Nephrologists at a research hospital are investigating the physiologic changes that occur in diabetes insipidus. The group develops a technique that permits sampling of tubular urine in experimental animals with physiology similar to that of humans. The animals then undergo hypophysectomy, after which tubular fluid samples are obtained from multiple sites throughout the nephron. In the absence of antidiuretic hormone, fluid from which of the following sampling sites is most likely to have the highest osmolarity?

Question

Nephrologists at a research hospital are investigating the physiologic changes that occur in diabetes insipidus.  The group develops a technique that permits sampling of tubular urine in experimental animals with physiology similar to that of humans.  The animals then undergo hypophysectomy, after which tubular fluid samples are obtained from multiple sites throughout the nephron.  In the absence of antidiuretic hormone, fluid from which of the following sampling sites is most likely to have the highest osmolarity?

Quizplus · Accepted Answer

11ec160b_3cfd_7ef0_9249_efc5b0b6a239_MD0001_00 Tubular fluid osmolarity varies along the different segments of the nephron depending on each segment's permeability to water, the osmolarity of the renal interstitium, and the presence or absence of antidiuretic hormone (ADH): (Choice F) When ADH levels are high (eg, dehydration), the collecting duct is highly permeable to water. Water leaves the tubular fluid driven by the high osmolarity of the medullary interstitium, and hypertonic urine is formed (up to 1200 mOsm/L). However, in this experiment the hypophysectomized animals are unable to produce ADH and will have dilute urine. Educational objective: Antidiuretic hormone (ADH) acts primarily on the collecting ducts, increasing their permeability to water. In the absence of ADH, the tubular fluid is most concentrated at the junction between the descending and ascending limbs of the loop of Henle and most dilute in the collecting ducts.

Nephrologists at a Research Hospital Are Investigating the Physiologic Changes