ICL 1.2: Renal Physiology I Flashcards
what is the glomerulus and juxtaglomerular apparatus?
glomerulus is the blood coming in through the afferent arteriole and leaving through the efferent arteriole and getting filtered in the glomerulus
everything except proteins and RBCs get filtered at the glomerulus
under normal conditions, there should be no protein in the urine or else it means there’s a problem!
what is the main barrier to the filtration of molecules through the glomerulus?
the size and charge of the basement membrane that actually contributes to the barrier for the filtration of proteins or any other molecule
as the size increases the filtration decreases
the charge also matters: 60% is filtered when it’s positive, 20% when it’s positive and 0% when it’s negatively charged so molecules of the same size will have increased filtration if they’re positively charged! –> if the size is small the charge doesn’t really matter though
water, sodium, glucose and insulin are 100% filterable but myoglobin and albumin are not!
what are glomerular diseases?
intrinsic glomerular cells (Mesangial cells, endothelial cells, podocytes, and parietal epithelial cells ) and leukocytes are critical to the healthy glomerulus and to glomerular dysregulation in disease
some examples include:
1. nephrotic syndrome
- nephritic syndrome
- glomerulonephritis
what is minimal change nephropathy?
a condition in certain kidney diseases in which the negative charges on the basement membrane are lost even before there are noticeable changes in kidney histology –> negative charges of the basement membrane usually repel negatively charged proteins so without it you’ll start to see albumin in the urine!
probably related to an immunological response with abnormal T-cell secretion of cytokines that reduce anions in the glomerular capillary or podocyte proteins
some lower molecular weight proteins, especially albumin, appear in the urine (proteinuriaoralbuminuria)
most common in young children but also seen in adults with autoimmune disorders
what is renal blood flow?
RBF is the combined blood flow through the kidneys
the kidney receives 20% of the cardiac output = about 1 L
the renal cortex receives most of it while the blood flow in the renal medulla (vasa recta) is only 1-2% of the RBF
what are the 2 equations for RBF?
RBF = RPF/(1-hematocrit)
RBF = (renal artery pressure - renal vein pressure)/total renal vascular resistance
RBF = renal blood flow
RPF = renal plasma flow; the flow of plasma
hematocrit = proportion by volume of RBF that consists of RBC
renal artery pressure = systemic arterial pressure
renal vein pressure = 3-4 mmHg
total renal resistance = afferent + efferent arteriole resistances
what is the equation for total renal resistance?
total renal resistance = afferent + efferent arteriole resistances
increasing ANY of the two reduces renal blood flow
what is GFR?
GFR = glomerular filtration rate
it’s how much blood is being filtered by all the individual nephrons combined per minute! it’s an index of kidney function
GFR is equal to the sum of the filtration rates of all functioning nephrons
normal = 60-120
kidney disease = 15-60
kidney failure = 0-15
glomerular ultrafiltration is the first step in line formation! the ultra filtrate has solute concentrations similar to blood plasma, except for proteins and formed elements
what is the filtration fraction?
FF = GFR/renal plasma flow
filtration fraction is the fraction of the renal plasma that is filtered
if renal plasma flow is 500 mL/min and hematocrit is 50%, what is the blood flow to the kidneys?
RBF = RPF/(1-hematocrit)
RBF = 500/(1-.50) RBF = 500/0.5 RBF = 1000 mL = 1 L/minute
calculate the filtration fraction if GFR = 120 mL/min and RPF = 500 mL/min
FF = GFR/renal plasma flow
FF = 120/500 FF = 0.24
the amount of blood that’s filtered out of the total amount
calculate the filtration fraction if GFR = 0.15 L/min and RPF = 600 mL/min
FF = GFR/renal plasma flow
FF = 150/600 FF = 0.25
convert the L into mL!
determine filtration fraction if renal blood flow = 1.25 L/min, Hct = 40% and GFR = 125 mL/minute
FF = GFR/renal plasma flow
RBF = RPF/(1-hematocrit) RPF = RBF*(1-Hct) RPF = 1250(1-0.4) RPF = 750
FF = GFR/RPF FF = 125/750 FF = 0.16
if the GFR is reduced by 1/2 due to a glomerular disease with no change in renal blood flow, the filtration fraction would be ____of the normal
FF = GFR/RPF
since RBF didn’t change then RPF didn’t change either but GFR is reduced by 1/2
so the filtration fraction would be 1/2 the normal!
what is the normal GFR, RBF, RPF and FF in an adult?
GFR = 125 mL/min
RBF = 1 L/min
RPF = 600 mL/min
FF = 0.2
what are the physical forces that effect GFR?
net filtration pressure is positive in the glomerular capillaries!
πB is basically zero because Bowman’s capsule oncotic pressure is zero because no protein gets filtered so there’s no protein in that space to contribute to the oncotic space! but there IS hydrostatic pressure because 20% of water gets filtered here
GFR = Kf x ( PG + πB – PB – πG)
GFR = Kf x ( PG – PB – πG)
what is the glomerular capillary filtration coefficient?
GFR = Kf x ( PG + πB – PB – πG)
Kf is the glomerular capillary filtration coefficient and it depends on the thickness of the capillaries! changes in Kf are not a primary mechanism for the normal day-today regulation of GFR
Kf= hydraulic conductivity X surface area of the glomerular capillaries
chronic uncontrolled HTN and DM decreases Kf by increasing the thickness of the glomerular capillary membrane and reducing hydraulic conductivity
so if Kf increases, GFR increases and if Kf decreases, GFR decreases
how does Bowman’s capsule pressure regulate GFR? what’s the equation for GFR based on Starling forces?
normally, changes in Bowman’s capsule pressure do not regulate GFR
but obstruction of the urinary tract increases PB and reduces GFR
GFR = Kf x ( PG + πB – PB – πG)
conditions that could cause this include precipitation of calcium or of uric acid may lead to “stones” that lodge in the urinary tract raising PB –> this eventually leads tohydronephrosis(distention & dilation of renal pelvis & calyces)
if the RBF is reduced by 1/2 with no change in GFR, the filtration fraction would be _____of the normal
FF = GFR/RPF
if RBF is reduced then RPF is reduced but GFR isn’t changed so FF is doubled!
if the RBF is reduced by half with no change in GFR, the unfiltered blood in the glomerulus will be ____and the proteins in the blood will be ____ compared to the normal
less and concentrated
if RBF is reduced it means that less blood is coming through the kidney but you’re still filtering the same amount of blood so there is less unfiltered blood! this means the amount of unfiltered proteins will be less because FF has increased
FF increases which means you filter more = less unfiltered blood in the glomerulus –> less unfiltered blood in the glomerulus means higher relative concentration of protein
if the GFR is reduced by half due to glomerular disease with no change in renal blood flow or filtration properties, the Bowman’s capsule oncotic pressure would:
A. double
B. 1/2
C. unchanged
C. unchanged
when the FF is increased the blood becomes more concentrated with protein –> if that’s the case then the Bowman’s capsule oncotic pressure will NOT change because protein never goes to the Bowman’s capsule!
if the RBF is reduced by 1/2 with no change in GFR or filtration properties, the glomerular capillary oncotic pressure would be:
A. increased
B. decreased
C. unchanged
RBF is reduced but GFR is unchanged, unfiltered blood is less and proteins will be more concentrated
so 500 mL of blood is coming, 125 is being filtered so 375 mL is unfiltered and it’s more concentrated with protein
so oncotic pressure in the glomerular capillary will be increased
this is because there is more protein in whatever solution is left behind so the capillary oncotic pressure is increased! part of the blood that’s coming is getting filtered but for some reason the part getting filtered doesn’t change yet less blood is coming so then the blood leaving the glomerulus in the efferent arteriole is more concentrated because the fluid volume is less which increases the oncotic pressure