Glomerular Filtration and Renal Blood Flow Flashcards
How does a high protein diet affect TGF?
enhances NaCl resorption before macula densa –> increased renin –> if persists for a long time, can desensitise TGF
What occurs if you constrict the afferent arteriole?
Puf and GFR decrease
What is creatinine useful for?
long-term monitoring of kindy function
freely filtered at the glomerulus, but a small amount is also secreted = not ideal marker, but easy to measure clinically
When does GFR = Clearance rate?
- substance must be freely filterable in the glomeruli
- substance must be neither reabsorbed nor secreted by tubules
- must not be made, broken down, or accumulated by the kidney
- must be physiologically inert (not toxic, doesn’t affect renal fxn)
What happens when there is decreased perfusion pressure?
macula densa –> JG –> secrete renin –> Angiotensin II –> efferent arteriolar vasoconstriction
also results in afferent dilation through NO
How does tubuloglomerular feedback work?
macula densa cells sense NaCl –> send signal to juxtaglomerular/granular cells to produce renin –> can also signal mesangial cells to contract
What is nephrin?
one of the proteins found in the filtration slit diaphragm
What is the effect of sympathetic stimulation on the kidneys?
constrict arterioles –> decrease RBF/GFR
activate alpha-1 receptors on afferent arterioles
How does the macula densa signaling work if there is too much NaCl?
NaCl will activate NKCC transporter a lot –> increased ATP/adenosine –> thru calcium signaling, will vasoconstrict afferent arterioles –> decreased GFR –> less salt coming in
What receptor is on tubular epithelial cells that, when stimulated, increases Na resorption?
alpha-1
note: acts on Na-K ATPase
How do Puf and πgc change from afferent to efferent arterioles?
πgc increases and Puf decreases
What arterioles does antiotensin preferentially act on?
efferent arterioles
What receptor is used for renin release?
beta-1 adrenoceptor
How does vascular hydrostatic pressure change from the renal artery to peritubular capillary?
high in renal A
decreases a lot across afferent a
stays relatively high in glomerular capillary
decreases a lot across efferent a
low in peritubular c
What happens if there is increased renal perfussion pressure?
macula densa signaled –> adenosine –> vasoconstriction of afferent arteriole
(similar to when it senses too much NaCl)
What are the intrinsic renal hemodynamics control mechanisms?
autoregulation
tubuloglomerular feedback
What are the 3 physical factors contributing to GFR?
hydraulic conductivity = permeability/porosity of the fenestrated endothelium
surface area for filtration
capillary ultrafiltration pressure
What is the autoregulatory range?
What happens outside this range?
10-170 mmHg is the range at which autoregulatory mechanisms are effective to maintain stable renal blood flow
below range –> blood flow will still decrease
above range –> blood flow will still increase
What is PAH used for?
estimates renal plasma flow
freely filtered and also secreted –> amount of PAH in plasma of renal arter is abt equal to the amount excreted in urine
must be administered by continuous IV fusion
What is the main thing altering Puf?
changing glomerular capillary pressure (Pgc)
What cells release renin?
granular cells
What does glomerulartubular balance do?
higher GFR –> more plasma water filtered –> higher oncotic pressure in efferent arteriole
increased GFR –> more water and sodium reabsorbed back into arterioles
If RBF decreases due to hemorrhage, what must happen to maintain normal FF?
GFR must increase
FF = GFR/RBF
What happens if you damage the filtration barrier so that the negative charges on the barrier are removed?
increased filtration of anions
How are plasma creatinine levels and GFR related?
inversely proportional
(the more creatinine still in the blood, the less is being filtered)
What is the filtration slit diaphragm?
complex of molecular barriers btw podocyte arms that acts to filter molecules as they pass through the filtration slit
What happens if you constrict the efferent arteriole?
GFR and Puf increase
What does a low BUN:Cr ratio indicate?
intrarenal problem
renal diseases reduce BUN reabsorption therefore decreasing plasma levels
What are the 3 layers of the glomerular filtration barrier?
capillary endothelium = fenestrae glomerular
basement membrane
podocyte epithelium = filtration slits
What does a high BUN/Cr ratio indicate?
>20:1
pre-renal problem
BUN reabsorption is increased
What receptor is used to constrict afferent arterioles?
alpha-1 receptors
What are the 2 main substances listed that follow the GFR = Cx rule?
inulin
creatinine (not perfect though)
As filtration fraction increases, what happens to the oncotic pressure of efferent arteriole?
oncotic pressure increases bc more fluid is pulled out of blood therefore it is more concentrated
What are the extrinsic control mechanisms of renal hemodynamics?
sympathetic nerves
hormones
composition of blood
What is the biogel made of and where is it located?
on capillary endothelium
made of glycocalyx = hyaluronan, and heparan sulfate
biogel = negatively charged, so other negatively charged molecules are repelled
What is the myogenic reflex?
increased pressure in blood vessels –> local reflex btw vascular smooth muscle cells –> afferent constriction and efferent dilation via calcium signaling
What is the estimated normal filtration fraction?
~20% = GFR/RBF
What are the relative filterabilities of neutral, anionic, and cationic molecules?
anionic = least filterable
neutral = middle
cationic = most filterable
What is special about inulin?
amount excreted in urine = amount filtered
GFR = Cx
Bc inulin isn’t reabsorbed or secreted
What size molecules are freely filtered?
What size molecules are not filtered at all?
< 20 A = Free
> 42 A = not filtered
What is a normal BUN:Cr ratio?
10-20:1
Where are there more alpha-1 receptors?
on afferent arteriole
(more than efferent - bc want to decrease filtration if you are fighting/flighting)
