Cardiovascular physiology: Skeletal muscle circulation
Skeletal muscle has some unique adaptations to its circulation.
Skeletal muscle comprises around 50% of total body weight and receives around 15-20% of cardiac output at rest. During exercise skeletal muscle may receive more than than 80% of the cardiac output.
Skeletal muscle provides a significant contribution to total peripheral resistance. Blood flow through skeletal muscle beds is restricted by sympathetic stimulation which causes vasoconstriction. An example of this in a clinical setting is the baroreceptor reflex where peripheral resistance is rapidly increased in response to a drop in central venous pressure.
Metabolic hyperaemia or functional hyperaemia refers to increased blood flow to tissues when they are active. Hyperaemia is the result of vasodilatation caused by metabolites such as:
An increase in these metabolites overrides sympathetic vasoconstriction in active muscle.
Skeletal muscle comprises around 50% of total body weight and receives around 15-20% of cardiac output at rest. During exercise skeletal muscle may receive more than than 80% of the cardiac output.
Skeletal muscle provides a significant contribution to total peripheral resistance. Blood flow through skeletal muscle beds is restricted by sympathetic stimulation which causes vasoconstriction. An example of this in a clinical setting is the baroreceptor reflex where peripheral resistance is rapidly increased in response to a drop in central venous pressure.
Metabolic hyperaemia
At rest capillaries are mostly unperfused. Capillaries become recruited via metabolic hyperaemia.In skeletal muscle the release of CO2, K+ and adensoine during exercise results in vasodilation of constricted capillaries. This is known as capillary recruitment.
Metabolic hyperaemia or functional hyperaemia refers to increased blood flow to tissues when they are active. Hyperaemia is the result of vasodilatation caused by metabolites such as:
- Carbon dioxide
- Potassium ions
- Hydrogen ions
- Adenosine
- Lactate
An increase in these metabolites overrides sympathetic vasoconstriction in active muscle.
Metabolic hyperaemia increases flow during muscle relaxation as during muscle contraction the contracted muscle compresses vessels and reduces blood flow.