Why is the olfactory epithelium pigmented

  Thumbnail overview nasal mucosa (Mucosa nasi):
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Respiratory regionRegio olfactoria The Breathing system (Terminologia histologica: Systema respiratorium; English: respiratory system) begins in the nose and ends with the lungs as the actual respiratory organ. Generally it is from arespiratory mucosa(Terminologia histologica: Tunica mucosa respiratoria; English: respiratory mucosa). This in turn begins with a respiratory epithelium lying on the lumen (Terminologia histologica: Epithelium respiratorium; English: respiratory epithelium), which is a multi-row ciliated epithelium (Terminologia histologica: Epithelium pseudostratificatum columnare ciliatum; English: pseudostratified columnare columnarized) also with Epithelial cells provided with kinocilia, the nuclei of which are arranged in several rows, whereby the highly prismatic cells are all in contact with the underlying basement membrane. In such an epithelium, in addition to the epithelial cells provided with kinocilia (Terminologia histologica: Epitheliocyti ciliati; English: ciliated cells), other likewise highly prismatic epithelial cells (Terminologia histologica: Epitheliocyti microvillosi; English: epithelial cells with microvilli) occur on their cell surface but not as regularly arranged as would be the case in a brush border. In addition, there are also basal cells that represent the as yet undifferentiated preliminary stages of the two cell types. In addition, goblet cells (Terminologia histologica: Mucocyti, Exocrinocyti caliciformes; English: mucous cells, goblet cells) occur in different numbers, which are responsible for the formation of tough mucus.
TheNasal cavity (Terminologia histologica: Cavitas nasi; English: nasal cavity) begins with the Nasal vestibule (Terminologia histologica: Vestibulum nasi; English: nasal vestibule), which extends about as far as you can insert a finger into your nose. In its initial part (Terminologia histologica: Pars cutanea; English: cutaneous region), as a continuation of the facial epithelium, there is a multilayered keratinized squamous epithelium (Terminologia histologica: Epithelium stratificatum squamosum cornificatum; English: keratinized stratified squamous epithelium) with up to 1.5 cm long pigmented hairs (Terminologia histologica:Vibrissae; English: hairs of vestibule of nose), which are similar to the whisker hair of rodents, but are not quite as finely innervated. This is followed by a transition area several millimeters wide (Terminologia histologica: Pars transitionalis; English: transitional region), which macroscopically corresponds to the arched Limen nasi, with multilayered uncornified squamous epithelium (Terminologia histologica: Epithelium stratificatum squamosum non cornamous epithelium) squat. Now follows the actual nasal cavity, the largest part of which is the respiratory area (Respiratory region; Terminologia histologica: pars respiratoria; English: respiratory region) is called. This is where the typical respiratory mucous membrane is found, the structure of which was described above. One basement membrane is followed by one Lamina propria from loose connective tissue. Many small tubulo-acinous mixed seromucous Bowmann's glands (Terminologia histologica: Glandulae nasales; English: nasal glands) send their thin ducts through the epithelium into the lumen of the nose. The nasal glands show mucous glandular epithelial cells (Terminologia histologica: Mucocyti; English: mucous cells), serous epithelial cells (Terminologia histologica: Serocyti; English: serous cells) and basal in the epithelium some myoepithelial cells (Terminologia histologica: Myoepitheliocyti; English: cells). Their secretion contributes to the sol-like component of the mucus. There are many blood vessels in the lamina propria, which are responsible for the swelling of the nasal mucous membrane: a dense subepithelial capillary network opens into a dense superficial network of veins, which then into a deeper venous plexus with jugular veins, especially on the nasal septum and the middle and lower The nasal concha swell to form cavernous cavernous bodies (Terminologia histologica: plexus cavernosus conchae; English: cavernous plexus of concha) and thus can swell the thickness of the mucous membrane up to 5 mm. The parasympathetic nervous system, influenced by local stimuli, ensures the swelling and leads to the contraction of the smooth muscle cells around the jugular veins, which then reduce their lumen in the end area, causing the blood to build up in front of it and the otherwise poorly filled jugular veins (actually they are venules) swell . The lower area of ​​the lamina propria is therefore also referred to as the jugular vein view (Terminologia histologica: Stratum cavernosum; English: cavernous layer).
The yellowish-brownish nasal mucous membrane used for olfactory perception (Terminologia histologica: Regio olfactoria; English: olfactroy region) lies in the area of ​​the upper nasal passage and opposite it on the rear upper nasal septum and is about 5 cm² on each side and significantly higher than the respiratory mucous membrane. Overall, it is also known as the olfactory organ (Terminologia histologica: Organum olfactorium, Organum olfactus; English: olfactory organ). The olfactory mucous membrane located here (Terminologia histologica: Tunica mucosa olfactoria; English: olfactory mucous membrane) is from Olfactory epithelium (Terminologia histologica: Epithelium olfactorium; English: olfactory epithelium) covered. Here go from the ones below, near the basement membrane Olfactory stem cells (Terminologia histologica: Cellulae olfactoriae precursoriae; English: olfactory stem cells) dieOlfactory cells (Terminologia histologica: Epitheliocyti neurosensorii olfactorii; English: olfactory sensory neurons). These highly prismatic epithelial cells, which are both bipolar nerve cells and primary sensory cells, have a more electron-dense cytoplasm. Your cell nucleus and the surrounding perikaryon are located in the middle to lower area of ​​the epithelium. Towards the lumen there is a dendritic process (Terminologia histologica: Dendritum; English: dendrite), which after breaking through the epithelial surface produces a bulb-like swelling (Olfactory bulb; Terminologia histologica: dendritic bulb; English: dendritic bulb) trains. In addition to mitochondria, the basal bodies of about 40 modified kinocilia can be found in this, which move in a star shape in all directions, but preferably to the side by a few micrometers. The real oneSmell takes place through specific olfactory proteins in the cell membrane of these moderately to barely mobile olfactory cilia (Terminologia histologica: Cilia; English: cilia) inside of which there are 9 lateral and 1 central pair of microtubules. Above all, "flowery", smelly and sweet smells are perceived on the cilia surface and via the axons with a diameter of approx. 0.2 µm (Terminologia histologica: Axona olfactoria, Neurofibrae olfactoriae; English: olfactory axons, olfactory nerve fibers) forwarded to the Olfactory fibers (Terminologia histologica: Fila olfactoria English: olfactory sensory neurons) bundle. The latter are not enveloped individually but as a whole bundle of Schwann cells (Terminologia histologica: Glia olfactoria; English: olfactory glia) as myelinated nerve fibers. The sum of all these fibers is called the olfactory nerve (olfactory nerve = 1st cranial nerve). A peculiarity of the olfactory sense cells is theirs Regenerative ability. The cells are said to have a lifespan of only approx. 40 days and are the only type of nerve cells that can still regenerate to a significant extent after birth. Pungent and irritating odors are more likely to be perceived through free epithelial nerve endings of the entire nasal and pharyngeal mucosa and reach the brain through branches of the trigeminal nerve.
In addition to the sensory cells, there are also microvilli on the surface with a lot of smooth endoplasmic reticulum in the upper area Support cells (Terminologia histologica: Epitheliocyti sustenantes; English: supporting epithelial cells), which also have a number of stabilizing tonofilaments (= bundles of cytokeratin intermediate filaments). These cells go out from undifferentiated basaln Epithelial cells (Terminologia histologica: Epitheliocyti basales; English: basal epithelial cells).
The glands located in the area of ​​the olfactory mucosa under the basement membrane in the loose connective tissue lamina propria are also called Olfactory glands (Terminologia histologica: Glandulae olfactoriae; English: olfactory glands). In addition to one type of serous cells with light = hardly electron-dense cytoplasm (Terminologia histologica: Cellulae clarae; English: clear cells), they show another type of serous-producing cells with electron-dense = dark cytoplasm (Terminologia histologica: Cellulae fuscae; English: dark cells) and some Myoepithelial cells (Terminologia histologica: Myoepitheliocyti; English: myoepithelial cells). Their secretion contributes to the sol-like component of the mucus.
Layers of mucus
On a slightly thinner one directly adjacent to the cells and their appendages Sol layerwhich comes mainly from the secretion of the seromucous nasal glands, a thicker one follows towards the lumen Gel layerwhich is mainly fed from the mucous secretion of the goblet cells. The kinocilia hit 6 - 12 times every second, with an impact in which their tip penetrates into the gel phase and causes effective transport is always followed by a recovery blow, which takes place against the low resistance of the sol layer and practically no transport of particles in the mucus causes. The mucociliary transport, which is always orderly towards the throat, takes place at a maximum of approx. 3 mm per minute in the anterior and 12 mm in the posterior nasal area. In about 20 minutes, the entire mucous membrane of the nasal cavity should be completely restored, with the removed mucus being swallowed. The Nasal secretions contains water and ions (Na+, K+, Approx++, Cl-) Mucins, polysaccharides, histamine, fibrinolysin, lysozyme, achetylcholinesterase and immunoglobulins preferably IgA. In addition to humidifying the air we breathe, it is used to purify the air to almost 100%, as well as for immune defense and to dissolve odorous substances. When the head is upright, the alternation of sympathetic and parasympathetic tone causes the venous plexus to swell for 2 - 5 minutes on one side, which means that hardly any air flows through the nose, then this happens on the other side. This is how the physiological arises Nasal cycle.

-> Kinocilia, glands, airways, lungs, sensory cells
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Three images were kindly provided by Prof. H. Wartenberg; other images, page & copyright H. Jastrow.