Bridge to renal physiology Flashcards
Hormones produced by the kidney
Renin
EPO
Calcitriol
Average values of GFR per minute and per day
125 ml/min
180 L/day
Average urine volume per day
1 L/day
Components of filtration coefficient
Total surface area available for filtration
Permeability per unit of surface area
Equation of net ultrafiltration (Puf)
Pgf - Pbs - pi gc
Equations for GFR
Kf x Puf
Kf [(Pgc-Pbs) - (pi gc - pi bs)]
Components of autoregulation/local control of renal blood flow
Myogenic response
Tubuloglomerular feedback
Components of systemic/reflex control of renal blood flow
SyNS
Angiotensin II
ANP
Prostaglandins
Myogenic response of local control of renal blood flow
Increase stretch triggers Na/K in smooth muscle –> cell depolarizes and Ca channel opens –> Ca binds to calmodulin and muscle contracts –> afferent arteriole constriction –> decreased RBF and limit increase of GFR
Brief description of tubuloglomerular feedback in local control of renal blood flow
Increased BP increases GFR –> extraglomerular mesangial cells trigger juxtuglomerular, mesangial, and afferent arteriole smooth muscle cells
-Juxtoglomerular cells decrease renin
-Mesangial cells and afferent smooth muscle cells cause vasoconstriction –> decrease GFR
General result of tubuloglomerular feedback control of renal blood flow
Afferent vasoconstriction limits increase GFR
Slight increase in glomerular capillary pressure
No change in efferent arteriole tone
Slight increase in renal blood flow
SyNS activity on renal afferent arterioles
Directly on alpha-1 receptors on smooth muscle –> constriction –> decrease GFR
SyNS activity on renal efferent arterioles
Acts on beta-1 receptors of granular cells to increase renin –> increase angiotensin II –> constriction of efferent arterioles –> increase GFR
Factors that increase renal prostaglandin synthesis
Increased SyNS activity
Increased angiotensin II
In response to low BP
Affect of prostaglandin on the kidneys
Modulates efferent constriction from angiotensin II and afferent constriction by SyNS –> overall decrease in RBF with minimal change in GFR
What drug class blocks prostaglandin synthesis in the kidneys?
NSAIDs
How do NSAIDs affect renal blood flow?
Constriction of both afferent and efferent arterioles, especially in pts with low CO
How do ACE inhibitors and ARBs affect renal blood flow?
Decrease angiotensin II –> relaxation of efferent arterioles
Affect of NSAID combined with ACE inhibitor or ARB on renal blood flow
Constriction of afferent arterioles and relaxation of efferent arterioles –> severe reduction in GFR
Affect of ANP and BNP on renal blood flow
Increase GFR and RBF to increase Na excretion
Affect of NO on renal blood flow
Vascular relaxation –> increase GFR and RBF
Vasoactive hormones that cause NO release
Acetylcholine
Histamine
Bradykinin
ATP
Filtration of BUN in kidneys
Freely filtered and 50% reabsorbed
Effect of dehydration on BUN
Increase
Effect of decreased GFR on BUN
Increase
What will happen to creatinine and BUN values if GFR is reduced by half?
Both with double, ratio generally unchanged
Reason by BUN/creatinine ratio increases in dehydration
BUN increases more than creatinine does
