In renal regulation of water balance, the functions of angiotensin II include:
A. Blood clotting within the nephron.
B. Increasing progesterone secretion into the renal tubules.
C. Catalyzing calcium-rich nutrients.
D. Selectively constricting portions of the arteriole in the nephron.
Correct Answer: D. Selectively constricting portions of the arteriole in the nephron.
As part of the renal regulation of water balance, angiotensin II selectively constricts portions of the arteriole in the nephron. ATII is a potent vasopressor, acting on vascular endothelial receptors. The two types of ATII receptors present in the heart and vascular smooth muscle that are responsible for signal transduction in mediating the vasoconstrictive action of ATII are the AT1 and AT2 receptors.
Option A: The kidney regulates plasma osmolarity by modulating the amount of water, solutes, and electrolytes in the blood. It ensures long term acid-base balance and also produces erythropoietin which stimulates the production of red blood cells. It also produces renin for blood pressure regulation and carries out the conversion of vitamin D to its active form.
Option B: In the normal circumstance, the PCT reabsorbs all the glucose and amino acids as well as 65% of Na and water. The PCT reabsorb sodium ions by primary active transport via a basolateral Na-K pump. It reabsorbs glucose, amino acids, and vitamins through secondary active transport with Na and an electrochemical gradient drives passive paracellular diffusion.
Option C: The next tubular segment for reabsorption is the distal convoluted tubule (DCT). There is a primary active sodium transport at the basolateral membrane and secondary active transport at the apical membrane through Na-Cl symporter and channels. This process is aldosterone regulated at the distal portion. There is also calcium reabsorption via passive uptake controlled by the parathyroid hormone.
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