what is the rate of renal blood flow?
1200 ml/minute
what part of kidney has a high flow rate?
cortex
blood enters glomerulus via _______ and leaves via ______
afferent arteriole; efferent arteriole
endothelial cells have fenestrations. what do fenestrations allow?
allow filtration to occur at a faster rate
what is GFR?
- rate at which plasma moves through glomerular capillaries
- females: 85-125 ml/min for 2 kidneys
- males: 97-140 ml/min for 2 kidneys
at what age do children reach adult proportions in regards to GFR?
around 2 years of age
what is the driving force of GFR?
- glomerular capillary hydrostatic pressure
why does GFR lower with age?
as you age, you lose gomeruli
pressure _____ as it goes from renal artery to arterioles
decreases
determinants of GFR
GFR = Kf (Pgc - (Pt + COPgc))
what is Kf?
- Kf = ultrafiltration coefficient. includes capillary surface area and fluid permeability
- tells us how open the filter is
- lower Kf = lower GFR
what is Pgc?
Pgc = glomerular capillary pressure
what is Pt?
- tubular pressure
- works against Pgc
what is COP?
- colloid osmotic pressure
- pressure that is set up by the fact that there is albumin in the blood/plasma but there is no albumin on urine side
- albumin unable to get through filtration barrier
- water molecules on other side diffuse back in order to dilute albumin concentration
- the pressure of flow going backwards is called colloid osmotic pressure
what is UFP?
- net filtration pressure (ultra)
UFP = (Pgc - (Pt + COPgc))
characteristics of a substance used to measure GFR
- must be freely filtered
- must not be reabsorbed or secreted
- must not be synthesized or catabolized by the kidney
- must not alter GFR
substances used to measure GFR
- inulin (gold standard)
- creatinine (clinical standard)
- cystatin C
why is creatinine the clinical standard?
- creatinine is excreted mainly by filtration
- produced by skeletal muscle at a constant rate from creatinine-phosphate
what is the equation to calculate how much of a substance is secreted?
amount excreted = amount filtered - amount reabsorbed + amount secreted
what RPF?
renal plasma flow rate
P in x GFR = U in x V
P in = plasma inulin
U in = amount of inulin in urine
V = volume of urine over 24 hours
measuring GFR - creatinine
GFR = ([Cr] urine x urinne flow rate (V/24hours)) / [Cr] plasma
measuring GFR - creatinine - requirements
- 12-24 hour urine collection (timed)
- mid-point blood sample
- [Cr] in urine and plasma
_____ clearance slightly _____ GFR
creatinine; overestimates
