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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—most notably in the lungs—where air reaches microscopic air sacs (alveoli in mammals and reptiles, and atria in birds) that have rich blood supplies, allowing gases to come into close contact with blood. Overall, the system functions by moving air between the external environment and these gas-exchange surfaces. Air travels through airways (such as the trachea, bronchi, and bronchioles) to reach the alveoli/atria, and breathing—driven by respiratory muscles—pumps air in and out. In aquatic animals, the respiratory system often uses gills, where water flows over thin, highly vascularized structures to support gas exchange; in amphibians, skin can also play a major role. Beyond gas exchange, the lungs contribute to defenses (e.g., cough/sneezing and immune-related secretions), help prevent alveolar collapse via surfactant, and support whole-body functions such as activating hormones and regulating certain substances in circulation.
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/atria) where air is brought into close contact with blood through a branching airway network.
Breathing moves air to and from the gas-exchange surfaces using respiratory muscles, while aquatic animals often rely on gills and some amphibians rely on skin for gas exchange.
The lungs also provide additional roles including local defense, preventing alveolar collapse through surfactant, and contributing to whole-body physiological regulation.
A biological system of organs and structures that performs gas exchange by moving gases between the environment and the body.
Microscopic air sacs in mammals where gas exchange occurs with blood in nearby capillaries.
Microscopic air sacs in birds that function similarly to alveoli for gas exchange.
The main airway that carries air from the upper respiratory tract into the lungs, where it branches into bronchi.
Small airways (without cartilaginous support in mammals and reptiles) that lead toward the microscopic gas-exchange sacs.
The muscular process that pumps air into and out of the lungs to deliver fresh air to gas-exchange surfaces.
Respiratory structures in many aquatic animals where water flows over thin, highly vascularized tissue to enable gas exchange.
A surface-active substance produced by type II alveolar cells that reduces surface tension and helps prevent alveolar collapse.
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