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Posterior Pituitary

Posterior Pituitary. Prof. K. Sivapalan. Structure and Blood Supply. Posterior lobe is supplied by inferior Hypophysial artery. Neurons in the hypothalamus, endings in posterior lobe. Anti Diuretic Hormone [Vasopresin]. 9 amino acids, 1000 mw. Half life- 18 minutes.

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Posterior Pituitary

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  1. Posterior Pituitary Prof. K. Sivapalan

  2. Structure and Blood Supply. • Posterior lobe is supplied by inferior Hypophysial artery. • Neurons in the hypothalamus, endings in posterior lobe. Hypophysis.

  3. Anti Diuretic Hormone [Vasopresin] • 9 amino acids, 1000 mw. • Half life- 18 minutes. • Action in physiologic doses: • Increase water and urea permeability in collecting ducts. • Anti diuresis. • Action in large doses: • Contraction of vascular smooth muscles. • Increase blood pressure. Hypophysis.

  4. Control of secretion of ADH. • Increased osmolality stimulates osmoreceptors in hypothalamus and increases secretion. • Increased blood volume stimulates volume receptors in IVC and Left atrium, inhibits secretion. Hypophysis.

  5. Stimulation: Increase of OP of plasma. Decreased ECF volume. Pain, emotion, stress, exercise. Nausea and vomiting. Standing Angeotensin II Carbamazapine, clofibrate Inhibition: Decreased Osmotic pressure. Increased ECF volume. Alcohol. Other Factors influencing ADH. Hypophysis.

  6. Abnormal Secretion. • Excess- water intoxication. • Reduced plasma osmolality. • Dilutional hyponatreamia. • ? Drinking water after surgery, child birth etc. • Insufficiency- diabetes Insipidus. • Polyurea and polydepsia. Hypophysis.

  7. Oxytocin. • 9 Amino acids. • Synthesized in hypothalamus and released in Post. Pituitary. Hypophysis.

  8. Actions of Oxytocin. • Contraction of myo-epithelial cells of the breast. • Contraction of pregnant uterus • Enhanced by estrogen • Inhibited by progesterone. • ?facilitate sperm trans port and fertilization • Contraction of Vas deferens during ejaculation. Hypophysis.

  9. Stimulation of Secretion. • Stimulation of nipple- milk ejection reflex. • Stretch of cervix of the uterus- parturition • Sexual stimulation. Hypophysis.

  10. Inhibition of Oxytocin Secretion. • Alcohol • Stress. • Pain • Discomfort. • Embarrassing conditions. • Fear • Anger. Hypophysis.

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