USMLE Step 1 Renal Physiology Review 59 07 Effect of ADH on the DCT & Collecting Duct

USMLE Step 1 Renal Physiology Review 59 07 Effect of ADH on the DCT & Collecting Duct

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Play USMLE Audio MP3 59 07 Effect of ADH on the DCT & Collecting Duct Below

Begin  59 07 Effect of ADH on the DCT & Collecting Duct Transcription

Where is the final concentration or osmolality of the urine determined?

  • In the collecting ducts.

What parts of the countercurrent system are directly affected by the absence or presence of antidiuretic hormone?

  • The distal convoluted tubule and the collecting duct.

What effect does circulating ADH have on the water permeability of the distal convoluted tubule and the collecting duct?

  • The presence of circulating ADH makes the distal convoluted tubule and the collecting duct highly permeable to water.

No matter what state of hydration the body is in, what kind of fluid is always presented to the distal convoluted tubule from the ascending limb of the Loop of Henle?

  • Hyposmotic.

In the absence of ADH what happens to the diluted urine from the ascending limb as it passes through the distal convoluted tubule and the collecting duct?

  • If anything, it becomes more diluted.

In the presence of ADH, what kind of fluid enters the collecting duct from the distal convoluted tubule?

  • Isosmotic.

And why?

  • The presence of ADH has made the distal convoluted tubule permeable to water.

What happens to the urine as it passes through the collecting duct when ADH is present?

  • The urine becomes hyperosmotic.

Why?

  • ADH has also made the collecting duct permeable to water.

When ADH is present, what is the urine equilibrating with as it passes through the collecting duct?

  • When ADH is present, the urine is equilibrating with the interstitium.

Does the urine in the collecting duct also equilibrate with the interstitium when ADH is absent?

  • No. In the absence of ADH the urine passing through the collecting duct doesn’t equilibrate with the interstitium.

Why not?

  • It can’t because the collecting duct is impermeable to water in the absence of ADH and water can’t leave the tubular fluid.

Student doctor, please pause the tape and summarize what we’ve discussed about the effect of ADH on the distal convoluted tubule and the collecting duct.

The distal convoluted tubule and the collecting duct are directly affected by the presence or absence of ADH. The presence of circulating ADH makes the distal convoluted tubule and the collecting duct highly permeable to water. The final concentration, or osmolality of the urine is determined in the collecting ducts. No matter what state of hydration the body is in, hyposmotic fluid is always presented to the distal convoluted tubule from the ascending limb of the Loop of Henle. In the absence of ADH, the diluted urine from the ascending limb remains hyposmotic or becomes even more hyposmotic as it passes through the distal convoluted tubule and the collecting duct. When ADH is present, isosmotic fluid enters the collecting duct from the distal convoluted tubule and then becomes hyperosmotic as it passes through the collecting duct. This occurs because ADH is made both the distal convoluted tubule and the collecting duct permeable to water and the urine is equilibrating with the surrounding interstitium. When ADH is absent the urine can’t equilibrate with the interstitium because water can’t leave the tubular fluid. This is because the distal convoluted tubule and collecting duct are impermeable to water without ADH.

****END OF TRANSCRIPTION****

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