L16: Glomerular Filtration Flashcards
Describe the anatomy of the renal corpuscle?
What are the forces that determine the rate of glomerular filtration? and how is it regulated?
Starling forces
How much filtrate is produced per minute?
How is the rate of glomerular filtration regulated?
- Intrinsic regulation
- Myogenic regulation
- Tubuloglomerular feedback - Extrinsic regulation
- Sympathetic nervous system
What is the composition of the initial filtrate?
Composition of the initial filtrate = plasma but minus proteins
Where does glomerular filtration occur?
Renal corpuscle
Key force favouring filtration in glomerulus? what s the other force?
Glomerular capillary hydrostatic pressure (60mm Hg)
- Other is bowman’s capsule oncotic pressure
Why is the bowman’s capsule oncotic pressure = zero mm Hg?
Pressure is zero since very few proteins get through
What is filtration?
?? Filtration is things going from blood into the tubules of the nephron?
Starling force that opposes filtration?
- Bowman’s capsule hydrostatic pressure (PBC = 15 mm Hg)
-> Fluid creates its own hydrostatic pressure, pushes opposing filtration - Glomerular oncotic pressure (πGC = 29 mm Hg)
-> Proteins found in blood creates oncotic pressure, tends to draw fluid back as well
What is the net filtration pressure in the glomerulus and how is it calculated? What does the value represent?
Glomerular filtration pressure formula:
Hydrostatic pressure
Fluid pressure
- ex. Glomerular capillary hydrostatic pressure, talks about the hydrostatic pressure in the glomerulus
Oncotic pressure
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
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
b. (50+0) - (10+20) =20mm Hg
Where is filtration happening in the body?
- In the glomerulus
- In the capillaries of the system circuit
What is the glomerular filtration rate? What is shocking about this value and what does it tell us?
= 125 mL/min = 180 L/day
- Blood is only 5L
- A lot filtrate but a lot re-absorbed since we need the volume back
systemic circulation filtration rate
Net filtration pressure = 2 mm Hg
Filtration rate = 3 L/day
How does myogenic control work?
- 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
How does tubuloglomerular feedback work?
How is blood pressure and Glomerular filteration rate related?
high blood pressure = increases in GFR
- But myogenic and tubuloglomerular feedback regulate this
Low BP = Decrease in GFR
total peripheral resistance
What is the end result of extrinsic regulation and why does this occur?
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
Steps of extrinsic regulation
