The nasal cavity is comprised of 2 air-filled spaces on either side of the nasal septum. Three conchae, or turbinates, divide each side of the cavity. The turbinates are rich in glands and have a large blood supply. The choanae are located at the posterior segment of the nasal cavity and open into the nasopharynx. The nasal cavity assists in respiration, olfaction, conditioning of inspired air, and immune defense. The large, humidified surface area of the nasal cavity makes it an ideal location to adjust the quality of inhaled air prior to oxygen exchange in the lungs. Nasal mucus protects the epithelium from external particles, particularly in times of inflammation. The unique sensory capability to smell is due to specialized nerve endings within the olfactory nerve. The nasal cycle leads to a spontaneous alternation of congestion and decongestion between the left and right sides of the cavity.
This article will discuss:
Epithelial Cells (Cilia)
Epithelial cells provide a physical barrier that prevents invasion of underlying tissue. Stratified squamous epithelium within the cavity gives way to pseudostratified columnar respiratory epithelium further along in the respiratory tract. Cilia at the apex of epithelial cells act to propel mucus, allergens, and foreign particles from the nasal cavity towards the pharynx where they are removed by swallowing. Epithelial cells are also involved in the inflammatory response by releasing cytokines.
Endothelial Cells (Underlying Blood Vessels)
The rich blood supply to the nasal mucosa is formed by endothelial cells. This thin layer of cells allows rapid warming of air entering the respiratory passage. Smooth muscle surrounding this endothelial layer allows constriction and dilation of blood vessels, functioning to regulate congestion of the nasal passage during an inflammatory response.
Mucus produced in the lamina propria is released via glands onto the epithelial surface. The mucus functions to trap external particles while also preserving the epithelial barrier. An increase in parasympathetic stimulation leads to an increase in mucus production and release. Lysozymes and IgA are found within the mucus and protect from invading microbes.
Receptor neurons in the roof of the nasal cavity recognize and bind odor molecules. These stimuli lead to depolarization of the neurons and ultimately signal propagation along the olfactory nerves toward the central nervous system (CNS).
The nasal structures are derived primarily from the ectoderm and neural crest. The ectoderm provides a pattern for developing structures and interacts with facial mesenchymal layers derived from neural crest cells. Paired thickenings of ectoderm lead to the development of nasal placodes which later develop into the nose and nasal cavities. Midbrain neural crest cells migrate to form the lateral nasal process, whereas the forebrain neural crest cells develop into the medial nasal processes.
During the fifth gestational week, the proliferation of the ectodermal placodes and the surrounding mesenchyme create a pair of depressions called the nasal pits. These pits continue to expand until fusing with the oral cavity, ultimately leading to the formation of the primordial choanae and the creation of a junction between the nasal cavity and the oropharynx.
The inferior surface of the nasal cavity is formed by the junction of the maxillary processes and medial nasal processes as the maxillary processes grow medially. The nasal septum grows inferiorly until it meets the newly formed palatal shelves.
The preturbinates form at the eighth week of gestation as 3 soft tissue elevations that are eventually replaced by a cartilaginous capsule. The superior, middle, and inferior turbinates are usually well formed by 16 weeks gestation. The superior and middle turbinates are ossified by outgrowths from the ethmoid bone and the inferior turbinate by the maxilla.
Dysfunctions in development can lead to a deviated nasal septum, inferior turbinate hypertrophy, a paradoxical middle turbinate, concha bullosa, and choanal atresia, among others.
The nasal cavity is part of the respiratory system and the first location that inspired air enters. Olfactory neurons send signals to the CNS.
The 3 primary functions of the nose are to aid in respiration, to filter and defend against external particles and allergens, and to enable olfaction. The nasal cycle is a physiologic alternation of resistance between the two nasal airways, created by changes in congestion and decongestion and has been suggested to aid in respiratory defense.
As air is inhaled, the nasal cavity assists in respiration by preparing air for oxygen exchange. Due to the narrow nature of the cavity, inhaled air is rapidly introduced to a large mucosal surface area with a rich supply of blood at body temperature. This facilitates rapid acclimation of inhaled air to a temperature better suited for the lungs. Humidification functions to protect the fragile respiratory and olfactory epithelia.
The nasal cavity also aids in the defense of respiratory tissues. Mucus secretions trap particles and antigens carried into the respiratory system during inhalation. As pathogens are trapped in these secretions, they are bound by secretory IgA dimers (a component of the adaptive immune response), which prevents attachment of pathogens to host epithelium, thus hindering invasion. Mucus can also contain IgE, which is involved in the allergic response and can cause a pathologic type 1 hypersensitivity reaction. Cilia within the nasal cavity also function to propel mucus away from the lungs in an attempt to expel trapped pathogens from the body. The bacterial normal flora in the nasal mucosa also protects from invasion by competing with invading bacteria for space and nutrients.
In addition, the nasal cavity enables olfaction. Olfaction helps to identify sources of nearby danger or nutrition, as well as influencing mood and sexuality. As air enters the nasal cavity, the turbinates function to direct a portion of the airflow to the higher regions of the cavity. The olfactory cleft is located at the roof of the nasal cavity in near proximity to the cribriform plate. Olfactory receptors located here bind to odorants carried into the nose during inhalation and send signals to the olfactory cortex and other brain regions.
Nasal endoscopy utilizes fiber optic cables and a light source to visualize the nasal and sinus cavities that otherwise would be impossible to see. Visualization is minimally invasive and the preferred method for evaluating a wide variety of medical problems affecting the nose and sinuses. Many common surgical procedures within the nasal cavity are completed under visualization by a nasal endoscope.
Rhinomanometry is used to evaluate the respiratory function of the nose by measuring pressure and flow during normal respiration. Obstruction will lead to higher than expected pressures and decreased flow. Two primary methods are used: anterior or posterior. Anterior rhinomanometry takes unilateral measurements of one nostril at a time, whereas posterior rhinomanometry evaluates both simultaneously. Anterior rhinomanometry is more commonly used, and primarily evaluates on which side of the septum the obstruction arises.
Acoustic rhinometry is primarily used to measure the cross-sectional area and length of the nose and nasal cavity. It uses sound waves and measures reflection in the nasal cavity. Evaluation of nasal cavity geometry and abnormalities can be performed. 
CT is the modality of choice for evaluating congenital, inflammatory, benign, and malignant pathologies in the sinonasal region. CT and MRI have the advantage of showing anatomic structures that could otherwise not be visualized, and they show fine anatomic detail.
The saccharin test is primarily used to measure the nasal mucociliary clearance time. A small drop of saccharin is placed below the inferior turbinate where it can be swept back toward the nasopharynx. A sweet taste should be perceived as the cilia sweep the saccharin posteriorly. Delayed taste recognition indicates poor ciliary performance.
Many smell identification tests are available, but the University of Pennsylvania Smell Identification Test (UPSIT) is the gold standard due to its reliability. The test consists of 40 questions, each with a different odor released upon scratching. The patient is asked to identify the odor released. This test can assist in the diagnosis of many conditions, such as Alzheimer disease, Parkinson disease, Huntington disease, and others. 
Allergic rhinitis is an IgE-mediated reaction that leads to irritation, pruritus, sneezing, and congestion. As allergens are introduced to the host, the immune system is sensitized. Repeat exposure causes cross-linking of IgE bound to mast cells which release histamine, bradykinin, and leukotrienes, ultimately resulting in increased mucus secretion and blood vessel dilation within the nasal cavity. These same chemical mediators also activate sensory receptors and lead to activation of CNS reflexes such as sneezing and nasal irritation. Nasal symptoms can last for a period of several hours and the airway can become more reactive to the initial insult and even nonallergenic stimuli including strong odors and environmental irritants.
Nasal polyps are localized expansions of edematous mucosa within the nasal cavity which can reach 3 to 4 centimeters in length. Chronic inflammation of the nasal mucosa can ultimately lead to the formation of nasal polyps. Inflammation leads to disruptions in the tight junctions between epithelial cells within the nasal cavity and a decrease in the effectiveness of cilia to clear mucus and antigens within the cavity, which may contribute to the formation of nasal polyps. The actual pathogenesis of nasal polyps has not been determined and is likely multifaceted.
Epistaxis, or nosebleed, occurs when a vessel within the nasal cavity is ruptured. The nasal mucosa is home to a rich blood supply, and rupture can occur spontaneously or due to trauma. Epistaxis in the pediatric population is most often due to digital trauma. Epistaxis rates increase in frequency during the winter months due to the decrease in humidity and temperature which causes a decrease in nasal humidification, making the cavity more susceptible to bleeding.
Nasopharyngeal carcinoma arises from the squamous epithelium within the nasal cavity. Epstein-Barr virus, ethnicity (particularly Southeast Asians), and environmental exposures have all been shown to play a role in the development of nasopharyngeal carcinoma.
Diseases of the nasal cavity can be due to a wide variety of etiologies. Viral, bacterial, and fungal pathogens can cause an infection within the nasal cavity or the surrounding sinuses. Particular consideration should be given to those infections that can spread from the nasal cavity to surrounding or connected structures. Because the Eustachian tube enters into the nasal cavity, an infection can spread through the tube to the middle ear. For patients with persistent otitis media, often children, tympanostomy tubes should be considered. Diabetics with poorly controlled glucose levels are also at risk for the serious but rare infection mucormycosis. If untreated, this infection can quickly spread from the nasal cavity to the CNS. Many viral and bacterial causes of pneumonia are spread through nasal inhalation and initially infect the nasopharynx.
Anatomic abnormalities can also cause complications requiring evaluation. Concerning symptoms include repeated sinus infections, sleep apnea, difficulty breathing, and loss of olfaction, among others.
Nasal cavity tumors are more often malignant than benign, and development of any mass within the nasal cavity warrants further evaluation.
|||Masuda N,Mantani Y,Yoshitomi C,Yuasa H,Nishida M,Arai M,Kawano J,Yokoyama T,Hoshi N,Kitagawa H, Immunohistochemical study on the secretory host defense system with lysozyme and secretory phospholipase A2 throughout rat respiratory tract. The Journal of veterinary medical science. 2018 Mar 2 [PubMed PMID: 29225322]|
|||Neskey D,Eloy JA,Casiano RR, Nasal, septal, and turbinate anatomy and embryology. Otolaryngologic clinics of North America. 2009 Apr [PubMed PMID: 19328886]|
|||Som PM,Naidich TP, Illustrated review of the embryology and development of the facial region, part 1: Early face and lateral nasal cavities. AJNR. American journal of neuroradiology. 2013 Dec [PubMed PMID: 23493891]|
|||Hasegawa M,Kern EB, The human nasal cycle. Mayo Clinic proceedings. 1977 Jan [PubMed PMID: 609283]|
|||Eccles R, A role for the nasal cycle in respiratory defence. The European respiratory journal. 1996 Feb [PubMed PMID: 8777979]|
|||Rouadi P,Baroody FM,Abbott D,Naureckas E,Solway J,Naclerio RM, A technique to measure the ability of the human nose to warm and humidify air. Journal of applied physiology (Bethesda, Md. : 1985). 1999 Jul [PubMed PMID: 10409601]|
|||Mercke U,Hakansson CH,Toremalm NG, The influence of temperature on mucociliary activity. Temperature range 20 degrees C-40 degrees C. Acta oto-laryngologica. 1974 Nov-Dec [PubMed PMID: 4451095]|
|||Olivé Pérez A,Cisteró Bahima A, [IgE values in nasal mucus in the diagnosis of perennial allergic rhinitis]. Allergologia et immunopathologia. 1981 Mar-Apr [PubMed PMID: 7293876]|
|||Munkholm M,Mortensen J, Mucociliary clearance: pathophysiological aspects. Clinical physiology and functional imaging. 2014 May [PubMed PMID: 24119105]|
|||Shinefield HR,Wilsey JD,Ribble JC,Boris M,Eichenwald HF,Dittmar CI, Interactions of staphylococcal colonization. Influence of normal nasal flora and antimicrobials on inoculated Staphylococcus aureus strain 502A. American journal of diseases of children (1960). 1966 Jan [PubMed PMID: 5900331]|
|||Patel RM,Pinto JM, Olfaction: anatomy, physiology, and disease. Clinical anatomy (New York, N.Y.). 2014 Jan [PubMed PMID: 24272785]|
|||Pinto JM, Olfaction. Proceedings of the American Thoracic Society. 2011 Mar [PubMed PMID: 21364221]|
|||K Maru Y,Gupta Y, Nasal Endoscopy Versus Other Diagnostic Tools in Sinonasal Diseases. Indian journal of otolaryngology and head and neck surgery : official publication of the Association of Otolaryngologists of India. 2016 Jun [PubMed PMID: 27340637]|
|||Tajudeen BA,Kennedy DW, Thirty years of endoscopic sinus surgery: What have we learned? World journal of otorhinolaryngology - head and neck surgery. 2017 Jun [PubMed PMID: 29204590]|
|||Roithmann R,Cole P,Chapnik J,Shpirer I,Hoffstein V,Zamel N, Acoustic rhinometry in the evaluation of nasal obstruction. The Laryngoscope. 1995 Mar [PubMed PMID: 7877416]|
|||Kandukuri R,Phatak S, Evaluation of Sinonasal Diseases by Computed Tomography. Journal of clinical and diagnostic research : JCDR. 2016 Nov [PubMed PMID: 28050473]|
|||Fatterpekar GM,Delman BN,Som PM, Imaging the paranasal sinuses: where we are and where we are going. Anatomical record (Hoboken, N.J. : 2007). 2008 Nov [PubMed PMID: 18951498]|
|||Plaza Valía P,Carrión Valero F,Marín Pardo J,Bautista Rentero D,González Monte C, [Saccharin test for the study of mucociliary clearance: reference values for a Spanish population]. Archivos de bronconeumologia. 2008 Oct [PubMed PMID: 19006634]|
|||Doty RL,Shaman P,Kimmelman CP,Dann MS, University of Pennsylvania Smell Identification Test: a rapid quantitative olfactory function test for the clinic. The Laryngoscope. 1984 Feb [PubMed PMID: 6694486]|
|||Wheatley LM,Togias A, Clinical practice. Allergic rhinitis. The New England journal of medicine. 2015 Jan 29 [PubMed PMID: 25629743]|
|||Widdicombe JG, Nasal pathophysiology. Respiratory medicine. 1990 Nov [PubMed PMID: 2287793]|
|||Wachs M,Proud D,Lichtenstein LM,Kagey-Sobotka A,Norman PS,Naclerio RM, Observations on the pathogenesis of nasal priming. The Journal of allergy and clinical immunology. 1989 Oct [PubMed PMID: 2477429]|
|||Soyka MB,Wawrzyniak P,Eiwegger T,Holzmann D,Treis A,Wanke K,Kast JI,Akdis CA, Defective epithelial barrier in chronic rhinosinusitis: the regulation of tight junctions by IFN-γ and IL-4. The Journal of allergy and clinical immunology. 2012 Nov [PubMed PMID: 22840853]|
|||Gudis D,Zhao KQ,Cohen NA, Acquired cilia dysfunction in chronic rhinosinusitis. American journal of rhinology [PubMed PMID: 22391065]|
|||Hulse KE,Stevens WW,Tan BK,Schleimer RP, Pathogenesis of nasal polyposis. Clinical and experimental allergy : journal of the British Society for Allergy and Clinical Immunology. 2015 Feb [PubMed PMID: 25482020]|
|||Guarisco JL,Graham HD 3rd, Epistaxis in children: causes, diagnosis, and treatment. Ear, nose, [PubMed PMID: 2676467]|
|||Fatakia A,Winters R,Amedee RG, Epistaxis: a common problem. The Ochsner journal. 2010 Fall [PubMed PMID: 21603374]|
|||Brennan B, Nasopharyngeal carcinoma. Orphanet journal of rare diseases. 2006 Jun 26 [PubMed PMID: 16800883]|
|||Turner JH,Reh DD, Incidence and survival in patients with sinonasal cancer: a historical analysis of population-based data. Head [PubMed PMID: 22127982]|