USMLE Step 1 Renal Physiology Review 59 08 The Vasa Recta & Countercurrent Exchange

USMLE Step 1 Renal Physiology Review 59 08 The Vasa Recta & Countercurrent Exchange

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Play USMLE Audio MP3  59 08 The Vasa Recta & Countercurrent Exchange Below

Begin 59 08 The Vasa Recta & Countercurrent Exchange Transcription

The hyperosmotic gradient of the medullary interstitium is generated by the Loop of Henle but what structures function to maintain this hyperosmotic gradient? They start with VR.

  • The vasa recta maintain the medullary interstitum’s hyperosmotic gradient.

And what are the vasa recta?

  • Long straight capillary loops that branch from the efferent arterioles of the juxtamedullary nephrons.

What do the vasa recta function as?

  • Countercurrent exchangers.

What two solutes are trapped in the medullary interstitium by this countercurrent exchange function?

  • Sodium chloride and urea. Sodium chloride makes a five stage journey through the countercurrent system.

First, from what part of the nephron does sodium chloride leave the tubular fluid?

  • From the thin and thick ascending limbs of the Loop of Henle.

What is the second part of sodium chloride’s trip through the countercurrent system?

  • After leaving the tubular fluid sodium chloride accumulates in the medullary interstitium.

And then where does it go from there?

  • It is absorbed by the descending vasa recta.

And then?

  • Then it flows into the ascending vasa recta.

Finally, where does the sodium chloride go after entering the ascending vasa recta?

  • It is returned to the medullary interstitium.

What substance enters the medullary interstitium from the descending vasa recta?

  • Water.

And then what happens?

  • The water diffuses across the interstitium into the ascending vasa recat.

What kind of pressure is making this happen? It starts with O.

  • Onocotic pressure.

What does the ascending vasa recta do with the water?

  • The ascending vasa recta returns the water to the general circulation.

Student doctor, please pause the tape and summarize what we’ve discussed about the vasa recta and countercurrent exchange.

The hyperosmotic gradient of the medullary interstitium is generated by the Loops of Henle but the vasa recta function to maintain the hyperosmotic gradient. The vasa recta are long straight capillary loops that branch from the efferent arterioles of the juxtamedullary nephrons. They function as countercurrent exchangers and trap sodium chloride and urea in the medullary interstitium. Sodium chloride makes a five stage journey through the countercurrent system. First, it leaves the tubular fluid from the ascending limbs of the Loop of Henle and accumulates in the medullary interstitium. From there it is absorbed by the descending vasa recta. Then it flows into the ascending vasa recta. Finally it is returned to the medullary interstitium. Water enters the medullary interstitium from the descending vasa recta. Then oncotic pressure causes it to diffuse across the interstitium into the ascending vasa recta which returns it to the general circulation.

****END OF TRANSCRIPTION****

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