L16: Glomerular Filtration

Question 1

Describe the anatomy of the renal corpuscle?

Question 2

What are the forces that determine the rate of glomerular filtration? and how is it regulated?

Answer 2

Starling forces

Question 3

How much filtrate is produced per minute?

Question 4

How is the rate of glomerular filtration regulated?

Answer 4

1. Intrinsic regulation
   - Myogenic regulation
   - Tubuloglomerular feedback
2. Extrinsic regulation
   - Sympathetic nervous system

Question 5

What is the composition of the initial filtrate?

Answer 5

Composition of the initial filtrate = plasma but minus proteins

Question 6

Where does glomerular filtration occur?

Answer 6

Renal corpuscle

Question 7

Key force favouring filtration in glomerulus? what s the other force?

Answer 7

Glomerular capillary hydrostatic pressure (60mm Hg)
- Other is bowman’s capsule oncotic pressure

Question 8

Why is the bowman’s capsule oncotic pressure = zero mm Hg?

Answer 8

Pressure is zero since very few proteins get through

Question 9

What is filtration?

Answer 9

?? Filtration is things going from blood into the tubules of the nephron?

Question 10

Starling force that opposes filtration?

Answer 10

1. Bowman’s capsule hydrostatic pressure (PBC = 15 mm Hg)
   -> Fluid creates its own hydrostatic pressure, pushes opposing filtration
2. Glomerular oncotic pressure (πGC = 29 mm Hg)
   -> Proteins found in blood creates oncotic pressure, tends to draw fluid back as well

Question 11

What is the net filtration pressure in the glomerulus and how is it calculated? What does the value represent?

Question 12

Glomerular filtration pressure formula:

Question 13

Hydrostatic pressure

Answer 13

Fluid pressure
- ex. Glomerular capillary hydrostatic pressure, talks about the hydrostatic pressure in the glomerulus

Question 14

Oncotic pressure

Answer 14

Protein pressure, attractability of h2o to proteins
- ex. bowman’s capsule oncotic pressure, talks about the proteins in the Bowmans capsule and their ability to attract h2o which exerts a force

Question 15

What is the net filtration pressure given the following values?

Glomerular hydrostatic pressure = 50 mm Hg Bowman’s capsule hydrostatic pressure = 10 mm Hg Glomerular oncotic pressure = 20 mm Hg
Bowman’s capsule oncotic pressure = 0 mm Hg

a 15 mm Hg
b 20 mm Hg
c 40 mm Hg
d 60 mm Hg

Answer 15

b. (50+0) - (10+20) =20mm Hg

Question 16

Where is filtration happening in the body?

Answer 16

1. In the glomerulus
2. In the capillaries of the system circuit

Question 17

What is the glomerular filtration rate? What is shocking about this value and what does it tell us?

Answer 17

= 125 mL/min = 180 L/day

• Blood is only 5L
• A lot filtrate but a lot re-absorbed since we need the volume back

Question 18

systemic circulation filtration rate

Answer 18

Net filtration pressure = 2 mm Hg
Filtration rate = 3 L/day

Question 19

How does myogenic control work?

Answer 19

• When mean arterial pressure goes up
• Afferent arteriole pressure goes up
• Glomerular capillary pressure goes up
• Glomerular filtration pressure increases
• therefore, glomerular filtration rate increases

So myogenic control comes into play:
-When mean arterial pressure goes up
- Afferent arteriole pressure goes up
- This stretches arteriolar smooth muscle
- Stretch causes constriction of arteriole
- Resistance goes up since now constricted
- Glomerular capillary pressure goes down since less blood flow into glomerular capillary

This counteracts the increase in glomerular filtration rate and the GFR actually stays the same

Question 20

How does tubuloglomerular feedback work?

Question 21

How is blood pressure and Glomerular filteration rate related?

Answer 21

high blood pressure = increases in GFR
- But myogenic and tubuloglomerular feedback regulate this

Low BP = Decrease in GFR

Question 22

total peripheral resistance

Question 23

What is the end result of extrinsic regulation and why does this occur?

Answer 23

The end result is a decrease in GFP which causes a decrease in the amount of urine formed
- this happens due to a wanting to reduce fluid loss in the body that was caused by hemorrhage or sweating

Question 24

Steps of extrinsic regulation

Question 25

What is the end result of intrinsic regulation and why does this occur?

Question 26

2 ways GFR is maintained after an increase in BP?

Question 27

What do the paracrine factors do? where are they located? What do they act on?

Question 28

When there is an increase in blood pressure, GFR is maintained. What is one reason for this?

a. The afferent arteriole constricts due to stretch of smooth muscle
b. The afferent arteriole dilates due to stretch of smooth muscle
c. Parcrines from the macula densa decrease systemic blood pressure
d. Paracrines from the macula densa cause the efferent arteriole to constrict

Answer 28

a.

Question 29

Filtered load equation and what does it tell us?

Answer 29

GFR × Plasma concentration of the substance (Px)
Example: Filtered load of glucose
GFR = 125 mL/min
Plasma [glucose] = 1 mg/mL

Filtered load of glucose =
(125 mL/min) × (1 mg/mL) = 125 mg/min

Tell us how much of a substance is filtered / per minute
- For something that is freely filtered