Your lungs work nonstop to keep you alive. They do it with respiration, which is a single complete act of breathing.
The process begins when you inhale. Air passes through your mouth and nose into your trachea. You can also call the trachea a windpipe. It splits into two main branches, or bronchi. One branch goes to the left lung. The other goes to the right lung. Then, each branches into smaller and smaller tubes, or bronchioles. The tiniest tubes end in grapelike sacs called alveoli.
One is an alveolus, but two or more are alveoli. Each alveolus is covered in a net of tiny blood vessels. We call these capillaries. Respiration is a gas exchange. It happens between the alveoli and the capillaries. Gases move between the blood in the pulmonary (lung) capillaries and the air in the alveoli.
