Biology » The Respiratory System » Systems of Gas Exchange

Summarizing Systems of Gas Exchange


Animal respiratory systems are designed to facilitate gas exchange. In mammals, air is warmed and humidified in the nasal cavity. Air then travels down the pharynx, through the trachea, and into the lungs. In the lungs, air passes through the branching bronchi, reaching the respiratory bronchioles, which house the first site of gas exchange. The respiratory bronchioles open into the alveolar ducts, alveolar sacs, and alveoli. Because there are so many alveoli and alveolar sacs in the lung, the surface area for gas exchange is very large. Several protective mechanisms are in place to prevent damage or infection. These include the hair and mucus in the nasal cavity that trap dust, dirt, and other particulate matter before they can enter the system. In the lungs, particles are trapped in a mucus layer and transported via cilia up to the esophageal opening at the top of the trachea to be swallowed.


alveolar duct

duct that extends from the terminal bronchiole to the alveolar sac

alveolar sac

structure consisting of two or more alveoli that share a common opening


(plural: alveoli) (also, air sac) terminal region of the lung where gas exchange occurs


(plural: bronchi) smaller branch of cartilaginous tissue that stems off of the trachea; air is funneled through the bronchi to the region where gas exchange occurs in alveoli


airway that extends from the main tertiary bronchi to the alveolar sac


domed-shaped skeletal muscle located under lungs that separates the thoracic cavity from the abdominal cavity


voice box, a short passageway connecting the pharynx and the trachea


complex glycoprotein found in mucus


sticky protein-containing fluid secretion in the lung that traps particulate matter to be expelled from the body

nasal cavity

opening of the respiratory system to the outside environment

particulate matter

small particle such as dust, dirt, viral particles, and bacteria that are in the air


throat; a tube that starts in the internal nares and runs partway down the neck, where it opens into the esophagus and the larynx

primary bronchus

(also, main bronchus) region of the airway within the lung that attaches to the trachea and bifurcates to each lung where it branches into secondary bronchi

respiratory bronchiole

terminal portion of the bronchiole tree that is attached to the terminal bronchioles and alveoli ducts, alveolar sacs, and alveoli

terminal bronchiole

region of bronchiole that attaches to the respiratory bronchioles


cartilaginous tube that transports air from the larynx to the primary bronchi

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