RENAL 03 - Filtration and blood flow Flashcards
What is the glomerular filtration barrier composed of (3)
Fenestrated capillary epithelium
fused basement membrane with negative charge barrier
podocyte foot processes (slit diaphragm)
Kidneys are activated by what branch of ANS, (and what branch does not affect kidneys)
SNS (PSNS does not affect them)
Majority of SNS innervation is on which arterioles set?
Afferent
Purpose of fenestrated epithelium
allow substances to pass through endothelial cells
purpose of basement membrane
negative charge helps with selectivity of what can go through -repels proteins
purpose of podocyte foot processes / slit diaphragm
processes can expand and contract out, helps by acting as filtration barrier against macromolecules
Why doesn’t albumin get into the tubular system?
it’s small, so it gets through the fenestrate, but it is repelled by the basement membrane’s negative charge
How does molecular weight impact filtration
the larger the molecule it is filtered less
how does electrical charge impact filtration
negatively charged molecules are filtered less, but positively charged molecules are filtered more (and even more filtered than neutral molecules)
Properties of inulin and filtration
although inulin is very complex, its overall molecular weight is low, so it is freely filtered, and it lacks a charge that is repelled by basement membrane so it gets through.
How much of the RPF passes through into the bowman’s space?
20%
Does glucose go through the glomerular filtration barrier?
Yes
Do large proteins go through glomerular filtration barrier?
No
What are direct determinants of glomerular filtration rate?
Starling forces (permeability, hydrostatic pressure, oncotic pressure, put together being the Net Filtration Pressure)
Compared to skeletal capillaries, the Kf of glomerular capillaries is (higher or lower)
higher because of the fenestrations (windows)
Blood flow to kidneys can be determined by what equation?
Q=deltaP/R
Kidneys have a vascular system in ___(series/parallel)__. What does this mean about the overall resistance?
Parallel; this means total resistance is quite low
Mean pressure in glomerular capillaries is ____(high/low)___ compared to skeletal capillaries?
High
What happens to oncotic pressure along the length of the glomerular capillary? Why?
It becomes higher. This is because you’re filtering out the fluid, so you’re concentrating the protein there (more protein per unit volume)
Hydrostatic pressure in glomerulus vs skeletal muscle interstitium?
It’s higher, but still much lower than the hydrostatic pressure in the glomerular capillary
Hydrostatic pressure in the glomerular capillary?
High throughout the length of the capillary and much higher than what you would find in skeletal muscle capillaries due to the fact that it is between two arterioles
Oncotic pressure in bowman’s space
near zero
Aside from just “fenestrations” what can be attributed to high amount of filtration going on in the glomerulus?
high surface area of openings in capillaries overall leading to a high amount of fluid coming out
What would the effect of renal arterial pressure increasing be on GFR?
This would increase GFR due to an increase in hydrostatic pressure
What would the effect of relaxation of glomerular mesangial cells be on the GFR?
This would increase glomerular surface area (increase in permeability) and as a result you increase filtration (increase in GFR)
What would the result of an intratubular pressure increase (ex. obstruction of a tubule, extrarenal urinary system obstruction) be on GFR?
This will DECREASE the GFR. This is because you would be increasing the hydrostatic pressure in the bowman’s space, which would oppose filtration
What would the effect of an increase in systemic oncotic pressure be on the GFR?
This will decrease filtration rate (decrease GFR)
What would a decreased RBF do to the GFR?
This will decrease GFR, partly due to an increase in the oncotic pressure along the glomerular capillaries (it becomes concentrated)
What would the effect of afferent arteriole dilation be on GFR?
This will increase GFR ; this is decreasing afferent arteriolar resistance and increasing flow to the area, therefore, the pressure is increasing.
What would the effect of constricting the efferent arteriole be on GFR?
This will increase GFR because you’re increasing resistance to flow on the exit side
If you have a decrease in effective circulating volume, what is the effect on GFR? What is a situation in which this might happen?
This would result in a decrease in GFR. This would happen in, for instance, heart failure or hemorrhage.
If you hve an immune complex on the glomerulus, what is the result of GFR?
This is going to lead to inflammation of the glomerulus which decreases overall glomerular filtration rate; however you also get holes in the capillaries so what DOES get through can be quite large and include RBC’s, WBC’s, and proteins
What is the result of kidney stones on glomerular filtration rate?
This would lead to a backup of pressure that eventually increases bowman’s space hydrostatic pressure and decreases the overall glomerular filtration rate
how do we calculate blood flow
Flow is equal to the pressure gradient of two locations over the resistance of the system
Where does the majority of blood flow go in the kidney
Cortex
Where is the vast MINORITY of vascularization in the kidney
inner medulla ; you really only have vasa recta here along the juxtamedullary nephrons
Where is the largest pressure drop in the kidney vascular pressure?
Think about the highest resistance vessels (just like what Jonathan taught us, it’s the arterioles, both afferent and efferent)
Where is oncotic pressure highest in the kidneys
Efferent arterioles (we concentrated protein in the glomerular capillaries and in the peritubular capillaries we’re going to dilute it back down when we save water)
Constriction of afferent arteriole leads to what affect of renal blood flow and what affect on GFR
Decrease RBF, decrease GFR (due to decrease in hydrostatic pressure in glomerular capillaries)
Constrition of EFFERENT arteriole leads to what affect on renal blood flow and what affect on GFR
This leads to a DECREASE in renal blood flow (resistance increases in the exit portion) but an INCREASE in GFR due to an increase in hydrostatic pressure along the glomerular capillary
Dilation of the efferent arteriole leads to what affect on renal blood flow and GFR
This will increase RBF and decrease GFR due to a decrease in hydrostatic pressure within the glomerular capillaries
What is the effect of dilation of the afferent arteriole on renal blood flow and GFR?
This is going to lead to an increase in renal blood flow and in increase in GFR due to an increase in glomerular capillary hydrostatic pressure
GFR and RBF can be maintained over….. what range of pressures?
A broad range of pressures (100-180mmHg)
Therefore if you increase arterial blood pressure, you don’t necessarily increase RBF and GFR
At what arterial blood pressure do kidneys begin to shut down?
70mmHg
Intrinsic regulation of GFR and RBF
vasoconstricting and vasodilating factors, myogenic response, tubuloglomerular feedback from vasa recta
Extrinsic regulation of GFR and RBF
Sympathetic nervous system, bloodborne or endogenous sybstances (ex. angiotensin II), stress factors such as hemorrhage
