Anatomy of the Upper Respiratory System


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a) diagram of ear; a closeup shows the bones and membranes of the middle ear. The eardrum is a flat disk labeled tympanic membrane. Behind this is the tympanic cavity (middle ear) which contains the bones. A tube boing downward from the middle ear is labeled Eustachian tube (auditory tube). b) A diagram of a cross section of the head. Above the nose is a space in the bone labeled frontal sinus.  The space in the nose is the nasal cavity and a duct in the nose is the nasolacrimal duct. A space in the bone behind the nose is the sphenoid sinus. At the back of the nose is the opening of the Eustachian tube (auditory tube). Behind that is the pharyngeal tonsil. Below that is a tube labeled nasopharynx which becomes the pharynx which because the oropharynx (behind the mouth) which becomes the laryngopharynx, which becomes the esophagus. Vocal folds are found just beyond the laryngopharynx in the larynx a tube which becomes the trachea. The epiglottis is a flap the determines if material in the pharynx travels to the esophagus or the trachea because the mouth also leads to the pharynx. The mouth contains the tongue. Underneath the tongue is the lingual tonsil and at the back of the mouth is the palatine tonsil. At the very back of the mouth is the fauces. In front of the trachea is the thyroid gland.
(a) The ear is connected to the upper respiratory tract by the eustachian tube, which opens to the nasopharynx. (b) The structures of the upper respiratory tract.

Source: OpenStax Microbiology

OpenStax Microbiology

The respiratory system can be conceptually divided into upper and lower regions at the point of the epiglottis, the structure that seals off the lower respiratory system from the pharynx during swallowing. The upper respiratory system is in direct contact with the external environment. The nares (or nostrils) are the external openings of the nose that lead back into the nasal cavity, a large air-filled space behind the nares. These anatomical sites constitute the primary opening and first section of the respiratory tract, respectively. The nasal cavity is lined with hairs that trap large particles, like dust and pollen, and prevent their access to deeper tissues. The nasal cavity is also lined with a mucous membrane and Bowman’s glands that produce mucus to help trap particles and microorganisms for removal. The nasal cavity is connected to several other air-filled spaces. The sinuses, a set of four, paired small cavities in the skull, communicate with the nasal cavity through a series of small openings. The nasopharynx is part of the upper throat extending from the posterior nasal cavity. The nasopharynx carries air inhaled through the nose. The middle ear is connected to the nasopharynx through the eustachian tube. The middle ear is separated from the outer ear by the tympanic membrane, or ear drum. And finally, the lacrimal glands drain to the nasal cavity through the nasolacrimal ducts (tear ducts). The open connections between these sites allow microorganisms to move from the nasal cavity to the sinuses, middle ears (and back), and down into the lower respiratory tract from the nasopharynx.

The oral cavity is a secondary opening for the respiratory tract. The oral and nasal cavities connect through the fauces to the pharynx, or throat. The pharynx can be divided into three regions: the nasopharynx, the oropharynx, and the laryngopharynx. Air inhaled through the mouth does not pass through the nasopharynx; it proceeds first through the oropharynx and then through the laryngopharynx. The palatine tonsils, which consist of lymphoid tissue, are located within the oropharynx. The laryngopharynx, the last portion of the pharynx, connects to the larynx, which contains the vocal fold.


Parker, N., Schneegurt, M., Thi Tu, A.-H., Forster, B. M., & Lister, P. (n.d.). Microbiology. Houston, Texas: OpenStax. Access for free at: