Pituitary Gland

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Biochemistry

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PITUITARY GLAND OR HYPOPHYSIS:

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

INTRODUCTION:

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

INTRODUCTION:

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

Pars distalis / adenohypophysis:

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

Trophic Hormones:

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)

TSH:

TSH Glycoprotein 30,000 Hexosamine Stimulates Thyroid gland – Thyroxine Hyperthyroidism Rapidly ↑ every phase of T 4 metabolism Activates thyroidal adenylcyclase ↑ thyroid growth

TSH:

TSH ↑ general metabolic activities such as glucose oxidation, O 2 consumption, Synthesis of Phospho lipids Protein synthesis RNA synthesis * In adipose tissue - Lipolysis

Regulation:

Regulation 1. TRF Hypothalamus Tripeptide ( Pyro glu – His – Pro CONH 2 ) Highly specific – acts only on TSH secreting cells 2. Low T 4 ↑ TSH ; High T 4 ↓ TSH

ACTH / CORTICOTROPHIN:

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

Functions:

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

Functions:

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

Regulation:

Regulation 1. CRF – Hypothalamus CRF is liberated under the influence of non specific stress, cold, emotional stress, drugs, toxic agents, Epinephrin, Oesrogens, T 4 , hGF, ADH etc 2. Conc. Of glucocorticoids

Gonadotrophins / gonadotrophic hormones:

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

FSH:

FSH Glycoprotein Gal, Man, Hex-NH 2 , 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)

LH (ICSH):

LH (ICSH) Peptide hormone 26000 lacks Trp but high Cys & Pro 1 LH 10 Glu-NH 2 + 3 Gal–NH 2 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

LTH:

LTH The most versatile of all adenohypophyseal hormones 1 st 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

LTH:

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)

Adenohypophyseal hormones:

Adenohypophyseal hormones Growth hormone

Growth Hormone / Somatotrophin:

Growth Hormone / Somatotrophin STH / GH is PP – 190 27000 Phe---------------Phe P I = 4.9 2 S-S bonds ; 53 - 164; 181 - 188

Functions:

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

Functions:

Functions Lipid Metabolism :- Lipolysis ↑  ↑ FA Oxidation  ↑ ketogenesis & ↓RQ ↑ intestinal absorption + excretion of Ca 2+ Helps in retaining Na + , K + , Mg 2+ ,Po 4 3- ,Cl - GH binds to membrane receptors for prolactin and ↑ growth + enlargement of M. glands

Regulation:

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

PARS INTERMEDIA:

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)

Functions:

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

Posterior pituitary / Neurohypophysis:

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

Histology:

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.,

Regulation and Secretion:

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

Oxytocin:

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

Milk ejection reflex / milk let down reflex (neuroendocrine reflex):

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

Vasopressin / ADH:

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

Functions:

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

Regulation:

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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