14. Renal Physiology Session 2 Flashcards
What is the length of molecules that are freely filtered in the glomerulus? What length is not filtered?
< 20 A are freely filtered
> 42 A are not filtered
What is the glycocalyx and what is its role in filtration?
An endothelial layer of proteins that give it a net negative charge. This makes it more difficult for negatively charged particles (like other proteins) to get through while making it easier for positively charged particles to get through.
How does one calculate urinary excretion?
Amount filtered - amount reabsorbed + amount secreted
How does one calculate the renal clearance of a substance (Cx)?
(Ux • V)/Px
Ux: concentration of X in urine
V: urine flow rate
Px: concentration of X in plasma
What equation do you use to solve for filtration factor?
FF = GFR/RPF
FF: filtration factor
GFR: glomerular filtration rate
RPF: renal plasma flow
What is the filtration fraction?
The fraction of renal blood that is filtered across the glomerulus.
What happens to oncotic pressure in efferent arterioles when FF increases, why?
Efferent arteriole oncotic pressure also increases because the concentration of proteins left behind is greater, leading to more oncotic pressure.
How does one calculate GFR of a substance when filtered amount is equal to excreted amount?
(Ux • V)/Px
Ux: concentration of X in urine
V: urine flow rate
Px: concentration of X in plasma
Under what conditions is GFR directly proportional to renal clearance?
- Substance must be freely filterable
- Must neither be reabsorbed or secreted by renal tubules
- Must not be made, stored, or broken down in kidneys
- Must be inert
Clearance of what substance is typically used in a clinical setting to determine GFR, why?
Creatinine (although not perfect because a small amount is secreted).
It is used instead of others like inulin because it is produced endogenously.
How does sympathetic innervation effect juxtaglomerular cells? What receptor is used?
Releases renin, activates RAAS.
Beta-1 receptor
How does sympathetic innervation effect tubular epithelial cells? What receptor is used?
Na-K ATPase activated, increased Na+ reabsorption.
Alpha-1 receptor
What is the main force that contributes to filtration in the glomerulus? What are the main forces that oppose filtration?
Glomerular hydrostatic pressure is the main driver of filtration.
Glomerular oncotic and Bowman’s hydrostatic forces oppose filtration.
How does one calculate the ultrafiltration coefficient (Kf)?
Hydraulic conductivity x surface area
How does one calculate GFR using an ultrafiltration coefficient (Kf)?
Kf x Puf
Puf = capillary ultrafiltration pressure
