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Breathing, the thorax and smoking
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Breathing moves air in and out of the lungs. Smoking damages the lungs and the circulatory system.
The thorax
Air passes down the trachea, which splits into two bronchi, then into smaller bronchioles, ending in tiny air sacs called alveoli.
The lungs are protected by the ribs. Intercostal muscles lie between the ribs, and the diaphragm is a sheet of muscle below the lungs.
Pleural membranes line the lungs and the inside of the thorax; fluid between them reduces friction.
The lungs are protected by the ribs. Intercostal muscles lie between the ribs, and the diaphragm is a sheet of muscle below the lungs.
Pleural membranes line the lungs and the inside of the thorax; fluid between them reduces friction.
Ventilation
Breathing in: the external intercostal muscles contract, moving the ribs up and out. The diaphragm contracts and flattens. The volume of the thorax increases, so the pressure falls below air pressure and air rushes in.
Breathing out: the muscles relax, the ribs move down and in and the diaphragm domes upwards. The volume decreases, pressure rises and air is pushed out.
Alveoli have a large surface area, thin walls and a good blood supply for fast diffusion.
Breathing out: the muscles relax, the ribs move down and in and the diaphragm domes upwards. The volume decreases, pressure rises and air is pushed out.
Alveoli have a large surface area, thin walls and a good blood supply for fast diffusion.
Smoking and breathing practicals
Tar contains carcinogens (lung cancer) and damages cilia, so mucus builds up, causing coughing and bronchitis.
Emphysema: alveolus walls break down, reducing the surface area.
Carbon monoxide joins with haemoglobin, so the blood carries less oxygen.
Nicotine is addictive and raises heart rate and blood pressure. Smoking narrows arteries, raising the risk of coronary heart disease.
Practical: exhaled air turns limewater milky faster than inhaled air; breathing rate rises during exercise.
Emphysema: alveolus walls break down, reducing the surface area.
Carbon monoxide joins with haemoglobin, so the blood carries less oxygen.
Nicotine is addictive and raises heart rate and blood pressure. Smoking narrows arteries, raising the risk of coronary heart disease.
Practical: exhaled air turns limewater milky faster than inhaled air; breathing rate rises during exercise.
Explain how contracting the diaphragm makes air enter the lungs.
- The diaphragm flattens, so the volume of the thorax increases.
- Larger volume means lower pressure inside the lungs.
- Air moves in from the higher pressure outside.
Answer: Thorax volume increases, pressure falls below atmospheric, air flows in.
Air goes trachea, bronchi, bronchioles, alveoli. Breathing in: intercostal muscles and diaphragm contract, volume up, pressure down, air in. Smoking: tar causes cancer and damages cilia, carbon monoxide reduces oxygen carried, nicotine is addictive, and the risk of coronary heart disease rises.
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