Pituitary Gland — Hormones, Functions, and Disorders

The pituitary gland is also known as hypophysis in medical science, consists of glandular epithelial tissues and neurosecretory tissue.

The pituitary gland is a small pea-sized gland that is situated in the basal part of the brain below the hypothalamus and above the nasal passage which plays a major role in regulating vital body functions and overall health. It is referred to as the body’s ‘master gland‘ because it controls the activity of other glands and their hormones.

Anatomy of the pituitary gland

• It is situated in the tiny space called sella–turcica of the sphenoid bone
• On the basis of its development, it is ectodermal in origin
• This gland is attached to the hypothalamus through a stalk which is called an infundibulum
• The lower terminal and of the infundibulum is the bulging type which is called as posterior lobe or pars nervosa
• Infundibulum and pars nervosa are collectively called neurohypophysis
• Adenohypophysis consists of pars distalis or anterior lobe and pars intermedia or middle lobe
• It is divided anatomically into two parts

1. Adenohypophysis (Anterior Pituitary)
2. Neurohypophysis (Posterior Pituitary)

The hypophyseal portal vein (part of the blood vascular system that connects the hypothalamus to the anterior pituitary gland) collects the blood from the hypothalamus and supplies it to the anterior pituitary.

Hormones of pituitary gland

Adenohypophysis hormones

Human growth hormone

Human growth hormone (hGH) is also called growth hormone (G.H) or somatotropin hormone (S.T.H). It is a type of peptide hormone that stimulates growth, cell division, and cell regeneration in humans and other animals.

It plays an important role in human growth and development. Growth hormone boosts growth in childhood and helps to maintain tissues and organs throughout life.

*Tropin means, the hormone released in the body by a certain gland produces a response in other glands, stimulating the release of other hormones.

a). Role of somatotropin in growth

1. It promotes the growth and elongation of bones by increasing the activity of osteoblast cells.
2. It promotes the liver to make an insulin-like protein that produces cartilage cells.
3. It promotes cell mitosis or cell division to increase the number of cells in visceral organs like the Liver,…
4. It increases protein synthesis and stimulates muscle growth and strength.

b). Role of somatotropin in metabolism

Fat: Increases breakdown of fat or lipolysis or fat catabolism. Under the influence of growth hormone, fat is used for energy in preference to carbohydrates and protein.

Carbohydrate: Growth hormone decreases uptake of glucose by the cells, and increases the blood glucose level that’s why it is also called diabetogenic hormone.

Protein: Growth hormone increases amino acid uptake by the cells of the liver and muscles and helps in protein synthesis or protein anabolism.

Sequence will be – [ Fat > Carbohydrate > Proteins ]

Disorders of Growth Hormone: Diseases caused due to excess or less amount of somatotropin hormone secretion.

a) Hyposecretion

Deficiency of growth hormone in childhood or adolescence results in dwarfism.

In childhood – Dwarfism

1. Ateliosis: Dwarfism caused defects of the pituitary known as pituitary dwarfism or ateliosis.
2. Clowns of the circus: They are such dwarfs, they are called midgets. This midget is physically and mentally normal while sexual maturation is delayed.

In adults

1. Simmonds disease (pituitary cachexia): It happens in an adult person, this syndrome ascribed to destruction or physiological exhaustion of the hypophysis (mainly the anterior portion). Which leads to atrophy of many of the viscera, including the heart, liver, spleen, kidneys, thyroid, adrenals, and gonads. Later it may results in emaciation and death if left untreated.

b) Hypersecretion:

In childhood

1. Gigantism: It is caused because of hypersecretion of growth hormone in early age or childhood, the bones of legs and hands become very long and height of that person increases very much. This leads to imbalanced postures, joint pain, back pain, …

In adults

1. Acromegaly: It is caused because of hypersecretion of growth hormone in adults mainly in middle age peoples can result in severe disfigurements like excess enlargement of bones of the face (Chimpanzee like face), vertebral column, and forelimbs (Gorilla like appearance), prognathous jaw/ protruded jaw. Which may lead to serious complications and premature death if persist for a long time.

Thyrotrophic hormone

The thyrotrophic hormone is also called thyroid-stimulating hormone (TSH). TSH stimulates the thyroid gland to secrete thyroxine. TSH helps in almost all steps of thyroid hormone synthesis & it causes growth of the thyroid gland.

Adrenocorticotrophic hormone or corticotropin (ACTH)

It accelerates the cortex part of the adrenal gland to secrete hormones, mainly glucocorticoids.

Follicle stimulating hormone (FSH)

• In males, it stimulates spermatogenesis in the seminiferous tubules of the testes.
• In females, it stimulates oogenesis and the development of Graafian follicles in the ovary (indirectly promotes estrogen secretion).
• Secretion of estrogen hormone from Graafian follicle is also regulated by FSH

Luteinizing hormone (LH)

• It stimulates ovulation and the formation of the corpus luteum in females.
• Progesterone hormone which is secreted by the corpus luteum is also stimulated by L.H.
• In men, LH is called Interstitial Cell Stimulating Hormone (ICSH). It affects the Leydig’s cells or Interstitial cells of testes and stimulates the secretion of the male hormone “Testosterone“.
• FSH and LH both are collectively called gonadotrophic hormones (GTH).
• Gonadotrophic hormones (FSH & LH) secretion starts during puberty. Their secretion is regulated by the hypothalamus.

Prolactin

Prolactin is also known as lactogenic or mammotrophin hormone (PRL). Prolactin is responsible for lactation (milk formation) in women after delivery.

Melanocyte stimulating hormone (MSH) or intermedine

• It is secreted by the middle lobe but in humans, the pars intermedia is reduced and almost merged with pars distalis.
• In man, MSH is secreted by the anterior lobe.
• It stimulates the melanocytes to synthesize melanin in mammals, but the role of MSH in determining skin color in humans is still doubtful.
• MSH is produced in all vertebrates but it is more effective in lower vertebrates.
• This hormone is related to changes in the color of skin in Amphibian and Reptiles. This phenomenon of color change is known as metachrosis.
• It darkens the complexion of the skin by distributing melanin pigment evenly under the skin.

Melatonin

Melatonin is the derivative of Tryptophan amino acid. Just opposite to MSH, melatonin secreted by the pineal gland, collects the melanin pigments at one place thus fairing the complexion of the skin.

Melatonin is an important hormone in circadian synchronization. This hormone is involved in many biological and physiological regulations in the body. It is an effective hormone for human biorhythm (circadian rhythm) or sleep-wake cycles and repeats roughly every 24 hours.

Neurohypophysis hormones

It is just like nervous tissue, consisting of supporting neuroglia cells (Pituicytes) and the axons of neuro-secretory cells of the hypothalamus. The swollen axon ends are called Herring bodies. Hormones are released in these bodies.

Posterior pituitary hormones are not synthesized in the gland itself but are synthesized in the neurosecretory cells (Nuclei) of the hypothalamus.

ADH or vasopressin

Released from supraoptic nuclei.

• It acts as a vasoconstrictor to increase B.P immediately.
• It acts mainly at the kidney and stimulates reabsorption of water and electrolytes in DCT and collecting duct of nephrons and thereby reduces loss of water through urine (Diuresis). Hence, it is also called as “Anti-diuretic hormone (ADH)“.
• Hyposecretion of ADH causes “Diabetes insipidus” (tasteless urine or drinker’s disease). Which is characterized by polyuria, diluted urine, dehydration, excessive thirst (polydipsia), excessive hunger (polyphagia), low BP (hypotension), …etc.
• Intake of coffee, tea, and excess alcohol, …etc. decreases the secretion of ADH (Diuretic substance).

Disorder of ADH

a) Hyposecretion

Diabetes Insipidus: It is caused due to hyposecretion of ADH, in which the volume of urine increases. Which causes frequent urination or polyurea, repeated thrust or polydipsia, and tasteless urine.

b) Hypersecretion

• In this condition Blood volume increases so blood pressure (B.P) increases.
• Blood becomes dilute and urine becomes concentrated.
• This condition is normally seen in the desert animals like Camel and Kangaroo Rat.

Oxytocin or pitocin

Released from paraventricular nuclei. Oxytocin acts on the smooth muscles of our body and stimulates their contraction.

• It is the main parturition hormone. Stimulates labor pain and assists the child’s birth by stimulating vigorous contractions and expansions of smooth muscles of the uterine wall at the last moment of the gestation period (pregnancy).
• Helps in the movement of sperms towards the fallopian tube after insemination.
• Brings back the uterine smooth muscles in their original shape.
• Promotes milk ejection in Cows and Buffaloes.
• Promotes egg production in birds.
• Increases pulsating movement in seminiferous tubules and vas deferens in the male.
• This hormone is secreted by the pituitary glands of the mother at the time of parturition.
• Oxytocin hormone contracts the myoepithelial cells present at all the sides of the alveoli of mammary glands. Thus it helps in milk ejection so it is also called milk ejection or milk let down hormone.
• In females, this hormone is also related to emotion. Even though, cry or sound of the baby can bring about the release of this hormone in lactating mothers.

Summary

Pituitary related FAQs

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