Posterior Pituitary

Prof. K. Sivapalan

08-01-14 Hypophysis. 2

Structure and Blood Supply.

• Posterior lobe is supplied by inferior Hypophysial artery.

• Neurons in the hypothalamus, endings in posterior lobe.

08-01-14 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.

08-01-14 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.

08-01-14 Hypophysis. 5

Other Factors influencing ADH.

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.

08-01-14 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.

08-01-14 Hypophysis. 7

Oxytocin.

• 9 Amino acids.• Synthesized in hypothalamus and

released in Post. Pituitary.

08-01-14 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.

08-01-14 Hypophysis. 9

Stimulation of Secretion.

• Stimulation of nipple- milk ejection reflex.

• Stretch of cervix of the uterus- parturition

• Sexual stimulation.

08-01-14 Hypophysis. 10

Inhibition of Oxytocin Secretion.

• Alcohol• Stress.• Pain• Discomfort.• Embarrassing conditions.• Fear• Anger.