Human Lungs (Respiratory System)

Components of the human respiratory system and their functions. The diaphragm and other muscles, as well as certain bones of the axial skeleton, have secondary roles in respiration.
Oral Cavity (Mouth)Supplemental airway when breathing is labored
EpiglottisCloses off larynx during swallowing
Pleural MembraneDouble-layer membrane that separates lungs from other organs; the narrow, fluid-filled space between its two layers has roles in breathing
Lung (One of a Pair)Lobed, elastic organ of breathing; site ofgas exchange between internal environment and outside air
Intercostal MusclesAt rib cage, skeletal muscles with roles in breathing. There are two sets of intercostal muscles (external and internal)
DiaphragmMuscle sheet between the chest cavity and abdominal cavity with roles in breathing
Nasal CavityChamber in which air is moistened, warmed, and filtered, and in which sounds resonate
Pharynx (Throat)Airway connecting nasal cavity and mouth with larynx; enhances sounds; also connects with esophagus
Larynx (Voice Box)Airway where sound is produced; closed off during swallowing
Trachea (Windpipe)Airway connecting larynx with two bronchi that lead into the lungs
Bronchial Tree: Increasingly branched airways starting with two bronchi and ending at air sacs (alveoli) of lung tissue

(B,C) Location of alveoli relative to the bronchioles and the lung (pulmonary) capillaries.