Lecture 2: Renal Blood Flow and GFR Flashcards
at rest, what % of cardiac output reaches the kidneys
20%
What are the functions of blood flow through the kidneys
- deliver O2, nutrients and hormones to the cells of the nephron while returning CO2 and reabsorbed fluids + solutes to general circulation
- determines the GFR
- modifies the rate of reabsorption by the proximal tubule
- concentration and dilution of urine
- delivery of substrates for excretion in urinef
what determines the GFR
blood flow through the kidneys
what renal functions are compromised during renal failure
- excretion of metabolic waste
- regulation of water, electrolytes, extracellular fluid volume and BP
the volume of plasma filtered into Bowman’s space per unit time
GFR
what things determine GFR
- permeability (glomerular filtration barrier)
- surface area
- net filtration pressure = the difference b/w the differentials of hydrostatic and oncotic pressure
what is the equation for GFR?
what factor(s) increase the filtration coefficient, K?
an increase in glomerular SA caused by the relaxation of mesangial cells
GFR increases
what factor(s) increase PGC
an increase in renal arterial pressure and dilation of afferent arteriole
GFR increases
what factor(s) increase PBS, what is this effect on GFR
an increase in intratubular pressure (ex: obstruction)
GFR decreases
What factor(s) increase πGC
An increase in systemic plasma oncotic pressure
GFR decreases
what is nephrolithiasis
renal stones in kidney
what is Urolithiasis
occurs when renal kidney stones exit the renal pelvis and move into the remainder of the urinary collecting system (ureters, bladder, urethra)
what disease causes a drop in plasma oncotic pressure
liver disease —> hypolbuminemia (low levels of blood albumin)
what can cause a decreased arterial oncotic pressure (which tends to increase GFR)
a decrease in arterial plasma protein concentration
what is the average capillary oncotic pressure?
28 mmHg
what happens to protein concentration as blood moves from the afferent to the efferent end of the glomerular capillary?
protein concentration increases
factors that affect afferent/efferent arteriolar resistance also effect what?
PGC
what happens if GFR gets too low?
the excretion of waste products becomes insufficient
what happens in GFR gets too high?
tubules might be overwhelmed with salt and water reabsorption. Furthermore, high vascular pressure could cause hypertensive damage.
Hydrostatic pressure is ______ in glomerular capillaries and falls to _____in the peritubular capillaries
60mmHg in glomerular capillaries and 20mmHg in peritubular capillaries
where does hydrostatic pressure remain relatively constant?
within the glomerulus
Dilation of the afferent arterioles raises hydrostatic pressure in ??
glomerular capillaries and GFR
what causes a decrease in hydrostatic
pressure in glomerular capillaries and GFR?
Constriction of the afferent arterioles
what causes a decreased hydrostatic pressure in glomerular capillaries and GFR
Dilation of the efferent arterioles
what happens if afferent and efferent arteriolar resistance change in the same direction
they exert opposite effects on hydrostatic pressure in glomerular capillaries and GFR
what are the autoregulatory mechanisms the kidneys have to keep RBF, PGC and GFR within a limited range?
myogenic response
tubulo-glomerular feedback
what is the purpose of keeping GFR within a limited range during changes in arterial pressure?
preventing changes in GFR prevents hypertensive damage
what is the myogenic response ?
Contraction and relaxation of arteriolar smooth muscle in response to changes in vascular pressure
what is the juxtaglomerular apparatus ?
s a specialized structure formed by the distal convoluted tubule and the glomerular afferent arteriole
what increases the flow of tubular fluid
increased glomerular blood flow
what is the effect of increased glomerular blood flow on salt reabsorption in the LoH and salt delivery to the macula densa
it increases salt reabsorption as well as increasing the delivery of salt to the macula densa
what component of the macula densa senses changes in salt concentration
Na+ ‐K+‐2Cl− cotransporter (NKCC) in its luminal membrane.
what vasoactive substance is released during tubuloglomerular feedback and what is its effect
Adenosine
- increases afferent tone
- renin production / secretion decreases
what prostaglandins are vasodilators that work primarily on afferent arterioles
PGE2, PGI2
what stimulates the release of vasodilator prostaglandins
- increased renal sympathetic nerve activity
- increased levels of angiotensin II
NSAIDs block ….
prostaglandins, compromising vasodilation
NE effect on afferent arteriole
causes vasoconstriction = increased afferent renal sympathetic nerve activity, decreases RBF and GFR
NE effect on collecting duct
increases Na and K exchange –> increases Na reabsorption and water retention
NE effect on Juxtaglomerular apparatus
stimulates renin release –> activate RAAS
