Question

Give reason why alveoli are surrounded by blood capillaries?

Answer 1

As per the structure of the lungs, the windpipe (trachea) branches into two bronchi (one to each lung). The bronchi split into smaller and smaller tubes called bronchioles. The bronchioles end in microscopic air sacs called alveoli.

These air sacs are lined with mucus and are surrounded by a network of blood capillaries.

The mucus surface of the alveoli allows oxygen to dissolve in it.

They have a very thin lining to allow oxygen to diffuse into the blood easily.

And surrounding blood capillaries pick up and transport oxygen.

There is an exchange of gases between the air sacs and their surrounding capillary blood vessels. Oxygen diffuses from the air sac into the blood. Carbon dioxide diffuses from the blood into the air sac.

The capillary network allows efficient gas exchange in tissues since they have a large surface area and they have thin walls.