Biology · Human gas exchange. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Air reaches the lungs through the larynx, trachea, bronchi and bronchioles, and ends in millions of tiny air sacs called alveoli. Here oxygen diffuses from the air into the blood, and carbon dioxide diffuses from the blood into the air. The alveoli suit this job: a huge surface area, walls one cell thick, a dense network of capillaries and a constant supply of fresh air.
Breathing moves the air. Muscles change the volume of the thorax; this changes the pressure inside, and air moves from higher pressure to lower pressure.
Goblet cells in the airways make sticky mucus that traps dust and pathogens. Cilia sweep the mucus up to the throat, where it is swallowed.
The diaphragm contracts when you breathe in, and contracting makes it flatter, not more domed. Also, air does not push the lungs open: the thorax gets bigger first, then air flows in.
Answer: 0.3 dm3 of oxygen per minute.
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