ECF Volume Regulation 1&2

Question 1

What are the effects of loop diuretics such as frusemide?

Answer 1

1. Blocks the reabsorption of NaCl at the ascending limb of loop of henle.
2. Loop diuretic work by blocking the Na, K, Cl transporters in the ascending limb of loop of henle.

Question 2

What is the pathway involved in the synthesis and release of ADH?

Answer 2

1. ADH (Vasopressin) is produced by Posterior pituitary.
2. ADH is produced in response to low electrolyte and fluid levels, i.e. dehydration.
3. The baroreceptors in the carotid sinus and atria of the heart detect the decreased fluid volume, and as a result discharge signals to the hypothalamus to start producing Vasopressin (ADH)
4. The pressure receptors in the carotid sinus and atria also signal for the sympathetic system to be triggered if the pressure falls.
5. The sympathetic system acts to increase blood pressure, and constrict vessels. In particular it constricts the arterioles of the kidney and stimulates renin release.
6. The production of renin and constriction of renal arterioles result in the production of angiotensin II, which increases the reabsorption of NaCl and H2O at the proximal tubule by decreasing the peritubular capillary hydrostatic pressure.
7. Angiotensin II then goes on to form aldosterone which acts on the distal tubule to increase reabsorption of NaCl and H2O.
8. Also, special nerve cells in the hypothalamus can detect if the tonicity of ECF has increased (due to increased water loss) and produce ADH to counteract the increased tonicity.

Question 3

What are the most important factors that control ADH release?

Answer 3

1. Decrease in blood volume or blood pressure
2. An increase in ECF tonicity (caused by excessive fluid loss)
3. Nausea, vomiting, thirst, pain.