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Kaplan medicals USMLE 1 qbook Physiology

Kaplan medicals USMLE 1 qbook Physiology
Тесты по физиологии на английском языке. 130 вопросов с ответами и объяснениями.
Questionnary book.
question 1
A new agent has been shown to block aldosterone’s interaction with its receptors. Which of the following is most likely to be decreased by the activity of this new drug?
A. Proximal collecting tubule brush border enzyme activity
B. Intracellular proximal collecting tubule hydrogen ion generation
C. Na-R-2C cotransport in the thick ascending limb
D. Hydrogen ion secretion from the intercalated cells of the collecting tubules
E. Urea reabsorption in the collecting tubules

Explanation:
Aldosterone is a mineralocorticoid hormone synthesized and released by the zona glomerulosa cells of the adrenal cortex. Aldosterone release is stimulated by angiotensin II, high serum potassium ion concentrations, and (to a small degree) ACTH.
Aldosterone is a component of the renin-angiotensin-aldosterone system, which is normally activated in times of low blood pressure, low visceral perfusion and low plasma volume. Aldosterone increases sodium and water reabsorption in the collecting ducts of the nephron, thus increasing circulating volume. A steroid hormone aldosterone crosses the cell membrane directly, binds a cytosolic protein receptor and subsequently moves into the nucleus to modify gene expression. Its net effect is to increase the number of Na/K-ATPase proteins and sodium channels in the cell membranes of the kidney’s cortical collecting ducts. Under the influence of aldosterone, sodium and water are removed from the tubular fluid actively and passively, respectively. As a consequence, potassium and hydrogen ions are lost into the tubular fluid. Thus, aldosterone promotes potassium ion and hydrogen ion secretion from the intercalated cells of the renal collecting tubules.
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