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Chapter 13. Urinary System

If the [NaCl] of the fluid in a thick ascending limb entering the juxtaglomerular apparatus is sensed by macula densa cells as being too high, a response is initiated that results in what change to a nearby structure?

A. The afferent arteriole constricts

B. The efferent arteriole constricts

C. The extraglomerular mesangial cells migrate into the renal corpuscle

D. The juxtaglomerular cells release renin

E. The podocytes contract

The answer is A: A high concentration of NaCl in the fluid of the thick ascending limb indicates that flow through the nephron is too rapid. A signal is sent (the release of adenosine triphosphate) that causes the afferent arteriole to constrict, which will reduce the pressure gradient across the glomerular capillaries, decrease the formation of initial filtrate, and slow the rate of fluid movement through the nephron.

Potentially therapeutic drugs may prove ineffective in clinical trials because they are modified by hepatocytes, released back into the blood, and then specifically eliminated by which cells?

A. Collecting duct cells

B. Distal convoluted tubule cells

C. Kupffer cells

D. Other hepatocytes

E. Proximal convoluted tubule cells

The answer is E: Hepatocytes can modify compounds present in the blood, such as therapeutic drugs, and then release them back into the circulation. Several kinds of modification reactions occur, for instance the addition of glucuronic acid (see Chapter 12). Proximal convoluted tubule cells contain transport systems that catalyze the movement of organic acids and bases from the blood into the filtrate. These acids and bases can include glucuronate-modified drugs, as well as toxins and metabolites that may or may not have been processed by the liver.

A researcher studying kidney function in live rats is using microsurgical techniques. She injects a small amount of a fluorescent, water-soluble dye into the blood of an afferent arteriole entering a cortical renal corpuscle in the kidney. She then observes the dye's movement into the renal corpuscle and beyond. What is the most likely route that this dye will follow?

A. All of the dye will travel down the proximal convoluted tubule

B. All of the dye will leave via the efferent arteriole and then enter a stellate vein

C. Some of the dye will travel down ...

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