Regulation of Arteriolar Resistance Flashcards
What is Darcy’s law?
Flow is equal to the change in pressure divided by the resistance
What is poiseuille’s law?
Resistance is equal to viscosity times by length times by 8 divided by r^4pi
What is varying the radius of resistance vessels used to do?
Control flow and redirect blood also regulates MAP
What is change in pressure equal to?
Flow x resistance
What does arteriolar radius affect?
Flow through individual beds and MAP
What are the two levels of control surrounding arterioles?
Intrinsic mechanisms
Extrinsic mechanisms
How do sympathetic nerves affect arterioles?
Innervates smooth muscle surrounding arterioles
Nerves release noradrenaline which binds to alpha 1 receptors and causes arteriolar constriction
Leads to decreased flow and increased TPR
Why do parasympathetic nerves have little effect?
No innervation from the parasympathetic system
What effect does adrenaline have?
Released from the adrenal medulla it binds to alpha 1 receptors and causes arteriolar constriction which causes decreased flow and increases TPR
What effect does angiotensin II have?
Produced in response to low blood volume and causes arteriolar constriction and therefore increases TPR
What effect does vasopressin have?
Released in response to low blood volume
Causes arteriolar constriction and therefore increases TPR
What effect does ANP and BNP have?
Released in response to high blood volume
Causes arteriolar dilation and therefore decreased TPR
Explain active hyperaemia?
Increased metabolic activity causes increased concentration of metabolites, increased sensed by capillaries
Triggers release of EDRF which causes dilation and increased flow
Explain pressure auto regulation
Decreased MAP causes decreased flow therefore metabolites accumulate
Triggers release of EDRF, arterioles dilate and flow is restored to normal
Adaptation to ensure that a tissue maintains blood supply despite changes in MAP
Explain reactive hyperaemia
Increase in blood flow in reaction to increasing of blood supply
Occlusion of blood supply causes a subsequent increase in blood flow
An extreme version of pressure autoregulation
