Session 3 - Filtration by the Glomerulus

Question 1

What are the 3 layers the glomerulus filters the blood through?

Answer 1

The glomerulus filters the blood through 3 layers:

1) Capillary endothelium
2) Basement membrane
3) Podocyte layer

Question 2

Why are proteins not able to move into the nephron?

Answer 2

basement membrane as it is charged negatively and therefore repels any proteins (proteins are also negatively charged).

Question 3

What is the average rate of filtration through the kidneys?

Answer 3

125 ml / min

Question 4

What is the average net filtration pressure?

Answer 4

10mmHg

Question 5

What sodium channels are found in the apical membrane of loop of henle?

Answer 5

Na-K-2Cl symporter

Question 6

What sodium channels are found in the apical membrane of PCT?

Answer 6

Na-H antiporter Na-glucose symporter

Question 7

What sodium channels are found in the apical membrane of Early DCT?

Answer 7

Na-Cl symporter

Question 8

What sodium channels are found in the apical membrane of Late DCT and CD?

Answer 8

ENaC

Question 9

How are organic cations secreted in the PCT?

Answer 9

• Entry of organic cation to the proximal tubular cell from the capillary by passive carrier mediated diffusion down favourable concentration
• Secretion into the lumen occurs by a proton-OC exchanger that is driven by the hydrogen ion gradient created by the Na-H antiporter
• Low intracellular sodium maintained by na-k atpase on the basolateral membrane.

Question 10

How is glucose, vitamins and amino acids reabsorbed in the kidney?

Answer 10

using sodium conc gradient

Question 11

What would you use to calculate GFR?

Answer 11

Calculated by taking a substance which is neither actively secreted or absorbed and seeing rate of excretion.

Question 12

What is the filtration fraction of the kidneys?

Answer 12

20%

Question 13

What proportion of blood is plasma?

Answer 13

55%

Question 14

What would you use to calculate renal plasma flow?

Answer 14

To calculate renal plasma flow (RPF), PAH is used. This compound is actively secreted by the renal tubules and so not only is the 20% of RPF but also the 80% that isn’t filtered, and so the renal plasma flow can be calculated.

Question 15

Define the clearance rate?

Answer 15

volume of plasma cleared of substance per minute

Question 16

What must a substance be for its clearance rate to be equal to the GFR? Give an example of a substance

Answer 16

For clearance rate to = GFR, the substance must not be reabsorbed or secreted and must not be changed in any way. Inulin is the ideal substance for this.

Question 17

Define the transport maximum

Answer 17

Renal threshold is the plasma concentration of a substance at which TM of a substance is reached and the substance starts spilling into the urine.

Question 18

What substance is used to calculate eGFR?

Answer 18

creatinine

Question 19

How would an increase in renal blood pressure be autoregulated?

Answer 19

o Afferent arteriole constriction

o Efferent arteriole dilation

Question 20

How would a descrease in renal blood pressure be autoregulated?

Answer 20

o Relaxing afferent arteriole

o Constriction efferent arteriole.

Question 21

Explain how tubular glomerular feedback can autoregulate BP in the kidneys. How does this system sense high and low BP? Is this system useful for chronic or acute changes in pressure?

Answer 21

1. Increase in arterial pressure = increase In Renal plasma flow and therefore GFR
2. Increase GFR = increased amount of plasma filtered and therefore increase in Sodium and chlorine ions in Distal tubule
3. Macula densa cells respond to changes in NaCl arriving in DCT. Macula densa cells sense Na and Cl ion concentrations using Na-K-2Cl cotransporter in the apical membrane of the macula densa cells. Based on Na and Cl ion conc, MD cells stimulate juxtaglomerular apparatus to release:

• Adenosine for vasoconstriction (decreasing GFR)
• Prostaglandins for vasodilation (increasing GFR) Useful for acute changes in pressure