Sun28November0440PM 8

Are the following true of antidiuretic hormone (ADH)?

True / False

Release is stimulated by a decreased plasma osmolality Correct

Is synthesised in the hypothalamus Correct

Activates adenylate cyclase Correct

Causes an increase in water permeability in the collecting ducts Correct

Release is decreased by nicotine Incorrect answer selected

Explanation

Antidiuretic hormone (ADH) in synthesised in the supraoptic nucleus of the hypothalamus as part of a large precursor molecule. This molecule is transported to the posterior pituitary where it is released.

Osmoreceptors in the hypothalamus detect alterations in plasma osmolality. The receptors regulate the release of ADH.

Water excess in the plasma causes a decrease in plasma osmolality, whilst water deficiency causes an increase in plasma osmolality. An increased osmolality leads to an increase in ADH secretion. A decreased osmolality causes a decrease in ADH secretion.

ADH acts on V2 receptors (a G coupled receptor), leading to the activation of adenylate cyclase. This activates a second messenger system that leads to the incorporation of water channels (aquaporin-2) into the apical membrane of collecting ducts increasing water permeability and hence water retention by the kidneys.

The release of ADH is also stimulated by nicotine.

Reference:

Lote CJ. Principles of Renal Physiology. 4th ed. Dordrecht: Kluwer Academic Publications; 2000.

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Average score: 70.21%

Times answered: 233