The nasal cavity, also called cavitas nasi, is paired and part of the respiratory tract. It thus plays an important role in respiration and also houses the olfactory mucosa, which is relevant to the olfactory process.
What is the nasal cavity?
The nose is formed by a bony framework supplemented by cartilaginous plates. The visible parts of the nose include the nostrils, the nasal septum and also the nostrils. However, the inner part of the nose is much larger than the outer visible part. It is formed by the nasal cavity (cavitas nasi). The nasal cavity is bounded at the bottom by the hard palate (palatum durum), which in turn is formed by the maxillary bone and the palatine bone. Upward and backward, the boundary is formed by the ethmoid bone (Os ethmoidale) of the skull base. Laterally, the nasal cavity is closed by the three turbinates, the so-called conchae, which project into the nasal cavity. The turbinates increase the mucosal surface area of the nose. The choanas, paired openings of the nasal cavity, form the transition from the nasal cavity to the pharyngeal cavity. The paranasal sinuses open into the side passages of the nasal cavity. The nasal cavity thus forms an almost triangular, pyramid-shaped cavity. This is divided in the middle into right and left halves by the partly cartilaginous, partly bony nasal septum.
Anatomy and structure
In the nasal cavity, the nasal vestibule, also called the vestibule nasi, located within the external nose, can be distinguished from the deeper nasal cavity (cavum nasi proprium). The nasal vestibule corresponds approximately to the extent of the nostrils and is lined with multilayered keratinized squamous epithelium. In addition, the skin of the nasal vestibule contains the nasal hairs and small sebaceous and sweat glands. At the so-called limen nasi, an arcuate groin, is the transition from the nasal vestibule to the nasal cavity. Here the lining of the nasal cavity also changes and there is a transition from the multilayered keratinized squamous epithelium to the respiratory epithelium. The respiratory epithelium is also referred to here as the nasal mucosa. It is a skin with many small cilia that can transport foreign particles from the respiratory air toward the nasopharynx. Goblet cells provide mucus production and numerous glands moisturize the mucosa. This mucosal area is interrupted by a small district lined with olfactory mucosa (pars olfactoria). The olfactory mucosa is found mainly in the upper turbinate and measures about 1.3cm² per side in adults. The nasal mucosa is nourished by the ophtalmic nerve and the maxillary nerve. Accordingly, blood supply is through the ophtalmic artery and branches of the maxillary artery.
Function and tasks
The nasal cavity has three main functions. First, it serves to warm, clean, and moisten the air we breathe. The mucosa of the nasal cavity is primarily responsible for this function. As already mentioned, there are cilia on the surface of the mucous membrane. These hairs move rhythmically in the direction of the nasopharynx, transporting small foreign particles such as dust particles. Goblet cells are located between the ciliated epithelium. These produce the mucus to which the foreign particles adhere. The ciliated epithelium and goblet cells also work together to humidify the air we breathe. The water vapor saturation in the nasal cavity is over 90%. In addition, a plexus of veins in the mucosa of the nasal cavity ensures that the air breathed is heated. Depending on the temperature of the air breathed, the small vessels are either dilated or constricted. The colder it is, the greater the blood flow to the venous plexus and the more the respiratory air is warmed. The nasal cavity also performs an important function in the olfactory process because it houses the olfactory organ. The olfactory cells embedded in the olfactory mucosa are the cell bodies of the olfactory nerve (nervus olfactorius). This ascends in many fine fibers through the ethmoid plate into the cranial fossa and passes on its information to the olfactory brain. In addition to these two tasks, the nasal cavity also fulfills a function as a resonating chamber for the voice.
Diseases
Due to the plexus of veins in the nasal mucosa and a distinct network of small capillaries at the transition from the nasal vestibule to the nasal cavity, the nasal mucosa is extremely well supplied with blood.Due to the small structures, the vessels are very fine and therefore also sensitive, so that even the smallest injury can cause a nosebleed (epistaxis). Nosebleeds can quickly be caused by breathing air that is too dry or by picking the nose. However, the trigger of the bleeding is not always so harmless. Especially in young children, when a nosebleed occurs, one should always also think of a foreign body in the nose. Also an increased bleeding tendency caused by malignant diseases of the blood can cause nosebleeds. It is not uncommon for nosebleeds to be one of the first symptoms of leukemia. However, the most common disease of the nasal cavity is simple rhinitis. Acute rhinitis is usually caused by viruses such as rhino- or adenoviruses. As a result of the infection, there is increased production of nasal secretions, and the patient complains of a “runny nose.” The mucous membranes swell, making it difficult to breathe through the nose. In addition, the nasal mucosa is reddened and possibly sore. If nasal breathing is permanently impeded and nasal secretion is constantly increased, this is called chronic rhinitis. Chronic rhinitis often leads to chronic sinusitis. Inflammation of the mucous membrane of the nasal cavity can also be caused by allergies. The main symptoms here are also obstructed nasal breathing and increased secretion. In addition, however, there are often sneezing attacks and severe itching in the nose.
