3. Renal Blood Flow and Glomerular Filtration

Question 1

Define glomerular filtration

Answer 1

Formation of an ultrafiltrate of plasma in the glomerulus

Question 2

Define renal failure

Answer 2

An abrupt fall in glomerular filtration

Question 3

What leads to reduced glomerular filtration?

Answer 3

Abnormalities in renal circulation

Question 4

What type of process in glomerular filtration?

Answer 4

Passive process

Question 5

Define passive process

Answer 5

Fluid is ‘driven’ through the semipermeable (fenestrated) walls of the glomerular capillaries into the bowmans capsule space by the hydrostatic pressure of the heart

Question 6

Describe the filtration barrier

Answer 6

A fenestrated endothelium of capillaries and semipermeable Bowman’s capsule

Question 7

What is the filtration barrier highly permeable to?

Answer 7

Fluids and small solutes

Question 8

What are small solutes?

Answer 8

‘Freely filtered’ same concentration in filtrate and plasma

Question 9

Define primary urine

Answer 9

A clear fluid, completely free from blood and proteins, is produced containing electrolytes and small solutes

Question 10

What is the driving force of glomerular filtration?

Answer 10

Hydrostatic pressure in glomerular capillaries (due to blood pressure)

Question 11

What are the opposing pressures of glomerular filtration?

Answer 11

Hydrostatic pressure of tubule Pt (pressure inside the tubules makes it more difficult for substances to pass through) + Oncotic pressure of plasma proteins in glomerular capillaries Pigc

Question 12

Give the equation for the amount excreted in the urine?

Answer 12

Amount excreted = Amount filtered + amount secreted - amount reabsorbed

Question 13

How do calculate the net ultrafiltration pressure?

Answer 13

Puf = Pgc - Pt - Pigc

This is approximately 10mmHg

Question 14

What is the equation for GFR?

Answer 14

GFR = Puf x Kf

Question 15

What is Kf

Answer 15

The ultrafiltration coefficient

Question 16

What are the two component of Kf?

Answer 16

Membrane permeability and the surface available for filtration

Question 17

What causes imbalances to the GFR?

Answer 17

Changes in filtration forces or Kf

Question 18

What effect do kidney diseases have on the Kf?

Answer 18

Reduces the number of functioning glomeruli = reduces the surface area = reduces the Kf

Question 19

Why is it important to measure GFR

Answer 19

To check kidney function

Question 20

How can Kf be increased?

Answer 20

Dilation of glomerular arterioles by drugs/hormones. During infection this occurs so white blood vells can enter

Question 21

What is the definition of GFR?

Answer 21

The amount of fluid filtered from the glomeruli into the bowmans capsule per unit of time (ml/min)

Question 22

What is the renal blood flow?

Answer 22

1L/min

Question 23

What is the renal plasma flow?

Answer 23

0.6L/min

Question 24

What component of blood is plasma?

Answer 24

60%

Question 25

What is the filtration fraction?

Answer 25

0.2

Question 26

What is the GFR in terms of RPF?

Answer 26

GRF = RPF x FF

Question 27

What is the glomerular filtration rate?

Answer 27

120ml/min

Question 28

What happens to the GFR during exercise?

Answer 28

Myogenic mechanism - when a blood vessel is underpressure it prevents it from dilating by contricting the smooth muscle of the arterioles. It keeps the GFR constant

Question 29

Define renal clearance

Answer 29

The number of litres of plasma that are completely cleared of the substance per unit time. The rate at which a substance is removed from the kidney

Question 30

What is the equation of renal clearance?

Answer 30

C = U x V/P ml/min ``` U = concentration of substance in the urine P = concentration of substance in the plasma V = rate of urine production ```

Question 31

How can you use renal clearance to estimate GFR?

Answer 31

Use a molecule that is freely filtered and neither reabsorbed nor secreted in the nephron E.g inulin and creatinine

Question 32

What are the properties of inulin that allow it to be used as a molecule to estimate GFR?

Answer 32

Freely filtered and neither reabsorbed nor secreted | Non toxic

Question 33

What is a practical measure of GFR?

Answer 33

Creatinine

Question 34

What are the advantages of creatinine

Answer 34

Found endogenously Amount is fairly constant If renal function is stable the amount of creatinine is also stable

Question 35

What is the clearance of inulin?

Answer 35

120ml/min same as the GFR

Question 36

What does low levels of creatinine clearance indicate?

Answer 36

Renal failure

Question 37

What does high plasma levels of creatinine indicate?

Answer 37

Renal failure