Respiratory system

The organs and structures that exchange oxygen and carbon dioxide between an organism and its environment. In humans, it also helps regulate blood pH and produce speech.

Ventilation: The movement of air into and out of the lungs or water across respiratory surfaces. It renews the air in the lungs so oxygen can enter and carbon dioxide can leave.
Respiratory epithelium: The specialized lining of much of the airway, including mucus-secreting cells and ciliated cells that move trapped material. Its mucus and cilia help keep inhaled particles away from delicate lung tissue.
Spirometry: A test that measures how much and how quickly a person can breathe air in and out. It assesses airflow and lung volume in respiratory disease.
Gills: Respiratory organs that extract dissolved oxygen from water and release carbon dioxide into it. They perform the same exchange task as lungs using water rather than air.
Alveolus: A tiny air sac in the lungs where gas exchange occurs across a thin barrier with surrounding capillaries. These microscopic sacs provide the principal gas-exchange surface in human lungs.
Bronchial tree: The branching system of bronchi and bronchioles that conducts air from the trachea toward the lung’s gas-exchange regions. Its branches distribute inhaled air throughout each lung.
Asthma: A chronic inflammatory airway disease marked by variable narrowing and heightened airway responsiveness. Its airway narrowing can make breathing difficult despite structurally intact lungs.
Tracheal system: A network of air-filled tubes that delivers gases directly to tissues in insects and some other arthropods. It transports air through branching tubes rather than relying on blood to carry most oxygen.
Pulmonary circulation: The flow of blood from the heart to the lungs and back. It carries carbon-dioxide-rich blood to the lungs and returns oxygenated blood to the heart.
Pleura: The double-layered membrane surrounding each lung, with a thin fluid-filled space between its layers. Pleural coupling helps the lungs follow movements of the chest wall.

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