Breathing
Resumen
You have taken roughly twenty thousand breaths since this time yesterday and noticed almost none of them. Each one is a small piece of engineering: a set of muscles changes the shape of your chest, the pressure inside it drops below the pressure of the room, and air does the rest by moving from where there is more of it to where there is less. Nothing sucks the air in. It is pushed in, by the atmosphere.
This lesson takes that machinery apart. You will trace the path air follows from the trachea down to the alveoli, learn the exact sequence of muscle, volume and pressure that the specification wants for inhaling and exhaling, and see why a gas exchange surface the size of a badminton court is folded up inside your ribcage. At the end you will meet the machines that take over when a patient stops breathing, and find out why some of them pull and others push.
Objetivos
- The respiratory (breathing) system takes air into and out of the body so that oxygen from the air can diffuse into the bloodstream and carbon dioxide can diffuse out of the bloodstream into the air. The lungs are in the upper part of the body (thorax), protected by the ribcage and separated from the lower part of the body (abdomen) by the diaphragm. Students should be able to recognise the following on a diagram of the respiratory system: ribs, intercostal muscles, diaphragm, lungs, trachea, bronchi, bronchioles, alveoli.
- To inhale: the intercostal muscles contract, pulling the ribcage upwards; at the same time the diaphragm muscles contract, causing the diaphragm to flatten; these two movements cause an increase in the volume of the thorax; the consequent decrease in pressure to below that of the air surrounding the body results in atmospheric air entering the lungs. To exhale: the intercostal muscles relax, allowing the rib cage to move downwards; at the same time the diaphragm muscles relax, allowing the diaphragm to resume its domed shape; these two movements cause a reduction in the volume of the thorax; the consequent increase in pressure results in air leaving the lungs.
- The alveoli provide a very large surface area, richly supplied with blood capillaries, so that gases can readily diffuse into and out of the blood.
- A healthy person constantly breathes automatically. However, spontaneous breathing may stop due to disease or injury. If this happens the patient can be helped to breathe by using a mechanical ventilator. There are two main types of mechanical ventilator: B; negative pressure ventilators, which cause air to be ‘drawn’ into the lungs; positive pressure ventilators, which force air into the lungs.
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Nota de la lección
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Evaluación de la lección
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- Which structure separates the thorax from the abdomen? A. The ribcage B. The diaphragm C. The trachea D. The bronchioles Answer: B
- Which of these happens when a person inhales? A. The diaphragm relaxes and becomes domed B. The volume of the thorax decreases C. The intercostal muscles contract and the ribcage moves upwards D. The pressure inside the thorax rises above atmospheric pressure Answer: C
- Approximately what percentage of exhaled air is carbon dioxide? A. 0.04% B. 4% C. 16% D. 21% Answer: B
- Which feature of the alveoli most increases the rate at which oxygen diffuses into the blood? A. Rings of cartilage that hold them open B. A large surface area with walls one cell thick and many capillaries C. A thick layer of muscle in their walls D. Cilia that sweep mucus away from them Answer: B
- How does a positive pressure ventilator help a patient who has stopped breathing? A. It lowers the pressure around the chest so that air is drawn in B. It forces air into the lungs under pressure C. It increases the percentage of carbon dioxide in the air breathed in D. It makes the intercostal muscles contract Answer: B
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