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The respiratory system is defined as the set of organs and structures used for gas exchange in animals and plants.
The respiratory system (also called the respiratory apparatus or ventilatory system) is a biological system made up of specific organs and structures that enable gas exchange in animals and plants. In land animals, the respiratory surface is internalized within the lungs, where air reaches microscopic air sacs (alveoli in mammals and reptiles; atria in birds) that have rich blood supplies so that air and blood can exchange gases efficiently. Its purpose is to move air between the external environment and these gas-exchange surfaces. In mammals and many other animals, breathing pumps air through airways (such as the trachea, bronchi, and bronchioles) into the alveoli, where gas exchange occurs. In aquatic animals, the respiratory system may instead rely on gills, where water flows over thin, highly vascularized structures to allow gas exchange. Overall, the system’s main function is to supply oxygen to the body and remove carbon dioxide, while also supporting additional roles such as defense mechanisms, preventing alveolar collapse via surfactant, and contributing to whole-body functions like hormone activation and blood pressure regulation.
The respiratory system is defined as the set of organs and structures used for gas exchange in animals and plants.
In land animals, gas exchange occurs in internal air sacs (alveoli in mammals/reptiles; atria in birds) with close contact between air and blood.
Breathing moves air through airways to reach the gas-exchange surfaces; aquatic animals often use gills instead.
Beyond gas exchange, the lungs help with local defenses, maintain alveolar stability via surfactant, and contribute to whole-body regulation (e.g., hormone processing and blood pressure effects).
A biological system of organs and structures that enables gas exchange between the environment and the body’s blood.
Microscopic air sacs in mammals where air and blood exchange gases.
Microscopic air sacs in birds where air and blood exchange gases.
The main airway that carries air from the upper respiratory tract into the lungs and branches into bronchi.
Small airways that open into alveoli in mammals and reptiles (and into parabronchi in birds).
Respiratory organs in many aquatic animals that exchange gases using water flowing over thin, vascularized tissues.
A lung surface-active substance that reduces alveolar surface tension and helps prevent alveolar collapse.
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