Breathing and Exchange of Gases Question 23
23. The figure given below shows a small part of human lung where exchange of gases takes place. In which one of the options given below, the one part A, B, C or D is correctly identified along with its function?
[2011]
Options :
(a) C : arterial capillary - passes oxygen to tissues
(b) A : alveolar cavity main site of exchange of respiratory gases
(c) D : capillary wall exchange of $O_2$ and $CO_2$ takes place here.
(d) B : red blood cell - transport of $CO_2$ mainly
Show Answer
Answer : b
Hints & Solution
(b) In the given figure the exchange of respiratory gases occurs in alveolar cavity. The thickness of the alveolar-capillary barrier varies from 0.2 to $2.5 \mu m$. The wall of the capillary endothelial cell is fused to that of the alveolar cell with only a very thin basement membrane between these two cells. This produces a very narrow gap across which oxygen and carbon dioxide can rapidly diffuse.
