Posterior Pituitary

Question 1

List physiological functions of oxytocin
Secreted by…..

Answer 1

1. Milk ejection
2. Contraction of myometrium during labour
3. During sexual intercourse (in males contraction of vas deferens, in females transport of semen from vagina to uterus.
   Neurohormonal reflex

Question 2

Oxytocin is regulated by +ve feedback during……

Answer 2

Delivery

Question 3

Enumerate renal effects of ADH

Answer 3

1. Increase the permeability of collecting ducts & tubules to water reabsorption through these ducts thus concentrates urine. This occurs by binding of ADH to V2 receptors which stimulate AC & inc cAMP leading to increasing aquaporins on luminal surface of ducts.
2. ADH inc flow of urea into medullary interstitium & so helps more water reabsorption

Question 4

Enumerate extrarenal effects of ADH

Answer 4

1. In large doses it causes direct strong VC (V1A receptor)
2. Inc ACTH release with 2ry inc in cortisol secretion (V1B or V3 receptor)

Question 5

Describe control of ADH production

Answer 5

1. Plasma osmolality, significant change in ADH release results from little inc in osmolality. Osmoreceptors are shrunken when osmolality inc thus their rate of discharge inc stimulating synthesis & secretion of ADH, & vice versa.
2. Hypovolemia, inc 15-25% strongly stimulates ADH secretion and produces VC and inc BP. Atria have stretch receptors when excited send signals to brain & inhibit ADH secretion
3. Other stimli:
   -it is stimulated by stress, exercise, emotion, N&V, morphine & nicotine, Ang II
   -inhibited by alcohol

Question 6

Diabetes insipidus may be……or……, its main symotoms are……

Answer 6

Central, nephrogenic
Polyuria, polydipsia

Question 7

GR: Hypersecretion of ADH in patients with pulmonary diseases

Answer 7

1. Interruption of inhibitory impulses in vagal afferents from the stretch receptors in atria & great veins
2. ADH secretion