Urinalysis and Body Fluids 6th Edition by Majorie DiLorenzo, Susan Strasinger

Exercise 31

Concentration of the tubular filtrate by the countercurrent mechanism depends on all of the following except:

A. High salt concentration in the medulla

B. Water-impermeable walls of the ascending loop of Henle

C. Reabsorption of sodium and chloride from the ascending loop of Henle

D. Reabsorption of water in the descending loop of Henle

Step 1 of 3

Counter current mechanisms in kidney:

• The tubules of the nephron balance the water and essential substances by removing and re-absorbing process.

• Concentration of urine starts in ascending and descending limb of loop of henle, for this, selective absorption of essential substances and removal of extra water has to be done.

• The ascending loop of henle is impermeable to water and descending loop is impermeable to sodium and chloride ions

• The proximal convoluted tubule, distal convoluted tubule and descending loop of henle are permeable to water.

• The final urine output will be more concentrated this mechanisms of balancing of the ions and water of urine by tubule is called counter current mechanisms

• Renal (kidney) medulla which has high salt content in it and reabsorbs water content.

• In ascending loop of henle, water cannot enter in and sodium and potassium ions are reabsorbed, making the urine concentrated