breathes

Breathes is the third-person singular present tense form of the verb breathe, meaning to take air into the lungs and to expel it. In common usage, to breathe refers to the act of inhalation and exhalation that supplies the body with oxygen and removes carbon dioxide, a process fundamental to cellular respiration.

Physiology: In mammals, breathing involves the coordinated action of the lungs, airways, and respiratory muscles. During inhalation, the diaphragm contracts and moves downward, the rib cage expands, and air flows into the lungs; during exhalation, these muscles relax, and air is expelled. Gas exchange occurs in the alveoli, where oxygen diffuses into the blood and carbon dioxide diffuses out to be exhaled.

Control: Breathing is regulated mainly by the brainstem, including the medulla oblongata and pons. Chemoreceptors monitor levels of carbon dioxide and pH in the blood and adjust rate and depth of breathing. The process is primarily automatic but can be influenced voluntarily by higher brain centers, such as the cerebral cortex, during speaking or breath-holding. Breathing rate and depth adapt to activity, health, altitude, and metabolic demand.

Clinical and biological variation: Normal breathing varies by age and fitness. Abnormalities include apnea (temporary cessation), dyspnea (shortness of breath), and hyperventilation. Persistent dysfunction can indicate respiratory or cardiac disease, such as asthma, chronic obstructive pulmonary disease, or infections. Across animals, breathing mechanisms vary, with humans relying on diaphragmatic breathing; birds use air sacs for efficient gas exchange; other animals have different adaptations such as cutaneous or gill respiration.