USMLE Step 1 Renal Physiology Review 59 04 Concentration & Dilution of Urine

USMLE Step 1 Renal Physiology Review 59 04 Concentration & Dilution of Urine

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Play USMLE Audio MP3 59 04 Concentration & Dilution of Urine Below

Begin  59 04 Concentration & Dilution of Urine Transcription

Now let’s talk about concentration and dilution of urine. What kidney process conserves body water when water intake is minimal?

  • Urine concentration.

What is the range of possible urine concentrations? Give your answer in milliosmoles/kg of water.

  • Urine concentration can range from 50 to about 1200 milliosmoles/kg of water.

What hormone is the main regulator of urine composition?

  • Antidiuretic hormone, ADH.

What is another name for ADH? It starts with V.

  • ADH is also called vasopressin which is short for arginine vasopressin.

What do low or nonexistent levels of circulating antidiuretic hormone tell us about the body?

  • The body is well-hydrated.

What kind of urine is produced in the absence of ADH?

  • Dilute or hyposmotic urine.

What kind of urine is produced in the presence of ADH?

  • Concentrated or hyperosmotic urine.

What percent of water is reabsorbed when the level of circulating antidiuretic hormone is at a maximum?

  • At the maximum level of circulating ADH, 99% of the water is reabsorbed.

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

The process of urine concentration conserves body water when water intake is minimal. Urine concentration can range from 50 to about 1200 milliosmoles/kg of water. Antidiuretic hormone, ADH, is the main regulator of urine composition. ADH is also called vasopressin which is short for arginine vasopressin. When the body is well-hydrated, ADH release is minimal or absent. In the absence of antidiuretic hormone, dilute or hyposmotic urine is produced and in the presence of ADH, concentrated or hyperosmotic urine is produced. At the maximum level of circulating antidiuretic hormone, 99% of the water is reabsorbed.

What is the term for the kidney system that causes urine to be either concentrated or dilute? It starts with CS.

  • The countercurrent system.

And what is meant by countercurrent?

  • The direction of flow becomes opposite to what it was.

At what two points does the flow of tubular fluid change direction?

  • The flow of tubular fluid changes direction at the hairpin turn of the Loop of Henle and again at the point where the urine enters the collecting duct. In all, there are seven components of the countercurrent system.

In proximal to distal order, list the five tubule components of the system. I’ll cue you with the first letters of each.

First, TDL.

Thin descending limb of Henle.

Second, TAL.

Thin ascending limb.

Third, TAL.

Thick ascending limb

and fourth, DCT.

Distal convoluted tubule.

Fifth, CD.

Collecting duct.

What occurs in this part of the system? It starts with CM.

  • Countercurrent multiplication.

What are the two remaining components of the countercurrent system? They start with MI and VR.

  • The medullary interstitium and the vasa recta are also part of the countercurrent system.

What are the two major solutes in the medullary interstitium? They start with U and SC.

  • The two major solutes in the medullary interstitium are urea and sodium chloride.

What occurs in the vasa recta? It starts with CE.

  • Countercurrent exchange.

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

The countercurrent system of the kidneys causes urine to be either concentrated or dilute. Countercurrent means that the direction of flow becomes opposite to what it was. The flow of tubular fluid changes direction at the hairpin turn of the Loop of Henle and again at the point where the urine enters the collecting duct. In all, there are seven components of the countercurrent system. In proximal to distal order, the five tubule components of the system are the thin descending limb of the Loop of Henle, the thin and thick ascending limbs of Henle, the distal convoluted tubule, and the collecting duct. Countercurrent multiplication occurs in this part of the system. The two remaining components are the medullary interstitium and the vasa recta. The two main solutes are in the medullary interstitium are urea and sodium chloride. Countercurrent exchange occurs in the vasa recta.

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