Unit 2, L12 Renal Filtration and Blood FLow Flashcards
What is the glomerular filtration barrier
A selective barrier, highly permeable to water and small solutes. It is impermeable to large substances in the blood (RBCs, WBCs, and proteins), and glomerular filtration is an ultrafiltrate of plasma
What is the glomerular filtration barrier composed of?
Fenestrated capillary endothelium, fused basement membrane with a negative charge barrier, and podocyte foot processes - slit diaphragm
Why can’t albumin cross through the filtration barrier?
It is small enough to fit through the fenestrations but the basement membrane is negatively charged so it can’t fit through
What factors affect the glomerular filtration barrier?
Molecular size of the molecules and electrical charge of molecules
How much of the RPF passes through into the Bowman’s space?
The filtration fraction is GFR/RPF, which is about 20%
Does glucose go through the glomerular filtration barrier?
Yes, as glucose gets filtered and completely reabsorbed
Do large proteins go through the glomerular filtration barrier?
No, they are too large to fit through the fenestrations
What is the equation for the rate of filtration
Rate of filtration = hydraulic permeability * surface area * NFP
What is NFP
Net Filtration Pressure, its the algebraic sum of the Starling forces that favor and oppose the glomerular filtration
What is the equation for Kf
Permeability GC * Area GC
What is the equationi for GFR
GFR = Kf * NFP
What is Kf
Filtration coefficient
Is total renal vasculature resistance high or low? Why?
Low, because everything is arranged in parallel
P GC (starling forces) means what
Hydrostatic pressure in the GC (+P GC) will push filtrate out of the blood and into the BS
P BS (starling forces) means what?
P BS is hydrostatic pressure in BS (- P BS) and will push filtrate out of BS and back into blood
pi GC (starling forces) means what
Pi GC is oncotic pressure in GC (-pi GC), which will pull filtrate out of BS and back into the blood
pi BS (starling forces) means what
Pi BS is oncotic pressure in the BS (+ pi BS = 0), which will pull filtrate out of blood into BS
What is the equation for net filtration pressure?
Net filtration pressure = P GC - P BS - pi GC + pi BS
What does the overall equation for GFR become after adding in starling forces?
GFR = Kf * (P GC - P BS - pi GC + pi BS)
Which pressure is greater on one end of the arterioles?
Oncotic pressure in the glomerular capillaries, stronger near the efferent arterioles
As arterial blood flows through glomerular capillaries, from afferent to efferent, what happens with P GC
It will fall slightly, from 60 to 58 mmHg
As arterial blood flows through glomerular capillaries, from afferent to efferent, what happens with Pi GC
It will increase greatly, from 28 to 35 mmHg, due to the concentration of proteins that are not being filtered
As arterial blood flows through glomerular capillaries, from afferent to efferent, what happens with pi BS
It will stay around 0, because no proteins filter out and the few that do get reabsorbed by pinocytosis
As arterial blood flows through glomerular capillaries, from afferent to efferent, what happens with P BS
This will remain around 15 mmHg as the pressure here is needed to drive urine through the entire kidney, all the way to the bladder
What is the starling force that favors filtration and what is the average value for it
Glomerular capillary blood pressure (P GC) and it is normally 60 mmHg
What are the starling forces that oppose filtration and what are their average values
1) Fluid pressure in Bowman’s space (P BS) and its normal value is 15 mmHg
2) Osmotic force due to protein in plasma (pi GC) and its normal value is 29 mmHg
What is the overall net glomerular filtration pressure
16 mmHg, favoring filtration
Prerenal diseases that affect the GFR
Heart failure or hemorrhage, both of which would decrease effective circulating volume, which would decrease GFR
Intrarenal diseases that affect the GFR
The immune complex deposition in glomerulus, leads to a decreased GFR. Examples being glomerulonephritis, proteinuria
How would leaky glomerular capillaries affect GFR
Increase GFR by increasing Kf
Postrenal diseases that may affect the GFR
Kidney stones would increase P BS, which would decrease GFR
What is glomerulonephritis
When an immune complex, like from strep, binds to the basement membrane and causes inflammation of capillaries. Loss of glomerular integrity results in RBCs and casts in urine
What are urinary casts
Cylindrical shaped aggregations from distal nephron, seen with low urine flow, acidic conditions, and proteinuria
Renal cortex gets what percentage of renal blood flow
90%
Outer medulla gets what percentage of renal blood flow
8%
Inner medulla gets what percentage of renal blood flow
2%
Average value for renal blood flow
1200 mL blood/min
Hydrostatic pressure decreases from __________ to _________
From renal artery to renal vein
Hydrostatic pressure has the largest decreases where
In the afferent and efferent arterioles, as they have high resistance
Oncotic pressure increases along _________
The glomerular capillaries, as plasma proteins are concentrated during filtration
Oncotic pressure decreases ___________
Decreases along peritubular capillaries, as plasma proteins are diluted during reabsorption
What happens if you constrict the afferent arteriole
Decrease in renal blood flow, decrease in P GC, decrease in GFR
What happens if you constrict the efferent arteriole
Decrease in renal blood flow, leads to an increase in P GC, leading to an increase in GFR
What happens if you dilate the efferent arteriole
Increase in renal blood flow, leads to a decrease in P GC, leading to a decrease in GFR
What happens if you dilate the afferent arteriole?
Increase in renal blood flow, increase in P GC, leads to an increase in GFR
What is autoregulation of GFR and RBF
Maintaining GFR and RBF relatively constant in the face of changing arteriole blood pressure
GFR and RBF will be (increased or decreased) when arterial blood pressure is > 180 mmHg
Increased
GFR and RBF will be (increased or decreased) when arterial blood pressure is < 100 mmHg
Decrease
At what point does renal shutdown occur?
< 70 mmHg
At what point does renal death occur?
0 mmHg
What is the intrinsic regulation for the GFR and RBF?
1) Intrinsic (vasoconstrictor and vasodilator) factors
2) Myogenic hypothesis
3) Tubuloglomerular feedback
What is the extrinsic regulation of GFR and RBF
1) Sympathetic nervous system
2) Blood borne or endogenous substances (ang II)
3) Stress factors (hemorrhage)
What are some of the vasoconstrictors for autoregulation
Sympathetic nervous system, catecholamines, ang II (extrinsic), and endothelin (intrinsic)
What are some vasodilators for RBF and GFR
Prostaglandins (intrinsic), NO (intrinsic), bradykinin, and dopamine
Explain the extrinsic regulation flow chart
Hemorrhage leads to a drop in arterial blood pressure. This leads to two things. 1) increased renin secretion, which will increase plasma and renal renin. This will then increase plasma and renal ang II. 2) an increase in activity of renal sympathetic nerves. Together, these will both cause constriction of renal arterioles. This will decrease RBF and GFR, and decrease renal excretion of sodium and water. Additionally, Ang II will increase tubular sodium and water reabsorption and facilitate the decreased excretion. Taken together, all of these will increase arterial blood pressure
