gfr Flashcards
kidney filters plasma how many times a day
about 60 times
filtrate =
plasma – proteins
glomerular capillaries are drained by
arterioles not venules
GFR formula
GFR: kf ((HPGC - HPT) - (OPGC - OPT))
hydrostatic pressure of glomerular capillaries (HPGC)
45-60 mmHg (higher than hydrostatic pressure of systemic capillaries which is about 15-35 mmHg)
oncotic pressure of glomerular capillaries (OPGC)
20 - 25 mmHg at afferent arteriolar end this increases to 35 mmHg at efferent arteriolar end (because proteins become highly concentrated after filtration of about one fifth of the plasma)
hydrostatic pressure of bowman’s space (HPT)
against filtration = 18 mmHg (increased in urinary tract obstruction)
oncotic pressure of bowman’s space (OPT)
zero (because proteins are not filtered to the Bowman’s space)
surface area of the membrane (SA)
0.8 m2 (for both kidneys)
surface area of the membrane increases or decreases by
contraction or relaxation of mesangial cells
decrease mechanism of mesangial cells is through
angiotensin 2 endothelia ADH, histamine leukotrienes and catecholamine decreases the SA
increase mechanism of mesangial cells is through
relaxation by ANP cAMP and dopamine increases the SA
substance used to measure gfr
inulin and creatine
fructose polymer administered by intravenous (I.V.) infusion
inulin
produced from creatine kinase (phosphocreatine) in muscles
creatine