Main parts of the human respiratory system include the mouth, nasal cavity, lungs, bronchial tubes, diaphragm and trachea, according to National Heart, Lung, and Blood Institute. Other facets of the respiratory system are the larynx, epiglottis, alveoli and the blood vessels that carry oxygen away from the lungs.
Air passes through the mouth, nasal cavity, larynx, trachea and bronchial tubes before reaching the lungs. The NHLBI explains the mouth and nose moisten the air before reaching further into the respiratory system. The epiglottis separates the trachea from the esophagus, and the flap of skin prevents food and drink from entering the lungs. The trachea, or windpipe, splits into two bronchial tubes that each go into a lung. Healthline explains the upper respiratory tract is located outside the chest cavity, and the lower respiratory tract are parts of the system lower than the larynx.
The diaphragm is a powerful muscle below the lungs that expands and collapses the organs when humans inhale and exhale. The NHLBI reveals the diaphragm is the main muscle used for breathing. Other breathing muscles line the ribs and collarbone. The respiratory system works by exchanging oxygen and carbon dioxide at the cellular level inside tiny alveoli. The aveloli are round air sacs at the end of tiny air tubes called bronchioles. Bronchioles are small airways that branch off from the bronchial tubes that go into each lung, according to the NHLBI.