-At which nephron site is the tubular fluid/plasma (TF/P) osmolarity lowest in a person who has been deprived of water?

Question

Quizplus · Accepted Answer

[VII B 3; Figure 5.16]. A person who is deprived of water will have high circulating levels of antidiuretic hormone (ADH). The tubular fluid/plasma (TF/P) osmolarity is 1.0 throughout the proximal tubule, regardless of ADH status. In antidiuresis, TF/P osmolarity is greater than 1.0 at site $C$ because of equilibration of the tubular fluid with the large corticopapillary osmotic gradient. At site $E$, TF/P osmolarity is greater than 1.0 because of water reabsorption out of the collecting ducts and equilibration with the corticopapillary gradient. At site $D$, the tubular fluid is diluted because $\mathrm{NaCl}$ is reabsorbed in the thick ascending limb without water, making TF/P osmolarity less than 1.0.

-At Which Nephron Site Is the Tubular Fluid/plasma (TF/P) Osmolarity