Human breathing involves two processes - inhalation and exhalation. During inhalation, the diaphragm contracts and flattens, increasing the volume of the thoracic cavity and causing the lungs to expand. This decreases air pressure in the lungs, allowing outside air to rush in. During exhalation, the diaphragm relaxes and expands, decreasing the thoracic cavity volume, compressing the lungs, and increasing air pressure to allow the exhaling of air from the lungs.

1. HUMAN BREATHING
MECHANISM

2. BREATHING INVOLVES TWO PROCESSES
INHALATION EXHALATION
•Breathe in
•The diaphragm contracts and
flattens
Volume in the thoracic cavity
increased
•The lungs expand
•Air pressure in the lungs
decreased
•The difference in air pressure
causes air to rush into the lungs
•Breathe out
•The diaphragm expand and relax
•Volume in the thoracic cavity
decreased
•The lungs compress
•Air pressure in the lungs
increased
•Air rush out of the lungs