Ventilation: Inspiration and Expiration

INSPIRATION/INHALATION (Breathing in)

•  Intercostal muscles and diaphragm contract
• Ribcage moves upwards and outwards and diaphragm flattens
• Volume of thorax increases, lung pressure decreases
• Causes air to flow into the lungs

Inspiration is an active process which requires energy

EXPIRATION/EXHALATION (Breathing out)

•  Intercostal muscles and diaphragm relax
• The ribcage moves downwards and inwards and the diaphragm contracts
• Thorax volume decreases, air pressure increases
• Air is forced out of the lungs

Expiration is a passive process - it does not require energy