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Unit 3 - Mechanism of Ventilation

Many students incorrectly refer to ventilation as respiration. Respiration is the process of releasing energy from glucose in every cell of the body. Ventilation is the medical word for breathing, the mechanism by which air enters and leaves the body. It is an automatic function, controlled by the central nervous system and this GCSE Biology quiz has a look at how it works.

The mechanism which mammals use to breathe has several parts: lungs, intercostal muscles, a rib cage and a diaphragm - all of which work together to allow breathing to take place. To breathe in, the intercostal muscles expand the rib cage and the diaphragm contracts, moving downwards. These two actions cause the chest cavity containing the lungs to increase in volume. This increase in volume lowers the air pressure inside the lungs and the external air pressure forces air to enter the body.

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At rest or during normal daily activity, the external air travels into the body via the nose. Here it is warmed and moistened. From the nose, it travels down the trachaea (windpipe) and into the lungs via the bronchi. Once in the lungs, the air travels through smaller tubes called bronchioles, to reach the alveoli. Alveoli are microscopic air sacs with very thin walls, found within the lungs. They increase the surface area for gaseous exchange. Oxygen diffuses from the air inside the alveoli into the blood and carbon dioxide diffuses out of the blood and into the alveoli. Breathing out (expiration) involves the opposite actions to breathing in (inspiration). The intercostal muscles and diaphragm reduce the volume of the chest (thorax) and the increased pressure causes the air to leave the lungs.

During heavy exercise, the body requires more air than normal. The response is to breathe more heavily and deeply, using the mouth to allow more air into the body. The air breathed in like this isn't warmed or moistened as effectively as breathing through the nose so when exercising in cold weather, the trachaea sometimes hurts. Singers learn to breathe 'from the stomach'. In other words, they use their diaphragm more than normal to help them to breathe in as much air as possible. It is said that this also helps them to control their breathing more precisely, helping them to sing better.

Do you know how oxygen passes into the blood, or what the function of the rib cage is? Try this quiz to see how well you understand the mechanism of ventilation.

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  1. Name the special muscles found in the ribs which enable breathing.
    There are three types of intercostal muscle, external, internal and innermost
  2. Ventilation is...
    Ventilation is an autonomous process. In other words, you don't have to think about it, it just happens
  3. Which of the following is another name for the chest?
    The diaphragm marks the bottom of the thorax and divides the torso into upper part (thorax) and bottom part (abdomen)
  4. Oxygen passes across the alveolus and capillary walls into the blood by...
    There is a concentration gradient from alveolus to capillary. Oxygen is a small molecule capable of simple diffusion. Oxygen will be at a much higher concentration within the alveolus compared with the blood, so oxygen diffuses down the gradient
  5. The large surface area of the lungs is due to lots of...
    If you took all of the alveoli from an undamaged pair of human lungs it is said that they would cover the area of a tennis court
  6. During inspiration, the chest cavity (volume)...
    The external intercostal muscles contract and pull the rib cage up and out when we breathe in. The internal and innermost intercostal muscles are involved in expiration (breathing out)
  7. When the chest volume increases, what happens to the pressure?
    Volume and pressure are inversely related. This means as one goes up, the other goes down. If volume increases then pressure decreases. During inspiration, chest volume increases, so pressure decreases which creates a pressure gradient. Air flows from a higher pressure to a lower pressure therefore in this case, air flows into the lungs
  8. Another word for breathing in is...
    To inspire means to breathe in
  9. During expiration, the diaphragm...
    Movement of the diaphragm upwards makes the chest volume decrease, so the pressure increases and air leaves the lungs
  10. The function of the rib cage is to protect the...
    Bones are found in mammals for protection, support of the body and to allow it to move

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