L04-Glomerular filtration

Question 1

What is the name of the first part of the nephron and the filtered blood that passes into here?

Answer 1

Bowmans capsule and the ultrafiltrate passes into it

Question 2

Why is there little pressure change throughout the glomerular capillaries?

Answer 2

As there is resistance downstream causing the pressure to remain constant in the golmerular capillaries.

Question 3

What filters through to bowmans capsule?

Answer 3

The plasma and solutes but not proteins as they are too large.

Question 4

What are the three layers of the glomerular membrane?

Answer 4

fenestrated capillary endothelium
Basement membrane
visceral epithelium made of podocytes

Question 5

What is a normal GFR?

Answer 5

120ml/min

Question 6

In the glomerular capillaries what are the typical values for capillary hydrostatic pressure, capillary oncotic pressure and the hydrostatic pressure of bowmans capsule?

Answer 6

Hydrostatic pressure capillary - 45mmHg
Capillary oncotic pressure - 25mmHg
Bowmans capsule hydrostatic pressure - 10mmHg

Question 7

How does oncotic pressure change along the glomerular capillaries?

Answer 7

as fluid leaves the capillary the oncotic pressure increases from 25 to 35 as protein concentration increases.

Question 8

What is the equation for filtration constant?

Answer 8

Kf(filtration constant) = surface area x permeability

Question 9

What is the GFR equation?

Answer 9

GFR=Kf (Pcap + oncbc) - (Pbc + onccap)

Question 10

RBF = 1100ml/min, since we know hematocrit how do you work out plasma flow rate?

Answer 10

Interested in renal plasma flow. By measuring haematocrit which at 45%, we know that plasma is 55% thus 1100 x 55/100 = 600

Question 11

What is the filtration fraction in words and equation?

Answer 11

proportion of plasma flow that is filtered by the glomerulus (fraction = GFR/RPF)

Question 12

What sort of substances are required to measure GFR give and example?

Answer 12

Substances that are freely filtered at the glomerulus and are neither secreted nor absorbed e.g. insulin or creatine

Question 13

How can you calculate GFR from Creatine?

Answer 13

The amount of creatine filtered is the same as that excreted so the creatine in the urine can tell us the amount filtered.
This means GFR=(Creatine in urine x volume per unit time)/creatine produced in body

Question 14

• Suppose a woman has a creatinine concentration
of 60 µM, and during a 24 hour urine collection (of
volume 1.8l) the urine creatinine concentration is 6
mM, what is the GFR?

Answer 14

GFR = CCr,uV
              CCr, p
= 6000µM × 1.8l 24hours
              60µM 
= 7.5l.hour
= 7.5
   60
 =125ml.min−1

Question 15

How does GFR change with age and why?

Answer 15

It falls as we lose nephrons as we age

Question 16

How big are the endothelial fenestrations of the glomerular capillaries and what does this prevent from being filtered?

Answer 16

60nm which is small enough to prevent the passage of platelets

Question 17

what is the equation for eGFR

Answer 17

k/plasma creatine conc
k is (140-age)xmassxc 
c is a constant that is 1.23 for and 1.04 for women