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PITUITARY GLAND

BIOCHEMISTRY

mprasadnaidu
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PITUITARY GLAND

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  1. PITUITARY GLAND OR HYPOPHYSIS M.Prasad Naidu MSc Medical Biochemistry, Ph.D.Research Scholar

  2. INTRODUCTION • Master gland / master of endocrine orchestra • Reddish / Gray • Oval • 10 mm • Brain – Optic chiasma – base of the brain • Extension – Hypothalamus • 0.6 – 0.7 gm  Males • 0.5 – 0.6 gm  Females

  3. INTRODUCTION • 3 Lobes • 1. an anterior / pars distalis / adenohypophysis • An intermediate / pars intermedia • A posterior / pars nervosa / neurohypophysis

  4. Pars distalis / adenohypophysis • 70% • Originates from an embryonic invagination of pharyngeal epithelium – Rathke’s pouch • 2 types of hormones • 1. Tropic / Trophic / Trophin hormones • 2. Growth Hormone

  5. Trophic Hormones • Secreted by one gland and controls the activities of other endocrine glands., Viz • 1. TSH (Thyroid Stimulating Hormone) • 2. ACTH ( AdrenoCorticoTropicHormone) • 2. Gonadal Hormones (Sex Hormones)

  6. TSH • Glycoprotein • 30,000 • Hexosamine • Stimulates Thyroid gland – Thyroxine • Hyperthyroidism • Rapidly ↑ every phase of T4 metabolism • Activates thyroidal adenylcyclase • ↑ thyroid growth

  7. TSH • ↑ general metabolic activities such as glucose oxidation, O2 consumption, Synthesis of Phospho lipids Protein synthesis RNA synthesis * In adipose tissue - Lipolysis

  8. Regulation • 1. TRF • Hypothalamus • Tripeptide ( Pyro glu – His – Pro CONH2) • Highly specific – acts only on TSH secreting cells • 2. Low T4↑ TSH ; High T4 ↓ TSH

  9. ACTH / CORTICOTROPHIN • Stimulates A. Cortex hormones • PP chain – 39 aminoacids • 4500 mol.wt • 1-23 – biological activity • 15-18 most potent • 1-24 & 34-39 no change

  10. Functions • Most Imp phy. regulator – A. Cortex except aldosterone • Hypertrophy with temporary reduction in A. lipids & vit C • ↑ blood flow to A. glands • ↑ formation of c- AMP in A. Cortex • In liver , retards metabolic degradation & conjugation of Corticosteroids • Thus ↑ half life & activity of hormones

  11. Functions • In AT, ↑ lipolysis • ↑ utilization of Glu- ↓ blood glu conc • ↑ glycogenesis by promoting insulin secretion • ↑ excretion of N,K,P & Uric acid • Retards the syn.of Urea • ↑ Gluconeogenesis • Retards protein syn in all tissues except liver • ↑ melanocyte stimulating activity  darkening of skin • Over secreting  Cushing’s syndrome

  12. Regulation • 1. CRF – Hypothalamus • CRF is liberated under the influence of non specific stress, cold, emotional stress, drugs, toxic agents, Epinephrin, Oesrogens, T4, hGF, ADH etc • 2. Conc. Of glucocorticoids

  13. Gonadotrophins / gonadotrophic hormones • Development & functioning of gonads • Function and maturation of Testis & Ovaries • Damage to Hypothalamus ↓ secretion of gonadotrophins • If this occurs b4 to puberty  simultaneous over eating • Since effect on feeding centre of hypothalamus • Obesity – adiposogenital syndrome / Frohlich’s syndrome / hypothalamic eunuchism • 3 types of gonodotrophins

  14. FSH • Glycoprotein • Gal, Man, Hex-NH2, sialic acid, fucose, uronic acid • 30,000 • Males  ↑ Spermatogenesis and production of androgens • Females  Growth & maturation & expulsion of ova & controls the internal secretions of ovaries • FSH is active during M.Cycle • FSH induces growth of graafian follicles ↑ wt of ovary • REGULATION: • FSH- RF ( Hypothalamus)

  15. LH (ICSH) • Peptide hormone • 26000 lacks Trp but high Cys & Pro • 1 LH 10 Glu-NH2 + 3 Gal–NH2 • In females  ripening & rupturing of ovarian follicles which later transform into Corpus lutea • Induces the development of interstitial cells of both testis & ovaries • Regulation: LH – RF ( Hypo ) deca peptide

  16. LTH • The most versatile of all adenohypophyseal hormones • 1st ante. pituitary hor obtained in pure form • Peptide – 198 aa – 23500 • 3 s-s bonds4 ; 4-14,58-173,190-198 • No carbohydrate ( unlike FSH & LH) • Thermolabile – destroyed by Tryptic dig. • In association with estrogens ↑ growth of M.glands & induces secretion of milk

  17. LTH • ↑ Glucose uptake • ↑ lipogenesis • Along with androgens causes development of 20 male sex characteristic • PL is credited with performing > 80 functions • Jack-of-all-trades • 5 major categories • 1. Reproduction 2. Osmoregulation 3. Growth • 4. integument • 5. Synergic effect with steroid hormones • ↑ Leydig tissue , therefore male accessory organ • Appears sharply after pregnancy in Urine • Regulation: PRF ( Hypothalamus)

  18. Adenohypophyseal hormones Growth hormone

  19. Growth Hormone / Somatotrophin • STH / GH is PP – 190 • 27000 • Phe---------------Phe • PI = 4.9 • 2 S-S bonds ; 53 - 164; 181 - 188

  20. Functions • ↑ Overall protein synthesis • ↑ Erythropoiesis & growth of liver, intestine kidney • ↑ chondrogenesis, ossification & Osteogenesis  Skeletal growth • CM:- 1. Hyperglycemia 2. In muscles – antagonises – insulin 3. diabetogenic effect ( degerative changes in islets of langarhans & adrenal enlargement) 4. ↑ blood glu by promoting the secretion of glucagon

  21. Functions • Lipid Metabolism:- • Lipolysis ↑ ↑ FA Oxidation  ↑ ketogenesis & ↓RQ • ↑ intestinal absorption + excretion of Ca2+ • Helps in retaining Na+, K+, Mg2+,Po43-,Cl- • GH binds to membrane receptors for prolactin and ↑ growth + enlargement of M. glands

  22. Regulation • 1. GH.RF / SRF ( Hypothalamus) • 2. Blood sugar • ↑ Glu ↑ GH secretion & vice versa • 3. EEE ↑ Exercise, Excitement & Exposure to cold • 4. Arg ↑ GH in plasma • Pituitary Diabetes:- Glu utilization is moderately depressed ( In DM No utilization of glucose) • No other side effects

  23. PARS INTERMEDIA • Absent in certain mammals – whale, Indian elephant • Secretes melanocyte ( melanophore ) MSH • 2 types • α- MSH (acylated------------13 Val-CONH2) • β- MSH (Asp---------------18 Asp) (Humans 22aa) • α- MSH – terminal groups are blocked • β- MSH - both the end groups are free • α- MSH > β- MSH ( biologic activity)

  24. Functions • ↑ deposition of melanin by melanocytes of human skin  darkening of skin • Regulation:- • Inhibitors: Cortisone, OH- Cortisone, Adrenalin, Nor-adrenalin

  25. Posterior pituitary / Neurohypophysis • 3 divisions • 1. the pars nervosa • 2. neural stalk • 3. the median eminence

  26. Histology • Posterior pituitary does not secrete hormones but stores the hormones • The cells of PP are of neural type • Consists of un myelinated nerve fibers and pituicytes ( glial cells ) These cells possess brown pigment granules • Pituicytes act as supporting cells and do not secrete any hormone • The PP also  blood vessels , hyaline bodies, neurological cells, mast cells etc.,

  27. Regulation and Secretion • PP is regulated by nerve fibers coming from the hypothalamus • PP does not secrete – therefore hormones are synthesized in hypothalamus & transported to PP ( stored in nerve endings) • When ever impulses from hypothalamus reach PP, these hormones are released from the nerve endings • Hormones are PP  Oxytocin & Vasopressin

  28. Oxytocin • ( Oxy G = Quick ; tokos G = birth) (Pitocin) • Nanopeptide • FUNCTIONS: • Ejection of milk • ↑ contraction of smooth muscles- uterus, • Also contraction of intestine, U.bladder, & ducts of M. glands • M. glands are lined by myoepithelial cells

  29. Milk ejection reflex / milk let down reflex (neuroendocrine reflex) • Many touch receptors around the nipple  • When the infant suckles the nipple  • Touch receptors stimulated  • Impulses are discharged  nerve fibers • Para ventricular nucleus ( Hypothal)  • Oxytocin  • Blood ( Oxytocin)  • Reaches Mammary gland  • Contraction of myoepithelial cells  • Ejection of milk

  30. Vasopressin / ADH • Produces constriction of blood vessels • Secreted by supra optic nucleus of hypothal • Small quantity by para ventricular nucleus of hypothal • Then transported via nerve fibers  PP

  31. Functions • 1. Regulation of H2O by acting on kidneys • water reabsorption from DCT , C. duct • In the absence of ADH  reabsorption of water does not – dil urine excreted – excess water via Urine – Diabetes insipidus • 2. Vasopressor effect of ADH:- • Constriction of arteries • However the amt of ADH req to cause vasopressor effect is very much more than the amt required to cause antidiuresis

  32. Regulation • 1. Volume of body fluid • 2. Osmolality of ECF • Potent Stimulators: • 1. ↓ in the vol of ECF • 2. ↑ in osmolar conc in ECF • ADH secretion ↑ emotional + physical stress, Ele stimulation, Ach, Nicotine, Morphin

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