678 SECTION VIII Renal Physiology
or baroreceptors. Increases in secretion occur when osmolality
is changed as little as 1%, thus keeping the osmolality of the plas-
ma very close to 285 mOsm/L.
■ The amount of Na+ in the ECF is the most important determi-
nant of ECF volume, and mechanisms that control Na+ balance
are the major mechanisms defending ECF volume. The main
mechanism regulating sodium balance is the renin–angiotensin
system, a hormone system that regulates blood pressure.
■ The kidneys secrete the enzyme renin and renin acts in concert
with angiotensin-converting enzyme to form angiotensin II.
Angiotensin II acts directly on the adrenal cortex to increase the
secretion of aldosterone. Aldosterone increases the retention of
sodium from the urine via action on the renal collecting duct.MULTIPLE-CHOICE QUESTIONS
For all questions, select the single best answer unless otherwise directed.
- Dehydration increases the plasma concentration of all the fol-
lowing hormones except
A) vasopressin.
B) angiotensin II.
C) aldosterone.
D) norepinephrine.
E) atrial natriuretic peptide. - In a patient who has become dehydrated, body water should be
replaced by intravenous infusion of
A) distilled water.
B) 0.9% sodium chloride solution.
C) 5% glucose solution.
D) hyperoncotic albumin.
E) 10% glucose solution. - Renin is secreted by
A) cells in the macula densa.
B) cells in the proximal tubules.
C) cells in the distal tubules.
D) juxtaglomerular cells.
E) cells in the peritubular capillary bed. - Erythropoietin is secreted by
A) cells in the macula densa.
B) cells in the proximal tubules.
C) cells in the distal tubules.
D) juxtaglomerular cells.
E) cells in the peritubular capillary bed. - When a woman who has been on a low-sodium diet for 8 d is
given an intravenous injection of captopril, a drug that inhibits
angiotensin-converting enzyme, one would expect
A) her blood pressure to rise because her cardiac output would
fall.
B) her blood pressure to rise because her peripheral resistance
would fall.
C) her blood pressure to fall because her cardiac output would
fall.
D) her blood pressure to fall because her peripheral resistance
would fall.
E) her plasma renin activity to fall because her circulating
angiotensin I level would rise.
6. Which of the following would not be expected to increase renin
secretion?
A) administration of a drug that blocks angiotensin-converting
enzyme
B) administration of a drug that blocks AT1 receptors
C) administration of a drug that blocks β-adrenergic receptors
D) constriction of the aorta between the celiac artery and the
renal arteries
E) administration of a drug that reduces ECF volume
7. Which of the following is least likely to contribute to the benefi-
cial effects of angiotensin-converting enzyme inhibitors in the
treatment of congestive heart failure?
A) vasodilation
B) decreased cardiac growth
C) decreased cardiac afterload
D) increased plasma renin activity
E) decreased plasma aldosterone
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