Regulation of Arteriolar Resistance Flashcards
What can varying the radius of a resistance vessel be used to control?
To control flow, redirect blood, TPR and MAP
What is the role of the intrinsic mechanisms?
To meet the needs of the individual tissue
What is the role of the extrinsic mechanisms?
To ensure that the total peripheral resistance of the whole body stays within the correct levels
How does the sympathetic system regulate extrinsic control
By releasing noradrenaline which binds to alpha 1 receptors and causes arteriolar constriction which decreases the flow through the tissues and increases the TPR
What effect does the parasympathetic system have on the extrinsic control?
Usually no effect
Where is epinephrine released from?
Adrenal medulla
How does epinephrine regulate extrinsic control?
By binding to alpha 1 receptors and causing arteriolar constriction but in some cells e.g. skeletal and cardiac muscle it also activates beta 2 receptors which causes arteriolar dilation and tends to decrease TPR
How does active (metabolic) hyperaemia regulate arteriolar resistance?
An increase in metabolic activity causes an increase in metabolites which triggers the release of EDRF which causes arteriolar dilation
How does a decrease in MAP regulate arteriolar resistance?
A decrease in MAP causes a decrease in flow which cause a build up of metabolites. This triggers the release of EDFR, the arterioles dilate and flow is restored to normal
What effect does occlusion of the blood supply cause?
An extreme version of pressure regulation
What effect does an injury have on arteriolar resistance?
The arterioles are dilated as blood flows to the area is increased and permeability is increased to allow the WBCs to reach the area
How does the coronary circulation overcome the interruption of blood supply during systole?
It shows excellent active hyperaemia and expresses lots of beta 2 receptors which swamp an sympathetic arteriolar constriction
How does the cerebral circulation maintain stability?
It has excellent pressure autoregulation
How does the pulmonary circulation use regulation of the arteriolar resistance to maintain ventilation when oxygen levels fall?
Low oxygen levels causes arteriolar constriction which redirects blood to the better ventilated parts of the lung
How does the renal circulation maintain blood pressure?
It has excellent pressure autoregulation
