Lecture 4: Renal Hemodynamics (Bolser) Flashcards
what is the blood flow distribution between the cortex and the medulla?
cortex = 90% medulla = 10%
control of RBF (renal blood flow)?
- blood pressure
- intrinsic autoregulation
- extrinsic innervation and hormones
as arterial pressure rises, both GFR and RBF rise until a plateau is reached where increases in arterial pressure elicit little change in either GFR and RBF. what is this range called?
auto regulatory range
how does autoregulation work? (there are 2 mechanisms)
autoregulation keeps changes in RBF and GFR small.
1. myogenic - when arterial smooth muscle is stretched by an increase in arterial blood pressure, it contracts and reduces flow in response to keep net filtration pressure and hence GFR relatively constant
- tubuloglomerular feedback - increased Na and Cl delivery to the macula densa causes the release of a vasoconstrictor which constricts the afferent arterioles and reduces GFR and RBF.
in the event of hemorrhage, what happens to RBF and GFR by way of renin secretion (think about that chart in our SCAVMA notes)
hemorrhage decrease in arterial blood pressure increase in renin secretion increase in plasma renin increase in plasma angiotensin II increase in constriction of renal arterioles decrease in RBF and GFR
in the event of hemorrhage, what happens to RBF and GFR by way sympathetic nerve activity (think about that chart in our SCAVMA notes)
hemorrhage
decrease in arterial blood pressure
increase in activity of renal sympathetic nerves
increase in constriction of renal arterioles
decrease in RBF and GFR
how do you measure renal plasma flow (RPF) and why?
you measure the clearance of PAH. because at low plasma levels (below secretory Tm), PAH is almost completely cleared in a single circuit of plasma flow by filtration and secretion
why do we not use clearance of PAH as a measure of RPF above Tm?
at higher plasma levels (above Tm) more PAH escapes secretion, causing a fall in the clearance of PAH
what is important to remember about the clearance of inulin?
it is independent of its arterial plasma concentration
it is freely filtered and not acted upon by the renal tubules. so whatever enters the renal tubules must leave via the urine
why is the clearance of glucose zero under 200mg/dL?
because no glucose reaches the bladder until the reabsoprtion processes in the kidney are satruated by increasing plasma levels of glucose.
why will the clearance of glucose always be less than the clearance of inulin?
because there is net reabsorption. - some of the filtered load is always removed by reabsorption.
why is the clearance of PAH always higher than that of inulin?
because secretory process always add more PAH to the tubular lumen than the amount that was filtered.
what is the filtration fraction? (FF)
GFR/RPF = Clearance of inulin / clearance of PAH = 20%
define the filtration fraction
the flow rate through the glomerular capillaries is high enough that only some of the water and electrolytes leave these vessels and enter the nephron.
the FF value can change depending on how renal plasma flow is regulated.
what type of energy metabolism occurs in the cortex?
oxidative - using primarily fatty acid substrates
