Countercurrent multiplier

Definition

The countercurrent multiplier is a mechanism in the kidney that creates a concentration gradient in the renal medulla, allowing for the reabsorption of water and production of concentrated urine. It involves the interaction between the descending and ascending limbs of the loop of Henle.

5 Must Know Facts For Your Next Test

1. The descending limb of the loop of Henle is permeable to water but not to solutes.
2. The ascending limb of the loop of Henle actively transports sodium and chloride ions out but is impermeable to water.
3. The countercurrent multiplier system helps maintain a high osmolarity in the renal medulla.
4. This mechanism allows for the kidneys to produce urine that is more concentrated than blood plasma.
5. ADH (antidiuretic hormone) increases water reabsorption by making collecting ducts more permeable to water.

Review Questions

• What role does the descending limb of the loop of Henle play in the countercurrent multiplier system?
• How does active transport in the ascending limb contribute to urine concentration?
• Why is maintaining a high osmolarity in the renal medulla important?

Related terms

Loop of Henle: A section of the nephron tubule that conserves water and minimizes urine volume.

Osmoregulation: The process by which organisms regulate fluid balance and concentration gradients.

Antidiuretic Hormone (ADH): A hormone that promotes water retention by increasing permeability of kidney tubules.