Control of blood flow Flashcards
What does Darcys Law state?
The role of pressure on flow.
Blood flow = Pa - CVP /TPR
Rearrange darcys equation to include G and what does G state?
G = Conductance is the reciprocal of TPR (how easily it flows)
CO = Pa - CVP x G
What does TPR control?
• TPR controls blood flow and blood pressure - Increase in resistance means need to increase pressure to keep same flow.
What controls TPR?
- Darcy’s and Poiseuille’s laws
- Myogenic response
- Blood viscosity
Describe how pressure, blood flow and TPR changes when during normal artery blood pressure, a lower artery blood pressure and higher artery blood pressure
Normal blood pressure in the artery:
The pressure drops between arteries and arterioles causes normal blood flow in capillaries
Lower blood pressure in the artery:
Vasodilation in the arteriole decreased TPR, decreased blood pressure upstream, but greater flow
Increased blood pressure in artery:
Vasoconstriction in the arteriole, increased in TPR, increased blood pressure upstream but less flow
What is hypertension?
Over constriction of the arterioles, higher arteriole blood pressure upstream but less flow.
Describe Changes in blood flow in response to changes in need
• Brain stem areas controlling sympathetic nervous activity to various areas of the body. These are coordinated by the brain stem and the medulla at the top of the spinal cord. Sedentary • Superior mesenteric dilated Increased flow to intestines • Common iliac constricted Decreased flow to legs • Superior mesenteric constricted Decreased flow to intestines Exercising • Common iliac dilated Increased flow to legs
What factors control TPR?
The radius of the vessel, blood viscosity and the length of the vessel all effect the resistance.
Why do small changes in radius size have a huge effect on TPR?
Small changes in radius have a huge effect of the resistance to flow. This is why contraction and relaxation have a big influence on TPR. It is because it is power of 4.
The longer the vessel the greater the…….?
TPR
What does Poiseuille’s Law state?
Describes parameters that govern TPR
What is Poiseuille’s equation for his law?
Resistance = (8 x blood viscosity x vessel length) / (Pi x radius^4)
What is the equation of Conductance (G)
Reciprocal of Poiseuille’s law equation
What is Darcys Law equation taking into account G
CO = Pa - CVP x G
Combine Darcy’s equation and Poiseuille’s equation
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