The Alveoli

When oxygen enters the nose and the mouth, it travels to the back of the throat (pharynx) where it takes the epiglottis – the passage that only allows air to go in and out of due to the small flap of tissue hanging at the entrance – and then down the trachea or windpipe towards two tubes named the main stem bronchi. This is what connects the two lungs. After that, the oxygen makes its way through many smaller bronchi in the lungs and to the smallest bronchi called bronchioles which end at the tiny air sacs called alveoli. The alveoli are an important aspect of the exchanges of oxygen and carbon dioxide because it is the main function of the lungs and what links the air we breathe in to the blood. 

Millions of alveoli make up the alveolar sacs and has an area that could nearly cover a tennis court. There is an estimated 300-400 million alveoli in each adult lung which means about 600-800 million alveoli altogether. Elastic connective tissues are in the spaces between each alveolus. They are important especially during exhalation because then the lungs can stretch without bursting as they are filled with oxygen while keeping their shape. A network of pulmonary capillaries surrounds the alveoli. The thin layer of alveoli wall separates the air in the alveoli from the blood in the pulmonary capillaries which is convenient because it lets the oxygen and carbon dioxide diffuse rapidly and easily into and out of the blood. The oxygen from the air sacs diffuses into the red blood cells of the capillaries which then travel towards the heart to be pumped efficiently into all the cells in the body. The carbon dioxide from the blood in the body travels into the ends of the capillaries where it diffuses into the air sacs to then be breathed up and out of the lungs and into the environment.

DID you know? We have 30,000 bronchioles in each lung and they are each the same size as a hair.

DID you know? Carbon dioxide - the gaseous waste we breathe out, is warm because when it was travelling around the body, it picked up the body’s heat.

Bronchi – plural
Bronchus – singular

Alveoli – plural
Alveolus – singular