Question

Physiology, Respiratory system

Under resting conditions, approximately 25% of the oxygen is extracted from the oxygenated blood into the tissues to maintain their basal metabolic need.  Describe (with all the possible mechanisms) how an individual can increase the unloading of oxygen from the oxygenated blood into the working tissues during exercise. (Worth 15 marks)

Please answer it so its worth about 15 marks

Answer 1

Under resting condition ,oxygen extraction ranges between 20% and 40%. During heavy exercise, approximately 70–80% of the oxygen delivered to the active muscles may be extracted, this means there is reserve amount of oxygen in the blood that can be utilized immediately by the active skeletal muscles at the onset of exercise. Increased extraction of oxygen from the blood is driven by decreases in perivascular PO2, which in turn are driven by reductions in cell PO2.. The other factor is that increased metabolism results  increased blood hydrogen ion and CO2 levels that are released into the tissue spaces, This facilitates unloading of oxygen from hemoglobin in the contracting skeletal muscles.

The increase in oxygen extraction from the blood lowers, venous oxygen content such that the arterio-venous oxygen content difference ((A-V)O2) increases,( arteriovenous oxygen difference is a measure of the amount of oxygen taken up from the blood by the tissues.) Increased arteriovenous oxygen difference occurs because of increased oxygen extraction in the active muscles like skeletal muscles heart, etc and also in peripheral organs where blood supplies were reduced by baroreceptor mediated vasoconstriction. Thus cardiac output and arteriovenous oxygen difference are the two factors that determine the overall oxygen uptake.

Regular exercise results in an increase in the size of mitochondria and in the mitochondrial enzyme activity. This allows each mitochondrion to extract more oxygen from the blood. Physically fit individuals have higher density of mitochondria which leads to more oxygen extraction and also there is increase in capillary density of skeletal muscles in these individuals, this increased capillary density will allow slower velocity of blood to each vessels so that the amount of time for oxygen extraction by the mitochondria increases.