Renal plasma flow equation
RPF = RBF x (1-Hct)
Filtration fraction equation
FF = GFR/RPF
Distribution of blood flow to the kidneys
- most flow through efferent arterioles into the peritubular capillaries of the cortex
- only 5-10% through the medulla
What generates filtration in the kidneys? (4)
- hydraulic pressure in glomerular capillaries
- renal blood flow rate
- blood oncotic pressure
- filtration coefficient
What is hydraulic pressure?
pressure resulting from the effects of liquids
What are the effects of vasoconstriction on the kidney?
- decreased flow
- increased pressure upstream
- decreased pressure downstream
What are the effects of pre- and post-glomerular capillary sphincters?
- increased glomerular capillary pressure leading to formation of filtrate
- decreased peritubular capillary pressure leading to reabsorption of fluid
Name 3 factors causing renal constriction
- sympathetic nervous system (key!)
- angiotensin II (key!)
- endothelin
Name 5 factors causing renal vasodilation
- PGE2 (key!)
- PGI2
- nitric oxide
- bradykinin
- dopamine (key!)
What are the effects of sympathetic innervation on the glomeruli?
- sympathetic nerve fibers activate alpha1 receptors on afferent and efferent arterioles
- causes vasoconstriction
- many more alpha1 receptors on afferent arterioles
How would SNS activation affect RBF and GFR? A. decreased RBF and decreased GFR B. decreased RBF and increased GFR C. increased RBF and decreased GFR D. increased RBF and increased GFR
A. decreased RBF and decreased GFR
Characteristics of angiotensin II
- potent vasoconstrictor
- affects both afferent and efferent arterioles
- greater effect on efferent arteriole
How would angiotensin II affect RBF and GFR? A. decreased RBF and decreased GFR B. decreased RBF and increased GFR C. increased RBF and decreased GFR D. increased RBF and increased GFR
B. decreased RBF and increased GFR
What are the effects of low levels of angiotensin II on the kidney?
- both AA and EA constrict
- EA constricts more, increased pressure in glomerular capillaries and increased GFR
What are the effects of high levels of angiotensin II on the kidney?
- both AA and EA constrict
- AA constricts more, decreased pressure in glomerular capillaries and decreased GFR
What do prostaglandins do in the kidney?
vasodilate both afferent and efferent arterioles
What are the effects of low levels of dopamine on the kidney?
dilates renal arterioles
What are the effects of high levels of dopamine on the kidney?
vasoconstricts renal arterioles
What is autoregulation?
- protects kidney function from large and abrupt changes in systemic BP
- protects glomerulus from systemic pressure
What are the two theories explaining auto regulation
- myogenic (stretch of arteriolar wall causes opening of smooth muscle Ca2+ channels leading to vasoconstriction)
- tubuloglomerular feedback
When does nephrotoxicity from NSAIDs occur?
- accidental overdosage
- as a risk factor with other causes for attention (like volume depletion)
Why is the kidney at risk for nephrotoxicity?
- high blood flow
- high metabolic rate
- reabsorption/secretion of toxic substances
- poor blood flow
- concentration of toxins
