MCAT Biology Question 139: Answer and Explanation

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Question: 139

4. Which of the following sequences correctly shows the passage of blood through the vessels of the kidney?

  • A. Renal artery → afferent arterioles → glomerulus → efferent arterioles → vasa recta → renal vein
  • B. Afferent arterioles → renal artery → glomerulus → vasa recta → renal vein → efferent arterioles
  • C. Glomerulus → renal artery → afferent arterioles → efferent arterioles → renal vein → vasa recta
  • D. Renal vein → efferent arterioles → glomerulus → afferent arterioles → vasa recta → renal artery

Correct Answer: A

Explanation:

Blood enters the kidney through the renal artery, which divides into many afferent arterioles that run through the medulla and into the cortex. Each afferent arteriole branches into a convoluted network of capillaries called a glomerulus. Rather than converging directly into a vein, the capillaries converge into an efferent arteriole, which divides into a fine capillary network known as the vasa recta. The vasa recta capillaries enmesh the nephron tubule, where they reabsorb various ions, and then converge into the renal vein. This arrangement of tandem capillary beds is known as a portal system.

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