Renal Circulation Flashcards
What is the equation for Renal Plasma Flow
RPF= RBF x (1-Hct)
What is the equation for Filtration fraction?
FF= Glomerular Filtration Rate/ Renal Plasma Flow
How much of the CO do the kidneys receive?
~20-25% of CO
What are the two major factors that generate filtrate?
- Hydraulic pressure in glomerular capillaries
2. Renal blood flow rate
What other factors contribute to filtrate formation?
Hydraulic pressure
Renal blood flow rate
Minor- Blood oncotic pressure
Filtration coefficient (how easily you can move fluid across: characteristics of vessel, SA)
What is the equation for blood flow?
Flow (Q)= Pressure Change/Resistance
What factors influence resistance in the vessels?
- Length of blood vessels
- Radii of blood vessels (MAJOR factor)
- Blood viscosity
What are the effects of vasoconstriction?
Decreased flow
pressure up stream increases
downstream pressure decreases
B/c of the presence of of both pre- and post- glomerular capillary sphincters:
- Glomerular capillary pressure is much (greater/less) than in most capillaries elsewhere in the body.
- Peritubular capillary pressure is (higher/lower) than in most capillaries elsewhere in the body
- greater
- lower
These pressure differences facilitate formation of filtrate in glomeruli and reabsorption of fluid from peritubular capillaries.
What are three factors that promote renal constriction?
- Sympathetic n (catechoamines)
- Angiotensin II
- Endothelin
What are 5 factors that promote renal constriction?
- PGE2
- PGI2
- NO
- Bradykinin
- Dopamine
What effect do sympathetic nerve fibers have?
They activate alpha 1 receptors on afferent and efferent arterioles –> vasoconstriction
How would SNS activation affect on RBF and GFR?
Decrease RBF and GFR
What effect does Angiotensin II have?
Potent vasoconstrictor
Affects both AA and EA
Greater effect on the efferent arteriole
How would Angiotensin II affect RBF and GFR?
Decrease RBF and Inc. GRF
Levels of ATII release influences the relative effects so…..
At low levels of ATII which vessel is influenced more?
At high levels of ATII?
At low levels: both AA and EA constrict, then EA> AA, –> inc. GFR
At high levels, both AA and EA constrict, then EA dec. GFR
What effect does Prostaglandins (PGE2 and PGI2) have?
Vasodilate both vessels
Activation of SNS and ATII also activates renal PG production, explain why. (also how it relates to Advil)
PG activation is a safety mechanism- vasodilates vessels deep in the kidney to maintain blood flow
What effect does Dopamine have on the kidneys (and other organs) at:
- Low doses
- High doses
- At low doses:; dilates renal, cerebral, cardiac and splanchic arterioles
constricts skeletal and cutaneous arterioles - At high doses: vasoconstricts renal arterioles
What is autoregulation?
system in place that limits changes in kidney function due to changing systemic BP. (protects glomerulus from systemic pressure)
What primarily controls autoregulation?
The Afferent arteriole.
Theories: Myogenic: physical stretch is detected, open sm. muscle Ca channels –> vasoconstriction
Tubuloglomerular: macula densa senses
Net flow across vessel wall depends on:
- Hydrostatic Pressure on each side
- Oncotic Pressure on each side
- Filtration coefficient of the vessel wall.
Why are NSAIDS toxic to kidneys?
They suppress PG production, can have too much vasoconstriction (PG is protective of kidney blood flow)
