Why are alveoli so smell and uncountable in number ?

Explanation

(1)The pouch-like air sacs at the ends of the smallest bronchioles are called alveoli .
(2)The walls of the alveolus are very thin and they are surrounded by very thin blood capillaries.
(3)It is in the alveoli that gaseous exchange takes place.
(4)There are millions of alveoli in the lungs. The presence of millions of alveoli in the lungs provides a very large area for the exchange of gases.
(5)And the availability of large surface area maximises the exchange of gases.