Question

How does urine volume change when GFR changes?

Answer 1

Answer

Glomerular filtration rate is mainly regulated by the blood pressure (hydrostatic pressure in the glomerular capillaries)

- Constriction of the afferent arterioles leads to a decrease in renal blood flow and GFR.

- Constriction of the efferent arterioles leads to an increase in GFR.

1) When GFR increases

• The filtrate is formed rapily.
• The fluid flows through renal tubules too rapidly, not providing time for selective reabsorption of solutes and water.
• Very little substances are reabsorbed and more filtrate becomes urine.
• As a result, urine volume increases.

2) When GFR decreases

• The filtrate is formed slowly.
• The fluid flows through renal tubules very slowly, provides musch more time for tubule cells to reabsorb water and electrolytes.
• Due to increased reabsorption, less amount of the filtrate becomes urine.
• As a result, urine volume decreases.