Question

How are alveoli designed to maximise the exchange of gases?
A) By increasing the surface area of trachea
B) By decreasing the surface area of the lungs
C) By increasing the surface area of the lungs for gaseous exchange
D) None of the above.

Answer 1

Gaseous exchange occurs within the lungs. Air enters through our nostrils, into the pharynx and trachea, and then down into the bronchi and bronchioles, with the end point being the alveoli.

Complete answer:
The way it is designed is fairly simple. AS we inhale, air enters from the upper respiratory tract, and is taken down in the lungs via the bronchi. Bronchi branch out into tiny bronchioles, which end in sac-like structures called alveoli. Alveoli are very thin walled sacs, covered with a network of tiny capillaries. The single epithelium walled structures makes the exchange of gases to and from the blood in the capillaries quick and efficient. Though alveoli themselves are very tiny, totally they have a surface area of around 100 metres square. Thus, they greatly increase the available surface area of the lungs.
Option (B) is the direct opposite of this, and is therefore incorrect.
Option A involves the trachea, which connects the upper respiratory tract to the lower respiratory trach. Trachea is not responsible for gaseous exchange, therefore this answer is incorrect.

Hence the correct answer is option ‘C’.

Note: Alveolar epithelium has two types of cells. Type 1 constitutes the blood-air barrier covering the surface of the alveoli, while type two cells have the interesting feature of being able to produce stem cells.