BRAINCAKEBreathing
Breathing (ventilation) is the movement of air into and out of the lungs. It is needed because gas exchange in the alveoli relies on diffusion, and diffusion is only fast when there is a steep concentration gradient. Ventilation constantly brings in fresh air that is high in oxygen and low in carbon dioxide, and removes stale air, so the gradients across the alveolar walls are maintained.
Air always moves from a region of higher pressure to a region of lower pressure. The lungs sit inside the airtight thoracic cavity (thorax), enclosed by the ribs, the intercostal muscles and the diaphragm, and lined by the pleural membranes. Changing the volume of the thorax changes the pressure inside it: at constant temperature, increasing the volume lowers the pressure and decreasing the volume raises it.
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Key terms in this lesson
- concentration gradient
- The difference in the concentration of a substance between two regions, which determines the direction of net diffusion.
More in Gas Exchange
- Effective Gas Exchange Systems
- The Human Gas Exchange System
- Gas Exchange in the Alveoli
- Adaptations of the Human Gas Exchange System
- Inhalation
- Exhalation
- Protecting the Lungs
- Gas Exchange in Insects
All 23 lessons in Gas Exchange · All Edexcel AS-level Biology topics