Question

GFR is tightly regulated not only to maintain extracellular homeostasis but also to maintain constant blood pressure. Predict the following based on changes to GFR:

A. If GFR is increased, what happens to urine output? Blood volume? BP?
B. If GFR is decreased, what happens to urine output? Blood volume? BP?
C. What is the main variable used to regulate GFR? And how is this done?

Answer 1

If GFR is increased, urine output will increase, blood volume might decrease slightly, and blood pressure might decrease slightly. If GFR is decreased, urine output will decrease, blood volume might increase slightly, and blood pressure might increase slightly. The main variable used to regulate GFR is the afferent arteriole diameter.

Step-by-step explanation:

A. If GFR is increased, urine output will increase.

This is because an increased GFR allows more filtrate to be produced, resulting in more urine.

Blood volume might decrease slightly due to the increased urine output, but it would not have a significant impact on blood volume.

Blood pressure might decrease slightly as a result of the increased urine output, as there is less fluid in the bloodstream.

B. If GFR is decreased, urine output will decrease.

This is because a decreased GFR leads to less filtrate production and therefore less urine.

Blood volume might increase slightly as a result of the decreased urine output, as more fluid is retained in the bloodstream.

Blood pressure might increase slightly due to the increased blood volume.

C. The main variable used to regulate GFR is the afferent arteriole diameter.

The afferent arteriole supplies blood to the glomerulus, where filtration occurs.

When the afferent arteriole diameter decreases, it reduces blood flow to the glomerulus, decreasing GFR.

When the afferent arteriole diameter increases, it increases blood flow to the glomerulus, increasing GFR.