Regulation of Arteriolar Resistance Flashcards
What laws of haemodynamics regulate arteriolar resistance?
Darcy’s and Poiseuille’s
How do you calculate the MAP?
CO x TPR
How do autonomic nerves have extrinsic control of arteriolar resistance?
Sympathetic - norepinephrine act on alpha-1 receptors and cause constriction
Parasympathetic - no effect usually
How do epinephrine have extrinsic control of arteriolar resistance?
Epinephrine - binds to A1 receptors - causes constriction
- In some skeletal and cardiac muscles it has the opposite effect when binding with B2 receptors
What other hormones have extrinsic effects on arteriolar resistance?What is their effect?
Angiotensin II - constriction
Vasopressin - constriction
Atrial and brain natriuretic peptide - responds to high blood volume - dilator
What local intrinsic controls are there?
- Active (metabolic) hyperaemia
- Pressure (flow) autoregulation
- Reactive hyperaemia
What is active hyperaemia?
Increase in metabolic activity leads to increased concentration of metabolites.
This in turn triggers the release of EDRF, causing dilation
What is pressure autoregulation?
Decrease in MAP causes metabolites to accumulated - EDRF released and dilates vessel
What is reactive hyperaemia?
Occlusion of blood supply causes a subsequent increase in blood flow (extreme version of pressure autoregulation)
What is special about the arteriolar regulation of the coronary artery?
Blood supply is interrupted at systole. Shows excellent active hyperaemia by expressing many B2 receptors, keeping it dilated
What is special about cerebral circulation?
Needs to be kept stable and therefore shows excellent pressure autoregulation
What is special about renal circulation?
Main function is filtration and therefore relies on pressure - changes in MAP have big effects on volume therefore the kidneys show excellent pressure autoregulation
What is meant by intrinsic effects?
Local
What is meant by extrinsic effects?
Distant - concerned with maintaining the TPR of the whole body
