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Ventilation

Applied Science: BTEC Level 3 National Extended Diploma, topic 4.6.2

Breathing In

When a human breathes in, air flows into the lungs and oxygen diffuses into the bloodstream. Breathing in is also called inspiration. The steps involved in this process are:

1) Muscle contraction

1) Muscle contraction

  • The external intercostal muscles (muscles that surround the ribcage) contracts.
  • The diaphragm contracts and moves downwards.
  • Energy is required to power the muscle contraction.
2) Thoracic cavity

2) Thoracic cavity

  • The external intercostal muscles move the ribcage upwards and outwards.
  • The diaphragm moves downwards.
  • The volume of the thoracic cavity increases.
3) Lung pressure decreases

3) Lung pressure decreases

  • The increasing volume in the thoracic cavity causes the pressure in the lungs to decrease.
  • A pressure gradient between outside the lungs and inside the lungs is created.
4) Air flow

4) Air flow

  • Air flows inside the lungs down the pressure gradient.
  • Air flows down the trachea and into the alveoli.

Breathing Out

When a human breathes out, air flows out of the lungs and carbon dioxide diffuses out from the bloodstream. Breathing out is also called expiration. The steps involved in this process are:

1) Muscle relaxation

1) Muscle relaxation

  • The external intercostal muscles relax.
  • The internal intercostal muscles also contract.
  • The diaphragm relaxes and moves upwards.
2) Thoracic cavity

2) Thoracic cavity

  • The internal intercostal muscles move the ribcage downwards and inwards.
  • The diaphragm moves upwards.
  • The volume of the thoracic cavity decreases.
3) Lung pressure increases

3) Lung pressure increases

  • The decreasing volume in the thoracic cavity causes the pressure in the lungs to increase.
  • A pressure gradient between outside the lungs and inside the lungs is created.
4) Air flow

4) Air flow

  • Air flows out from the lungs down the pressure gradient.
  • Air flows out of the alveoli and up the trachea.

Test yourself on Ventilation

  • Steps Involved in Breathing In

  • Which of the following statements about breathing in are true?

  • What are the steps involved in breathing in?

  • Steps Involved in Breathing Out

  • What causes air to flow out from the lungs during expiration?

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