glomerular filtration

Question 1

how much filtrate does the glomerulus produce a day?

Answer 1

180 L/day

Question 2

Starlings forces

Answer 2

GFR ∝ (Pcap + IIbc) - (Pbc + IIcap)

Question 3

what is the glomerular filtration rate in ml/min?

Answer 3

125ml/min

Question 4

what is the autoregulatory blood pressure range required to maintain GFR?

Answer 4

80-200 mmHg

Question 5

DEFINE: juxtaglomerular apparatus

Answer 5

structure formed by the distal convoluted tubule and the glomerular afferent arteriole. maintains GFR

Question 6

how many times does the total volume of the plasma pass the filtration barrier?

Answer 6

65 times a day

Question 7

what does the filtration barrier consist of?

Answer 7

1. endothelial cells - blood cells and platelets will not pass through
2. basement membrane - ions, water and solutes will pass through
3. podocytes - structural support + phagocytosis of foreign bodies

Question 8

what factors determine whether something will be filtered?

Answer 8

molecular weight - increase in mW = decrease in likelihood of filtration
charge - negatively charged molecules less likely to be filtered because basement membrane is negatively charged
in small mW range, charge does not have much of an effect

Question 9

what are the forces governing filtration?

Answer 9

• Kf = filtration coefficient - measure of permeability of filtration barrier
• Starling’s forces

Question 10

why does IIbc = 0?

Answer 10

there are very small amounts of protein in the filtrate in Bowman’s capsule

Question 11

why is Pbc constant along the length of Bowman’s capsule?

Answer 11

fluid enters Bowman’s capsule at the same rate as fluid drains into the proximal tubule

Question 12

why does Pcap decrease slightly along the length of Bowman’s capsule?

Answer 12

filtration occurs as plasma moves down the length of Bowman’s capsule
volume of plasma decreases

Question 13

what is the net filtration pressure?

Answer 13

10mmHg

Question 14

how is GFR autoregulated by the kidney?

Answer 14

regulating afferent arteriole resistance to compensate for small changes in blood flow and GFR e.g.
if arterial BP falls:
1. stretch receptors are not stimulated. signals to afferent arteriole smooth muscle to dilate in response
2. vasodilation decreases afferent arteriole resistance
2. increase in RBF
3. larger volume of blood in capillaries increases hydrostatic pressure
4. GFR increases

Question 15

tubuloglomerular feedback theory

Answer 15

macular densa cells in distal tubule have cilia projecting from apical surface
detect rate of flow of tubular fluid
rate of flow changes? - macular densa cells release vasoconstrictors/vasodilators causing the afferent arteriole to vasoconstrict/vasodilate