The first portion of the respiratory tract comprises the external nose, and an open inner chamber called the nasal cavity inside the nose.
The nose is the only means to transport warm, moist air to the lungs.
It is the main entrance organ for inspired air; this cavity is entirely covered by mucosa that contains immunoglobulin and provides an immunological defense by filtering particles in the inspired air.
These barriers provide mechanical protection against the invasion of infectious and allergenic pathogens.
Anatomy of the nostrils
The nostrils are a complex anatomical structure, from the external opening or nostrils to the pharynx, which is the upper part of the throat, where it joins the rest of the respiratory system.
The nostrils are separated in the middle by the nasal septum, a structure or cartilage that shapes and separates the nostrils.
Each nostril is composed of a roof, floor, and walls. The nasal cavity can be divided into the vestibule, respiratory sections, and olfactory region.
The nasal vestibule is the dilated area in the nose window, anterior to the nasal cavity.
The respiratory region of the nasal cavity is referred to as the entrance area where the air travels to the respiratory system and is covered by ciliated epithelium, interspersed with mucus-secreting cells.
The respiratory section of each nostril contains four protuberances, called conchae or turbinates, that are bones covered by the nasal mucosa.
Some conduits behind these turbinates connect the nasal cavity with the paranasal sinuses.
The olfactory region is located at the top of the nasal cavity; in this area are the olfactory receptors.
There are three structures surrounding the nasal passages; a ring of paranasal sinuses surrounds the nasal cavity; these develop as carnosities of the nasal cavity and drain towards it.
The mucosa of the sinuses is connected to the nasal mucosa. The nasolacrimal ducts connect the lacrimal ducts in the eye with the nasal cavity. The nasal cavity is separated from the oral cavity (inside the mouth) by the hard palate.
In the upper part, the nasal cavity is circumscribed by several bones, such as the nasal bone, the frontal bone, the cribriform plate of the ethmoidal bone, and the body of the sphenoid bone.
In the anterior area, you can see the nasal bones, cartilage, and attached skin on the outside of the nose, with the two nostrils of constant exchange with the external environment.
In the lower one, the palatine of the maxilla and the horizontal plate of the maxilla from the solid baselined by the respiratory epithelium. In the posterior zone, the changes are located.
The superior area is the frontal bone, the nasal bone, the lamina cribosa of the ethmoid bone, and the sphenoid body.
There are a series of cranial bones in the upper lateral area which enclose the cavity, such as the sphenoid, the inferior nasal concha, the maxilla, the ethmoid bone, the palatal bone, and the lacrimal bone.
The septum in the middle of the pits, separating them symmetrically, is composed of the septal cartilage, the ethmoid bone’s perpendicular plate, and the vomer.
The nostrils receive irrigation from several arteries and can be listed as:
- Anterior and posterior ethmoidal artery (Ophthalmic).
- Sphenopalatine and more significant palatine artery (Maxillary).
- Septal branch of the superior labial artery.
The more significant palatal artery irrigates the anterior part of the septum, where the five streets meet.
On the other hand, the external nose receives irrigation from the anterior ethmoidal artery and the septal branch of the superior labial artery.
Functions of the nostrils
The structures and functions of the nostrils are interconnected; their anatomical characteristics serve to fulfill the following positions:
Respiratory function: The air that passes through these cavities is introduced into the respiratory tract and excreted from them, the nasal passages exerting a process of cleaning, hydration, and heating.
Olfactory function: The recognition of odors begins when small particles of odorous substances are captured in the peripheral processes of the olfactory nerve. Then, this information enters the brain, where the smell is analyzed and perceived.
Resonating function: The nasal passages, the vocal cords, the oral cavity, and the paranasal sinuses make possible the formation of the sound of the voice; for that reason, the voice sounds different when the nose is covered by a cold.
Protective function: Secretory cells of the nasal epithelium secrete substances such as mucins and lysozyme of antibacterial function.
These substances bind with the pathogenic particles, are deposited in the ciliated epithelium, and removed from the cavity. This dense capillary network provides captures and destroys bacteria, fungi, and viruses.
The nasal mucosa plays a vital role in giving immune responses to the presence of allergens and infectious particles that enter through the nose, invade the nasal cavity and spread to other body structures.
Trapping pathogens allows mucus components to attack and destroy microbes.
Lysozyme, the enzyme that breaks down bacteria, is a nasal mucus component. Its function is to degrade pathogenic microbes.
The epithelial cells from the superficial layer of the nasal mucosa provide a physical barrier to the invasion of allergic particles and infectious microorganisms.
The epithelial cells of the nasal mucosa wear out and are replaced by new cells; this provides additional protection because it ensures that the pathogens that manage to burst are eliminated as the epithelial cells detach.
Together with the mucous glands and cilia, they secrete and eliminate mucus and foreign particles from the nasal cavity.
These epithelial cells present immune responses if the physical barrier fails and the pathogens enter the nasal mucosa cells.
This series of processes through which “T” cells, which are nothing more than a type of white blood cell present in the human body, begin to recognize and respond to allergens.
Endothelial cells line the walls of the arteries that feed the nasal mucosa.
These are also involved in allergic responses, and their function is to attract leukocytes or white blood cells, which circulate in the blood to the site where inflammation occurs.
The glands in the nasal mucosa are responsible for producing a viscous mucus that moistens the air and where the bacteria adhere when they enter the respiratory system.
Cilia or tiny hairs that emerge from the epithelium and line the nasal mucosa create movements that help drain mucus from the nasal fossa to the pharynx, where it is swallowed and digested in the stomach.
The activity of the cilia will depend on the temperature; in cold environments, the cilia become less active.
The mucus can accumulate and drip from the nostrils, called nasal discharge.
Infectious particles and allergens can also affect the activity of cilia and cause symptoms such as a runny or stuffy nose.
The underlying blood vessels are thin-walled veins where the nasal mucosa is located and works by heating the air that enters the airways.
Since there is a high concentration of blood vessels in the nasal passages, the changes in these blood vessels contribute to causing nasal congestion.
Cancer: An unusual form of cancer that affects the nasal passages and sinuses, can occur caused by exposure to toxic fumes, excessive smoking, and the presence of strains of human papillomavirus.
Symptoms include lumps or sores inside the nose and pain around the eyes or upper teeth, nosebleeds, nasal obstruction, pus secretion, reduced sensitivity to smell, etc.
The most common treatments include chemotherapy, radiation therapy, and surgery to remove the tumor.
Nasal polyps: Sometimes, there are small benign masses that grow in the nasal passages or sinuses, caused by chronic inflammation from infections, chronic asthma, allergies, or immune disorders.
Generally, they do not cause any problems; when they develop a large size, you can experience sneezing, taste and smell issues, nasal congestion, runny nose, frequent infections, and facial pain and itching.
Rhinitis is a swelling and inflammation of the mucous lining of the nasal passages; it can be of allergic and non-allergic origin—the latter results from environmental changes, some viral infection, or even hormonal imbalances.
The symptoms are irritation, burning sensation, runny nose or dry nose, stuffy nose, and sneezing.
Sinus infection: It is caused by viruses, bacteria, and fungi. It has several symptoms, such as:
- Inflamed and inflamed nasal cavity.
- Pain and pressure in and around the sinuses, forehead, eyes, and teeth.