Fig.: A diagram of a section of an alveolus with a pulmonary capillary

𝗘𝗫𝗖𝗛𝗔𝗡𝗚𝗘 𝗢𝗙 𝗚𝗔𝗦𝗘𝗦

Alveoli are the primary sites of exchange of gases.

Gaseous Exchange in Lungs

● At alveoli level, gaseous exchange occur through respiratory membrane (diffusion membrane) which is 0.2 mm thick (total thickness is much less than a mm).

● 𝗜𝘁 𝗰𝗼𝗻𝘀𝗶𝘀𝘁 𝗼𝗳 𝘁𝗵𝗿𝗲𝗲 𝗹𝗮𝘆𝗲𝗿𝘀:

(i) Alveolar epithelium (thin squamous epithelium)

(ii) Basement substance in between them (composed of a thin basement membrane supporting the squamous epithelium and the basement membrane surrounding the single layer endothelial cells of capillaries)

(iii) Endothelium of alveolar blood capillaries

● Exchange of gases also occur between blood and tissues.

● O2 and CO2 are exchanged in these sites by simple diffusion mainly based on pressure/concentration gradient

● Pressure contributed by an individual gas in a mixture of gases is called partial pressure and is represented as pO2 for oxygen and pCO2 for carbon dioxide.

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