Renal Flashcards
8 core functions of the kidneys
- excretion of waste and foreign substances
- water/electrolyte balance
- extracellular fluid volume
- plasma osmolality
- RBC production (EPO)
- vascular resistance
- acid base
- vitamin D production
2 parallel circuits of blood flow in kidneys
both start with glomerular capillaries
- peritubular capillaries - cortex, 90%
- vasa recta capillaries- medulla, 10% (most in outer medulla)
from renal capsule to bladder
capsule –> cortex –> medulla –> minor calyx –> major calyx –> ureter –> bladder
pathway through the nephron
blood enters via afferent arteriole- bownman’s capsule/renal corpuscle - proximal convoluted tubule- HENLE (straight proximal tubule- descending thin limb- ascending thin limb- ascending thick limb)- macula densa- distal convoluted tubule- cortical collecting duct- medullary collecting duct- papillary duct
3 layers of the filtration barrier for capillaries in the glomerulus
- endothelium of capillaries
- capillary basement membrane
- interdigitated podocytes
proximal tubule vs loop of henle vs distal tubule
PT: high volume, low gradient reabsorption; brush border; lots of mitochondria
LH: makes interstitial osmolarity, poorly developed cell surfaces
DT: low volume, high gradient reabsorption; lots of folds; lots of mitochondria
what is clearance?
the volume of plasma completely cleared of any substance in 1 min; mL/min
two equations for excretion
- excretion= filtered + secreted- reabsorbed
2. excretion= U(concentration)*V(flow)
conservation of mass for kidney
PaRPFa= PvRPFv + U*V
formula for clearance
UV= PC
what does inulin measure? creatinine? BUN? PAH?
1) inulin, creatinine, BUN all measure GFR (what you clear is exactly what was filtered)
- creatinine is overestimate b/c there is some secretion (BUN= creatinine x 10)
2) PAH measures renal plasma flow b/c it is all excreted; have some in venous blood so actually multiply by 1.1
calculate renal blood flow from renal plasma flow? what is more and how do they relate to GFR? what is GFR?
RBF= RFP/1-hct
RBF>RPF>GFR>V
RBF= 25% CO
GFR= measure of overall renal function
what is the filtration fraction?
FF= GFR/RPF or 125/660
Inulin clearance/PAH clearance (normal= 20%)
Glomerular capillaries are +/- charged, so it inhibits the passage of +/- charged substances such as __
negatively charged for both, albumin
polycationic molecules are filtered freely
what is the equation for GFR? how is it regulated?
GFR= Kf * (Hydrog - Hydrob - oncoticg + oncoticb)
- regulated by changes in afferent/efferent arteriolar resistance
what happens to GFR, Pgc, and RBF when you constrict the efferent arteriole?
GFR and PGC increase
but constriction ALWAYS decreases renal blood flow
ways intrinsic autoregulation occurs to regulate GFR and RBF
1) smooth muscle myogenic theory
2) tubuloglomerular feedback theory- more Na in macula densa causes afferent arteriole to constrict
3) intrinsic vasodilators and vasoconstrictors
what is the take away from Fick’s principle in the kidney?
if blood flow is restricted to the kidney, the kidney requires less oxygen
what are Tm and RPT? which is reached first and why?
Tm- transport maximum
RPT- renal plasma threshold (mg/ml)
- RPT reached first because of splay
how do you calculate the Tm for glucose? PAH?
- glucose is actively reabsorbed: Tm= PaGFR-UV
- PAH is actively secreted:
Tm= UV-Pa*GFR
what percent of water/Na/Cl/K is reabsorbed in the proximal tubule?
what percent of glucose/aa’s is reabsorbed in the proximal tubule?
2/3rds or 67% of water/Na/Cl/K reabsorbed in PT
100% glucose/AAs reabsorbed in PT
how is Na+ transported in the loop of henle? what is the percent reabsorbed? which segment is impermeable to sodium?
- Na/K/2Cl symporter
- 25%
- thin descending loop
how is Na+ transported in the distal tubule? what is the percent reabsorbed? collecting duct?
- NaCl symporter early
- Na+ channels late
~5 % - collecting duct is 3%, Na channels only
where is no water reabsorbed?
- thin ascending & thick ascending limbs of Henle
- distal tubule
