A) capillaries surrounding the tissue cells
B) arteries of the body
C) capillaries surrounding the alveoli
D) left auricle of the heart
Correct Answer: A
Solution :
Gaseous exchange between blood and alveolar air across respiratory membrane occurs by simple diffusion. The blood drained from lungs includes not only oxygenated blood but also some deoxygenated blood that has supplied its oxygen to tissue cells. The \[\text{P}{{\text{o}}_{\text{2}}}\]of this blood is about 95-97 mm hg. After recieving this blood from the lungs the heart pumps, it into the arteries which carry it to all parts of the body while flowing through the capillary networks in various tissues, this blood supplies \[{{O}_{2}}\] to all cells in exchange of \[C{{O}_{2}}.\] The average \[\text{P}{{\text{o}}_{\text{2}}}\]in tissue fluid is about 40 mm Hg. whereas the \[\text{P}{{\text{o}}_{\text{2}}}\] in arterial blood supplying the tissues is 95 mm hg. This pressure difference ensure vary rapid deoxygenation of the unstable oxyhaemoglobin in the tissue and diffusion of released \[{{O}_{2}}\] into tissue fluid and then into the cells. The arterial blood normally supplies about 25% of its \[{{O}_{2}}\] to the tissue.
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