Corpus: Nasal mucosa

The nasal mucosa is a thin layer of tissue that lines the entire nasal cavity, with the exception of the nasal vestibule.

A distinction is made between two regions of the nasal mucosa:

• Respiratory nasal mucosa or Regio respiratoria: It occupies almost the entire nasal cavity and consists of a respiratory ciliated epithelium.
• Olfactory mucosa or Regio olfactoria: It is located in the upper nasal passage (superior meatus nasi) and consists of the specialised sensory epithelium of the olfactory mucosa.

Respiratory nasal mucosa[Bearbeiten]

The respiratory nasal mucosa (Regio respiratoria) consists of 3 tissue layers

• Multi-row ciliated epithelium with goblet cells
• Basal membrane
• Lamina propria with connective tissue cells

The lamina propria of the nasal mucosa has a dense network of blood capillaries that open into a superficial venous plexus. Particularly in the area of the middle and lower nasal concha, this plexus forms a cavernous body whose volume changes can modify the nasal air flow. Scattered in the nasal mucosa are numerous seromucous glands that produce nasal secretions.

All cells of the epithelium originate from the basal membrane, but mainly only ciliated and goblet cells reach the free surface. Regeneration takes place from the basal cells. Chronic mechanical disturbances, including air turbulence, lead to the transformation of the ciliated epithelium into squamous epithelium. However, normal ciliary function can be restored through regeneration at all stages of the disorder.

Orfactory mucosa[Bearbeiten]

The olfactory mucosa (Regio olfactoria) also consists of 3 tissue layers, but differs from the respiratory nasal mucosa in the uppermost layer.

• Specialised olfactory epithelium
• Basal membrane
• Lamina propria with connective tissue cells

The olfactory epithelium consists of a single layer of supporting cells, between which so-called olfactory cells are found. These are primary neurones whose nerve cell processes (axons) are bundled in the submucosa. The extensions of the olfactory cells float in a layer of mucus formed by Bowman's glands. Basal cells are found below the supporting cells. They are the stem cell reservoir of the olfactory cells, which die after about 60 days and then have to be replaced by new cells.

Conditioning[Bearbeiten]

The nasal mucosa warms and moisturises the air we breathe, conditioning it for the lower airways. Due to the rich capillarisation of the nasal mucosa, heat is transferred from the bloodstream to the inhaled air. This raises its temperature level to around 32-24 °C. At the same time, water evaporates from the nasal secretions and increases the relative humidity to around 80 %.

Filtration[Bearbeiten]

The nasal mucosa serves to separate particles from the air we breathe and thus filter it. The constant flickering of the cilia of the respiratory nasal mucosa removes the particles separated from the air we breathe. This process is known as mucociliary clearance.

The normal mucus film ("nasal mucus") is divided into an inner, thin sol layer, in which the cilia beat, and an outer, discontinuous gel layer, which is transported by the cilia beat. The two layers are separated by a surfactant, which can be described as the "transport layer".

The transfer of the secretion from the sol to the gel occurs at a pH value of 7.5 to 7.6 through the effect of the carbonic acid in the respiratory air.^[1] Optimal viscosity of the secretion is achieved at a relative ambient humidity of more than 80% and a temperature of 35 °C.

The most important components of mucus are mucins, which give it its viscoelastic properties. There are currently 13 different mucins (MUC 1-13). In addition to mucins, small mucin-associated molecules, so-called trefoil peptides, are also important. Mucins also play a central role in cell adhesion, the immune response, interaction with the surrounding microflora and in numerous diseases.^[2] In the case of disease, any therapy aims to restore normal mucosal function.

Infection defence[Bearbeiten]

The nasal mucosa fulfils an important function in the defence against pathogens. Beneath the nasal mucosa is a specialised lymphoid tissue, the NALT ("Nasal Associated Lymphoid Tissue"). Known antigens are bound by immunoglobulins in the nasal mucus - primarily IgA and IgG.

Nasal cycle[Bearbeiten]

In order for the nasal mucosa to fulfil its complex moisturising and defence functions, it requires regeneration phases. These are ensured by periodic swelling and decongestion of the mucous membrane as part of the nasal cycle.

Inflammation of the nasal mucosa is known as rhinitis. It can be triggered by microorganisms (especially viruses), allergens or toxins.

Walter Messerklinger made pioneering discoveries on the physiology of the nasal mucosa and paranasal sinuses in the 1960s. By observing cilia movement and secretion transport in human cadavers and during sinus surgery, Messerklinger was able to describe the path of normal secretion transport for the first time.

• Image source podcast: © Diana Polekhina / Unsplash