2: Renal Blood Flow and Glomerular Filtration Flashcards
What percentage of CO goes to the kidneys?
20%
Describe the blood flow from the renal artery to the vein
blood enters through the renal artery at the hilum
divides into smaller arteries –> arcuate arteries –> cross the top of eahc pyramid in the cortex –> lead to interlobular arteries (cortical radial arteries) –> project to the kidney surface –> give off arterioles –> each leads to a Bowman’s capsule and Glomerulus i.e., afferent arterioles –> efferent arterioles –> most divide into a second set of capillaries (besides glomerular capillaries) = peritubular capillaries –> rejoin to form veins –> hilum –> leave kidneys
(all this is in the cortex only)
efferent arterioles of glomeruli at the cortico-medullary border (juxtamedullary glomeruli) –> do not branch inot peritubular capillaries, instead descent to the outer medulla –> form the vasa recta = bundle of capillaries surrounding the Henle’s loops and collecting ducts in the outer medulla
vasa recta blood flow is about 1% of that in the cortical blood flow
How does the difference in magnitude of blood flow affect the cortical and medullary interstitium?
high blood flow in the cortex –> interstitium is very similar to plasma
low blood flow in the medulla/vasa recta –> interstitium here is very different from plasma
The resistance of any single vessel in a function of xxxxxx, xxxxxxx, and xxxxxxxx.
blood viscosity, vessel length, and vessel radius
What are the pressures in the afferent arteriole, the efferent arteriole, and the peritubular capillaries?
100 mm Hg –> afferent arterioles –> 60 mm Hg by the time it reaches the glomerulus –> efferent arterioles –> drops to 20 mm Hg by the time it reaches the peritubular capillaries
What are the 3 layers of the glomerular filtration barrier?
- endothelial cells of the glomerular capillaries
- capillary basement membrane
- epithelial cells - podocytes - gaps filled by slit diaphrams
What is the basement membrane made of?
the basement membrane is a gel-like acellular meshwork of glycoproteins and proteoglycans
what determines whether a molecule will pass through the glomerular filtration barrier?
its molecular size
its electrical charge
up to what molecular weight are moleculres freely filtered through the glomerulus without hinderence?
up to 7000 Da
nothing filtered >70,000 - from 7000 to 70,000 the filtration rate drops
Describe the equation for Net filtration pressure and GFR
NFP = (hydrostatic pressure in the glomerular capillaries - hydrostatic pressure of the bowman’s space) - (oncotic pressure in the glomerular capillaries - oncotic pressure in the bowman’s space)
nearly no protein in the bowman’s space, so:
NFP (hydrostatic pressure glomerular capillaries - hydrostatic pressure bowman’s space) - oncotic pressure glomerular capillaries
GFR = filtration coefficient (Kf) x NFP
Kf = denotes the product of hydraulic permeability and surface area
What is the normal average glomerular net filtration pressure?
16 mm Hg
How does the net filtration pressure change throughout the length of the glomerulus?
filtration pressure will decrease because due to water loss and retaining protein in the glomerular capillary blood –> oncotic pressure will rise
What could lead to a change in the bowman’s capsule hydrostatic pressure and therefor GFR?
an obstruction in the tubules or ureter/urethra –> will increase hydrostatic pressure everywhere all the way to the bowman’s capsule –> decrease in GFR
How do liver disease and dehydration affect GFR?
liver disease - hypoalbuminemia - decreased plasma oncotic pressure –> decreased glomerular capillary oncotic pressure –> increased net filtration pressure –> increased GFR
dehydration - hemoconcentration - increased plasma oncotic pressure from high proteins –> increased glomerular capillary oncotic pressure –> decreased net filtration pressure –> decreased GFR
Explain how low renal blood flow would lower the GFR
If the renal blood flow is lower but everything else the same –> larger portion of the bloof flow will be filtered –> more water removed from less blood –> more protein left over –> capillary oncotic pressure higher –> NFP lower –> lower GFR
i.e., filtration fraction (GFR/renal plasma flow) higher –> higher glomerular capillary oncotic pressure –> less GFR
