Function of the Respiratory System (OCR GCSE Physical Education (PE)): Revision Note

Inhaling & exhaling

• Our bodies need oxygen in order to function and breathing is the term given to the process of taking air into and out of the lungs

• This process of breathing in and out is known as ventilation

  • Breathing in = inhalation or inspiration

  • Breathing out = exhalation or expiration

• Changes in air pressure cause inhalation and exhalation

• The rate of inhalation and exhalation can also be controlled by two key muscles:

  • The intercostal muscles

    • These muscles are attached to the inside and outside of the rib cage

  • The diaphragm

    • muscle beneath the rib cage

    • the relaxed diaphragm forms a dome which flattens when the muscle contracts

The process of inhalation (breathing in)

• The following events enable inhalation:

  • The diaphragm contracts and moves downwards

  • Intercostal muscles contract to pull the rib cage up and out

  • This increases the volume inside the chest cavity leading to a decrease in air pressure

  • A pressure gradient is created, pulling air into the lungs through the mouth or nose

The process of exhalation (breathing out)

• The following events enable exhalation

  • The diaphragm relaxes and moves upwards back into a dome shape

  • Intercostal muscles relax allowing the rib cage to drop down and in

  • This decreases the volume inside the the chest cavity leading to a increase in air pressure

  • The volume of the chest cavity decreases, leading to an increase in air pressure inside the lungs relative to the external environment

  • A pressure gradient is created and air is pushed out through the mouth or nose

Exercise and breathing

• During exercise the demand for oxygen increases therefore the ventilation process has to happen more rapidly

  • During inhalation

    • The lungs can expand more with the action of pectoral and sternocleidomastoid muscles allowing more air to be drawn into the lungs

  • During exhalation

    • The rib cage is pulled down to force air out more rapidly by the contraction of abdominal muscles