RBF And GFR Flashcards
The kidneys receive 1/4 of the entire cardiac output. Why?
They need high flow to support filtration.
Not because they are super metabolically active
How do you calculate the Filtration Fraction?
GFR
FF= _________
RPF
(Plasma flow, not blood)
How do you calculate renal plasma flow?
RPF= (1-Hct)RBF
(1-Hct) gives you the amount of blood that is plasma, so this makes sense
What effect will angiotensin II, ADH, ATP and endothelin have on RBF and GFR
Decreased
Although the effects of ATII on GFR are variable
Which arteriole is more sensitive to angiotensin II at lower concentrations?
Efferent arteriole
so when you have a low concentration of ATII, you reduce RBF, but maintain GFR
What effects will atrial natriuretic peptide, glucocorticoids, NO and prostaglandins have on RBF and GFR?
Increase
Does the blood flow and GFR remain constant when your blood pressure changes?
Yes, the kidney AUTOREGULATES as long as the pressure is between 80-180mmHg.
Can the autoregulation of RBF and GFR be overridden?>
Yes, large increases in SNS tone or severe blood loss will decrease RBF and GFR
What are the 2 mechanisms the kidney uses to autoregulate its blood flow and GFR?
- Myogenic mechanism- the vascular smooth muscles will contract if they stretch too much
- Tubuloglomerular feedback (“flow dependent”)- if GFR increases, more NaCl will flow through the LOH, and the macula densa will sense it and cause the afferent arteriole to contract, thus decreasing RBF and GFR
How does the macula densa help the nephron maintain a constant GFR and RBF?
It maintains a constancy of SALT load delivered to the distal tubule
True or false:
The fluid in Bowman’s capsule is essentially a protein-free filtrate of blood plasma
True
Everything in the blood except for the proteins gets filtered out initially
In the filtration barrier, there are 3 layers: the endothelial cells of the capillary, the basal lamina, and the podocytes/slits.
Which ones are the barriers to protein?
The basal lamina and filtration slits
The fenestrae between the endothelial cells will let protein through
How does the filtration barrier separate substances that are allowed to go into the Bowman’s capsule?
Size- small gets through
Electrical charge- (+) charges get through
Are the filtration slits between podocytes just open hallways for shit to filter through?
No they are bridged by diaphragms
How do you calculate GFR using the Starling Equation?
GFR= (Kf)(NFP)
NFP= [(Pgc-Pbc)-(ηgc-ηbc)]
Kf= filtration constant
Pgc and Pbc= hydrostatic pressure of glomerular capillary and Bowman’s capsule
ηgc and ηbc= osmotic pressure of glomerular capillary and Bowman’s capsule
(ηbc should be 0, since there should never be any protein getting through)
How do you calculate the net filtration pressure (NFP) in the glomeruleus?
(Pgc-Pbc)-(ηgc-ηbc)
η= osmotic pressure of glomerular capillaryor Bowman’s capsule
P= hydrostatic pressure of capillary or Bowman’s cap
what is Kf?
The filtration rate produced by each mmHg of net filtration pressure
Which has a higher Kf:
Glomerular capillaries or regular capillaries
Glomerular capillaries have a Kf 50-100x greater
Can Kf in the nephron be altered?
Yes, when the mesangial/M cells respond to angiotensin II, they will contract and reduce Kf.
(Therefore reducing GFR….but it will be balanced out by the kidney releasing prostaglandins)
Which is the driving force for GFR:
Pgc
Pbc
ηgc
Pgc (the blood pressure in the glom capillary)
What effect will increased Pbc (back pressure in Bowman’s capsule have on GFR?
Decrease GFR
What effect will an increased ηgc have on GFR?
ηgc is the oncotic pressure of glomerular capillary blood
It will decrease GFR
What happens to ηgc from the beginning of the capillary to the end?
It increases, as more water is drawn out of the blood and it is more concentrated
Does Pgc change from the beginning of the capillary to the end?
No, it is constant.
The osmotic pressure of the capillary DOES change though (increases)
What should ηbc always equal?
0
Should not be proteins in filtrate
So as you move from the beginning of the capillary to the end, the pressure of the capilary stays the same, but the oncotic pressure of the blood increases. What does this do to NFP?
NFP will drop to zero by the end of the capillary
Since the oncotic pressure of the capillary increases from beginning to end, does that mean that fluid is reabsorbed towards the end of the capillary?
No, it will never flow back into the capilary since the hydrostatic pressure of the blood remains so high
When afferent and efferent arteriolar resistances increase, what happens to the hydrostatic pressure of the capillary blood?
What happens to RBF?
Pressure of the blood does not change
RBF decreases dramatically
(This is something that would happen if you were hemorrhaging blood)
What effect will vasoconstriction at just the afferent arteriole have on Pgc and RBF?
Both will decrease
What effect will vasoconstriction at just the efferent arteriole have on Pgc and RBF?
Pgc increases
RBF decreases
What effect do NSAIDs have on prostaglandins?
Block their effects
What do prostaglandins do for the kidney?
In response to SNS stimulation and subsequent vasoconstriction, as well as high levels of angiotensin II, they will vasodilate the afferent arterioles in order to maintain blood
Where are the PGE2 and PGI2 prostaglandins made?
In the kidney
How do NSAIDs affect RBF?
They prevent the synthesis of prostaglandins (COX inhibitors) and therefore interfere with the protective effects of prostaglandins on RBF.
Too many NSAIDs can starve the capillaries of blood flow
