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Physiology

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Kidney

Question
19 out of 26
 

Aldosterone does not act on



A PCT
B ascending limb of loop of Henle

C DCT
D collecting duct

Ans. A PCT

I. Aldosterone is a steroid hormone (mineralocorticoid family) produced by the outer section (zonaglomerulosa) of the adrenal cortex in the adrenal gland.

II. It acts mainly on the distal tubules and collecting ducts of the nephron.

III. Aldosterone tends to promote Na+ and water retention, and lower plasma K+ concentration by the following mechanisms:

a. Acting on the nuclear mineralocorticoid receptors (MR) within the principal cells of the distal tubule and the collecting duct of the kidney nephron, it upregulates and activates the basolateral Na+/K+ pumps, which pumps three sodium ions out of the cell and two potassium ions into the cell. This results in reabsorption of sodium (Na+) ions and water (which follows sodium) into the blood, and secreting potassium (K+) ions into the urine (lumen of collecting duct).

b. Aldosterone upregulates epithelial sodium channels (ENaCs), increasing apical membrane permeability for Na+.

c. Cl- is reabsorbed in conjunction with sodium cations to maintain the system's electrochemical balance.

d. Aldosterone stimulates the secretion of K+ into the tubular lumen.

e. Aldosterone stimulates Na+ and water reabsorption from the gut, salivary and sweat glands in exchange for K+.

f. Aldosterone stimulates secretion of H+ in exchange for K+ in the intercalated cells of the cortical collecting tubules, regulating plasma bicarbonate (HCO3−) levels and its acid/base balance.

Kidney Flashcard List

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