Fysiologie van het Urogenitale Systeem III: Urineconcentratie en -verdunning

The kidneys are vital for maintaining water and electrolyte balance by regulating urine concentration.

The nephron, particularly the loop of Henle, plays a vital role through the countercurrent multiplication system, which establishes a high osmolarity in the renal medulla.

In the descending loop of Henle, water moves out into the hyperosmotic medulla due to its high water permeability.

In contrast, the ascending loop of Henle actively transfers sodium, potassium, and chloride ions into the medulla without reabsorbing water, preserving the medullary osmotic gradient.

Additionally, antidiuretic hormone plays a vital role in sustaining this gradient to facilitate water reabsorption.

When the body experiences dehydration, the hypothalamus produces antidiuretic hormone, which is then released by the posterior pituitary gland.

Elevated ADH levels increase water reabsorption in the collecting ducts by inserting aquaporin channels, concentrating the urine.

Conversely, when hydration is sufficient, ADH levels drop, the collecting ducts remain impermeable to water, and dilute urine is excreted to maintain balance.