USMLE Step 1 Renal Physiology Review 59 09 Urea & ADH

USMLE Step 1 Renal Physiology Review 59 09 Urea & ADH

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Play USMLE Audio MP3  59 09 Urea & ADH Below

Begin 59 09 Urea & ADH Transcription

What increases the inner medullary collecting ducts’ permeability to urea?

  • ADH.

Are the cortical and outer medullary collecting ducts also made permeable to urea by ADH?

  • No. They are impermeable to urea with or without ADH.

How does the urea concentration of tubular fluid change in the cortical collecting duct in the presence of ADH?

  • Urea concentration increases.

Why?

  • Because water leaves the cortical collecting duct but urea stays.

What is the major solute in the tubular fluid that enters the inner medullary collecting duct?

  • Urea.

What happens to water and urea in the inner medullary collecting duct in the presence of ADH?

  • Both water and urea leave the urine and enter the medullary interstitium.

What traps the urea in the medullary interstitium?

  • The countercurrent exchange function of the vasa recta.

This causes a high concentration of urea in what part of the kidney?

  • The answer begins with IM. In the inner medulla.

How does the urea that enters the interstitium from the collecting duct affect the tubular fluid in the thin descending limb of the Loop of Henle?

  • It causes water to be removed from the tubular fluid.

How does this affect tubular sodium chloride concentration?

  • Tubular sodium chloride concentration rises above the sodium chloride concentration of the interstitium.

This in turn has what effect on sodium chloride reabsorption from the thin ascending limb of Henle?

  • It increases.

Does water diuresis mean ADH is or isn’t present?

  • ADH isn’t present with water diuresis.

During water diuresis what percent of medullary interstitial osmolality comes from urea?

  • About 10 percent.

What is the opposite of water diuresis?

  • Antidiuresis.

During antidiuresis what percent of renal papillary osmolality is due to urea?

  • Between 40 and 50 percent.

Student doctor, please pause the tape and summarize what we’ve discussed about ADH and urea.

The inner medullary collecting ducts’ permeability to urea is increased by ADH. With or without ADH the cortical outer medullary collecting ducts are impermeable to urea. In the presence of ADH urine urea concentration increases in the cortical collecting duct because water leaves and urea stays. The major solute in the tubular fluid that enters the inner medullary collecting duct is urea. From the inner medullary collecting duct both water and urea diffuse into the medullary interstitium in the presene of ADH. The countercurrent exchange function of the vasa recta traps the urea in the medullary interstitium. This causes a high concentration of urea in the inner medulla. The urea that enters the interstitium from the collecting duct causes water to be removed from the tubular fluid in the thin descending limb of the Loop of Henle. This causes tubular sodium chloride concentration to rise above the interstitium’s sodium chloride concentration. This in turn increases sodium chloride reabsorption from the thin ascending limb of Henle. During water diuresis about 10 percent of medullary interstitial osmolality comes from urea. During antidiuresis between 40 and 50 percent of renal papillary osmolality is due to urea.

 

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