Shadlinski V.B., Abdullayev A.S.
Azerbaijan Medical University, Department of Human anatomy, head of department, member of RAMS, doctor in medicine, professor
Azerbaijan Medical University, Department of Human anatomy, associate professor, PhD in Medicine
Structural features of the labial salivary glands of newborns and children up to 1 year
Summary. Preparations of the upper and lower lips of 12 newborns and 5 children up to 1 year were used. In newborns the largest salivary glands are located in the upper lip, where they are located in the submucosal layer of 3-4 rows, mainly along the branching vessels and nerves. The size of the inferior labial gland is significantly smaller than the upper labial glands. The difference in the number of glands of the upper lip in children under 1 year and newborns is not statistically significant. The size of the upper labial glands increases significantly compared with the previous age period.
The morphological and functional properties of the mucous membrane of the upper and lower lips are largely predetermined by the fact that, because of their anatomical location, they come into contact with food and inhaled air before their other organs of the oral cavity and by their secretion are not only involved in the initial stages of splitting carbohydrates, but also have a significant effect on some physiological processes occurring in the oral cavity [1, c.4-6; 2, p.157-162; 3, p.71-75; 4, p.146-154].
Despite the relatively small size, the large number of labial glands, localized in the submucosa and opening with its ducts to the epithelial surface of the mucous membrane of the lips prevents it from drying out, besides their secret restores cracks and abrasions on the lips, which, with reduced secretion, can have malignant transformations, performs epithelial function [5, c.90-93; 6, c.122-128; 7, c.28-31; 8, p.869-877; 9, p.802-809]. The growth of interest in morphologists in their studies of the labial salivary glands is obvious [10, p.934-938; 11, p. 847-856]. This is due, first of all, to specific topography and easily involvement of labial glands in many systemic and local pathological processes [12, p.717-721]. Using immunohistochemical methods, it has been established that secretor immunoglobulin A is produced in the labial glands, which participates in the immunology of the oral cavity [13, c.27-30; 14, p.223-232; 15, p.407-411; 16, p.167-177]. In recent years, the salivary glands have become the object of research in connection with the study of the correlation between their fatty infiltration and age, obesity and diabetes [17, p.537-542; 18, p.685-689]. The first of these studies found that age is correlated, although obesity also plays a significant role in changes. In the second study, it is argued that susceptibility to pathologies of the oral cavity in diabetes is associated with a decrease in secretion by the labial glands of statherin.
Researches has established that the labial glands themselves can become the etiological cause of lip cancer and in terms of the frequency of tumors of the salivary glands, the rank second, second only to the parotid gland [19, p.370-373; 20, p.275-280; 21, p.128-132]. The topography of the labial glands is of great importance for the normal functioning of the teeth of the frontal group – canines and incisors, their periodontium, for the development of caries in them and processes of stone formation and dental deposits [22, p.525-528; 23, p.234-242].
However, in our opinion, the morphological features of the labial glands in the early stages of postnatal ontogenesis, in particular, in the neonatal period and in children up to 1 year old, require closer attention. It is during this period that the main adaptive mechanisms of the mucous membrane of the upper and lower lips in children are laid and develop; the secretion carried out by the labial glands plays a significant role in this.
The labial glands of children with cleft lip were used in the study [24, p.502-510]. Along with adults, the labial glands of 3-year-old children were also studied [25, p.535-539]. Also, despite the abundance of literary sources on the morphology of the labial glands, it is necessary to note some contradictory data, especially regarding the amount of secretion produced by the minor salivary glands of the oral cavity; the work indicates that the small salivary glands produce half of the total oral cavity secret [26, p.243-254], whereas, there are studies in which this figure is defined as less than 10% [12, p.717-721]. This once again proves the importance of studying the quantitative indices of the glands, especially in the early periods of postnatal ontogenesis. There are some works related to this subject, however, the morphological and morphometric features of the labial glands in the early stages of postnatal life have not been studied in detail.
The purpose of the study was to study the structural organization of the salivary glands of the upper and lower lips based on histological, histochemical and morphometric research methods.
Material and methods. For microscopic examination, preparations of the upper and lower lips of 12 newborns and 5 children up to 1 year were used. At the same time, the upper and lower lips in the middle divided from the side of the skin into two parts — right and left. On the upper lip, an incision was made in the middle of the philtrum. Then both the right and left parts of the upper and lower lips were once again divided into two parts — the medial and lateral, i.e. the part closer to the corner of the mouth. Thus, a total of 8 pieces were obtained. The sizes of the pieces were as follows: length 10-15 mm, width 5-10 mm, thickness 3-4 mm, which corresponds to the general rules for taking material for fixation. Taking into account the specifics of the forthcoming study, the pieces intended for light-optical study were fixed in a 10% solution of acid formalin, dehydrated in alcohols of ascending concentration and housed into paraffin. Microtome sections with a thickness of 5 μm were stained both with trivial histological (hematoxylin-eosin, van Gieson’s stain, thionin) and selective histochemical methods (PAS-reaction). To clarify the relationship of the labial glands with the nerve structures of this area, silver impregnation method (according to Rasskazova) was applied. The arithmetic data obtained was subjected to statistical processing by methods of variation statistics. The nonparametric Wilcoxon U-test (Mann-Whitney) was used.
The results of the investigation and their discussion. The total number of salivary glands of the upper lip in newborns reaches 73.0 (64-79). The lower labial glands in newborns are statistically significantly higher with a level of probability p <0.001; at average number of 87.58, they have a minimum value of 77 and a maximum of 101 (table). In the lateral parts of the lower lip, 45.75 glands were found (31-58). The difference in the number of glands from the lateral areas of the lower and upper lips has a significant difference (p <0.001). In this age, compared with the previous one, no noticeable changes in the topography and the shape of the glands are observed. Some increase in the size of these glands should be noted. The largest salivary glands are located in the upper lip, where they are located in the submucosal layer of 3-4 rows, mainly along the branching vessels and nerves. The upper lip gland occupies an average area of 0.15 cm². The size of the inferior labial gland is significantly smaller than the upper and reaches an average value of 0.13 cm² (p <0.001).
Table of ratios of the number and area of the salivary glands of the upper and lower lips in newborns.
|The salivary glands
|The parts of lips||Total|
|Number of glands||Upper lip||38.42
|p1||Statistically not significant|
|P2||Statistically not significant||˂0.001||˂0.001|
Note: p – the statistical significance of the differences in the corresponding indices of the salivary glands of the lip according to the Wilcoxon criterion (Mann-Whitney) : p1 – the middle and angle of the lip; p2 – upper and lower lips.
In some glands the size and number of several lobules located along the length of the main excretory duct also increase. In the region of the lower lip, the secretor parts of the glands consist of 3-5 relatively large lobes, closely adjacent to one another. They have a rounded or oval shape and are located at the initial section and lateral branches of the main excretory duct. Their common duct is relatively wide, straight and opens on the epithelial surface of the mucous membrane with a funnel-shaped hole. In the area near the angles of the mouth among the glands, there are also bunch-form glands, looking like grapes. The main sections of them consist of a large number (from 10 to 14) of small, rounded lobules located on the lateral branches of their relatively narrow common excretory duct. According to its histological structure, the labial salivary glands of newborns are complex mixed (tubular-alveolar) glands, consisting of mucosal and serous cells. Each mucosal cell is bordered by a serous demilunes or crescents of Giannuzzi. Both types of cells are cylindrical in shape; single granular inclusions are located on the apical part of the cytoplasm.
The nucleus with poorly developed chromatin is localized at the base of the cells. Outside, the glands are braided by dark-crumbled, basket-shaped myoepithelial cells. The nuclei of these cells are oval, localized in the center of the cells. Excretory ducts lined by one, sometimes two-layer epithelium of cylindrical shape. Only occasionally in the cytoplasm of cells of the excretory ducts is determined perpendicular, very weakly pronounced striation. The common excretory ducts are lined with 3-layer epithelium with sharp borders and cylindrical cells.
Histologically in the glands are detected myelin and non-myelin nerves, following along the vessels and ducts. They form the nerve endings in the walls of blood vessels, on the end sections and in the excretory ducts of the glands. In some places in the lamina propria of the mucous membrane, a mildly expressed nerve plexus is revealed, from which the nerve fibers depart to epithelium. Nerve fibers entering the epithelium branch out among the epithelial cells and end with free nerve endings.
Children up to 1 year. In children up to 1 year, the total number of labial salivary glands is individual and varies. In the upper lip, the number of glands varies from 59 to 93 and has an average value of 75.6. The difference in the number of glands of the upper lip in children under 1 year and newborns is not statistically significant. The size of the upper labial glands increases significantly compared with the previous age period and reaches 0.192 cm² (p <0.001).
The lower labial glands, at 88.0, have minimum and maximum values of 68 and 105, respectively. In the central areas of the lower lip, an average of 42.0 glands are found (29-52), and in the lateral areas 46.0 glands (36-58). The area occupied by the lower labial glands is 0.159 cm² and is significantly less than the area of the upper labial glands (p <0.01). The lobes of the main sections of such glands, in turn, consist of lobules of various sizes and shapes, rather closely adjacent to one another. The excretory ducts of these glands are somewhat narrower, but longer than the ducts of the glands of the upper lip and often in the middle part of them are dilated in the form of an ampoule.
The ducts of the glands of the upper and lower lips are mostly straight, facing the cleft of mouth and perforate the mucosa for the most part at a right angle. The shape of the glands on the border of the lips and cheeks, near the angles of the mouth is different from the shape of the glands of the lips. The labial glands near the angles of the mouth have a complex, somewhat retracted shape. The ducts of such glands are long and narrow, are located in the center of the body of the gland and represent the main highway, from which narrow, short side branches extend at an acute angle to both sides (from 12 to 17). One part of such lateral branches of the main duct ends in lobes of a rounded shape, each of which consists of several small lobules of various shapes. Another part of the lateral branches is blunt, curved, short tubules.
Some main ducts of the glands of the magistral branching type are slightly curved near their openings and narrowed within the openings themselves and perforate the mucous membrane at an acute angle. Microscopic examination of the mucous membrane of the lips consists of loose unformed fibrous connective tissue. Proper plate forms microscopic size of papilla and is covered with stratified squamous epithelium.
In the submucosal layer of the lips, a significant number of labial glands are noted, which, in the form of their secretor parts, belong to complex tubular-alveolar formations. The structural features of the labial glands are mixed, but with a predominance of mucosal secretor sections and have the crescents of Giannuzzi. Mucosa cells larger in comparison with serous occupy the central part of the secretor section. The nuclei of mucosal cells are always located at their base, they are flattened. The cytoplasm of mucocytes has a cellular structure.
Intercellular secretor canaliculi are located between the glandular cells. Outside of the mucocytes are myoepithelial cells. Striated ducts are moderately developed, they are long and branching. There are often narrowings and balloon-like extensions found in them. The cylindrical epithelium lining them has mild basal striation.
In the postnatal period, the nervous apparatus of the mucous membrane of the lips undergoes further differentiation due to the changed conditions of existence and the way of feeding. In a well vascularized mucous membrane, predominantly the myelin nerve fibers along the vessels are passed. At the base of the papillae of the lips and salivary glands, receptor devices are found in the form of encapsulated glomeruli. The myelin nerve fiber enters the papilla and the secretor section of the glands, its covering expands as a bulb.
As noted, interest in the study of the morphology of the labial salivary glands is steadily increasing and the clinical significance of these studies is quite large. It is noted that in the postnatal period, the epithelial layer of the mucous membrane of the lips increases in thickness by two times and reaches up to 600 microns by the puberty period [27, с.19]. The glands of the lips increase significantly in childhood. However, in the childhood period, as indicated in the study, labial glands are characterized by lability of structural and functional differentiation, which lasts up to 14-15 years. It should be noted that the researchers did not associate the reason for such a lability of structural differentiation with the changed living conditions and nutritional patterns in children compared with the preterm intrauterine period. When studying the serous secretory parts of the labial glands in newborns and children, it was established that in the first serous acini consists of cells with basophilic cytoplasm [28, p.7-10]. In children, the secretory cells of the serous regions contain PAS-positive apical granules. Further, in the cytochemical relation, an increase in sialomucins and sulfomucins in these cells is observed. In addition to the qualitative changes in secretory cells, it is necessary to note the different features of the topography of the labial glands, namely the differences in their localization in the medial and lateral parts of the lips, finding them also between the muscle bundles, especially near the corners of the mouth. Our data are consistent with other studies on this issue [29, p.1552-1556].
Thus, given the importance of the secretion of the labial glands when restoring the mucous membrane of the upper and lower lips and taking into account our data on topographic-anatomical features, relationships with nerves and blood vessels, areas of the highest concentration of the salivary glands of the lips, more gentle surgical interventions are recommended. in the clinics of the maxillofacial, plastic surgery for the removal of tumors, congenital defects in order to preserve the integrity of the structure of the glands.
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