Glomerular Filtration

Question 1

Where does filtration occur?

Answer 1

The glomerulus within the nephron

Question 2

What is the function of filtration?

Answer 2

To excrete waste and excess fluid from the blood and maintain ECF volume

Question 3

How much fluid does the kidney filter daily?

Answer 3

180l/day

Question 4

How much blood do the kidneys recieve?

Answer 4

1200ml/min = 20-25% of cardiac output

Question 5

What is the rate of renal plasma flow?

Answer 5

660 ml/min

55% x 1200 = 660

Question 6

What is the Glomerular Filtration Rate?

Answer 6

125ml/min

Question 7

What is the filtration fraction ?

Answer 7

125/660 = 19%

Question 8

What is glomerular filtration dependent on?

Answer 8

Hydrostatic Forces and Osmotic Pressure

Question 9

What do hydrostatic forces favour?

Answer 9

Filtration

Question 10

What does osmotic pressure favour?

Answer 10

Reabsorption

Question 11

What is the function of the glomerular endothelial cells?

Answer 11

To prevent filtration of blood cells but they do allow for plasma components to pass through

Question 12

What is the function of the basal lamina of the glomerulus?

Answer 12

Prevents filtration of large proteins (prevents them from passing through)

Question 13

What is the function of the slit membranes?

Answer 13

To prevent medium proteins from undergoing filtration

Question 14

What does the afferent arteriole do?

Answer 14

Delivers blood to glomerulus

Question 15

What does the efferent arteriole do?

Answer 15

Carries blood away from glomerulus

Question 16

Why do arterioles change size?

Answer 16

To increase or decrease blood pressure in glomerulus

Question 17

Why is Glomerular Capillary Pressure (Pgc) higher than most capillaries?

Answer 17

As the afferent arteriole is short and wide and thus, resistance to blood flow is low.

Means that blood arriving at glomerulus has a high hydrostatic pressure

Question 18

What affect does the length and width of the efferent arteriole have on capillary resistance?

Answer 18

The long and narrow efferent arteriole results in a high post capillary resistance

Question 19

What does increased resistance do to hydrostatic pressure in the glomerulus?

Answer 19

High resistance = upstream hydrostatic pressure is high, downstream pressure is low

Low resistance = upstream pressure low, downstream pressure high

Question 20

How do sympathetic VC nerves affect GFR?

Answer 20

Afferent and efferent constriction is observed but there is greater sensitivity in afferent arteriole

Question 21

What effect do circulating catecholamines have on GFR?

Answer 21

Constriction occurs primarily in afferent arteriole

Question 22

How does angiotensin II affect GFR?

Answer 22

Constriction occurs in EFFERENT @ low concentration, in AFFERENT AND EFFERENT @ high concentration

Question 23

What is glomerular hydrostatic pressure equal to?

Answer 23

55mmHg

Question 24

What is Blood Colloid Osmotic Pressure equal to?

Answer 24

30mmHg

Question 25

What is Capsular Hydrostatic Pressure equal to?

Answer 25

15mmHg

Question 26

What is the net outward pressure of the glomerular filtration system?

Answer 26

10mmHg | 55-30-15=10

Question 27

What occurs when there is an increased resistance in the afferent arteriole?

Answer 27

Increased Hydrostatic pressure, Decreased capillary blood pressure = decreased GFR

Question 28

What occurs when there is an increased resistance in the efferent arteriole?

Answer 28

Increased hydrostatic pressure = Increased GFR

Question 29

What occurs when there is a decreased resistance in the afferent arteriole?

Answer 29

There is an increase in hydrostatic pressure resulting in increased GFR

Question 30

What is the intrarenal auto-regulatory range in humans?

Answer 30

60-130mmHg

Question 31

What occurs when blood pressure drops to 60mmHg?

Answer 31

Filtration fails

Question 32

What occurs when blood pressure drops to 50mmHg?

Answer 32

Filtration stops

Question 33

How much fluid filtrated by the glomerulus is excreted as urine?

Answer 33

~1l

Question 34

Where is the majority of filtered products reabsorbed?

Answer 34

The peritubular capillaries

Question 35

Why do peritubular capillaries offer such a low hydrostatic pressure?

Answer 35

Resistance is present across whole tube = large pressure drop = low hydrostatic pressure of 15mmHg LOW HYDROSTATIC PRESSURE IS NOT FAVOURABLE FOR FILTRATION

Question 36

What does an decrease in Ppc and an increase in πp result in ?

Answer 36

Favourable conditions for re absorption