The respiratory system allows you to breathe—bringing oxygen in (inhalation) and bringing carbon dioxide out (exhalation). Its seven functions are to (1) move air, (2) produce sounds, (3) gas exchange, (4) pulmonary defense, (5) acid-base balance, (6) olfactory, and (7) regulate blood volume and blood pressure.

The trachea (windpipe) is the large tube that delivers air to the bronchi from the upper respiratory tract. It warms and moisturizes the air and catches debris and microbes before they enter the lungs. Lining the trachea are mucosal membranes comprised of epithelial cells, mucus-secreting goblet cells, and cilia. It is also traversed by a network of blood vessels and lymphatic vessels.

From the nasal cavity to the bronchi, the majority of the respiratory tract is lined by pseudostratified columnar ciliated epithelium. The bronchioles are lined by simple columnar to the cuboidal epithelium, and the alveoli possess a lining of thin squamous epithelium that allows for gas exchange. The bronchioles carry air to small sacs in your lungs called alveoli.

The epiglottis is a cartilage flap in the shape of a leaf located below the tongue and at the top of the larynx. The epiglottis’ primary role is to temporarily close the windpipe while eating to prevent food entering the trachea. Additionally, the epiglottis aids in specific areas of sound creation in particular languages.