Regulation of arteriolar resistance Flashcards
What is Darcy`s Law?
Flow is equal to pressure diff devided by resistance
What is Poiseuille`s Law?
Resistance is equal to viscosity by length by 8 divided by radius to the power of 4 x pi
What does increasing the haematocrit do?
Increases viscosity of blood
Pressure is equal to what?
Flow x Resistance
How can you apply pressure = flow x resistance to systemic circulation?
MAP- CVP= COx TPR
Why can CVP be ignored?
Because its so small
What is the average MAP?
90/95mmHg
What is the average CVP?
0-5mmHg
What happens when total peripheral resistance is reduced?
Mean arterial pressure is also reduced
Can you affect one vascular bed and not mean arterial pressure
NO YE GIT
How do you keep the blood flow to each vascular bed sufficient and keep mean arteial pressure in the right range?
Intrinisc mechanisms -selfish needs of each individual tissue
Extrinsic mechanisms-
How does the sympathetic system affect extrinsic control?
- releases norepinephrine
- binds to alpha1- receptors
- Causes arteriolar constriction
- Reduces flow through tissue and increases TPR
What effect does parasympathetic system have on extrinsic control?
NON
How does hormonal control affect Extrinic control?
ADRENALINE (released from adrenal medulla) -Binds to alpha 1 receptors -causes arteriolar consriction -Therefore decrease flow through that tissue Increase TPR
IN SOME cases
-binds B2 receptors in skeletal and cardiac to cause arteriolar dilation
What effect does Angiotensin 2 have?
Causes arteriolar constriction
Increases TPR
When is angiotensin 2 produced?
in response to low blood volume
Long term porduced in kidney
When is vasopressin released?
in response to low blood volume
What is another name for vasopressin?
antidiuretic hormone
Long term porduced in kidney
When are artial natriuretic peptide & brain natriuretic peptide released?
-Released in response to high blood volume
What does artial natriuretic peptide & brain natriuretic peptide do?
-Causes artiolar dilation
Decreases TPR
(Long term produced in kidney)
What does EDRF mean?
endothelium derived relaxing factor
Why is EDRF released?
in response to metabolites from hard working tissue
Name some of the metabolites released by hard working tissue
- CO2
- H+
- K+
What does EDRF cause?
arteriolar dialitation
Why does EDRF cause arteriolar dilation?
To wash out metabolites
How does the body respond to a decrease in MAP and flow locally?
Releases EDRF
What is reactive hyperaemia
- occulsion of blood (rubber band on arm) supply causes a subsequent increase in blood flow
- (an extreme version of pressure autoreg)
Describe the injury response?
C fibres pick up pain
release substance P which causes mast cells to release histamine
Increased permeability causes white cells to be allowed out
What does histamine cause?
increase in blood flow
increase in permeability
What happens when heart contracts ?
It cuts off its own blood supply
How does coronary circulation cope with increased demand during exercise?
- excellent hyperaemia
- Expresses many B2 receptors
- These swamp any sympathetic arteriolar constriction
What type autoregulation does the cerebral circ show?
Excellent pressure autoregulation
What is the main function of renal circ?
Filtration which depends on pressure
What do changes in MAP have a big affect on?
Blood volume
What type of auto regulation does the renal circ show?
Excellent pressure regulation
What is pressure regulation?
EDRF released in response to MAP decreased and decreased flow
