Table of Contents
Definition of Breathing
Breathing is the process of drawing air into and expelling air from the LUNGS, also called pulmonary respiration.
Breathing occurs through the mechanical actions of MUSCLEmovement. The DIAPHRAGM (the large, flat muscle that extends across the floor of the thoracic cavity) and the intercostal muscles (the muscles between the ribs) contract to expand the thoracic cavity, pulling air into the lungs (inhalation).
Inhalation is an active process.
Simultaneously the EPIGLOTTIS, a cartilaginous flap at the top of the throat normally closed across the top of the TRACHEA to prevent food and other materials from entering the lungs, opens to allow the air to pass. The air flows through the trachea into the bronchi, bronchioles, and alveoli. When the diaphragm and the intercostal muscles relax the thoracic cavity returns to its resting position, pressuring air out of the lungs (exhalation) in reverse sequence. Exhalation is a passive process.
Breathing patterns help the doctor assess pulmonary function and respiratory effectiveness. Breathing may be varying combinations of rapid (TACHYPNEA) or slow (bradypnea), regular or irregular, deep or shallow. Though an individual may influence breathing through conscious focus, breathing is an involuntary process under control of the brainstem. The concentration of carbon dioxide in the BLOOD is the primary trigger for initiation of a RESPIRATORY CYCLE (one inhalation and one exhalation), triggering the brainstem to signal the diaphragm and the intercostal muscles to contract.