flow and filtration

Question 1

define glomerular filtration

Answer 1

formation of ultrafiltrate of plasma in glomerulus

Question 2

define glomerular filtration rate

Answer 2

amount of fluid filtered from glomeruli into Bowman’s capsule per unit of time (ml/min) - sum of filtration rates of all functioning nephrons

Question 3

what is renal failure

Answer 3

abrupt fall in glomerular filtration, caused by abnormalities in renal circulation

Question 4

what does “freely filtered” mean

Answer 4

same concentration in filtrate and plasma (may change further along nephron)

Question 5

describe the passive process of glomerular filtration

Answer 5

fluid “driven” through semipermeable, fenestrated walls of glomerular capillaries into Bowman’s capsule space by hydrostatic pressure of heart

Question 6

what is the filtration barrier highly permeable to

Answer 6

fluids, “freely filtered” small solutes

Question 7

what is the filtration barrier impermeable to

Answer 7

cells, proteins, drugs bound to proteins

Question 8

what is the “primary urine” produced by glomerular filtration

Answer 8

clear fluid (ultrafiltrate), completely free from blood and proteins, containing electrolytes and small solutes

Question 9

process of going from glomerulus to Bowman’s capsule

Answer 9

fenstrations in capillary walls and Bowman’s capsule

Question 10

what is amount excreted equal to

Answer 10

amount filtered + amount secreted - amount absorbed

Question 11

how do kidney diseases affect glomerular filtration rate

Answer 11

reduce number of functioning glomeruli, reducing SA and therefore the ultrafiltration coefficient, reducing glomerular filtration rate

Question 12

how does dilation of glomerular arterioles by drugs/hormones e.g. inflammation affect glomerular filtration rate

Answer 12

increase SA (increasing size of fenestrations), increasing ultrafiltration coefficient, increasing glomerular filtration rate

Question 13

effect of loss of nephrons on glomerular filtration rate

Answer 13

loss of SA, resulting in fall in ultrafiltration coefficient, resulting in reduced glomerular filtration rate

Question 14

what is the filtration fraction

Answer 14

ratio between renal plasma flow and amount of filtrate filtered by glomerulus

Question 15

what is the filtration fraction as a %

Answer 15

20% (of amount - it remains same concentration as still freely filtered)

Question 16

calculate glomerular filtration rate from renal blood flow and filtration fraction

Answer 16

renal blood flow x filtration fraction; 0.6 x 0.2 = 120ml/min

Question 17

what 5 factors does glomerular filtrate rate depend on

Answer 17

glomerular capillary pressure, plasma oncotic pressure, tubular pressure, glomerular capillary surface area, permeability

Question 18

what regulates glomerular filtrate rate

Answer 18

neural/hormonal input to afferent/efferent arteriole causing changes in net ultrafiltration pressure

Question 19

name of mechanism of glomerular filtrate rate autoregulation

Answer 19

myogenic autoregulation

Question 20

describe myogenic autoregulation

Answer 20

arterial pressure rises → afferent arteriole stretches → arteriole contracts (vascular smooth muscle constricts when stretched) → vessel resistance increases → blood flow reduces → blood pressure reduced so glomerular filtrate rate kept constant

Question 21

how does a severe haemorrhage affect glomerular filtration rate

Answer 21

reduce cardiac output, lowering driving force, decreasing glomerular filtration rate

Question 22

how does an obstruction in nephron tubule affect glomerular filtration rate

Answer 22

opposing pressures elevated, decreasing glomerular filtration rate

Question 23

how does a reduced plasma protein concentration affect glomerular filtration rate

Answer 23

opposing pressures decrease, increasing glomerular filtration rate

Question 24

how does a small increase in blood pressure affect glomerular filtration rate

Answer 24

no effect as myogenic autoregulation mechanism

Question 25

what is the normal glomerular filtration rate

Answer 25

120 ml/min