The Pituitary Gland

PITUITARY GLAND



ANTERIOR PITUITARY GROWTH HORMONE

ALSO CALLED SOMATOTROPHIC HORMONE Synthesized by acidophil cells of anterior pituitary. Secreted episodically with diurnal variation, peak occurs at night time after sleep. Regulatory mechanisms GH releasing hormone and GH inhibitory hormone. Factors increasing GH secretion 1. 2. 3. 4. 5. Hypoglycemia Exercise Glucagon Protein meals Stress Factors decreasing GH secretion 1. 2. 3. 4. GH Glucose Cortisol Free fatty acids



ACTIONS 1. Stimulates skeletal growth through somatedins.



2. Before epiphyseal closure, GH stimulates increase in linear skeletal growth. 3. After epiphyseal closure GH accelerates bone thickening through periosteal growth. 4. Protein metabolism Anabolic hormone Positive nitrogen balance Excretion of amino acids 5. Increase reabsorption of Ca+, Na+, and K+ from kidneys. 6. Carbohydrate metabolism Diabetogenic -- causes hyperglycemia 7. fat metabolism Catabolic effect -- increases free fatty acids. Ketogenic -- increases ketone bodies formation by hepatic oxidation of fatty acids. 8. GH increases growth of thymus APPLIED  Gigantism Overproduction of GH before epiphyseal closure Characteristic features  Tall body  Giant hands and feet  Gynaecomastia (bilateral)  Acromegaly Overproduction of GH after epiphyseal closure Characteristic features: Prognathism – widening of mandible Prominent brow --- enlargement of frontal, ethmoid, maxillary and mastoid sinuses. Facies -- thickening of the skin and coarse facial features Kyphosis



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Hypertrophy of body organs such as liver, heart, spleen. DWARFISM Deficiency of secretion of GH is called dwarfism

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Characteristic features  Slow skeletal development  Small genitalia  Immature faces  Low GH level



Adrenocorticotropic Hormpne ACTH



PROLACTIN

Synthesized by acidophil cells of anterior pituitary Factors increasing prolactin secretion  Pregnanacy – Prolactin levels in blood start increasing during first trimester of pregnancy and reaches peak concentration at term  Breast stimulation leads to release of Prolactin Release Factor (PRF), causing increased prolactin secretion  Exercise  Sleep- Prolactin secretion increases during sleep  Hypothyroidism- TRH is increased that stimulates PRF and prolactin secretion is increased in primary hypothyroidism  Dopamine antagonist , serotonin agonists increase prolactin level Factors decreasing prolactin secretion  Prolactin Inhibitory Factor (PIF) is released by hypothalamus that inhibits prolactin secretion  Dopamine agonists ACTIONS During pregnancy prolactin promotes the growth of mammary ducts that differentiates into lobules and alveoli that are secretory in nature



POSTERIOR PITUITARY (I) ANTI DIURETIC HORMONE [ADH] (II) OXYTOCIN



ANTI-DIURETIC HORMONE (ADH) ADH is synthesized in cells of supraoptic nucleus of hypothalamus and then stored in posterior pituitary. ADH is subsequently released by impulses from hypothalamohypophysial tract.



ACTIONS Increase permeability of DCT and CD to water ↓ Increase water reabsorption ↓ Urine volume decrease ↓ Urine osmolality increases Acts via V2 (vasopressin) receptors At high doses cause s peripheral vasoconstriction Regulation Factors stimulating secretion of ADH 1. Hypovolemia MOST POTENT STIMULUS 2. INCREASED PLASMA OSMOLAITY FACTORS INHIBITING ADH secretion 1 Increased blood volume 2. CO2



HPOVOLEMIA due to hameorrage, shock, dehydration ↓ STIMULATES ADH SECRETION ↓ ADH cause INCREASED WATER REABSORPTION FROM DCT AND CD INCREASED PLASMA OSMOLALITY ↓ STIMULATES OSMORECEPTORS IN HYPOTHALAMUS ↓ STIMULATES ADH SECRETION



APPLIED Syndrome of Inappropriate ADH secretion (SIADH) Excessive secretion of ADH Cause  Excessive secretion form posterior pituitary  Ectopic source such as bronchogenic carcinoma Characteristic features  Increase in blood volume due to water retention  Decrease aldosterone secretion due to increased ECF Volume leading to hyponatremia  Increases urine osmolality DIABETES INSPIDUS (DI) Two types  Central DI- Partial or complete failure to secrete ADH  Nephrogenic DI- Decreased or no response of kidneys to ADH Characteristic features

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Polyuria- Decreased water reabsorption by DCT and CD Polydipsia



OXYTOCIN

It is synthesized in hypothalamus and stored in posterior pituitary gland. ACTIONS  Milk ejection from the mammary ducts  Contraction of smooth muscle of the uterus Factors increasing oxytocin secretion  Stimulation of the breasts  Stimulation of the genital tract  Stimulation of cholinergic nerve fibers



Factors decreasing oxytocin secretion  Stress  Stimulation of sympathetic nervous system