Explain ADH secretion and how it is controlled.

control of ADH secretion by negative feedback;

ADH controls water reabsorption in kidney;

osmoreceptors in hypothalamus monitor water content (in blood);

ADH produced by neurosecretory cells in the hypothalamus;

transported (down axons of these cells) to the posterior pituitary;

low water content/high solute concentration in blood ((usually) causes action potential to be sent to posterior pituitary);

posterior pituitary releases ADH which travels to collecting ducts of kidney;

more water reabsorbed (by collecting ducts) making water content (of blood) higher/solute concentration lower;

less ADH released;

This was probably the best answered question in the paper. Many candidates gained all marks for ADH; there were nevertheless some answers lacking the details required by some marking points and a number of confused and incomplete answers.