family and isn’t generally passed on from parents to children.

Causes:

In most cases, though, the cause of growth hormone deficiency is simply unexplained.

  • Underdeveloped, damaged, or malfunctioning pituitary gland.
  • Hypothalamus: This can happen before or during birth or can be caused later by an accident or trauma or certain diseases.
  • Tumors near the pituitary gland, like craniopharyngioma, can also damage the hypothalamus and pituitary gland and affect growth.

Symptoms:

  • Growth in Height: Affected children have an abnormally slow growth rate.
  • Head: Head circumference increases normally in GHD.
  • Adiposity: Due to deficient breakdown of fats, patients have a much higher level of adipose tissue than normal for their age, especially around the waist.
  • Muscle: Due to poor protein synthesis, lean body mass, reflected particularly in muscle development, is correspondingly lower than normal for age.
  • Genitals: Males are underdeveloped for their age, even when gonadotropin secretion is apparently normal.
  • Blood Sugar Levels: Due to inadequate breakdown of glycogen into glucose, hypoglycemia can occur and seizures may arise if this is severe and untreated.
  • Phenotypic Appearance: The above signs and symptoms lead to a “typical” phenotypic appearance for the GHD patient. Thus, as well as short stature, patients have a chubby appearance, and usually a high-pitched voice. They may seem precocious because their appearance suggests a younger child but their speech and abilities are that of an older child.

Treatment:

  • Self Care: As growth hormone deficiency can cause a lack of energy and strength, patients should eat a balanced diet, get regular exercise, and get plenty of sleep.
  • Medications: The doctor may prescribe growth hormone,also called somatropin (Humatrope, Genotropin). The drug is given as a shot a few times a week that is injected underneath the fat of the patient’s skin.
  • Hormone Therapy: Children and some adults with growth hormone deficiency will benefit from growth hormone therapy.The goals of treatment are to increase growth in children and restore energy, metabolism, and body composition.

Tips for the parents:

  1. Treat your child according to age, not size. Also inform their teacher about the correct age.
  2. Encourage your child to participate in physical activities he or she enjoys.
  3. Increase your child’s comfort at home by making sure that important items are within reach, such as the radio, television, stereo, books, etc.
  4. If necessary, obtain professional counseling for yourself and/or your child.
  5. Self-esteem reflects perceptions or feelings about oneself. Teasing and bullying can have a negative effect on any child’s self-esteem. Keep the lines of communication open. Encourage your child to discuss any situations or circumstances that may be troubling him or her.

It can be tough having a growth disorder as a teen because it can affect a person’s body image and self-esteem. Talking with a mental health professional is one way some people deal with feelings and concerns about their growth.

2. AdrenoCorticoTrophic hormone (ACTH):

Chemistry:

  • It is a straight chain polypeptide with a molecular weight of about 4,500.
  • It consists 39 amino acids residues in mammals like man, ox, sheep & Pig.
  • The most potent segment of activity is from residue 15 to 18.

Functions:

  • ACTH increases the synthesis of corticosteroids by the adrenal cortex and also stimulates their release from the gland.
  • ACTH is found to increase the transfer of cholesterol from plasma lipoproteins into the fasciculata cells.
  • The ACTH induces rise in cAMP, brings about phosphoryl and activation of “Choleseryl esterase”
  • the enzyme action ultimately makes a large pool of free cholesterol.
  • It activates the rate-limiting enzyme for conversion of cholesterol to pregnenolone (Cholesterol desmolase) .
  • It activates dehydrogenases of HMP to increase the concentration of NADPH required for hydroxylation.
  • It activates “Hormone-sensitive lipase”, which is involved in lipolysis which increases the level of free fatty acids.

Normal level:  
The circulating concentration of ACTH in normal is 0.1 to 2.0 m µ/dl.  The pituitary gland stores 5 to 10mg.

Abnormality (or) Clinical importance:  
Cushing’s disease: Over secretion of ACTH leads to cushing’s disease, because of tumor (or) hyperplasia of β-cells of the anterior pituitary gland lobe. This leads to hypersecretion of corticosteroids specially glucocortucoids. This produces symptoms like hyperglycemia, glycosuria, muscle wasting, atrophy of skin, high urinary negative nitrogen balance. Abnormal retention of fats giving moon shape face appearance, retention of Na + and water and hypertension.

3.  Leutinizing Hormone:  

Chemistry:

  • LH is glycoprotein in nature; it contains sialic acid, hexose and hexosamine as the carbohydrate moiety (16%).
  • Molecular weight of LH is 40,000
  • LH is dimer in nature; it consists of α-chain and β-chains linked noncovalently.
  • The β-chain of human FSH and LH has 112 amino acid residues.

Functions: This hormone also known as “Interstitial Cells Stimulating Hormone (ICSH)”
 In females:

  • It causes the final maturation of graffian follicles and stimulates ovulation.
  • Stimulates secretion of estrogen by the THECA and Grannulosa cells.
  • It helps in the formation and development of corpus lutem for leutinization of cells.
  • In the ovary it can stimulate the non-germinal elements, which contain the interstitial cells to produce the androgenes, androstenedione, DHEA and testosterone.

4. Follicle Stimulating Hormone (FSH):

Chemistry:

  • Molecular weight of  FSH is 25,000.
  • These are dimers of α-chain and β-chains linked noncovalently.
  • α-Chain is identical to LH, TSH, but the β-chain of human FSH has 118 amino acid residues.
  • Glycoprotein in nature, with sialic acid, hexose and hexosamine as the carbohydrate moiety (16%)

Functions:

It brings about its action by specific receptor binding and cAMP
In Females:

  • It promotes follicular growth
  • Prepares the graffian follicle for the action of LH.
  • Enhances the elease of estrogen induces by LH.

In Males:

  • It stimulates seminal tubular and testicular growth.
  • Plays an important role in maturation of spermatozoa.

5. Thyroid Stimulating Hormone (TSH):

Chemistry:

  • It is glycoprotein with molecular weight 30,000.
  • Each molecule has 8 to 9 cysteine residues.
  • This is produced by “Basophil cells” of anterior pituitary gland lobe.
  • It consists with of α-chain and β-chains linked noncovalently. • The  α-chain sub unit of TSH, LH, HCG & FSH are nearly identical.
  • The α-sub unit consists 92 amino acid & β-sub unit consist 112 amino acids.

Functions:

It stimulates the activity of thyroid gland and enhances the rate of certain reactions, such as,

a) Removal of iodine form blood by thyroid.

b) Conversion of iodide to thyroid hormones.

c) Release of hormonal iodide from thyroid.

II ) Middle lobe:

Melanocyte stimulating Hormone (MSH):  
The hormones secreted by intermediate lobe (or) middle lobe of pituitary gland are called “MSH”.

  • POMC (Propiomelanocortin) is the precursor molecule, which is cleaved by “Proteases” to give ACTH, and β-MSH is common to both α-MSH and ACTH.
  • The ACTH further cleaved to β-MSH, which has 13 amino acids.
  • It also α-MSH which is present in larger quantities.
  • Amino acids 11 to 17 of β-MSH are common to both α-MSH and ACTH.

Functions: 

MSH darkens the skin and is involved in skin pigmentation by deposition of mammalian by melanocytes.

Abnormality:  Addison’s disease: MSH is in excess, which increases the synthesis of melanin resulting in brown pigmentation of skin. Such a condition occurs in this disease.

III ) Posterior Pituitary Gland Lobe:

The Posterior pituitary gland lobe contains two hormones.

1) Vasopressin

2) Oxytocin (or) Ocytocin

1) Vasopressin:

It is also called “Arginine Vasopressin”(AVP) • If “Arg” is replaced by “Lysine”, it is called “Lysine vasopressin” (LVP). • It is  “Nona peptide”, it consists with nine amino acids.

Mechanism of Action:  
ADH binds to membrane receptor and activates adenyl cyclase. The cAMP thus produced will activate the protein kinase. This, in turn, phosphorylates proteins of the microtubules and microfilaments. The net effect is the reabsorption of water.

Functions:

a) Antidiuresis:  
Vasopressin causes “Antidiuresis”. It increases the permeability of the collecting ducts and tubules to water and allows most of the water to be reabsorbed as the tubular fluid passes through these ducts, there by conserving water in the body and producing very concentrated urine.

b) Urea-retention effect:  

Permeability of meduallry collecting dusts to urea is increases by vasopressin. This leads to retention of urea and subsequently contributes to hypertonicity of the medullary intersitium.

c) Pressor effect:  It stimulates the contraction of smooth muscles and thus causes vasoconstiction by increasing cytosolic Ca +2 contraction.
e) Glycogenolytic effect:  By increasing intracellular Ca +2 concentration, it causes glycogenolysis.

Abnormality:  

Deficiency of ADH leads to “Diabetes insipidus”, it is characterized by excretion of large volumes of dilute urine. Excess secretion of ADH often results from ectopic production of ADH by malignant tumors, referred to as the “Syndrome of Inappropriate secretion of ADH” (SIADH). There is hypotonic expansion of extracellular volume, with hyponatremia.

2) Oxytocin (or) Ocytocin:

The term literally means (Ocy G=quick; tokos G=birth) “to stimulate birth”.  It is polypeptide, each containing 9 amino acids, so it calls Nona peptide.

Mechanism of action:

Oxytocin acts on an estrogen-primed uterus. When the uterus labor is near, the numbers of oxytocin receptors are increases to 100 to 200 times.

Function: Oxytocin mainly causes smooth muscle contraction.
a) Effect on the uterus and on birth: Oxytocin causes the contraction of the pregnant uterus especially toward the end of gestation and is partially responsible for effecting birth.
b) Effect of oxytocin on milk ejection: Oxytocin has an effect on the mammary gland. Suckling generates a neurogenic reflex, which stimulates the production of oxytocin of oxytocin. It causes contraction of the myoepithelial called expelling the milk into milk ducts from the acinii.

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