Which feature of the alveoli is the most important adaptation for efficient gaseous exchange?
- A. Their supporting rings of cartilage
- B. Their walls, one cell thick, giving an enormous surface area with a dense capillary network
- C. The cilia lining their inner surface
- D. The mucus that coats them
Explanation
Around 300 million alveoli give a surface of roughly 70 square metres, and a wall a single cell thick lying against an equally thin capillary means oxygen diffuses across a distance well under a micrometre. Continual blood flow and ventilation keep the diffusion gradient steep. Alveoli contain no cartilage or cilia, and a coat of mucus would in fact lengthen the diffusion path.
Related questions
Most of the carbon dioxide carried in the blood travels as
One molecule of haemoglobin can combine with
An increase in carbon dioxide concentration makes haemoglobin release oxygen more readily. This is known as
The rate and depth of breathing are regulated mainly by the level of
The chloride shift refers to the movement of chloride ions