Local Hormones

Prof. K. Sivapalan

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Pineal gland• Remnant of third eye

in lower animals• Secrets Melatonin• 0.1 – 0.18 g. • In infants it is large• Begins to involute

before puberty. Calcium carbonate and phosphate [pineal sand] accumulates.

• X’ ray- landmark.

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Synthesis of Melatonin.

• Tryptophan• 5- hydroxy

tryptophan.• N-Acetyl-5-Methoxy

tryptamine

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Regulation of Secretion.

• Dark [absence of light]

• Sympathetic increases at dark and stimulates synthesis and release.

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Actions of Melatonin.

• ? Onset of puberty.• Secretion decreases

with age.• Actions not clearly

understood.• ?inhibit gonodotropins

from pituitary

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Endocrine functions of Kidney

• Erythropoietin.• Renin.• 1,25-Dihydroxy cholycalciferol.

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Erythropoietin.

• Glycoprotein with 165 Amino acids.• 85% from Kidney and 15% from liver.• By interstitial cells in peritubular capillary bed

and perivenous hepatocytes.• Liver cannot compensate when kidneys are

damaged.• Hypoxia stimulates secretion.• Increases committed stem cell and haemopoisis.• Renal disease- normocytic normochromic

anaemia.

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1, 25- dihydroxycholecalciferol

• Conversion in kidney • Regulated by PTH.

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Renin

• Mw- 37326,.half life- 80minutes.

• From Juxta Glomerualar Apparatus, by juxta glomerular cells of afferent arterioles.

• Action- angeotensinogen to angeotensin I.

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Regulation of Renin secretion.

• Stimulation-• Increased sympathetic activity.• Increased circulating catecholamines.• Prostaglandins.• Inhibition-• Increased Na and Cl absorption across

macula densa.• Increased afferent arteriolar pressure.• Angeotensin II.• Vasopressin.

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Conditions that increase secretion

• Sodium depletion.• Diuresis• Hypotension• Haemorrhage• Upright posture• Dehydration• Cardiac failure.• Cirrhosis• Constriction of renal artery• Various psychological stimuli.

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Angeotensinogen

• 453 amino acids and 13% carbohydrate.• Circulating levels increased by-

– glucocorticoids.– thyroid hormones– estrogens– several cytokinins

• Converted to angeotensin I by Renin.• Angeotensin converting enzyme in lungs and

other endothelial cells converts it into Angeotensin II.

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Activation of Angeotensinogen.

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Actions of Angeotensin II

• Vasoconstriction, more in Efferent arterioles.

• Stimulates aldosteron secretion.• Reduces sensitivity of baro-reflex in CNS.• Stimulates thirst centre.• Stimulates secretion of vasopressin and

ACTH.

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Endocrine Function of the Heart.

• Left Atrium Secrets Atrial Natriuretic Peptide.

• Stimulation is increased NaCl intake and increased ECF volume.

• Increases Na loss from Kidney- ?increased GFR.

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Intestinal Hormones.

• Gastrin.• Secretin• Cholecystokinin.• Gastriic inhibitary peptide.• Vasoactive Intestinal Peptide.

Peptide YY

• Secreted by L cells of intestine• Blood level is proportional to calories in

the food• Controls appetite• Peripheral administration of PYY3-36

inhibits food intake for several hours in both rodents and man

• May be important in the everyday regulation of food intake

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Leptin

• Secreted by adipose tissue in proportion to fat storage

• Regulates food intake

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Histamine.

• Found in Mast cells and basophils with heparin.

• Also found in gastric mucosa.

• Neurotransmiter.

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Effects of Histamine.

• Arteriolar and capillary dilatation.• Smooth muscle contraction in Bronchus

and GIT.• Acid secretion in stomach.• Itching and pain.• Anaphylaxis.

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Seerotonin.

• Found in platelets and GIT and some tissues.

• Stimulates smooth muscle contraction in, arteriols, bladder, intestine, uterus etc.

• Nervous system- neurotransmitter..

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Prostaglandins.

• Synthesized from Arachidonic Acid.

• Several varients are found in several tissues.

• They may be the ultimate mediators of all actions.