4 - glomerular filtration

Question 1

what is the daily GFR?

Answer 1

180L/day

Question 2

C.O. - how much do kidneys receive?

Answer 2

25%

Question 3

what is the result of kidneys receiving huge amount of C.O.?

Answer 3

they’re vulnerable to vascular disease

Question 4

what is passed though to Bowman’s capsule?

Answer 4

no RBCs and a fraction of plasma

Question 5

what happens to the material which does not filter through the bowman’s capsule?

Answer 5

passes via efferent arterioles into the peritubular capillaries - then to renal v

Question 6

how much of the blood vol is plasma?

Answer 6

55%

Question 7

how to work out filtration fraction?

Answer 7

work out 55% of 1200 = 660 pls/min (renal plasma flow)

then 125/660x100 = 19%

Question 8

what is the renal plasma flow?

Answer 8

this is the % of plasma in BV x 1200mls/min -

55% of 1200 = 660

Question 9

what is glomerular filtration dependent on?

Answer 9

balance between hydrostatic forces and oncotic pressure

Question 10

what do hydrostatic forces favour?

Answer 10

filtration

Question 11

what does oncotic pressure favour?

Answer 11

reabsorption

Question 12

name 3 things which affect the filterability of solutes across the glomerular filtration barrier?

Answer 12

molecular size
electrical charge
shape

Question 13

what is the function of the fenestration of the glomerular endothelial cell?

Answer 13

prevents filtration of blood cells but allows all components of blood plasma to pass through

Question 14

function of basal lamina of glomerulus?

Answer 14

prevents filtration of larger proteins

Question 15

function of slit membrane pedicles?

Answer 15

prevents filtration of medium sized proteins

Question 16

compare pressure of capillaries and the glomerular capillary pressure (Pgc)?

Answer 16

Pgc is much higher

Question 17

why is the Pgc much higher than that of the pressure of other capillaries in the body?

Answer 17

the afferent arteriole is short and wide and offers little resistance to flow -
therefore blood arriving at glomerulus still has a high hydrostatic pressure

Question 18

result of the efferent arteriole’s structure?

Answer 18

structure is long and narrow and so offers a high post-capillary resistance -
therefore blood at glomerulus has low hydrostatic pressure

Question 19

golden rule of circulation?

Answer 19

if there is high resistance, hydrostatic pressure upstream is increased and pressure downstream is decreased

Question 20

what occurs at the glomerular capillaries?

Answer 20

filtration ONLY

Question 21

what is net filtration pressure?

Answer 21

10mmHg

Question 22

what is the 1y factor affecting GFR?

Answer 22

Pgc - dependent on the afferent and efferent arteriolar diameters ant therefore the balance between them

Question 23

sympathetic VC nerves - effect on GFR?

Answer 23

leads to afferent and efferent constriction, greater sensitivity of afferent arteriole

Question 24

circulating catecholamines - effect on GFR?

Answer 24

constriction of primary afferent angiotensin II

-> leads to constriction of efferent arterioles at low concentration, and efferent and afferent at high concs.

Question 25

reabsorption?

Answer 25

Substances that the body wants are reabsorbed -
those it doesn’t want stay in the tubule
and are excreted

Question 26

secretion?

Answer 26

Substances may be specifically removed from the body in this way

Question 27

auto regulation of BP?

Answer 27

via control and adjusting of resistance in response to changes in arterial BP

Question 28

range of mean BP?

Answer 28

60-130mmHg

Question 29

what happens when BP falls below 60mmHg?

Answer 29

filtration falls or ceases altogether (50 and below)

Question 30

what happens when there is an increase in MAP?

Answer 30

there is an automatic increase in afferent arteriolar constriction, preventing a rise in glomerular Pgc

Question 31

what occurs as MAP decreases?

Answer 31

dilation

Question 32

where does auto regulation occur and what is its control?

Answer 32

control - independent of nerves or hormones

occurs in denervated and isolated perfused kidneys

Question 33

what happens when blood vol/ BP face a steroid compromise?

Answer 33

activation of sympathetic VC nerves overrides auto regulation -
leads to availability of blood for organs which need it most

Question 34

how much blood can be spared at the expense of the kidneys?

Answer 34

up to 800mls

Question 35

result of prolonged exposure to steroid compromise?

Answer 35

reduces renal blood flow for prolonged period -

• > irreparable damage to kidneys
• > death (due to dysfunction of homeostasis)