Bhawna Bhardwaj ,subject matter expert at Edumarz
Solution:The lungs contain millions of alveoli, which serve as gas exchange sites. The walls of alveoli contain a significant number of blood vessels. Alveoli have a huge surface area where gases can be exchanged. The exchange of gases is maximized when the surface area is big. Lungs are built in this way to optimize the area available for gas exchange in humans.
A pair of lungs are present in humans. Each lung has a complex breathing system. Alveoli are a small circular sac-like structure with a network of capillaries and incredibly thin walls.Alveoli of lungs are the site of respiration so are thin walled ,moist and vascular. There are more than 80m2 of alveoli in all. It is several times larger than the entire human body’s surface area.There are about 750 million alveoli in both the lungs of human which collectively provide a large surface area for exchange of gases.