Glomerular filtration

Question 1

What are the 3 basic renal processes

Answer 1

filtration
reabsorption
secretion

Question 2

Give some examples of substances reabsorbed

Answer 2

sodium chloride, water, glucose, amino acids

Question 3

Give some examples of substances secreted

Answer 3

organic ions, drugs,

Question 4

How much of the cardiac output do the kidneys receive and what is the significance of this?

Answer 4

20-25%

vulnerability to damage by vascular disease

Question 5

What tissue in the body has the highest BF/g?

Answer 5

kidneys!

Question 6

Why does the kidneys receive such a large blood flow?

Answer 6

filtration! - not for oxygen

Question 7

How long does it take for the volume for the total BV to pass through the renal circulation?

Answer 7

5 mins

Question 8

Are red cells filtered into bowmans capsule?

Answer 8

no

Question 9

What is the renal plasma flow?

Answer 9

660mls/min

Question 10

What is the % filtration fraction?

Answer 10

19% - usually say 20

Question 11

What is glomerular filtration dependent on the balance between?

Answer 11

starling’s forces

hydrostatic and oncotic pressures

Question 12

Which of hydrostatic and oncotic pressure favours reabsorption and which favours filtration?

Answer 12

Hydrostatic - filtration

oncotic - reabsorption

Question 13

3 things the permeselectivity of glomerular barrier is dependent on

Answer 13

molecular size, charge and shape

Question 14

How does the glomerulus make sure proteins don’t get filtered

Answer 14

fenestration pore - prevents filtration of blood cells only
basal lamina - prevents filtration of larger proteins
slit membrane between pedicles - prevents filtration of medium proteins

Question 15

Is the glomerular capillary pressure higher or lower than most capillaries? why?

Answer 15

higher

afferent arteriole - short and wide and little resistance

Question 16

Does the blood arriving at the glomerulus have high or low hydrostatic pressure?

Answer 16

high

Question 17

What is the efferent arteriole of the glomerulus like?

Answer 17

long and thin and high post capillary resistance

Question 18

If there is high resistance what happens to hydrostatic pressure upstream and downstream?

Answer 18

upstream increases

downstream decreased

Question 19

Why does only filtration occur at glomerular capillaries?

Answer 19

afferent and efferent arterioles contribute to high glomerular capillary hydrostatic pressure. This pressure always exceeds oncotic pressure and so only filtration occurs.

Question 20

primary factor affecting GFR

Answer 20

PGC - dependent on arteriolar diameter and resistance

Question 21

3 extrinsic controls affecting GFR

Answer 21

angiotensin 2
sympathetic VC nerves
catecholamines

Question 22

Is the afferent or efferent arteriole more sensitive to sympathetic VC control?

Answer 22

afferent

Question 23

How do circulating catecholamines affect the GFR?

Answer 23

constrict primarily the afferent arteriole

Question 24

What does angiotensin 2 do to the glomerular arterioles?

Answer 24

constrict efferent at [low] and both at [high]

Question 25

What is meant by autoregulation in terms of the renal vasculature?

Answer 25

intrinsic ability to adjust resistance in response to arterial bp changes keep BF and GFR relatively constant

Question 26

What mbp is autoregulation effective over? when does it fall and when does it cease?

Answer 26

60-130mmHg below 60 50

Question 27

What happens to the afferent arteriole if the MAP increases

Answer 27

increase in constriction and prevent a rise in glomerular PGC

Question 28

Is autoregulation dependent or independent of hormone and nerves?

Answer 28

independent

Question 29

In haemorrhage what can override autoregulation? why?

Answer 29

extrinsic controls eg sympathetic VC and A2 | liberates blood for more immediately important organs

Question 30

How much blood can be directed elsewhere in expense of the kidneys?

Answer 30

800ml/min

Question 31

What happens in prep for a marathon to prevent taking away from kidney BF

Answer 31

adaption of skeletal muscle to become more efficient

Question 32

What volume of blood per day is a - filtered at glomerulus b - excreted

Answer 32

180l | 1-2l

Question 33

Why does only reabsorption take place in the efferent arteriole?

Answer 33

oncotic pressure exceeds hydrostatic as 20% volume ahs been removed and is now more concentrated with proteins