Question

Will a highly active muscle receive more, same or less oxygen than a resting muscle? Explain the mechanism that may influence oxygen delivery to this muscle. Appropriate diagrams/graphs describing relevant hemoglobin properties are required in order to receive full credit.

Answer 1

Highly active muscle will recive more oxygen than a resting membrane.

Skeletal muscle accounts for about 20% of cardiac output.

Duringe extreme physical exertion, more than 80% of cardiac output can be directed to contracting muscle.

Blood flow Increases even before start of exercise.

Causes of Increased blood flow to the exercising muscle :

- Intramuscular vasodilation (50%): Caused by increased muscle local vasoactive metabolites, Adenosine K+, CO2 and lactic acid which caused dilation of arterioles and precapillary sphincter.

- Moderate increase in BP(30%): The increase in pressure forces also stretches the walls of the arterioles and further reduces the vascular resistance.
− Adrenergic sympathetic vasoconstrictor nerve: secretes NE, can decrease muscle blood fow. But
sympathetic system secretes large amount of E
and NE from adrenal medulla. The epinephrine
excites more beta-adrenergic (vascular beta2-
adrenoceptors produce vasodilation) receptor to
produce muscle vasodilation.

Increase in ventilation is proportional to O2 consumption and CO2 output, up to a maximum and .This proportional increase in ventilation easily compensates the fall in venous blood PO2 (from 40 to 25 mm Hg) or, the rise in venous blood PCO2. So, the arterial blood PO2, PCO2 and pH remains normalup to moderate grade of exercises.