K3 - Filtration and Renal Blood Flow

Question 1

what bakes up the glomerular membrane?

Answer 1

• glomerular capillary endothelium
• basement membrane
• slit processes of the podocytes

Question 2

why will plasma proteins not cross the membrane?

Answer 2

basement membrane is acellular and is made up of collagen and glycoproteins and so is negatively charged which repels proteins

Question 3

what forces favour filtration?

Answer 3

• glomerular capillary blood pressure (55mmHg)

- bowman’s capsule oncotic pressure (0mmHg)

Question 4

what forces oppose filtration?

Answer 4

• bowman’s capsule hydrostatic pressure (15mmHg)

- capillary oncotic pressure (30mmHg)

Question 5

what is the Glomerular filtration rate (GFR)?

Answer 5

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

Question 6

what is the equation for GFR?

Answer 6

GFR = Kf x net filtration pressure

Kf - filtration coefficient

Question 7

what is the ‘normal’ value of GFR?

Answer 7

125ml/min

Question 8

what is the major derterminat of GFR?

Answer 8

Glomerular capillary fluid (blood) pressure (BPGC

Question 9

what is the extrinsic regulation of GFR?

Answer 9

sympathetic control via baroreceptor reflex

Question 10

what is the intrinsic control of GFR?

Answer 10

(a) Myogenic mechanism

(b) Tubuloglomerular feedback mechanism

Question 11

What effect will an increase in the arterial blood pressure have of GFR?

Answer 11

increased glomerular capillary blood pressure

increased net filtration pressure

increases GFR

Question 12

what effect will a decrease in arterial blood pressure have on GFR?

Answer 12

decreased glomerular capillary blood pressure

decreased net filtration pressure

decreased GFR

Question 13

what effect will vasoconstriction of afferent arteriole have on GFR?

Answer 13

decrease

Question 14

what effect will vasodilation of arteriole have on GFR?

Answer 14

increase

Question 15

how does the sympathetic nervous system control alterations in arterial blood pressure?

Answer 15

fall in blood volume

decrease arterial blood pressure

detected by aortic and carotid sinus baroreceptors

increases sympathetic supply

generalised arteriole vasoconstriction

constriction of afferent arterioles

decreases glomerular capillary blood pressure

decreases GFR

decreases urine volume

Question 16

what is the importance of auto-regulation?

Answer 16

prevents short term changes in systemic arterial pressure affecting GFR

Question 17

what is the myogenic response of the kidneys?

Answer 17

if vascular smooth muscle is stretched (i.e. arterial pressure is increased), it contracts thus constricting the arteriole

Question 18

what is the Tubuloglomerular feedback

response of the kidneys?

Answer 18

Involves the juxtaglomerular apparatus where if GFR rises, more NaCl flows through the tubule leading to constriction of afferent arterioles

Question 19

what cells sense NaCl in the Juxtaglomerular apparatus?

Answer 19

macula densa

Question 20

describe the negative feedback regulation of salt concentration in the kidneys?

Answer 20

• increase in GFR > increase in tubular fluid
• tubular fluid will have more salt
• macula densa cells will detect this increase and release vasocative chemicals to act on smooth muscle
• causes contraction > narrows diameter of smooth muscles > decreases GFR

Question 21

what effect will an kidney stone have pn GFR?

Answer 21

increase bowman’s capsule hydrostatic pressure causing GFR to decrease

Question 22

what effect will an increase in the capillary oncotic pressure have on GFR ?

Answer 22

decrease

Question 23

what effect will a decrease in Kf have on GFR?

Answer 23

decrease

Question 24

what is plasma clearance?

Answer 24

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

Question 25

what is the equation of plasma clearance?

Answer 25

Clearance of substance X = [X]urine x Vurine / [X]plasma

Question 26

what is the units of clearance?

Answer 26

ml/min

Question 27

why does inulin clearance = GFR?

Answer 27

freely filtered at glomerulus

• neither absorbed nor secreted
• not metabolised by kidney
• not toxic
• easily measured in urine and blood

Question 28

when does clearance = 0 (glucose)?

Answer 28

For substances which are filtered, completely reabsorbed and not secreted

Question 29

when is clearance < GFR (urea)?

Answer 29

For substances which are filtered, partly reabsorbed and not secreted

Question 30

when is clearance > GFR (H+) ?

Answer 30

For substances which are filtered, secreted but not reabsorbed

Question 31

how is renal plasma flow calculated using para-amino hippuric acid?

Answer 31

PAH is

1) freely filtered at glomerulus,
2) secreted into the tubule (not reabsorbed)
3) completely cleared from the plasma

• all the PAH in the plasma that escapes filtration is secreted from the peritubular capillaries

Question 32

what is filtration fraction ?

Answer 32

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

Question 33

what is the equation of filtration fraction?

Answer 33

filtration fraction = GFR/Renal Plasma Flow = 125ml.min/650ml.min
= 0.19 = 20%

• 20% of the plasma that enters the glomeruli is filtered

Question 34

what properties should a clearance marker have?

Answer 34

(1) Non-toxic
(2) Inert (i.e. not metabolised)
(3) Easy to measure

Question 35

what property a GFR marker have?

Answer 35

should be filtered freely not secreted or reabsorbed

Question 36

what property should a RPF marker have?

Answer 36

should be filtered and completely secreted