Breathing

Breathing is the cyclical movement of air into and out of the lungs. It supplies oxygen for gas exchange and removes carbon dioxide.

Diaphragm: A dome-shaped skeletal muscle that separates the chest cavity from the abdomen and drives quiet inhalation. Its contraction enlarges the chest cavity and draws air into the lungs.
Respiratory system: The organs and structures that bring air into the body and exchange gases with the blood. Breathing is its ventilation step, distinct from gas exchange in the lungs.
Spirometry: A test that measures the volume and flow of air a person can inhale and exhale. It quantifies airflow and lung volumes during breathing maneuvers.
Cellular respiration: The biochemical process by which cells use nutrients to produce ATP, often consuming oxygen and releasing carbon dioxide. It uses oxygen delivered by breathing but is not the movement of air.
Intercostal muscles: Muscles between the ribs that move the chest wall during breathing. They assist chest expansion and help force air out during active exhalation.
Lungs: A pair of elastic organs containing branching airways and gas-exchanging alveoli. Their expansion and recoil make the cyclical movement of air possible.
Tidal volume: The volume of air inhaled or exhaled during a normal breath. It measures the size of an ordinary breathing cycle.
External respiration: The exchange of oxygen and carbon dioxide between alveolar air and pulmonary blood. It follows ventilation in the lungs and occurs by diffusion rather than bulk airflow.
Intrapleural pressure: The pressure within the fluid-filled space between the lung and chest wall. Its normally subatmospheric level helps keep the lungs expanded as the chest moves.
Alveolus: A tiny air sac in the lungs where gases diffuse between air and blood. Air delivered by breathing reaches these sacs for oxygen uptake and carbon dioxide release.

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