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A-Level Biology OCR A

Pressure Normal Thorax Muscles Lungs Describe Process Expiration

Front Describe the process of normal expiration linking the action of muscles to the movement of strucrtures, change in pressure within the lungs and direction of airflow.
Back Normal expiration:
  • Diaphragm relaxes and domes upwards
  • External intercostal muscles relax, ribs move down and inwards
  • Alveolar elastic fibres recoil to normal length
  • Volume of thorax decreases so pressure in thorax increased
  • Higher pressure in thorax than atmospheric pressure - air moves thru bronchioles, bronchi, trachea, nasal passages out of the lungs until atmohperic and thoracic pressure equalise

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