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Breathing and asthma
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Breathing

Efficient gas exchange needs a constant supply of fresh air. This is needed to bring in oxygen and get rid of waste carbon dioxide. This fresh air is supplied every time you breathe in and out. Sometimes this is called external respiration or lung ventilation.
How do we draw in air?
Picture 9. When you breath in, your diaphragm moves down and your ribs move up to make the chest cavity expand.
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Control of breathing

Your breathing does not stay the same all of the time. It changes depending on the amount of activity and the amount of oxygen need by the cells of the body. The speed and depth of breathing is controlled by the respiratory centre in the brain which monitors levels of carbon dioxide and oxygen in the blood.

If you are active, muscles need more oxygen to increase their level of respiration and supply the energy for the extra activity. They will also produce a lot more carbon dioxide which needs to be excreted by the lungs. To supply the extra oxygen, and get rid of the carbon dioxide, the rate of breathing increases and also each breath is deeper to take in and out more air. As well as this, the heart rate increases to carry these extra gases to and from the active muscle cells.

When you are relaxed, the body needs less oxygen to carry out a much lower level of respiration. Your brain monitors the levels of dissolved gases in your blood and so slows the breathing and heart rates. This is just enough to supply the oxygen your cells need for their basic level of respiration.
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Question 3

a) List the parts of the breathing system which air passes through on its way to the lungs.

b) Explain why an 800m runner needs to breath
heavily during the race.

Volume of chest increases.
Diaphragm contracts and pulls down.
Air pressure in lungs decreases.
Air is pulled into lungs down nose and trachea.
Intercostal muscles contract and pull ribs up.