6. Introduction to Renal Blood Flow and GFR 2

Question 1

What is the equation to calculate GFR given the hydraulic conductivity, surface area for filtration, and capillary ultrafiltration pressure?

Answer 1

GFR = K_f x P_UF

Where K_f = hydraulic conductivity x surface area for filtration

Question 2

How do you calculate the ultrafiltration pressure?

Answer 2

Some of the startling forces, keeping in mind that the glomerulus does not typically have an oncotic gradient

Question 3

How might mesangial cells influence GFR?

Answer 3

They can decrease the surface area for filtration, which is a component of the ultrafiltration coefficient (K_f)

Question 4

How does oncotic pressure change as we pass from the afferent to efferent arterioles?

Answer 4

As fluid passes through the filtration barrier, the oncotic pressure increases in the glomerular capillaries.

Question 5

Which section of capillary is predominantly affected by angiotensin II?

Answer 5

The efferent arteriole.

Question 6

Oxygen use in the kidneys increases linearly along with what other metric?

Answer 6

Sodium reabsorption

Question 7

Which arteriole do alpha-1 receptors predominantly affect?

Answer 7

The afferent arteriole

Question 8

What is the effect on the arterioles as a result of the local myogenic feedback reflex?

Answer 8

Afferent arterioles constrict, efferent arterioles dilate.

(This functions on both ends with the goal of decreasing GFR in proportion to its increase from the high blood pressure)

Question 9

What is the mechanism for the action of the macula densa when there is increased renal perfusion pressure?

Answer 9

Sodium and chloride are delivered to the macula densa
this causes an increase in ATP and adenosine
ATP and adenosine trigger calcium release in afferent arterioles smooth muscle

GFR decreases

Question 10

What is the action of the macula densa when there is decreased renal perfusion pressure?

Answer 10

The macula densa detects there is a decrease in the amount of salt being presented to it and signals the juxtaglomerular cells to produce renin.
Renin causes the production of angiotensin II which constricts the efferent arterioles and increases GFR.

Also the afferent arteriole is dilated by nitrous oxide.

Question 11

What is the effect of the sympathetic nervous system on renin secretion, and what receptor is used?

Answer 11

Beta adrenergic receptors increase renin secretion.