Ultrafiltration and Glomerular filtration Rate

Question 1

1. what percentage of blood is plasma?

Answer 1

55%

Question 2

2. How much blood do kidneys receive every minute and therefore how much plasma is filtered every minute?

Answer 2

• receive ~1.25L blood/min
• therefore 625ml/min of plasma is filtered

Question 3

3. What are the three basic renal processes?

Answer 3

1. Glomerular filtration
2. Tubular reabsorption
3. Tubular Secretion

Question 4

4. Define glomerular filtration.

Answer 4

the transfer of fluid and solutes from the glomerular capillaries along a pressure gradient into Bowman’s capsule

Question 5

define tubular reabsorption

Answer 5

selective movement of filtered substances from the tubular lumen into the peritubular capillaries

Question 6

define tubular secretion

Answer 6

selective movement of non filtered substances from the peritubular capillaries into the tubular lumen

Question 7

1. What percentage and therefore amount in ml of plasma is filtered in each filtration cycle?

Answer 7

20% AKA 125ml/min

Question 8

8. What is the glomerular filtration rate?

Answer 8

the rate at which plasma is filtered by both kidneys

Question 9

9. How can the glomerular filtration rate be expressed numerically?

Answer 9

120 + or - 25ml/min/1.73m^2

Question 10

10. What are the 3 filtration layers of the glomerular filtration barrier?

Answer 10

1. the fenestrated endothelium
2. Glomerular basement membrane
3. Podocytes

Question 11

11. What does kD mean in unit of measure?

Answer 11

a kilodalton

Question 12

12. What is filtered into the tubules where it is is then excreted?

Answer 12

plasma and anything < 70kD

Question 13

13. What stays in the blood and is not filtered? Give examples as well.

Answer 13

Anything > 70kD stays in the blood

• Examples: Immunoglobulins, Ferritin, Cells, Plasma Proteins

Question 14

14. Why can’t albumin be filtered?

Answer 14

• Because it is negatively charged

Question 15

1. What 4 forces, in order, are responsible for driving ultrafiltration?

Answer 15

1. Glomerular blood hydrostatic pressure
2. Capsular hydrostatic pressure
3. Blood colloid osmotic pressure
4. Net filtration Pressure

Question 16

2. What is the value and units for Glomerular blood hydrostatic pressure?

Answer 16

55 mmHg

Question 17

3. What is the value and units for capsular hydrostatic pressure?

Answer 17

15 mmHg

Question 18

4. What is the value and units for blood osmotic pressure

Answer 18

30 mmHg

Question 19

1. What is the normal value and units for Net filtration pressure?

Answer 19

10 mmHg

Question 20

6. How is net filtration pressure calculated?

Answer 20

NFP = GBHP - CHP - BCOP

Question 21

7. Does GFR change when blood pressure changes?

Answer 21

No

Question 22

8. What is the definition of autoregulation?

Answer 22

the ability of a tissue to automatically adjust its blood flow to match its metabolic demands without nerves or hormones

Question 23

9. What 2 ways is negative feedback achieved in autoregulation of renal blood flow?

Answer 23

1. Tubuloglomerular feedback
   2.Myogenic control

Question 24

10. What is Tubuloglomerular feedback

Answer 24

When tubular flow rate is detected by the macula densa & vasoactive mediators are released from the JGA to act on the arterioles.

Question 25

what do the chemicals do in tubular feedback

Answer 25

The chemicals dilate or constrict the afferent arteriole as needed to keep the GFR within normal range

Question 26

11. Give examples of vasoactive mediators that 1. Vasocontrict 2. Vasodilate that are released from the JGA in Tubuloglomerular feedback

Answer 26

Vasoconstrict: - Angiotension II & endothelin Vasodilate: - Atrial natriuretic peptide, prostaglandins nitric oxide

Question 27

12. What is myogenic control?

Answer 27

The afferent or efferent arteriolar diameter automatically increases or reduces to oppose pressure changes

Question 28

13. What mean arterial pressure range is the GFR autoregulated at

Answer 28

80-180mmHg

Question 29

14. How do the efferent and afferent arterioles constrict?

Answer 29

sympathetic nerves which constrict the vessels via α1adrenoceptors

Question 30

15. What does constriction of the efferent and afferent arterioles do?

Answer 30

reduces plasma flow to the glomerular filter and slows filtration. This means less is excreted. This conserves plasma in the circulation to help maintain blood pressure.

Question 31

what 2 ways can tubuloglomerular feedback and myogenic control be reduced

Answer 31

Pathological conditions - Glomerulopathies - E.g. immune complexes, toxins, - Inherited disease Non-pathological conditions Pregnancy, kidney removal, ageing GFR may be reduced