Sun14November1246PM 45

Antidiuretic hormone:

True / False

Is stored in the posterior pituitary Correct

Release is controlled by a hypothalamic releasing factor Correct

Acts via cyclic-AMP Correct

Is an octapeptide Incorrect answer selected

Directly increases glomerular filtration rate Correct

Explanation

Antidiuretic hormone or vasopressin is stored in the posterior pituitary. It is a nonapeptide (a nine amino acid protein chain).

Principle factors stimulating secretion include:

Osmotic factors: Osmoreceptors in the paraventricular nuclei and supraoptic nuclei of the hypothalamus respond to increases in plasma osmolarity

Hypovolaemia: Low pressure receptors in the atria and to a lesser extent the baroreceptors in the carotid sinus and aortic arch stimulate ADH

Other factors influencing secretion include: Stress, exercise, atrial natriuretic peptide (inhibition) and drugs (opioids and nicotine).

ADH is an agonist for two receptor subtypes:

V1: Mediates a powerful vasoconstrictor effect

V2: Mediates an increase in water permeability of the apical membrane of the cells of the distal tubule and collecting ducts in the cortex and medullar. A rise in cyclic-AMP following a sequence of events on the cell membrane of metabotropic receptors. This in turn triggers the opening of aquaporin-2 channels thus allowing water reabsorption.

ADH does not directly affect the glomerular filtration rate (GFR). It will eventually return the GFR back to normal in a hypovolaemic patient.

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Average score: 65.27%

Times answered: 258