Filtration & Clearance - IN Flashcards
what is the first step in forming urine
glomeruLOL filtration
what is the starling equation
Filtration Rate = Kf [(PGC – PBS) – (πGC – πBS)]
(PGC – PBS): difference in hydrostatic pressure inside glomerular capillary and Bowman’s space
(πGC – πBS): difference in oncotic pressure inside glomerular capillary and Bowman’s space
what stops glomerular filtration
when the Starling forces favoring/opposing filtration become equivalent. This occurs towards the efferent end of the glomerular capillary bed.
what is the fractional excretion of water
fraction of glomerular filtrate not reabsorbed from tubular fluid along nephron, appears as urine
what does a measurement of GFR give you
an index of the number of functioning nephrons in kidney disease
when does renal failure begin
GRF < 20ml/min or a loss of function of 85% of nephrons
click for renal hemodynamics facts
Approximately 25% of CO perfuses the kidneys (pretty much the highest of all the organ systems). Thus a person whose CO is 5L/min has a renal blood flow of 1.25 L/min (1800 L/day)
~55% of renal blood flow is renal plasma flow (600-700ml/min), and 20% of that is filtered in the glomeruli (125ml/min).
are nephrons connected in series or parallel?
The individual nephrons that make up both kidneys are connected in parallel. However, flow through a single nephron represents 2 arterioles and 2 capillary beds connected in series. Connected in series are the high-pressure filtering capillaries of the glomerulus and the low-pressure reabsorbing peritubular capillaries.
what determines renal blood flow
directly proportional to the pressure gradient between the renal artery and the renal vein, and is inversely proportional to the resistance. (Q=∆P/R).
how does sympathetic activation affect the kidneys
both afferent and efferent arterioles are innervated by sympathetic nerve fibers that produce vasoconstriction (via α1 receptors). However, there are far more α1 receptors on afferent arterioles, so increased sympathetic nerve activity causes a decrease in both RBF and GFR.
what the fuck is an angiotensin II
a potent vasoconstrictor of both afferent and efferent arterioles, increasing resistance and decreasing blood flow. However, efferent arterioles are more sensitive to angiotensin II
what is atrial natriuretic peptide
ANP - causes dilation of afferent arterioles and constriction of efferent ones
how do prostaglandins affect kidneys
cause vasodilation of both afferent and efferent vessels
when does RBF begin to increase
when renal arterial pressure drops below 80mmHg
what is clearance
the rate at which substances are removed from the plasma
the higher the renal clearance, the more plasma that is cleared of the substance in question
