Filtration and Renal Blood Flow

Question 1

What are the barriers to glomerular filtration?

Answer 1

glomerular capillary Endothelium - RBC
Basement Membrane - plasma protein barrier
Slit processes of podocytes - plasma protein barrier

Question 2

What are the forces that comprise net filtration pressure?

Answer 2

Glomerular capillary blood pressure
Bowmans capsule hydrostatic pressure
Capillary Oncotic Pressure
Bowman’s capsule oncotic pressure

Question 3

Which forces favour filtration?

Answer 3

Glomerular capillary pressure

Bowmans Capsule Oncotic pressure

Question 4

Which forces oppose filtration?

Answer 4

Bowmans Capsule Hydrostatic Pressure

Capillary Oncotic Pressure

Question 5

What is oncotic pressure?

Answer 5

the pressure that tends to pull water back into the blood

Question 6

What are the typical values of the forces favouring filtration?

Answer 6

GCBP - 55mmHg

BCOP - 0mmHG

Question 7

What are the typical values of the forces opposing filtration?

Answer 7

BCHP - 15mmHg

COP - 30mmHg

Question 8

What is the typical net filtration pressure?

Answer 8

10mmHg towards the bowmans

Question 9

What is the GFR?

Answer 9

the rate at which protein free plasma is filtered from the glomeruli into the Bowman’s capsule per unit time

Question 10

What is the equation for GFR?

Answer 10

GFR = Kf x net filtration pressure

Question 11

What is a normal GFR?

Answer 11

125ml/min

Question 12

What is the major determinant of GFR?

Answer 12

glomerular capillary blood pressure

Question 13

What are the extrinsic controls of GFR?

Answer 13

sympathetic control via baroreceptor reflex

Question 14

What are the intrinsic or autoregulatory controls of GFR?

Answer 14

myogenic mechanism

tubuloglomerular feedback mechanism

Question 15

What is the effect of an increase in arterial blood pressure?

Answer 15

increased GCBP increases net filtration and GFR

Question 16

What causes the GCBP to fall?

Answer 16

constriction of the afferent arteriole

Question 17

What does increased sympathetic activity do to the GFR?

Answer 17

it decreases it in order to compensate for a fall in blood volume

Question 18

What does autoregulation prevent?

Answer 18

short term changes in systemic arterial pressure affecting GFR

Question 19

What is protected from changes in MABP over a wide range of MABP?

Answer 19

RBF and GFR

Question 20

What is myogenic control?

Answer 20

if vascular smooth muscle is stretched, it contracts thus constricting the arteriol

Question 21

What is tubuloglomerular feedback?

Answer 21

involves juxtaglomerular apparatus

If GFR rises, more NaCl flows through the tubule leading to constriction of afferent arterioles

Question 22

What senses the NaCl content of tubular fluid?

Answer 22

macula densa

Question 23

What may also determine GFR?

Answer 23

kidney stone - increase BCHP - decrease GFR
diarrhoea - increase COP - decrease GFR
burns patients - decrease COP - increase GFR
decrease in Kf - surface area change - decrease in GFR

Question 24

What is plasma clearance?

Answer 24

the volume of plasma completely cleared of a particular substance per minute

Question 25

What is are the units of clearance?

Answer 25

ml/min

Question 26

What are the equations for clearance?

Answer 26

``` Cl = rate of excretion/plasma conc Cl = X urine x V urine / X plasma ```

Question 27

Why is inulin good for calculating GFR?

Answer 27

``` freely filtered neither absorbed or secreted not metabolised not toxic easy to measure ```

Question 28

What can be used to measure clearance instead of inulin?

Answer 28

Creatinine

Question 29

What does it mean when a substance has a clearance of O?

Answer 29

completely reabsorbed and not secreted - glucose | not filtered and not secreted

Question 30

What does it mean when the clearance is less than GFR?

Answer 30

partly reabsorbed, not secreted i.e. urea

Question 31

What does it mean when clearance is greater than GFR?

Answer 31

substance is filtered, secreted and not reabsorbed

Question 32

What does it mean if clearance is equal to GFR?

Answer 32

the substance is neither reabsorbed or secreted

Question 33

What is used to measure renal plasma flow?

Answer 33

para-amino hippuric acid - PAH

Question 34

What is renal plasma flow normally about?

Answer 34

650ml/min

Question 35

What makes PAH suitable for calculating RPF?

Answer 35

freely filtered secreted and not reabsorbed completely cleared from plasma

Question 36

What is creatinine?

Answer 36

a muscle metabolite produced at a near constant rate

Question 37

What are the properties of a clearance marker?

Answer 37

non-toxic inert - not metabolised easy to measure

Question 38

What are the properties of a GFR marker?

Answer 38

freely filtered | not secreted or absorbed

Question 39

What are the properties of an RPF marker?

Answer 39

should be filtered and completed secreted

Question 40

What is the filtration fraction?

Answer 40

the fraction of plasma flowing through the glomeruli that is filtered into the tubules

Question 41

What is the equation for filtration fraction?

Answer 41

filtration fraction = GFR/RPF | i.e. 20% is filtered, the rest is secreted in peritubular capillaries

Question 42

What is the calculation for RBF?

Answer 42

RBF = RPF x 1/1-Hct

Question 43

What is Hct?

Answer 43

haematocrit - 1.85