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This lesson covers the structures of the respiratory system and the pathway that air takes from the moment it enters the body to the point where gaseous exchange occurs in the lungs. A clear understanding of respiratory anatomy is essential for the AQA GCSE PE specification (3.1.1.2) and provides the foundation for the lessons on gaseous exchange, breathing mechanics and spirometry that follow.
The respiratory system is responsible for bringing air into and out of the body so that gaseous exchange can occur — the process by which oxygen enters the blood and carbon dioxide is removed. The respiratory system works closely with the cardiovascular system to ensure that oxygen reaches the muscles and organs, and that carbon dioxide (a waste product of respiration) is expelled.
The main components of the respiratory system are:
| Structure | Function |
|---|---|
| Mouth and nose | Entry points for air |
| Pharynx (throat) | Passageway connecting the nasal cavity and mouth to the larynx |
| Larynx (voice box) | Contains the vocal cords; connects the pharynx to the trachea |
| Trachea (windpipe) | Main airway leading from the larynx towards the lungs |
| Bronchi (singular: bronchus) | Two branches of the trachea, one leading to each lung |
| Bronchioles | Smaller branches of the bronchi within the lungs |
| Alveoli (singular: alveolus) | Tiny air sacs at the ends of bronchioles where gaseous exchange occurs |
| Diaphragm | Dome-shaped muscle beneath the lungs that assists breathing |
| Intercostal muscles | Muscles between the ribs that assist breathing |
| Pleural membranes | Double-layered membranes surrounding each lung, reducing friction during breathing |
When you breathe in (inspiration or inhalation), air follows this pathway:
Air enters the body through the mouth or nose. The nose is the preferred route because it performs several important functions:
During exercise, we often breathe through the mouth as well because it allows a greater volume of air to be inhaled more quickly, even though the mouth does not filter, warm or moisten air as effectively as the nose.
Air passes from the nose and mouth into the pharynx, a shared passageway for air and food. The epiglottis (a flap of cartilage) closes over the top of the trachea during swallowing to prevent food from entering the airway.
Air passes through the larynx, which contains the vocal cords. The larynx sits at the top of the trachea and is sometimes visible as the "Adam's apple" in the neck.
The trachea is a tube approximately 10–12 cm long that carries air from the larynx towards the lungs. It has several important features:
At the base of the trachea, the airway divides into two bronchi (singular: bronchus) — the left bronchus and the right bronchus. Each bronchus enters one lung. Like the trachea, the bronchi are supported by rings of cartilage and are lined with mucus and cilia.
Inside the lungs, each bronchus divides repeatedly into smaller and smaller tubes called bronchioles. Bronchioles do not have cartilage rings; instead, they have smooth muscle in their walls that can contract or relax to control the diameter of the airway.
At the end of the smallest bronchioles are clusters of tiny, balloon-like air sacs called alveoli (singular: alveolus). There are approximately 300–500 million alveoli in the lungs, providing an enormous surface area for gaseous exchange — estimated at around 70 square metres (about the size of half a tennis court).
The alveoli are the site of gaseous exchange, where oxygen passes from the air into the blood, and carbon dioxide passes from the blood into the air. This process is covered in detail in the next lesson.
graph TD
A[Mouth / Nose] --> B[Pharynx]
B --> C[Larynx]
C --> D[Trachea]
D --> E[Left Bronchus]
D --> F[Right Bronchus]
E --> G[Bronchioles]
F --> H[Bronchioles]
G --> I[Alveoli]
H --> J[Alveoli]
I --> K[Gaseous Exchange]
J --> K
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