Glomerular Filtration and Calculations Flashcards
Is everything able to into Bowmans space?
No, due to 3 barriers of filtration
What limits surface area for filtration?
Slits between podocytes
What is the % of blood that is filtered into Bowmans space from each glomerulus?
20%
How does unfiltered blood exit the capillaries?
Leaves through the efferent arterial
What are the 4 pressures that affect glomerular filtration?
- Hydrostatic Pressure of Glomerular Capillaries
- Colloid Osmotic pressure of Glomerular Capillaries
- Hydrostatic Pressure of Bowmans Capsule
- Colloid Osmotic Pressure of Bowmans Capsule
What happens when net filtration pressure is positive?
Plasma will filter into Bowmans space
What happens when net filtration pressure is 0 or less?
Plasma will not filter out of the glomerular capillaries
What is proper filtration pressure?
10mmHg
What is Hydrostatic Pressure of Glomerular Capillaries?
The pressure of the fluid in the glomerulus
- pressure caused by blood flowing into the glomerulus
- promotes filtration
- largest pressure (55mmHg)
What is colloid osmotic pressure of glomerular capillaries?
Within the glomerulus there are proteins which are attracted to water.
- The pressure is caused by the presence of proteins in the glomerulus
- inhibits filtration (30mmHg)
What is Hydrostatic pressure of Bowmans capsule?
The pressure caused by filtrate that remains in Bowmans space
-inhibits filtration (15mmHg)
What is Colloid osmotic pressure of Bowmans Capsule?
Pressure caused by the presence of proteins IF in Bowmans capsule (because proteins shouldn’t be in this space)
-Promotes filtration IF proteins are present in Bowmans Space
What is the Globular Filtration Rate (GFR)?
The amount of fluid/solutes that are filtered per unit time into Bowmans space
What happens when if renal blood flow or blood pressure increases?
Would result in an increase in net filtration
What are the 2 things that affect GFR?
Net Filtration Pressure
Filtration Coefficient
What is the filtration coefficient?
Due to the leakiness of the globular capillaries
- really hard to measure
- influenced by the surface area of the capillaries and the permeability between capillaries
What happens when GFR increases and decreases?
When GFR increases more solutes are excreted
When GFR decreases less solutes are excreted
What is Net Filtration pressure influenced by?
Renal Blood flow
Blood Pressure
What is the filtration coefficient influenced by?
The surface area of the capillaries available for filtration
The permeability of barriers between capillaries and Bowmans Capsule
How do wed regulate GFR?
Auto-regulatory mechanisms are triggered to maintain blood pressure within the glomerulus of each nephron even when body blood pressure is high
What are the 2 auto-regulatory mechanisms used to regulate GFR?
Myogenic response
Tubuloglomerular Feedback
What is the Myogenic response?
Quickly modifies how much fluid is being filtered
-modifies how fast blood is going through the corpuscle
What is tubuloglomerular feedback?
When the actual content of the filtrate can also regulate the GFR locally with help of the macula dense cells
What is the function of the macula dense cells?
Act as salt detectors in tubuloglomerular feedback
In tubuloglomerular feedback, what happens when blood pressure increases?
Increased blood pressure increases the amount of fluid being filtered. As a consequence of that is the increase in NaCl being filtered. When NaCl is too high, macula dense cells release a paracrine factor that stimulate the afferent arteriole specifically to constrict and therefore reduce GFR
How is the GFR mostly regulated?
Via local constriction of the afferent and efferent arterioles
What happens to filtration when the afferent arteriole constricts?
A decrease in diameter will decrease blood flowing into the glomerulus.
-less blood=less pressure=less fluid can filter
What happens when the efferent arteriole constricts?
A decrease in diameter increases the GFR
- Blood cant leave as fast, pooling up in the corpuscle
- Pressure of blood increases= increases filtration rate
What happens when both afferent and efferent arterioles are restricted?
GFR decreases
- but the first constriction (afferent) is more important
- there is less blood entering through afferent
How do you measure GFR?
Through urine analysis
What is the excretion equation?
Filtration - Reabsorption + Secretion
What is the right substance to test GFR with?
A substance that is filtered easily but not reabsorbed into the body and it fully excreted in the urine
What are some examples of the “right” substance to measure GFR in urine?
Waste products
Creatinine
Where does creatinine come from?
Creatinine comes from Creatine which is found in bones. The amount of Creatinine will depend on how much bone you have
What is renal handling?
What happened to the substance after it got filtered into Bowmans space
What is the filtered load equation?
[X]substance in plasma x GFR
How can % reabsorption change?
Depending on how much is ingested
