Level: JHS, Basic 8 | Subject: Integrated Science | Strand: Systems | Topic: The Human Body System (Respiratory System)
Curriculum reference: B8.3.1.1 Understand the respiratory system and gaseous exchange in humans. Indicator B8.3.1.1.1: Describe the structure and function of the human respiratory system. All the exemplars are merged into one set of notes.
1. What is Respiration and Breathing?
Breathing is taking air into the body and sending air out. Respiration is the release of energy from food inside the cells. Breathing brings in the oxygen that cells need for respiration and removes the carbon dioxide that the cells make.
2. Parts of the Respiratory System
| Part | Function |
|---|---|
| Nose | Air enters here. Hairs and mucus trap dust and germs. The air is warmed and moistened. |
| Trachea (windpipe) | A tube held open by rings of cartilage. It carries air to the chest. |
| Bronchi (one is a bronchus) | Two tubes. The trachea divides into them, one going to each lung. |
| Bronchioles | Small branches of the bronchi inside the lungs. |
| Alveoli (one is an alveolus) | Tiny air sacs at the ends of the bronchioles. Gaseous exchange takes place here. |
| Lungs | Two spongy organs in the chest that hold the bronchi, bronchioles and alveoli. |
| Ribs and intercostal muscles | Protect the lungs and move to help breathing. |
| Diaphragm | A sheet of muscle under the lungs that helps in breathing. |
The path of air is: nose, trachea, bronchi, bronchioles, alveoli.
3. The Mechanism of Breathing
| Inhalation (breathing in) | Exhalation (breathing out) | |
|---|---|---|
| Ribs | Move up and out | Move down and in |
| Diaphragm | Contracts and flattens | Relaxes and curves upward |
| Chest volume | Increases | Decreases |
| Air pressure in the lungs | Falls, so air rushes in | Rises, so air is pushed out |
4. Gaseous Exchange in the Alveoli
The walls of the alveoli are very thin, moist and covered with tiny blood vessels called capillaries. Oxygen in the air in the alveoli dissolves and passes into the blood. Carbon dioxide passes from the blood into the alveoli. Both gases move by diffusion, from where there is more of them to where there is less. The blood carries oxygen to all the cells, and the carbon dioxide is breathed out.
| Gas | Inhaled air | Exhaled air |
|---|---|---|
| Oxygen | About 21% | About 16% |
| Carbon dioxide | About 0.04% | About 4% |
| Water vapour | Less | More |
5. Features of the Alveoli that Help Gaseous Exchange
- Very thin walls, so gases pass quickly.
- A large surface area because there are millions of alveoli.
- A moist lining so gases can dissolve.
- A rich supply of blood capillaries.
6. Keeping the Respiratory System Healthy
- Do not smoke and avoid smoke from bush fires and burning rubbish.
- Cover the nose and mouth when you sneeze or cough.
- Take regular exercise and sit in well ventilated rooms.
- See a health worker for a long cough, asthma or tuberculosis.
Remember: Oxygen goes into the blood and carbon dioxide comes out, all by diffusion in the alveoli.
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Education Always (education.inspiringalways.com). Original notes written to follow the NaCCA Basic 8 Integrated Science curriculum.