Biology AS · 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 passes down the trachea, into the two bronchi, through smaller and smaller bronchioles and into the alveoli, where gas exchange takes place. Each alveolus is wrapped in a network of capillaries.
The tissues change along this path. The trachea and bronchi have cartilage to hold them open, and a lining of ciliated epithelium with goblet cells. Bronchioles have no cartilage but have smooth muscle. Alveoli have a wall of squamous epithelium with elastic fibres.
Oxygen diffuses from the alveolar air into the blood, and carbon dioxide diffuses the other way. The path is very short: one thin alveolar cell and one thin capillary cell. Ventilation and blood flow keep the concentration gradients steep.
Writing that cilia trap or filter dust. Mucus traps the particles; cilia only move the mucus.
Answer: A bronchiole.
Type what you are stuck on. The helper finds the explanation, worked examples and the notes to read, free and instant.