The Respiratory System

This lesson covers the structure and function of the respiratory system — the pathway of air from the mouth and nose to the alveoli — as required by the Edexcel GCSE PE specification (1PE0 — Topic 1). You need to know each structure in the respiratory pathway, its function, and how the system delivers oxygen to the blood for transport to working muscles.

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Overview of the Respiratory System

The respiratory system is responsible for bringing oxygen into the body and removing carbon dioxide. It works closely with the cardiovascular system to ensure that working muscles receive the oxygen they need during exercise.

The key structures of the respiratory system form a pathway that air follows from the outside to the alveoli deep within the lungs:

graph TD
    A["Mouth / Nose"] --> B["Pharynx (throat)"]
    B --> C["Larynx (voice box)"]
    C --> D["Trachea (windpipe)"]
    D --> E["Bronchi (left and right)"]
    E --> F["Bronchioles"]
    F --> G["Alveoli (air sacs)"]

    style A fill:#4a90d9,color:#fff
    style D fill:#e67e22,color:#fff
    style G fill:#27ae60,color:#fff

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The Pathway of Air

1. Mouth and Nose

Air enters the body through the mouth and/or nose.

• The nose warms, moistens, and filters the air (tiny hairs and mucus trap dust and particles).
• During exercise, we tend to breathe through the mouth as well, because it allows a greater volume of air to enter more quickly.

2. Pharynx and Larynx

The pharynx (throat) is a shared passage for both air and food. The larynx (voice box) sits below the pharynx and contains the vocal cords. The epiglottis is a flap of tissue that closes over the larynx during swallowing to prevent food entering the airway.

3. Trachea (Windpipe)

The trachea is a tube approximately 10-12 cm long that carries air from the larynx towards the lungs. It is held open by C-shaped rings of cartilage that prevent it from collapsing. The inner lining produces mucus that traps particles, and tiny hair-like structures called cilia sweep the mucus upward to be swallowed.

4. Bronchi

The trachea 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.

5. Bronchioles

The bronchi divide repeatedly into smaller and smaller tubes called bronchioles. These are much narrower than the bronchi and no longer have cartilage rings. Instead, they have smooth muscle in their walls, which can contract or relax to control airflow:

• Bronchoconstriction — narrowing of the bronchioles (occurs during an asthma attack).
• Bronchodilation — widening of the bronchioles (occurs during exercise to allow more air in).

6. Alveoli

The bronchioles end in clusters of tiny, thin-walled air sacs called alveoli (singular: alveolus). There are approximately 300 million alveoli in each lung, giving a huge surface area for gas exchange.