LEARNING OBJECTIVES
By the end of this chapter, you should be able to:
- identify breathing structures
- explain alveolar adaptation
- compare inspired and expired air
- explain ventilation and exercise responses
THE BIG IDEA
How ventilation maintains steep gradients at specialised alveoli.
This chapter builds each process from its structures, inputs and outputs. Follow the connections rather than memorising isolated facts, then use precise biological terms when explaining cause and effect.
01
SECTION 01
Airways and alveoli
Air passes through larynx, trachea, bronchi and bronchioles to alveoli. Cartilage keeps the trachea open; goblet-cell mucus traps particles and cilia move it towards the throat.
DETAILED EXPLANATION
- Alveoli provide large area, one-cell-thick walls, strong blood supply and ventilation.
- Oxygen diffuses into capillaries while carbon dioxide diffuses into alveoli.
1trachea→
2bronchus→
3bronchiole→
4alveolus ⇄ capillary
02
SECTION 02
Ventilation
Thoracic volume changes alter pressure, moving air down a pressure gradient.
DETAILED EXPLANATION
- Inhale: external intercostals contract, ribs rise, diaphragm flattens, volume rises and pressure falls.
- Exhale: muscles relax, ribs lower, diaphragm domes, volume falls and pressure rises.
- Internal intercostals assist forced exhalation.
1volume ↑ → pressure ↓ → air in→
2volume ↓ → pressure ↑ → air out
03
SECTION 03
Air composition and activity
Expired air has less oxygen, more carbon dioxide and water vapour, while nitrogen changes little. Limewater tests increased carbon dioxide.
DETAILED EXPLANATION
- Active muscles produce more carbon dioxide.
- The brain detects its rise and increases breathing rate and depth.
- A fair investigation standardises exercise duration and intensity.
QUICK CHAPTER SUMMARY
The ideas to carry forward
- Alveoli are large, thin, supplied and ventilated.
- Pressure changes drive breathing.
- Expired air differs because of respiration.
- Exercise increases ventilation.