The structure of the mucous membrane of the jaws. Precancerous conditions and oncology. Pathological processes of the oral mucosa
Oral cavity(cavitas oris) is the initial department digestive tract. It is limited in front and sides by the lips and cheeks, above by the hard and soft palate, and below by the bottom of the oral cavity. When the lips are closed, the mouth opening has the shape of a slit; when the lips are open, it has a rounded shape.
Oral cavity consists of two sections: the anterior, or vestibule of the mouth (vestibulum oris), and the posterior section - the oral cavity itself (cavitas oris propria). The vestibule of the mouth is limited in front and on the sides by the lips and cheeks, and behind and from the inside by the teeth and the mucous membrane of the alveolar processes of the upper and lower jaws. The oral cavity itself is connected to the pharyngeal cavity through the pharynx.
The formation of the oral cavity, which occurs by the end of the second month of intrauterine life, is closely related to the development of the bones of the facial skull. During this period, the risk of developmental anomalies is greatest. Thus, if the frontal process of the mesial nasal process does not fuse with one or both processes upper jaw, then a soft tissue cleft occurs. If the right and left processes of the hard palate do not fuse, a cleft of the hard palate occurs.
Oral mucosa(tunica mucosa oris) consists of 3 layers: epithelial, lamina propria and submucosa.
Epithelial layer. The oral mucosa is lined with stratified squamous epithelium. Its structure is different in different parts of the oral cavity. On the lips, cheeks, soft palate, and floor of the mouth, the epithelium under normal conditions is keratinized and consists of a basal and spinous layer. On the hard palate and gums, the epithelium under normal conditions undergoes keratinization, and therefore it contains, in addition to the indicated layers, granular and horny. It is believed that keratinization of the epithelium serves as its response to the influence of an irritant, primarily mechanical.
Between the cells of the basal layer there are individual leukocytes. They can enter the oral cavity through the ischelium, especially the epithelium of the gingival sulcus, and are found in the oral fluid. In some areas of the breast, melanocytes—cells that form melanin—can be found. The epithelium of the oral mucosa has a high level of activity of enzyme systems. At the border of the epithelial layer and the lamina propria of the mucous membrane there is a basement membrane consisting of no fibrous structures.
lamina propria of the mucous membrane(lamina mucosa propria), on which the layer of epithelium is located, consists of dense connective tissue. At the border with the epithelium, it forms numerous projections - papillae, which protrude to varying depths into the epithelial layer. Connective tissue is represented by fibrous structures - collagen and reticular fibers and cellular elements - fibroblasts, mast and plasma cells, segmented leukocytes. The lamina propria of the mucous membrane of the cheek and lips is richest in cellular elements.
Macrophages, which perform a protective function, phagocytose bacteria and dead cells. They are actively involved in inflammatory and immune reactions. Labrocytes (mast cells), characterized by the ability to produce biologically active substances - heparin, histamine, ensure microcirculation and vascular permeability. Labrocytes take part in delayed-type hypersensitivity reactions.
The lamina propria of the mucous membrane, without a sharp boundary, passes into the submucosa (tunica submucosa), formed by looser connective tissue. It contains small vessels and minor salivary glands. The severity of the submucosa determines the degree of mobility of the oral mucosa.
Innervation of the oral mucosa. Sensitive reaction the mucous membrane of the palate, cheeks, lips, teeth and anterior two-thirds of the tongue is provided by the trigeminal nerve (V pair of cranial nerves), the branches of which are peripheral processes nerve cells trigeminal (Gasserian) node. The lingual-copharyngeal nerve (IX pair) is responsible for the sensitivity of the posterior third of the tongue, which also perceives taste stimuli from the posterior third of the tongue. From the anterior two-thirds of the tongue, taste sensitivity is perceived by the facial nerve (VII pair of cranial nerves). Sympathetic fibers influence the blood supply to the mucous membrane and secretion salivary glands.
The structure of the mucous membrane in various parts of the mouth
Lips. The red border of the lips is a transition zone between the skin and the mucous membrane. Because of this, there is no hair on her and sweat glands, but the sebaceous ones remain. There is no submucosa, but at the border of the muscular layer and the mucous membrane there is a large number of small salivary glands. The red border is covered with stratified squamous keratinizing epithelium, and on the side of the vestibule of the oral cavity - with stratified squamous non-keratinizing epithelium. The frenulum of the upper and lower lips, when attached to the gums short, can contribute to the displacement of teeth - the occurrence of diastema.
Cheeks. There is a pronounced submucosal layer on the cheeks, which determines the mobility of the mucous membrane. When closing the mouth, the mucous membrane forms folds. The submucosa contains many small
vessels, sebaceous glands (Fordyce glands), sometimes forming yellowish conglomerates. Often these formations are mistaken for pathological. On the mucous membrane of the cheek, at the level of the second large molar tooth (molar) of the upper jaw, it opens excretory duct parotid salivary gland, the epithelium of which does not keratinize.
Gums. Anatomically, three sections of the gum are distinguished: marginal, or marginal, alveolar, or attached, and gingival papilla. There is no submucosa in the gum and therefore the mucous membrane is tightly connected to the periosteum of the alveolar process. The epithelium of the alveolar process of the marginal part of the gum has all the signs of keratinization.
Solid sky. The mucous membrane of the hard palate has a different structure. In the area of the palatal suture and the transition of the palate to the alveolar process, the submucosa is absent and the mucous membrane is tightly attached to the periosteum. In the anterior section, the submucosa of the hard palate contains adipose tissue, and in the posterior section there are mucous glands, which determines the pliability of these areas of the mucous membrane. On the palate, near the central incisors of the upper jaw, there is an incisive papilla, which corresponds to the incisive canal located in the bone tissue. In the anterior third of the hard palate, 3-4 folds diverge on both sides of the palatine suture.
Soft sky. Mucous membrane soft palate characterized by the presence of a significant number of elastic fibers at the border of the lamina propria of the mucous membrane and the submucosa (the muscular lamina of the mucous membrane is absent). The mucous salivary glands are located in the submucosa. The multilayered squamous epithelium does not become keratinized, but in some areas acquires ciliated features.
Floor of the mouth. The mucous membrane of the floor of the oral cavity is very mobile due to the pronounced submucosal layer; the epithelium does not normally keratinize.
Language. This is a muscular organ of the oral cavity involved in chewing, sucking, swallowing, articulation, and determining taste. There are apex (tip), body and root, as well as upper (back), lower surfaces and lateral edges of the tongue. The lower surface of the tongue with a paired fringed fold located on it is connected by a frenulum to the floor of the oral cavity.
The lamina propria of the mucous membrane of the tongue, together with the epithelium covering it, forms projections - the papillae of the tongue. There are filiform, mushroom-shaped, leaf-shaped and grooved papillae of the tongue.
Filiform papillae(papillae filiformes) - the most numerous (up to 500 per 1 sq.cm). They are located on the entire surface of the back of the tongue, covered with stratified squamous keratinizing epithelium, which gives them a whitish tint. When the normal rejection of keratinizing scales is disrupted, for example, due to pathology of the gastrointestinal tract, a white coating forms on the tongue - a “coated” tongue. Intensive rejection of the outer layer of the epithelium of the filiform papillae in a limited area is possible. This phenomenon is called desquamation. Filiform papillae have tactile sensitivity.
Fungiform papillae(papillae fungiformes) are located on the lateral surfaces and tip of the tongue. There are fewer of them on the back of the tongue. The fungiform papillae have a good blood supply. Due to the fact that the epithelial layer covering them does not keratinize, they look like red dots. The fungiform papillae contain taste buds (bulbs).
Leaf-shaped papillae(papillae foliatae) are located on the lateral surface of the tongue and in the posterior sections (in front of the grooved ones). The leaf-shaped papillae also contain taste buds (bulbs).
Vital papillae(papillae vallatae - papillae of the tongue, surrounded by a shaft) - the largest papillae of the tongue - are located in one row (9 - 12 each) in a ledge (like the Roman numeral V) at the border of the root and body of the tongue. Each papilla has the shape of a cylinder with a diameter of 2-3 mm and is surrounded by a groove into which the excretory ducts of the small salivary glands open. The walls of the grooved papillae contain a large number of taste buds (bulbs).
The tongue is supplied with blood by the lingual artery. Venous drainage occurs through the lingual vein. On the lateral surface at the root of the tongue, a vascular (venous) plexus of larger or smaller sizes is visible, which is sometimes mistaken for pathological. Lymphatic vessels are located mainly along the arteries.
With age, a number of changes are observed in the structure of the oral mucosa. The epithelial layer becomes thinner, the size of cellular elements decreases, elastic fibers thicken, and collagen bundles become unfibered. In people over 60 years of age, there is a violation of the integrity of the basement membrane, which may result in the growth of the epithelium into the lamina propria of the mucous membrane.
The anatomical and histological features of the structure of the mucous membrane covering the alveolar processes of the jaws, the hard and soft palate and other parts of the oral cavity have a certain significance in the choice of the method of prosthetics for the patient and in its success. According to its position, the mucous membrane belongs to the tissues of the boundary environment, therefore it is resistant to the action of various irritants of a mechanical and thermal nature to which it is exposed when eating, drinking, chewing, etc. The mucous membrane of the oral cavity has great regenerative abilities, which has been confirmed by many years observations of the healing of wounds, ulcerative stomatitis and burns.
Its tissues contain nerve receptors for various purposes. Some of them help determine the consistency and taste of food, others help determine temperature, pressure, pressure, etc.
Tactile stimulation is best perceived by the tip of the tongue. Cold and heat are perceived by the entire mucous membrane of the oral cavity. The feeling of cold occurs at a temperature from 0 to 10°, at a temperature of 20-30° a feeling of slight warmth appears, at a temperature of 30-50° - warmth. The sensation of hotness appears at temperatures exceeding 50°. The posterior parts of the hard and soft palate are especially sensitive to temperature changes.
Taste buds are located in the mucous membrane of the tongue and some parts of the posterior surface of the soft palate. The presence of a large number of receptors in the oral mucosa allows us to consider it as a receptor field, irritation of which can cause various responses not only from the organs of the oral cavity, in particular the salivary glands, but also from other distant organs of the digestive tract.
The oral mucosa has great absorption capacity. As studies by A.I. Marchenko have shown, its absorption capacity is influenced by interoceptive influences from the nerves of the mucous membrane of the stomach and intestines. Mechanical irritation of the receptors in the stomach and rectum of animals stimulates absorption by the mucous membrane of the tongue. Experimental gastritis and enteritis increases the absorption activity of the mucous membrane of the tongue. When the vagus nerve is cut in these diseases, absorption is not enhanced, but rather inhibited. These data undoubtedly confirm the functional relationship of the oral mucosa and the underlying parts of the gastrointestinal tract.
With removable prosthetics, the mucous membrane is subjected to unusual irritations, since it becomes the supporting tissue for the base of the prosthesis. This radically changes her condition.
In the clinic of orthopedic dentistry, a distinction is made between mobile and immobile mucous membrane. The mobile mucous membrane makes excursions when the facial muscles contract. A stationary shell does not have this ability. However, the concept of “fixed mucous membrane” is relative. When pressure is applied, it can move towards the bone it covers. This passive mobility is called compliance in the prosthetic dentistry clinic. For example, the mucous membrane covering the hard palate, without active mobility, at the same time, has vertical compliance, which is unequally expressed in different areas.
When the mucous membrane transitions from the alveolar process to the lip and cheeks, a vault is formed, called a transitional fold. Along the transitional fold there are anatomical formations, the position and severity of which are of great practical importance in prosthetics. On the upper jaw in the vestibule of the oral cavity, by midline the frenulum of the upper lip (frenulum labii superioris) is located (Fig. 39). One end of it merges with the transitional fold, the other is attached to the mucous membrane of the alveolar process slightly above the gingival margin. Sometimes the bridle has a low attachment, with its lower end located between the incisors, which can be moved apart. The labial frenulum serves as a fixed point for the lips, thereby limiting the range of their movements.
The lateral fold (frenulum laterale), located on the upper jaw in the premolar area, limits the anterior part of the vestibule from the lateral part. The function of these folds is similar to that just described. There is also a pterygomaxillary ligament coming from the hook pterygoid process to the crest of the buccal muscle on the lower jaw.
On the lower jaw on the vestibular side there is a frenulum of the lower lip (frenulum labii inferioris) and a fold in the premolar area (plicae buccales inferiores). On the lingual side, the lingual frenulum is attached to the alveolar process. The height of its attachment is great importance for the function of the tongue, as well as when determining the boundaries of the prosthesis on the lingual side. On the hard palate in the anterior third there are transverse folds of the mucous membrane (plicae palatinae transversalis), well pronounced in young people and less pronounced in older people. On the inner side of the alveolar process of the upper jaw in the midline, behind the central incisors there is an incisive papilla. With the loss of teeth, it atrophies, but sometimes it can remain, being sensitive to the pressure of the denture base.
The oral cavity with all its structural formations belongs to the anterior section of the digestive system. Derivatives of the oral cavity are lips, cheeks, gums, hard and soft palates, tongue, tonsils, salivary glands, teeth. The taste organ is located in the oral cavity.
1. DEVELOPMENT OF THE ORAL CAVITY. GILL APPARATUS AND ITS DERIVATIVES
The development of the oral cavity, associated with the formation of the face, occurs as a result of the interaction of a number of embryonic rudiments and structures.
At the 3rd week of embryogenesis, at the cephalic and caudal ends of the body of the human embryo, as a result of invagination of the skin epithelium, 2 pits are formed - the oral and the cloacal. Oral pit or bay (stomadeum), represents the rudiment of the primary oral cavity, as well as the nasal cavity. The bottom of this fossa, in contact with the endoderm of the foregut, forms the oropharyngeal membrane (pharyngeal or oral membrane), which soon breaks through,
Rice. 1.The oral fossa (stomadeum) is separated from the primary intestine
pharyngeal membrane): 1 - oral fossa; 2 - pharyngeal membrane; 3 - forebrain; 4 - foregut; 5 - heart
in this case, a communication occurs between the cavity of the oral fossa and the cavity of the primary intestine (Fig. 1).
Plays an important role in the development of the oral cavity gill apparatus, which consists of 4 pairs of gill pouches and the same number of gill arches and slits (V pair is a rudimentary formation).
Gill pouches represent a protrusion of the endoderm in the pharyngeal region of the foregut.
Gill slits- invaginations of the skin ectoderm of the cervical region, growing towards the protrusions of the endoderm.
The places where both meet are called gill membranes. In humans they do not break through.
Areas of mesenchyme located between adjacent pockets and crevices grow and form roller-like elevations on the anterior surface of the embryo's neck - gill arches(Fig. 2). The mesenchyme of the branchial arches has a dual origin: the central part of each arch consists of mesenchyme of mesodermal origin; it is surrounded by ectomesenchyme, resulting from the migration of neural crest cells.
Rice. 2.Gill arches in a longitudinal section: 1-4 - gill arches; 5 - gill arteries; 6 - stomadeum; 7 - remains of the pharyngeal membrane; 8 - pericardium; 9 - heart (according to Falin L.I., 1976, as amended)
The gill arches are covered on the outside with cutaneous ectoderm, and on the inside are lined with the epithelium of the primary pharynx. Subsequently, an artery, nerve, cartilage and muscle tissue are formed in each arch.
The first gill arch - the mandibular - is the largest, from which the rudiments of the upper and lower jaws are formed. From the second arch - the hyoid - the hyoid bone is formed. The third arch is involved in the formation of the thyroid cartilage.
Subsequently, the first branchial cleft turns into the external auditory canal. From the first pair of gill pouches the cavities of the middle ear and eustachian tube arise. The second pair of gill pouches is involved in the formation of the palatine tonsils. From the III and IV pairs of gill pouches, the anlage of the parathyroid glands and thymus is formed. In the region of the ventral sections of the first 3 gill arches, the rudiments of the tongue and thyroid gland appear (see table).
Gill apparatus and its derivatives
With the development of the oral cavity, the first branchial arch is divided into 2 parts - the maxillary and mandibular. At first, these arcs in front are not combined into a single bookmark.
At the end of the 1st - beginning of the 2nd month of embryogenesis, the entrance to the oral fossa looks like a gap limited by 5 ridges, or processes. The unpaired frontal process is located superiorly (processus frontalis), on the sides the opening is limited by paired maxillary processes (processus maxillaris). The lower edge of the oral opening is limited by paired mandibular processes (processus mandibulares), which, merging along the midline into a single arcuate mandibular process, form the anlage for the lower jaw.
In the anterolateral parts of the frontal process, depressions are formed, surrounded by ridges - the nasal olfactory pits. The eye pads are located laterally. Nasal processes form in the middle part of the frontal process (rocessus nasalis) And nasal septum. The nasal pits gradually deepen, and their blind ends reach the roof of the primary oral cavity. At this point, a thin septum is formed, which then breaks through, giving rise to 2 openings - the primary choanae.
The primary palate is horseshoe-shaped and separates the nasal passages (primary nasal cavity) from the oral cavity. Subsequently, the anterior (proximal) part of the final palate is formed from it.
Simultaneously with the formation of the primary choanae, the rapid growth of the maxillary processes begins, they move closer to each other and to the medial nasal processes. As a result of these processes, the anlage of the upper jaw and upper lip is formed.
The mandibular processes also fuse together along the midline and give rise to the formation of the lower jaw and lower lip.
The division of the primary oral cavity into the final oral cavity and nasal cavity is associated with the formation of lamellar projections - palatine processes - on the internal surfaces of the maxillary processes (Fig. 3).
At the end of the 2nd month, the edges of the palatine processes grow together. In this case, most of the palate is formed. The anterior part of the palate arises when the palatine processes fuse with the anlage of the upper jaw. The septum that arises as a result of these processes represents the rudiment of the hard and soft palate. The septum separates the terminal oral cavity from the nasal cavity.
After the fusion of the palatine processes and the formation of the palate, the primary choanae no longer open into the oral cavity, but into the nasal chambers. The chambers communicate with the nasopharynx through the final definitive choanae.
Disruption of morphogenetic processes during embryogenesis can lead to various developmental defects. The most common of them is the formation of lateral clefts of the upper lip. (They are located along the line of fusion of the maxillary process with the medial nasal process.) Median clefts of the upper lip and upper jaw are much less common. (They are located in the place where the embryo’s medial nasal processes fuse with each other.) When the palatine processes are underdeveloped, their edges do not come close and do not fuse with each other. In these cases, the child develops a congenital malformation - a cleft of the hard and soft palate.
Rice. 3.Development of the palate and separation of the oral cavity
from the nasal cavity: a - embryo at the 6th week of development; b - embryo at the 8th week of development; 1 - nasal septum; 2 - language; 3 - palatine process; 4 - Meckel's cartilage (according to Bykov V.L., 1999, as amended)
2. GENERAL MORPHOFUNCTIONAL CHARACTERISTICS OF THE MUCOSA
MININGS OF THE ORAL CAVITY. TYPES OF MUCOSA
Oral cavity (cavitas oris) limited above by the hard and soft palate, below by the tongue and muscles of the floor of the mouth, in front and on the sides by the lips and cheeks (Fig. 4). In front it opens with the oral fissure (rima oris), which is limited by the lips (labia). Through the pharynx (fauces) the oral cavity communicates with the pharynx.
The alveolar processes of the jaws and teeth divide the oral cavity into 2 sections: the vestibule of the mouth (vestibulum oris) and the oral cavity itself (cavitas oris propria).
The vestibule of the mouth is an arched gap between the cheeks and gums with teeth. The oral cavity itself is limited in front and on the sides by the teeth, on top by the palate, and below by the bottom of the oral cavity.
The oral cavity with all its structural components is the beginning of the digestive system.
The oral mucosa is formed by stratified squamous epithelium, located on the basement membrane, and the lamina propria, which is formed by loose fibrous connective tissue. The lamina propria of the mucous membrane passes into the submucosa without a sharp boundary. (Muscular plate of the mucous membrane, characteristic of the mucous membrane alimentary canal, is absent in the oral cavity.)
Visually, the surface of the oral mucosa is flat and smooth over a large area. The hard palate has transverse folds. There may be small yellowish spots on the lips and cheeks.
cottony elevations are Fordyce spots. These are the excretory ducts of the sebaceous glands, which open onto the surface of the mucous membrane. They are a product of the secretion of ectopically located sebaceous glands, which are usually located in the skin near the hair follicles. Fordyce spots are more often found in the oral cavity of older people. They are rare in children and adolescence. On the mucous membrane of the cheek along the washing line
Rice. 4. Oral cavity: 1 - hard palate; 2 - soft palate; 3 - palatal suture; 4 - tongue; 5 - palatine tonsil; 6 - back of the tongue (according to Sinelnikov R.D., 1966, as amended)
teeth grinding ( white line) there is an area of increased keratinization. There are papillae on the dorsal surface of the tongue.
The oral mucosa performs a variety of functions, the main of which are protective (barrier), sensory, immunological control, food tasting, etc. The epithelium of the mucous membrane protects the underlying tissues from the damaging effects of mechanical, chemical, and thermal factors.
The lingual tonsil, part of the lymphoepithelial pharyngeal ring, is one of the components of the body's immune system.
Sensory function is associated with the presence in the oral mucosa of receptors that perceive tactile, temperature and pain stimuli.
Taste buds, located on the dorsal surface of the tongue, are the peripheral part of the taste analyzer.
The thin mucous membrane at the bottom of the mouth is easily permeable to a number of substances, so some medications are recommended to be placed under the tongue.
Based on the morphofunctional features in the oral cavity, it is customary to distinguish 3 type of mucosa: chewing (tunica mucosa masticatoria), lining (tunica mucosa vestiens) and specialized. The chewing mucosa lines the hard palate and gums. The lining (integumentary) mucous membrane is characteristic of the cheek, lip, floor of the mouth, alveolar processes, the anterior surface of the soft palate and the lower (ventral) surface of the tongue. A specialized mucous membrane covers the upper (dorsal) surface of the tongue.
2.1. EPITHELIA OF THE ORAL MUCOSA
In the oral cavity, 3 types of stratified epithelium can be distinguished:
1 - multilayer flat non-keratinizing;
2 - multilayer flat, keratinizing by orthokeratosis (orthos- true);
3 - multilayer flat, keratinizing by parakeratosis (para- near).
The thickness of the epithelial layer varies in different areas. About 50% of the entire area of the oral cavity is lined with keratinizing epithelium, 30% is non-keratinizing (~20% is the share of teeth).
Non-keratinizing epithelium is characteristic of the lining mucosa.
A tendency to keratinization is found in areas experiencing increased mechanical stress: in the epithelium of the hard palate, gums, cheeks,
the line where the teeth meet, on the upper surface of the tongue.
Epithelial cells (keratinocytes) form keratin in the surface layers of stratified keratinizing epithelium normally and in non-keratinizing epithelium - under mechanical, chemical influence or injury to the oral mucosa. In addition to the differential of keratinocytes, the epithelial layer contains a number of other cells, which are collectively called “light”. Thus, Langerhans cells process antigen, are antigen-presenting and participate in immune reactions. Merkel cells and afferent nerve fibers form tactile mechanoreceptors that respond to touch. The presence in the cytoplasm of granules containing bombesin, vasointestinal polypeptide, enkephalin allows us to classify Merkel cells as diffuse endocrine system. Melanin pigment is formed in melanocytes of neural origin. The number of melanocytes varies. They are more common in people with dark skin.
Increased pigmentation can be observed in some diseases of the oral cavity (malignant melanoma, etc.).
Stratified squamous non-keratinizing epithelium
In stratified squamous non-keratinizing epithelium (epithelium stratificatum squamosum non cornificatum) There are 3 layers: basal, intermediate (spinous), superficial (layer of flat cells).
The nasal layer is represented by prismatic or cubic cells located on the basement membrane. Epithelial stem cells capable of mitotic division are localized in the basal layer. Due to the newly formed cells entering differentiation, the epithelial cells of the overlying layers of the epithelium are replaced. Epithelial cells of the basal layer participate in the formation of components of the basement membrane.
The intermediate layer forms the bulk of the stratified squamous non-keratinizing epithelium. It consists of round or polygonal cells that lose the ability to undergo mitosis.
The surface layer is formed flat cells, which are replaced during the process of tissue renewal. The maturation of cells is accompanied by their migration to the surface of the epithelial layer.
In the oral cavity, the layer of non-keratinizing epithelium is often much thicker than the keratinizing one. Epithelial cells of non-keratinizing epithelium can
We produce substances that have an antimicrobial effect (calprotectin, etc.).
Stratified squamous epithelium keratinizing with orthokeratosis
Stratified squamous epithelium keratinizing with orthokeratosis (epithelium stratificatum squamosum cornificatum), found only in the hard palate and attached gum. The process of keratinization is most clearly expressed here.
The epithelium has 4 layers: basal, spinous, granular, and horny. The shiny layer, characteristic of highly keratinized areas of the epidermis, is not expressed in the oral mucosa.
The process of keratinization (keratinization) is associated with differentiation epithelial cells and the formation in the outer layer of postcellular structures - flattened horny scales.
The differentiation of keratinocytes is associated with their structural changes due to the synthesis and accumulation of specific proteins in the cytoplasm - acidic and alkaline cytokeratins (filaggrin, keratolinin, etc.).
Flattened horny scales without nuclei contain keratin. The membrane of the oral scales is thickened. They have mechanical strength and resistance to chemical substances. Horny scales slough off during physiological tissue regeneration.
Stratified squamous epithelium keratinized by parakeratosis
Stratified squamous epithelium keratinized by parakeratosis (epithelium stratificatum squamosum paracornificatum), typical for the cheek in the area where the teeth meet and for the attached gum. It is also localized on the dorsal surface of the tongue in the area of the specialized mucous membrane.
Parakeratinization is one of the unique characteristics of a healthy oral cavity. In the skin, this type of epithelium is found in pathology.
In the parakeratinized epithelium, the same 4 layers are distinguished as in the orthokeratinized one. However, the granular layer may be poorly visible or even absent. The surface layer in the parakeratinized epithelium is formed by nucleated cells, in the cytoplasm of which keratin is detected. These cells with pyknotic nuclei are not viable.
The epithelium of the cheek along the line of closure of the teeth during mechanical injury or due to chemical exposure
may become hyperkeratinized. During a medical examination, such patients have fixed white spots on the mucous membrane of the cheek (similar spots occur in patients with chronic fungal infection, nicotine stomatitis and some other diseases).
As the body ages, the epithelium becomes thinner and degenerative changes are noted.
Cytological study of the processes of differentiation of epithelial cells and the nature of the expression of cytokeratins in them, taking into account the regional specifics of the epithelium, has a certain diagnostic value. Disruption of these processes is a sign of pathological changes and is most often observed during tumor growth.
2.2. LAMINA PROPRIETARY MUCOSA AND SUBMUCOSA BASE
lamina propria of the mucous membrane (lamina propria mucosae), located under the basement membrane, forms the papillae. The height of the papillae and the nature of their location in the oral mucosa vary.
In the lining mucosa, the papillae are usually few and low. A small amount of elastic fibers contained in loose fibrous connective tissue ensures stretching of the mucous membrane during chewing and swallowing.
In the area of the chewing mucosa, two layers are often distinguished in the lamina propria: 1 - papillary layer, formed by loose fibrous connective tissue; 2 - mesh layer, represented by dense connective tissue with big amount collagen fibers. Tall, “slender” papillae, characteristic of the mucous membrane of the chewing type, seem to create a strong, durable base - the “foundation” necessary for chewing.
The lamina propria usually contains a network of capillaries that provides nutrition to the entire mucous membrane. Free and encapsulated nerve endings are also localized here.
The lamina propria of the mucous membrane without a sharp boundary passes into the submucosa (tela submucosa), where, along with loose connective tissue, there are often accumulations of fat cells, end sections small salivary glands. A well-defined submucosa forms a kind of “cushion” that ensures the mobility of the mucous membrane and the possibility of a certain compression.
The submucosa is not expressed in the suture area and the lateral parts of the hard palate, in the gums, on the upper and lateral surfaces of the tongue. In these places, the mucous membrane is fused with layers of connective tissue located between the muscles, or with the periosteum of the corresponding bones.
Knowledge of regional features of the morphology of the oral mucosa is important for developing treatment issues and its clinical transplantation. Transplantation is used for congenital or acquired defects, after surgical removal of tumors, and during reconstructive operations. Currently, methods for growing tissues of the oral mucosa based on the principles of tissue engineering are being actively developed. The probability of successful clinical use of tissue-engineered bioconstructions is higher, the closer they are in their morphofunctional characteristics to the native mucous membrane of the oral cavity.
3. LIPS
In the lip area (labia oris) there is a gradual transition of the skin located on outer surface lips, into the oral mucosa. The transition zone is the red border of the lips. Accordingly, the structure of the lip is divided into 3 sections (Fig. 5): cutaneous (pars cutanea), intermediate (pars intermedia), mucous (pars mucosa).
Cutaneous part of the lip has the structure of the skin. It is covered with stratified squamous keratinizing epithelium, there are sebaceous, sweat glands and hair. The connective tissue papillae are small. Muscle fibers are woven into the dermis, which ensures the mobility of this part of the lip.
In the intermediate section (red border) sweat glands and hair disappear, but the sebaceous glands remain. The excretory ducts of the sebaceous glands open directly on the surface of the epithelium. When the ducts are blocked, the glands become noticeable in the form of yellow-white grains visible through the epithelium. Multilayer flat
The keratinizing epithelium in the red border of the lips has a thin stratum corneum.
The lamina propria of the mucous membrane forms numerous papillae, which are deeply embedded in the epithelium. Capillary networks come close to the surface and easily “shine through” the epithelium, which explains the red color of the lips. The red border contains a large number nerve endings. In newborns, in the inner zone of the red border of the lips (villous zone) there are epithelial outgrowths, or “villi,” which gradually smooth out and disappear as the body grows.
Mucous department The lips are lined with a thick layer of stratified squamous non-keratinizing epithelium. The papillae in the lamina propria are few and lower than in the red border of the lips. In the submucosa there are bundles of collagen fibers that penetrate into the intermuscular layers of connective tissue (m. orbicularis oris). This prevents the possibility of wrinkles. The submucosa also contains accumulations of fat cells and the secretory end sections of the mucous and mixed salivary glands (glandulae labiales), the excretory ducts of which open into the vestibule of the oral cavity.
4. CHEEK
Cheek (bucca)- a muscle formation covered on the outside with skin, on the inside with mucous membrane (Fig. 6). Between the skin and the buccal muscle there may be a fairly thick layer of fatty tissue, forming fat body cheeks, which is especially well developed in children.
In the mucous membrane of the cheek there are 3 zones: upper or maxillary (zona maxillaris), lower, or mandibular (zona mandibularis), and middle or intermediate (zone intermedia), located between them along the line of closure of the teeth.
Maxillary And mandibular zone the cheeks have a structure similar to the structure of the mucous part of the lip. On the surface there is a thick layer of stratified squamous non-keratinizing epithelium.
The lamina propria of the mucous membrane forms small, sparsely located papillae.
The submucosa contains the salivary glands of the cheek - gl. buccalis. The salivary glands are often embedded in the muscle. The largest glands lie in the area of the molars.
Intermediate zone The buccal mucosa has some structural features. The epithelium along the line of closure of the teeth, as noted earlier, becomes keratinized through parakeratosis (white line).
The lamina propria of the mucous membrane is involved in the formation of rather high papillae. There are no salivary glands, but there are sebaceous glands.
In newborns, in the intermediate zone of the buccal mucosa, epithelial “villi” are often found, similar to those in the inner zone of the red border of the lips. This feature apparently indicates that in the embryonic period the cheeks are formed due to the fusion of the edges of the upper and lower lips.
The buccal muscle forms the muscular layer of the cheek.
Perioral (juxtaoral) organ of Khivitsa
In the cheek of humans and mammals there is a paired perioral organ (ORO), described in 1885 by Hivitz. It is considered as a normal anatomical structure. The ORO is located surrounded by soft tissue within a muscle (buccoceotemporal fascia) on the medial surface of the mandible near its angle. Macroscopically, the ORO is an elongated formation in the form of a white cord, resembling a nerve. In adults, its length is 7-17 mm, diameter - 1-2 mm. IN in rare cases ORO may protrude into the oral cavity.
The occurrence of OPO is associated with the course of development of the parotid gland or with the separation of a section of epithelium in the area of the border between the maxillary and mandibular processes after their fusion during embryonic development.
The organ is surrounded by a connective tissue capsule. The stroma of the OPO is formed by moderately dense connective tissue. The parenchyma of the organ is formed by strands of epithelial cells surrounded by a thick basement membrane. In some places, epithelial cells form tubes, the lumen of which is filled with secretory material that does not react to mucins. The structures described often resemble a gland in structure. There is no keratinization. According to the ultrastructural characteristics, epithelial cells of the oral cavity in humans and animals are similar to the epithelial cells of the oral mucosa, especially its basal layer.
The function of OPO has not been clearly established. Some authors believe that the OPO does not perform any function in the body at all and is only an epithelial remnant resulting from the fusion of the maxillary and mandibular processes, similar to the epithelial remnants in the palatal suture formed by the fusion of the palatine processes in embryogenesis. Other researchers consider the OPO as a functionally active organ and suggest two possible options its functions:
Rice. 6.Histological specimen. Cheek of a human fetus (a-c - at high magnification)Mucous surface of the cheek (a): 1 - stratified squamous non-keratinizing epithelium; 2 - lamina propria of the mucous membrane. Maxillary zone (b): 1 - striated skeletal muscle fibers; 2 - buccal salivary gland Skin surface of the cheek (c): 1 - stratified squamous keratinizing epithelium; 2 - hair; 3 - terminal section of the sebaceous gland
1 - glandular (in particular, neuroendocrine);
2 - mechanoreceptor. The receptor function of OPO is indicated by the presence in it of numerous nerve fibers and endings, lamellar bodies of Vater-Pacini.
Clinicians are sometimes not sufficiently informed about the topography and structure of the ORO. Since ORO is deeply immersed in soft fabrics, if it is accidentally discovered during x-ray examination or on histological preparations of biopsy specimens, ORO can be mistaken for well-differentiated squamous cell carcinoma or tumor metastasis internal organs.
5. SOFT PALATE AND ULGULA
Soft palate (palatum molle) separates the oral cavity from the pharynx. The basis of the soft palate is made up of thick bundles of striated muscle fibers and dense connective tissue. During swallowing, the soft palate is pulled upward and backward, closing the entrance to the nasopharynx. There are anterior (oropharyngeal) surface of the soft palate, uvula and posterior (nasopharyngeal) surface (Fig. 7, 8).
Anterior surface (facies orophayngea) of the soft palate covered with stratified squamous non-keratinizing epithelium. The lamina propria, in which numerous vessels are located, forms rather high papillae. At the border of the lamina propria of the mucous membrane and the submucosa there is a layer of elastic fibers. The submucosa contains the terminal sections of numerous mucous glands, the excretory ducts of which open on the oral surface of the soft palate. Sometimes the end sections of the glands penetrate into the spaces between the bundles of muscle fibers. Lobules of adipose tissue are located in the submucosa (see Fig. 8, a).
Posterior surface (facies nasopharyngea) of the soft palate, facing the nasopharynx, it is covered with a single-layer multirow ciliated epithelium, characteristic of the respiratory tract. In the lamina propria of the mucous membrane there are the end sections of mixed or mucous glands and lymphoid nodules (see Fig. 8, b).
There is no submucosa on the posterior nasopharyngeal surface of the soft palate. The base of the soft palate is formed by the tendon-muscular plate (lamina tendinomuscularis), consisting of fibers of striated muscle tissue and their fascia.
Rice. 7.Scheme of the structure of the soft palate:1 - mixed glands; 2 - lymphoid nodule; 3 - adipose tissue; 4 - mucous glands; 5 - elastic fibers
Rice. 8.Histological specimen. Soft palate: a, b - at high magnification
The mucous membrane of the anterior surface (a): 1 - stratified squamous non-keratinizing epithelium; 2 - lamina propria of the mucous membrane. Mucous membrane of the posterior surface (b): 1 - multirow ciliated epithelium; 2 - lamina propria of the mucous membrane
Uvula- growth of the soft palate. In adults, both surfaces of the uvula are covered with stratified squamous non-keratinizing epithelium. In newborns, on the posterior surface of the uvula there is a multi-row ciliated epithelium, which is later replaced by stratified epithelium.
6. HARD PALATE
Solid sky (palatum durum) covered with a chewing mucous membrane. The mucous membrane is tightly fused with the periosteum, motionless, very thin in the area of the palatine suture and somewhat thicker in the posterior parts of the palate.
The epithelium covering the hard palate is stratified squamous and keratinized.
The lamina propria of the mucous membrane forms numerous narrow finger-shaped papillae that penetrate deeply into the epithelium.
The structure of the submucosa varies in different parts of the hard palate. In accordance with its morphological characteristics, it is customary to distinguish 4 zones: fatty, glandular, palatal suture zone, marginal (Fig. 9).
In the fatty zone (zona adiposa), the corresponding anterior third of the hard palate, the submucosa contains accumulations of fat cells (Fig. 10). IN glandular zone (zona glandularis), occupying the posterior 2/3 of the hard palate, in the submucosa on the
the terminal sections of the mucous palatine glands are distributed (Fig. 11). Palatal suture area (medial zone) located in the form of a narrow strip along the midline of the hard palate. Marginal (lateral) zone adheres directly to the teeth.
The palatal suture zone and the marginal zone are fibrous (zona fibroza).
Despite the presence of a submucosa, the mucous membrane of the fatty and glandular zones of the hard palate is motionless. It is tightly fixed to the periosteum of the palatine bones by thick bundles of dense connective tissue.
In the lamina propria of the mucous membrane of the palatine suture, accumulations of epithelial cells (“epithelial pearls”) are sometimes detected. They are formed during embryogenesis during the fusion of the palatine processes and represent the remains of the epithelium “embedded” in the underlying connective tissue.
7. GUM. ALVEOLAR MUCOSA
Gum (gingiva) is part of the chewing mucous membrane of the oral cavity. The gums surround the teeth and border the alveolar mucosa. Visually, the gums differ from the alveolar mucous membrane in a paler, matte shade.
Rice. 9.Diagram of the zones of the mucous membrane of the hard palate:1 - fatty zone; 2 - glandular zone; 3 - area of the palatal suture; 4 - marginal zone (according to V.L. Bykov, 1998, as amended)
Rice. 10.Diagram of the structure of the fatty part of the hard palate
Rice. eleven.Scheme of the structure of the glandular part of the hard palate
Rice. 12.Topography of the gums and alveolar mucosa: 1 - alveolar mucosa; 2 - attached part of the gum; 3 - interdental groove; 4 - free part of the gum; 5 - gingival papilla; 6 - border between the attached part of the gum and the alveolar mucosa; 7 - gingival groove; 8 - gingival margin
The mucous membrane of the gums is divided into 3 parts: attached, free and gingival interdental papillae (Fig. 12).
Attached part of gum tightly fused with the periosteum of the alveolar processes of the jaws.
Free (marginal) part of the gum adheres to the surface of the tooth, but is separated from it by a narrow gap - the gingival groove - and does not have a strong attachment to the periosteum.
Gingival interdental papillae- triangular-shaped areas of gums lying in the spaces between adjacent teeth.
The gingival epithelium is a multilayered squamous keratinizing epithelium. Keratization in the gums occurs through both parakeratosis (75%) and true keratosis (15%).
The gingival epithelium passes into the non-keratinizing epithelium of the gingival sulcus and the attachment epithelium, which fuses with the cuticle of the tooth enamel.
In the lamina propria of the gum mucosa, loose connective tissue forms papillae that protrude deeply into the epithelium. There are a large number of blood vessels here. Dense connective tissue with thick bundles of collagen fibers forms the reticular layer of the mucous membrane. Bundles of collagen fibers attach the gingiva to the periosteum of the alveolar process (attached gingiva) and connect the gingiva to the cementum of the tooth (gingival fibers of the periodontal ligament).
Alveolar mucosa covers the alveolar processes of the jaws. It has a bright pink color, as it is lined with non-keratinizing epithelium, through which blood vessels are clearly visible. The alveolar mucosa is firmly attached to the periosteum. The lamina propria of the mucous membrane forms conical papillae of varying sizes.
The transition zone between the lining alveolar mucosa and the attached gingiva is well defined in histological preparations. (In the gum area, the epithelium is multilayered flat keratinizing, and in the alveolar mucous membrane area it is non-keratinizing.)
8. BOTTOM OF THE ORAL CAVITY
The mucous membrane of the floor of the mouth is limited by the gum and extends to the lower (ventral) surface of the tongue. The mucous membrane is mobile and easily folds (Fig. 13).
The epithelium is a multilayered squamous non-keratinizing (thin layer).
The lamina propria of the mucous membrane is formed by loose connective tissue, contains a large number of blood and lymphatic vessels, and forms sparse low papillae.
Small salivary glands are located in the submucosa.
Rice. 13.Oral cavity (the tongue is raised, sections of the mucous membrane are removed on the left, the sublingual gland and lingual gland are visible): 1 - dorsum of the tongue; 2 - fringed fold; 3 - lower surface of the tongue; 4 - sublingual fold; 5 - floor of the mouth; 6 - sublingual meat; 7 - gums; 8 - edge of the tongue; 9 - lingual salivary gland; 10 - lingual nerve; 11 - tongue muscle; 12 - frenulum of the tongue; 13 - sublingual gland; 14 - excretory duct of the submandibular gland; 15 - gums (according to R.D. Sinelnikov, 1966, as amended)
9. LANGUAGE
9.1. LANGUAGE DEVELOPMENT AND ITS MAIN STRUCTURAL COMPONENTS
Language development
Language (lingua) develops from several rudiments (tubercles) located at the bottom of the primary oral cavity. At the 4th week of embryogenesis, an unpaired middle lingual tubercle appears (tuberculum impar), located between the ends of the I and II gill arches. A small portion of the dorsum of the tongue develops from this tubercle. Anterior to the unpaired tubercle, on the inner side of the first (mandibular) gill arch, 2 paired thickenings are formed - the lateral lingual tubercles. Merging together, they give rise to most of the body of the tongue and its tip. The root of the tongue arises from the tubercle (copula), located between the ventral ends of the II and III branchial arches.
The rudiments of the tongue quickly grow together, forming a single organ.
Subsequently, the boundary between the root and body of the tongue is the line of fusion - the terminal groove of the tongue (sulcus terminalis). It forms an angle open anteriorly, at the top of which there is a small fossa - a blind foramen. (foramen cecum). The foramen cecum is a rudimentary thyroglossal duct.
The epithelium of the tongue is initially represented by 1 or 2 layers of cells. By the end of the 2nd month of embryogenesis, the epithelium becomes multilayered and the papillae of the tongue begin to form. At the 8th week of development, the rudiments of taste buds appear in the epithelium of the tongue. The epithelium differentiates under the inducing influence of a number of growth factors.
The striated skeletal muscles of the tongue develop from myotomes.
A single anlage of the tongue gradually separates from the floor of the mouth by forming deep grooves that penetrate under the anterior and lateral sections of the tongue, due to which the body of the tongue acquires mobility.
The tongue has a complex innervation system. This is due to the fact that it develops from the material of several gill arches, each of which is innervated by its own nerve.
At the 5th month of embryogenesis, due to the migration of lymphocytes in the root of the tongue, the lingual tonsil develops.
Basic structural components of language
The formed human tongue is a muscular organ covered with a mucous membrane.
with a spoon. Bundles of fibers of striated muscle tissue go in 3 directions: vertically, horizontally, transversely. Between the muscles there are layers of loose connective tissue with blood vessels and nerves, and accumulations of fat cells. The salivary glands are located deep in the muscle tissue. At the root of the tongue is the lingual tonsil.
On the upper surface of the tongue, between the muscles and the lamina propria of the mucous membrane, there is a thick connective tissue plate consisting of intertwining bundles of collagen and elastic fibers. This is a kind of aponeurosis of the tongue. It is well developed in the area of the terminal groove.
The tongue is divided into 2 symmetrical halves by a longitudinal partition made of dense connective tissue.
The relief of the mucous membrane of the tongue is different on the lower, lateral and upper surfaces. The mucous membrane of the lower surface of the tongue is of the lining type, the mucous membrane of the upper (dorsal) surface is specialized. There is no submucosa on the upper surface of the tongue. The lower surface of the tongue has little mobility due to the presence of a submucosa.
9.2. PAPIPLES OF THE TONGUE
The specialized mucous membrane of the dorsal surface of the tongue contains papillae, formed by multilayered squamous non-keratinizing or partially keratinizing epithelium and the lamina propria of the mucous membrane.
There are 4 types of papillae (Fig. 14): filamentous (papillae filiformes), mushroom-shaped (papillae fungiformes), leaf-shaped (papillaefoliatae), grooved (papillae vallatae). All papillae have overall plan buildings. The basis of the papilla is an outgrowth (primary papilla) of the lamina propria of the mucous membrane. From the top of the primary papillae several thinner connective tissue secondary papillae extend into the epithelium.
Valve papillae of the tongue(papillae surrounded by a shaft) are located in a V-shaped terminal groove (between the body and the root of the tongue), their number ranges from 6 to 12. They are large (length 1-1.5 mm, diameter 1-3 mm), even clearly visible with the naked eye. The circumvallate papillae have a narrow base and a wide, flattened free part. Around the papilla there is a narrow, deep slit - a groove that separates the papilla from the ridge. The thickening of the mucous membrane surrounding the papilla is called a roller. Numerous flavoring agents are located in the thickness of the roller.
Rice. 14.Topography of the papillae of the tongue: 1 - palatine tonsil; 2 - blind opening of the tongue; 3 - leaf-shaped papillae; 4 - grooved papillae; 5 - fungiform papillae; 6 - filiform papillae; 7 - root of tongue; 8 - lingual tonsil; 9 - body
language (according to Sinelnikov R.D., 1966, as amended)
buds (taste buds). At the bottom of the groove, the ducts of the serous salivary glands (Ebner's glands) open. The secretion of the glands helps flush the grooves.
Filiform papillae of the tongue- the most numerous and smallest (about 0.5-1 mm long). They evenly cover the tip and body of the tongue. On the surface of the filiform papillae, the epithelium forms a thin stratum corneum (Fig. 15).
In a number of diseases, the process of rejection of superficial keratinizing epithelial cells may slow down. In this case, powerful horny layers (tongue coated with white coating) are formed.
Filiform papillae perform a predominantly mechanical function.
Fungiform papillae of the tongue are not numerous and lie singly among smaller filiform papillae. The largest number of them is concentrated on the back of the tongue. They reach a height of 2 mm and are shaped like a mushroom (narrow base and wide top). In the thickness of the epithelium, in the area of the “caps” of the fungiform papillae, taste buds are found.
Rice. 15.Histological specimen. Human tongue: a - dorsal surface of the tongue with filiform papillae (specialized mucous membrane); b - ventral surface of the tongue, covered with stratified squamous non-keratinizing epithelium (lining mucous membrane)
Leaf-shaped papillae of the tongue well developed in early childhood and are located mainly on the lateral surfaces of the tongue. The length of the papillae is 2-5 mm. They are formed by parallel leaf-shaped folds of the mucous membrane, separated by slits. The leaf-shaped papillae contain taste buds. In an adult, the leaf-shaped papillae are reduced.
9.3. TASTE BUDS
Taste buds, or taste buds (gemmae gustatoriae, caliculi gustatoriae), in adults they are located in the stratified squamous epithelium of the lateral walls of the grooved and fungiform papillae of the tongue. In children, they can be found in the leaf-shaped papillae, as well as on the lips, back wall pharynx, external and internal surfaces of the epiglottis. The number of taste buds in humans reaches 2 thousand.
The taste bud has an ellipsoidal shape and occupies the entire thickness of the epithelial layer (Fig. 16, 17). It consists of 40-60 cells, among which there are: sensoroepithelial, supporting, basal and perihemal, located on the periphery of the kidney (see Fig. 16).
The apex of the bud communicates with the surface of the tongue through the taste pore. Small depression
between the surface epithelial cells is called the taste pit.
Sensoepithelial (receptor) cells taste buds are the most numerous and have an elongated shape. In their basal part, synapses are formed with unmyelinated nerve fibers of the facial, glossopharyngeal and vagus nerves.
On the apical part of the receptor cells there are microvilli containing specific protein receptors on the membrane.
Flavoring substances are adsorbed between the villi and on the near-membrane layer of the microvilli cytolemma. Exposure to the corresponding substances leads to conformational changes in receptor protein molecules, permeability of the membrane of the sensoroepithelial cell, and changes in potential. Excitation is transmitted through synapses to the dendrites of sensory neurons. The bodies of the latter are located in ganglia located along the cranial nerves. Axons extending from the bodies go to the corresponding parts of the brain.
Apparently, receptor proteins in microvilli are tuned to perceive a certain taste. Thus, a sweet-sensitive receptor protein was found in the taste buds of the front part of the tongue, and a bitter-sensitive protein was found in the back part. Sensitivity to salty and sour is greatest on the lateral surfaces.
Rice. 16.Scheme of the structure of a taste bud:1 - supporting cells; 1a - microvilli; 2 - sensoroepithelial cells; 3 - light flattened epithelial cells of the tongue; 4 - basal undifferentiated cells; 5 - peripheral cells; 6 - basement membrane; 7 - nerve fibers; 8 - mucoproteins; 9 - taste time (according to Vinnikov A.Ya., Afanasyev Yu.I., Yurina N.A., 1999)
Rice. 17.Histological specimen. Taste buds in the leaf-shaped papillae of the tongue:a - medium, b - high magnification: 1 - taste buds; 2 - stratified squamous non-keratinizing epithelium
At the same time, there is evidence that the same taste cell is capable of perceiving several taste stimuli.
Supporting cells take part in the synthesis of the adsorbent. There are microvilli on the surface of the tall supporting epithelial cells, and secretory granules are found in the cytoplasm.
Basal epithelial cells are poorly differentiated cells and serve as a source of regeneration. From the basal cells, supporting and sensoroepithelial cells develop, which are continuously renewed. The lifespan of sensoroepithelial cells is approximately 10 days.
In formation taste sensations Nonspecific afferent endings (tactile, pain, temperature), which are present in the mucous membrane of the oral cavity and pharynx, also take part. Their arousal is associated with the color of taste sensations (“hot” taste of pepper, etc.).
10. TONSILS. LYMPHOEPITHELIAL PHARYNGEAL RING
The entrance to the respiratory and digestive tracts is surrounded by large accumulations of lymphoid tissue. They form the lymphoepithelial pharyngeal
Pirogov's ring. Depending on their location, the palatine, pharyngeal and lingual tonsils are distinguished. Accumulations of lymphoid tissue in the area auditory tubes form tubal tonsils, and in the ventricles of the larynx - laryngeal tonsils. The morphology of all tonsils is similar.
Tonsil (tonsilla) consists of several folds of the mucous membrane, in the lamina propria of which there are numerous lymphoid nodules (nodulus lymphoideus). Slit-like invaginations extend from the surface of the tonsil deep into the organ - crypts (cripta tonsillae). Note that there is only one crypt in the lingual tonsil. The mucous membrane is covered with multilayered squamous non-keratinizing epithelium, which is usually infiltrated by cells involved in inflammatory and immune reactions - granulocytes, lymphocytes, macrophages (Fig. 18). The submucosa, located under a cluster of lymphoid nodules, forms a capsule around the tonsil, from which connective tissue septa extend deep into the tonsil. Outside the submucosa are striated muscles - an analogue of the muscularis propria.
Lymphoid nodules of the tonsils, often having germinal centers, are classified as B-cell zones. The structure of lymphoid nodules includes a dark zone facing the crypt lumen, light basal and light apical zones of the reactive center, as well as a crown. Apparently, the full version can unfold in the amygdala
Rice. 18.Histological specimen. Lingual tonsil:
1 - multilayered squamous non-keratinizing epithelium; 2 - crypt; 3 - lymphoid nodules; 4 - terminal sections of the palatine salivary glands
humoral immune reaction, in which “ordinary” B2 lymphocytes participate. During the local humoral immune response, antibodies are formed, mainly of the immunoglobulin (Ig) A isotype. Secretory IgA blocks the attachment of bacteria to epithelial cells, protecting the mucous membrane from many infections.
In addition, the amygdala contains a significant number of B1 cells. The precursors of this subpopulation of B-lymphocytes are resettled from bone marrow into the abdominal and pleural cavities and support the pro-
proliferation and differentiation of B1 lymphocytes throughout life autonomously from bone marrow stem cells. Most B1 cells express the CD5 marker. B1 cells spontaneously synthesize so-called natural, normal antibodies to certain bacterial antigens, as well as to autoantigens. B1 cells produce mainly immunoglobulin M, as well as some IgG and IgA. The immune response of these cells is rapid and not very specific. Natural antibodies are thought to form the first line of defense against microbes.
The oral mucosa has its own characteristics that distinguish it from other mucous membranes. It is resistant to various irritants: mechanical, chemical, temperature, etc., has increased regenerative ability and is relatively resistant to infection. In some parts of the oral cavity, the mucous membrane is mobile and pliable, while in others it is immobile. Such qualities of the mucous membrane are determined by its structure.
In the structure of the oral mucosa, three layers are distinguished: stratified squamous epithelium, the mucosal layer itself and the submucosal layer.
The multilayered squamous epithelium lining the mucous membrane has different structure. In the area of the lips, cheeks, soft palate, lower surface of the tongue, floor of the mouth and transitional folds of the vestibule, the epithelium of the oral mucosa consists of two layers of cells: basal and spinous. The absence of the stratum corneum explains its pink color and here it does not keratinize. In those areas where the mucous membrane is subject to the greatest friction and pressure during food intake, it is found in its superficial layers different stage keratinization of the epithelium. This is the mucous membrane of the hard palate and gums. Similar phenomena are observed at the tips of the filiform papillae of the tongue.
Histological examination reveals glycogen in the epithelium of the mucous membrane. An inverse relationship was found between glycogen content and the process of keratinization. Where the mucous membrane does not undergo keratinization, it contains a lot of glycogen, but where it undergoes keratinization, there is little glycogen. Obviously, it plays the role of a source of energy or plastic material in the process of formation of the stratum corneum.
The thickness of the epithelial layer in different parts of the mucous membrane is uneven. For example, at the bottom of the mouth, on the lip and the lower surface of the tongue, the layer of epithelium is thin. In other areas the layer is much thicker. With age, the thickness of the epithelium changes. In children, it is thin and delicate; with age, its thickness increases, and in old age, due to atrophy, it becomes thinner again. The epithelium performs a barrier function, protecting the mucous membrane from various damages. In addition, the surface epithelial cells are constantly exfoliated, along with them a large number of microorganisms are removed from the surface of the mucous membrane. This protective property of the epithelium is to prevent microorganisms from penetrating deep into the mucous membrane. The epithelium is connected to the underlying connective tissue by a basement membrane.
Under the epithelium is its own layer of the mucous membrane, which consists of dense connective tissue containing cellular elements, fibers and ground substance. The proper layer in the form of papillary projections is embedded in the underlying layer of epithelium. Each papilla contains blood vessels and nerves. Papillary projections increase the area of contact of the epithelium with its own layer of the mucous membrane, which provides best exchange substances between them and a more durable attachment of the epithelial layer. In addition, the lamina propria contains lymphatic vessels, sebaceous glands and numerous salivary glands.
The proper layer of the mucous membrane passes into the submucosal layer without a sharp boundary. The latter consists of looser connective tissue and contains a deep vascular network and deeper-lying small salivary glands.
Language is a muscular organ, has powerful striated muscles. There is no submucous membrane in the tongue, and therefore the own mucous membrane passes into the intermuscular connective tissue, therefore the mucous membrane of the tongue is motionless and does not fold. The tongue has several surfaces: the front (back of the tongue), tip and root, side surfaces and the bottom, facing the floor of the mouth. The lower surface of the tongue is smooth, and the back is rough due to the presence of 4 types of papillae: filiform, mushroom-shaped, leaf-shaped and surrounded by a shaft, or grooved. The papillae of the tongue are nothing more than protrusions of the mucous membrane itself along with the epithelium covering it.
Filiform papillae are located along the entire back of the tongue. Superficial epithelial cells tend to become keratinized and slough off in the form of whitish scales. In some diseases, especially of the digestive system, the desquamation of epithelial cells slows down and the tongue acquires a whitish color, which is clinically called a “coated” tongue. In some pathological conditions of the body surface layer The epithelium can become completely keratinized, then the tongue takes on a “hairy” appearance. With old age, atrophy of the filiform papillae is possible, and then the surface of the tongue becomes smooth.
Fungiform papillae have a narrow base and a wider, rounded apex. The epithelium of the fungal papillae does not keratinize, therefore they have a bright red color and are scattered in the form of red dots among the filiform papillae in the region of the anterior 2/3 of the dorsum of the tongue.
Leaf-shaped papillae look like parallel folds 2-5 mm long, separated by a narrow groove. They are located on the lateral surface of the tongue. Their epithelium contains a large number of taste buds.
The papillae, surrounded by a shaft or grooved, are located in the form of a Roman numeral V on the border between the root and body of the tongue in the number of 8-15. The papilla has a rounded shape, is somewhat immersed in the mucous membrane and is surrounded by a shaft. They contain a large number of taste buds and are abundantly supplied with nerve receptors.
On the midline of the tongue, slightly posterior to the papillae, surrounded by a shaft, there is a blind fossa. Behind it and on its sides is the follicular apparatus, which is united under the general name “lingual tonsil”. Some of the follicles move to the lateral surface of the tongue. These follicles are mistakenly mistaken by some for pathology. This is followed by the left and right lingual-epiglottic folds, then the epiglottis and pharynx.
Lips consist of circular muscles covered on the outside with skin, their inner side is lined with mucous membrane. Its submucosal layer is tightly fused with intermuscular fibers, which determines its smoothness and prevents the formation of folds. The thickness of the mucous membrane contains many small salivary glands of a mixed (mucous-serous) nature. The red border has a transitional structure from the skin to the mucous membrane. It lacks hair and sweat glands. Complete enclosure of the epithelium on the red border does not occur. Located under the epithelium, its own layer in the form of numerous papillae is embedded in the epithelium. Each papilla contains wide capillary loops that come close to the surface and are easily visible through the epithelium, which explains the red color of the lips.
The junction of the red border with the mucous membrane of the lip is called Klein's zone.
Upon examination, the mucous membrane of the cheeks and lips appears quite smooth. At the level of the upper second molar there is a papillary elevation, in the center of which is the opening of the duct of the parotid salivary gland. In the area of the middle of the upper and lower lips, the mucous membrane forms folds (frena) dividing the vestibule of the oral cavity into the right and left half. The mucous membrane of the cheeks also contains salivary and sebaceous glands. Forming a transitional fold, the mucous membrane passes to the alveolar process, where it is called the gums. The edge of the gum is adjacent to the necks of the teeth and fills the interdental spaces, forming interdental papillae.
Normally, each papilla is quite dense and resembles a pyramid, the base of which is at the level of the necks of the teeth, and the apex is adjacent to the equatorial line of the teeth. The mucous membrane does not have a submucosal layer, so its own layer is directly fused to the periosteum, which ensures its immobility. It does not contain mucous glands, is rich in blood vessels and poor in nerves.
The relief of the mucous membrane of the floor of the mouth is uneven. Along the midline from the alveolar process to the tongue stretches a fold of the mucous membrane, or the frenulum of the tongue. To the right and left of the frenulum there are papillary elevations into which the ducts of the submandibular and sublingual salivary glands open. Somewhat posterior to the ducts lie the sublingual folds, on which the small ducts of the sublingual gland open.
Solid sky. There are transverse folds in the anterior part of the hard palate. Anterior to these folds, along the midline, not far from the central incisors, there is an incisive papilla, the position of which corresponds to the incisive foramen. Posterior to the transverse folds, along the longitudinal suture, is the palatine eminence. The mucous membrane in the midline and marginal zone does not have a submucosal layer and is firmly fused with the periosteum. In other areas, it has a submucosal layer, in which there is an accumulation of adipose tissue in the anterior part of the palate, and a large number of mucous glands in the posterior part.
The functional significance of the mucous membrane of the oral cavity and tongue is that it prevents the penetration of microorganisms into the underlying tissues, has absorption and excretory ability, and is involved in heat regulation. Thanks to the presence of receptors, the mucous membrane of the mouth and tongue perceives taste, pain, tactile, temperature and other irritations. The tongue is involved in the act of speech and chewing food. The mucous membrane of the oral cavity and tongue is highly reactive and its changes often express the presence of certain painful conditions of the body.
Doctor of Medicine, Professor, Head of Department therapeutic dentistry Altai State medical university(Barnaul)
Ph.D., Associate Professor, Department of Therapeutic Dentistry, Altai State Medical University (Barnaul)
Relevance of the problem
Physiological processes and presence systemic diseases the body, according to a number of authors, significantly affect the condition of the oral cavity. Aging, although not a disease, creates the preconditions for the development of age-related pathology. Among chronic diseases, diseases of the blood vessels and heart, central nervous system, gastrointestinal tract, diabetes and cancer.
There is reason to believe that the oral mucosa (ORM), being a complex multifunctional system, even before the period of the appearance of pathological elements can serve as an indicator general health body. However, studies devoted to this problem are few and concerned mainly with its changes in various diseases.
Purpose of the study
Assessment of changes in the oral mucosa at the light-optical and ultrastructural levels in some forms of visceral pathology, taking into account the age factor.
Material and methods
During the work, volunteer patients over 60 years of age with diseases were examined of cardio-vascular system(CC) - 10 people, gastric ulcer and duodenal ulcer - 10 people - and diabetes mellitus (DM) - 10 people. The control group consisted of relatively healthy elderly people without visible pathology of the oral mucosa.
To study the morphology of the mucous membranes, we used histological and electron microscopic studies of the areas of the mucous membranes where processes associated with pathological keratinization most often occur: underlip in the Klein zone, the cheek at the level of the closure of the teeth, the border of the hard and soft palate, the lateral surface of the tongue.
Light-optical examination of microbiopsy specimens measuring 2x2 mm and scrapings was carried out on a Jenaval microscope (Carl Zeiss, Jena, Germany) at a magnification of x250-400 using semi-thin sections (0.4-1 µm) stained with a 1% Azur II solution; electron microscopic examination of ultrathin sections, sequentially contrasted with uranyl acetate and lead citrate, under electron microscope Hitachi-600 (Japan) at a magnification of x3500-30,000.
Results and discussion
In biopsy specimens from non-keratinizing areas of the oral mucosa (lip and cheek) of relatively healthy elderly individuals, light-optical examination revealed the presence of a fairly pronounced superficial layer (up to 6-10 layers). The epithelial cells of the surface layer contained pyknotically altered nuclei and keratohyalin granules (Fig. 1).
Unevenly expanded perinuclear spaces were observed.
An ultrastructural study of individuals in the control group revealed a disruption of intercellular contacts with the formation of optically transparent areas between cells with fragments of the cytoplasmic processes of neighboring cells. Single mitochondria showed signs of destruction. Intercellular connections had the appearance of locking fastenings, but towards the apical surface the contours of the membrane were smoothed out, and the number of jagged connections and desmosomes decreased.
On the apical surface of the biopsy specimens, several layers of keratinocytes with increased osmiophilicity of the cytoplasm were determined. Superficial cells were larger in size and had fewer tonofilaments in the cytoplasm.
In the stratum spinosum, epithelial cells were connected to each other by jagged-wavy connections (Fig. 2).
Intercellular distances expanded unevenly closer to the surface layer. In the cytoplasm of spinous cells, large bundles of tonofilaments were oriented towards the peripheral parts of the cytoplasm and towards the zone of cell contacts. Ribosomes and mitochondria were concentrated predominantly in the central and perinuclear zones, and the presence of large keratohyaline granules was characteristic. The cytoplasm became vacuolated; quite large vacuoles were encountered, displacing the nucleus towards the cytoplasmic membrane. At the border of the spinous and basal layers, single Langerhans cells were found.
In the basal layer, cylindrical cells were located evenly along the basement membrane, intercellular spaces were not defined. Mitotically dividing cells were grouped predominantly at the bottom of the epithelial ridges. The number of mitoses reached 1-2 per 50-100 cells.
Intercellular contacts were maintained in the form of desmosomes and hemidesmosomes. Cytoplasmic organelles had a chaotic location, but their perinuclear concentration was traced. The filaments were structurally associated with ribosomes, less often with the outer membranes of mitochondria, which reflected the active processes of fibrillar protein synthesis. Single transepithelial migrating leukocytes were observed.
During light-optical examination, the basement membrane was a thin continuous line, uniformly stained with azure; its composition consisted of electron-transparent and electron-dense parts.
In the lamina propria of the mucous membrane, the papillary and reticular layers were distinguished. In biopsy samples of the lips and cheeks, the lamina propria formed numerous papillae, embedded in the epithelium, containing thin-walled vessels. In the case of atrophy, the lamina propria of the mucous membrane looked swollen, intense leukocyte infiltration was observed, the amount of collagen increased, and the thickness of the vessel walls increased.
In the mucous membrane of the tongue, regional histoarchitecture was preserved, the ratio of layers was not disturbed. The horny, granular, spinous and basal layers were differentiated. The biopsy specimens revealed a moderately pronounced stratum corneum, with microflora accumulating on the surface of the epithelium.
The study of scrapings on the keratinizing epithelium (the border of the hard and soft palate) made it possible to study the structural features of the chewing type of the oral mucosa. In the scraping, dark and light keratinocytes were differentiated (Fig. 3).
As a rule, narrow osmiophilic cells (dark) predominated, reflecting the process of intensive keratinization characteristic of the hard palate. They were characterized by a dense packing of thick bundles of tonofilaments embedded in an amorphous material. In dark cells, the fibrillar material was compactly located and lay against the background of a finely granular matrix.
Coccal microflora was found on the surface of the cells. In light-colored nucleated cells, the cytoplasm was filled with loosely arranged tonofibrillar material, among which rare small cisterns of the endoplasmic reticulum, lipid droplets, mitochondria with lysed matrix and cristae, and small accumulations of fine-granular material (ribosomes) were visible. There was slight adhesion of the same type of coccal microflora on the surface of dark keratinocytes.
In patients with various forms of somatic diseases, a change in the nature of keratinization was observed: on the one hand, hyperkeratosis developed in nonspecific areas (lip, cheek), which, as a rule, was of a protective nature; on the other hand, signs of atrophy and a decrease in the stratum corneum in the area of the hard palate appeared and on the lateral surface of the tongue. Violation of the histoarchitecture of the mucous membrane with hyperkeratosis indicated disturbances in the processes of differentiation, and with the development of atrophy - the process of desquamation of the epithelium.
Along with this, in the patients of the study groups, the amount of light-optically identified keratohyalin in the form of granules in the cytoplasm of the cells of the superficial and stratum corneum increased compared to the control. This indicated a violation of exocytosis, which ensures the barrier function of the epithelium. In the cells of the granular and spinous layers, especially in diseases of the gastrointestinal tract, keratohyalin was practically absent, which was noted in the literature earlier.
An ultrastructural feature of visceral pathology at the level of spinous epithelial cells was a change in the structure of tonofilaments, a violation of their clear orientation, and fragmentation of fibrillar material. As a consequence, in all main groups there was an expansion of intercellular distances (Fig. 4) and disruption of intercellular contacts (82±5.8% of observations), regarded as acantholysis.
Isolated desmosomes, fragments of cytoplasmic processes and organelles were detected in the expanded intercellular spaces. Decompensation of the barrier-protective function can be associated with a decrease in the amount of glycosaminoglycans in the intercellular spaces, since the glycogen content in polyhedral cells was significantly lower.
Against the background of somatic diseases, especially diabetes mellitus, the tinctorial properties of the cells of the spinous layer changed. In the preparations, three phenotypically different types of cells were differentiated in relation to azure staining - light, dark and intermediate. Light cells, classified as parakeratotic, were most often located in groups, Dark cells - narrow and long with osmiophilic cytoplasm due to randomly located thick bundles of tonofilaments - lay scattered.
The prevalence of light and intermediate forms in preparations of the hard palate in patients with visceral diseases indicated a violation of the histoarchitecture of the epithelium. In addition, differences in microbial colonization of dark and light cells were observed (Figure 5).
This phenotypic division of epithelial cells, and not differentiation processes, as some authors claim, in our opinion, explains the unevenness of their microbial contamination. It is important to note that microorganisms did not penetrate the cytoplasm of epithelial cells, but were located along the membrane. The exception was intracellular infections, in particular chlamydia, whose elementary and reticular bodies were found in isolated observations. In this regard, it can be assumed that the oral mucosa is an area for the introduction of microorganisms only when its integrity is violated or when specific infections invade.
Rare fixation of mitoses (1 per 200 cells) or their absence in basal epithelial cells in individuals with visceral pathology reflected a violation of the regeneration process. This is consistent with data on a decrease in the mitotic index in the elderly. An indicator of a decrease in the proliferative activity of the epithelium in elderly people with diseases of internal organs was an electron microscopically determined decrease in the number of pinocytotic vesicles and an increase in the number of tonofilaments in epithelial cells compared to young people, and its natural outcome was the development of atrophic processes.
A decrease in the barrier function of the epithelium was indicated pathological changes basement membrane, which consisted of its thickening, discontinuity and loosening, as well as disturbances in the lamina propria of the mucous membrane, which was characterized by an increase in the number of collagen fibers and a decrease in the height of the epithelial papillae. Thickening of the walls of blood vessels, expressed especially in patients with cardiovascular diseases, reflected the course of the systemic pathological process.
Sclerotic changes in the connective tissue and basement membrane and the relative reduction of the capillary bed of the lamina propria of the mucous membrane of the mucous membrane reduced the transport of electrolytes and plasma components into the epithelium and were the direct cause of the degenerative changes developing in it.
Some morphological signs (rare appearance of polymorphonuclear neutrophil leukocytes and Langerhans cells in scrapings and microbiopsy material, absence of functionally active segmented neutrophils and lymphocytes) indirectly indicated a decrease in the protective mechanisms of the mucous membrane.
Destructured neutrophils were observed extremely rarely, which confirms previously obtained data in the study of healthy oral mucosa. It should be noted that there was a decrease in the intensity of transepithelial diapedesis of lymphocytes, which generally reflected general decline activity of immunocompetent cells, associated both with the course of combined chronic somatic diseases and with the age of patients. These phenomena also occurred in the lamina propria of the RS.
Conclusion
In general, when conducting light-optical and electron microscopic examination of biopsy samples of the oral mucosa in elderly people who did not have somatic pathology, a violation of the histoarchitectonics of the lining epithelium (hyperkeratosis), moderately expressed acantholysis and dystrophic changes in the epithelial cells of the superficial and spinous layers, a decrease or absence of Langerhans cells, which can be regarded as age characteristics SOPR structures. At the same time, preservation of the mitotic activity of the basal epithelium and transepithelial migration of mononuclear cells was noted.
Analyzing samples of the oral mucosa in patients with various somatic diseases, it should be noted that there is a change in the basic tissue and cellular mechanisms of protection of the mucous membrane. In particular, physiological barriers were disrupted (atrophy, hyperkeratosis, formation of intraepithelial blisters), the level of nonspecific humoral factors (epithelial dystrophy, decrease in the number of Langerhans cells) and cellular mechanisms (absence of granulocytes, decrease in the level of transepithelial diapedesis) decreased.
The list of references is in the editorial office
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