USMLE Step 1 Renal Physiology Review 59 05 Loop of Henle’s Role

USMLE Step 1 Renal Physiology Review 59 05 Loop of Henle’s Role

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Play USMLE Audio MP3 59 05 Loop of Henle’s Role Below

Begin  59 05 Loop of Henle’s Role Transcription

Where in the Loop of Henle does the initial concentration of urine occur?

  • Initial concentration of urine occurs in the thin descending limb of the Loop of Henle.

What substance is the thin descending limb highly permeable to?

  • Water.

From where to where does water diffuse all along the thin descending limb?

  • Water diffuses out of the tubular fluid into the medullary interstitium.

Why?

  • The osmotic gradient between tubular fluid and interstitium causes this to happen. In other words, the medullary interstitium is hypertonic to the tubular fluid.

What two substances does the thin descending limb have a low permeability to?

  • The thin descending limb of Henle has a low permeability to sodium chloride and urea.

What are the two urine diluting portions of the nephron?

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

Which of these is permeable to urea?

  • The thin ascending limb of the Loop of Henle is permeable to urea.

Discuss the permeability of the ascending limbs of the Loop of Henle to water and sodium chloride.

The thin and thick ascending limbs of Henle are impermeable to water and permeable to sodium chloride.

How does this dilute the urine?

  • Sodium chloride is reabsorbed but the water stays in the tubular fluid which dilutes its concentration.

Is sodium chloride reabsorption in the thin ascending limb active or passive?

  • Passive.

And what about sodium chloride reabsorption in the thick ascending limb?

  • Sodium chloride reabsorption in the thick ascending limb is active.

What is the most important thing that the Loop of Henle does toward the production of either concentrated or dilute urine?

  • The Loop of Henle’s most important contribution to the production of urine is to generate the osmotic gradient in the medullary interstitium.

Student doctor, please pause the tape and summarize what we’ve discussed about the Loop of Henle’s role in the countercurrent multiplier system.

Initial concentration of urine occurs in the thin descending limb of the Loop of Henle which is highly permeable to water. All along the thin descending limb, water diffuses out of the tubular fluid into the medullary interstitium. The osmotic gradient between tubular fluid and interstitium causes this to happen. In other words, the medullary interstitium is hypertonic to the tubular fluid. The thin descending limb has a low permeability to urea and sodium chloride. The two urine diluting portions of the nephron are the thin and thick ascending limbs of the Loop of Henle which are impermeable to water and permeable to sodium chloride. This dilutes the concentration of the urine because sodium chloride is reabsorbed but the water stays in the tubular fluid. Sodium chloride reabsorption is passive in the thin ascending limb and active in the thick ascending limb. The thin ascending limb is also permeable to urea. The Loop of Henle’s most important contribution to the production of urine is to generate the osmotic gradient in the medullary interstitium.

 

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