Durning strenuous exercise, the muscle interstitial fluid `pO_(2)` falls to `20` mm Hg. The oxygen delivered by blood that passes through the exercising muscle tissus will be

Options

A. five times as much as normal
B. double to the normal
C. three times as much as normal
D. none of these.

Answer

C

Explanation

The given graph shows the relationship between partial pressure of oxygen with the amount of oxygen that can bind with haemoglobi. The `PO_(2)` of the air within alveoli is about `100` mm Hg. As the blood travels through the systemic blood capillaries, oxygen leaves the blood and diffuses into the tissuess. Consquently, the blood that leaves the tissues in the veins has a `PO_(2)` that is decreasing (in a resting person) to about `40` mm Hg. Therefore, A depicts oxygenated blood and B depicts systemic blood.
The steep portion of the curve from `60` down to `20` mm Hg is ideal for unloading oxygen in the tissue, i.e., for a small decrease in `PO_(2)` (due to diffussion of oxygen) a large quantity of oxygen can be unloaded to the peripheral tissue capillary. Durning strenous exercise, the muscles acclerated metabolism uses more oxygen from the capillary blood and thus decreases the vanous blood `PO_(2)`, for example the `PO_(2)` of the venous blood could drop to `20` mm Hg. Hence, `D, E`, and `F` shows the venous blood in exercise, normal venous blood and normal arterial blood respectively.
As we know, in the resting person, the `PO_(2)` of tissue is `40` mm Hg, which is favourable for oxygen diffusion from artieral blood to the tissues. Oxygen unloaded to the tissues by arterial blood is `5 "mL"//100 "m"` of blood (`20` mL - `15` mL `= 5"mL"//100 "mL"`, from the graph). During strenous execrise, the muscle interstitial fluid is `15 "mL"1//100 "mL"` of blood , `(20 - 5) "mL"//10 "mL" = 15 "mL"//100 "mL"`, from the graph i.e., thre times as much as normal.