Book - Oral Histology and Embryology (1944) 10
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Orban B. Oral Histology and Embryology (1944) The C.V. Mosby Company, St. Louis.
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Chapter X - Glands of the Oral Cavity
The salivary glands of man are exocrine glands, the primary function of which is to transform and secrete materials brought to them via the circulating ﬂuids of the body. This function represents active Work in producing and discharging complex substances, such as mucin and ptyalin, which are not found in the circulating blood and lymph. The cells give morphologic evidence of their secretory function, and because they remain intact throughout a cyclic process of formation and discharge, these glands are classiﬁed as merocrine in type.
A secondary function of the salivary glands is to excrete certain substances. Evidence of this may be seen in comparing the constancy of the ratio between salivary and blood urea, nitrogen and creatinine.”
Saliva is the term applied to the accumulated secretory and excretory products discharged by the salivary glands into the oral cavity. The saliva is the ﬁrst of many digestive ﬂuids to act upon the food elements in the diet, its main actions being to assist in the mastication of food and to act as a solvent for bringing components into solution, thus facilitating the stimulation of the taste organs. Albuminous or serous cells of the glands liberate the enzyme ptyalin or amylase which causes a preliminary breakdown of carbohydrates. The mucous celLs liberate mucin which counteracts tendencies to desiccation of the oral membranes and dental hard structures, and aids in the lubrication of the bolus of food for deglutition. The proteins and salts of saliva act as buﬁers which tend to counteract the acids and alkalies in the oral cavity. Saliva is mechanically protective inasmuch as it serves to ﬂush the surfaces of the teeth and mucous membranes of food and debris. Its action of removing bacteria from ducts and surfaces is a safeguard against infection.
First draft submitted by Virgil D. Cheyne.
There is some indication that saliva, normally, contains an antibacterial factor which inhibits the growth and activity of aciduric bacteria in the oral cavity, and may act to prevent dental caries.‘ 1° There is also evidence, however, that the saliva of some individuals may supply the proper culture medium needed for the bacteria found in the mouth. Because of these contradictions the role of saliva in dental caries is as yet unsettled and requires further investigation.
The total daily amount of saliva secreted by man is approximately 1,500 c.c. This quantity is subject to great variation, depending upon age, exercise, and diet. It is materially inﬂuenced by physical and psychologic stimulation and varies Widely in different individuals. Of the total amount secreted, the large salivary glands (parotid, submaxillary, and sublingual) contribute by far the greatest amount. The quality is directly dependent upon the type of glands which participate in its formation.
The methods of collection and the type of stimulus have an important inﬂuence upon the composition of saliva. In man, the mixed excretions from the glands may be collected in the unstimulated or resting state by simply cxpectorating into a receptacle or, in the stimulated or active state, by chewing paraﬁin. Pure secretions from the individual glands may be collected by the use of Lashley’s double metal cup instrument which can be applied to the mucous membrane surrounding the papillae of the salivary ducts,” or by direct canalization of the ducts of the parotid, submaxillary, or sublingual glands. Saliva obtained in this manner is a clear, colorless ﬂuid. The function of certain glands or groups of glands in animals has been clariﬁed by selectively removing salivary tissue,‘ or by the experimental production of a ﬁstula, the duct being diverted to the outside of the oral cavity.
Mixed saliva is a frothy, slightly opalescent ﬂuid containing water, proteins, mineral salts, ptyalin, mucin, food particles, desquamated epithelial cells and salivary corpuscles. Its viscosity is dependent upon the predominating type of saliva secreted. Serous saliva imparts the Watery characteristics to the ﬂuid; mucin in the saliva renders it thick and ropy.
The speciﬁc gravity of mixed saliva varies from 1.000 to 1.020, the freezing point being lower than for the other secretions of the digestive glands. Results of hydrogen-ion determinations (pH) of saliva vary greatly, owing to individual variation, time of day, and diﬁerence in methods used for its determination. The mean or average pH of resting saliva is approximately 6.8, ranging from 5.6 to 7.6 and being highest just before meals.‘ Undoubtedly, oral hygiene and the nature of the oral ﬂora are also inﬂuencing factors.
Chemically, human, mixed saliva is a dilute solution containing about 0.2 per cent inorganic solutes and 0.5 per cent organic matter. The bulk of the inorganic portion consists of potassium and phosphate ions. The following elements, however, are found in appreciable amounts: Cl, P. Na, K, Mg, Ca, and S. The amount of NaCl is approximately 90 mg. per 100 c.c.; the amount of carbonate, as C0,, 13.0 mg. The C0._., Ca, and K present in the saliva exceed the concentration in the blood, While the sodium chloride concentration is lower in saliva. Oxygen is present in the human parotid saliva in amounts varying from 0.84 to 1.46 c.c. per 100 c.c.
Fig. 208. Smear of human saliva (Wright's stain). (Orban and Weinmannﬂ)
A large portion (0.4 per cent) of the organic matter in mixed secretions is mucin. With the exception of mucin, the principal organic constituents of saliva are albumin, globulin, amylase, and cholesterol. Urea, uric acid, creatinine, maltase, and ammonia are found in varying amounts. The ammonia originates largely from the decomposition of urea. In normal subjects values range from 1.28 to 13.66 mg. of ammonia nitrogen per 100 c.c. of saliva.” Total nonprotein nitrogen, urea plus ammonia, nitrogen, and uric acid average 37 per cent and 40 per cent, respectively, of the corresponding constituents of blood.” Blood amino-acids and polypeptides are not found in appreciable amounts in the saliva.
Sulfocyanate is generally present in the saliva to the extent of several milligrams per cubic centimeter. It is greatest in habitual smokers. The signiﬁcance of sulfocyanate in the saliva is not known, but it probably comes from ingested cyanides present in certain fruits, tobacco, and from the disintegration of protein material. It is, apparently, not related to tooth decay.”
The opacity of saliva is attributed mainly to the presence of desquamated epithelial cells and salivary corpuscles (Fig. 208), the latter consisting of polymorphonuclear leucocytes and lymphocytes. The epithelial cells are large and ﬂat with oval nuclei. They may be round or roughly irregular, with a granular cytoplasm. The salivary corpuscles are derived from the mucous membrane of the mouth, the tonsils and salivary glands. The average number of salivary corpuscles is, usually, less than 25 cells per cubic mm. of saliva, but higher counts (500 to 1,000) have been reported.” Lymphocytes constitute a relatively minor proportion of this number. Corpuscle counts are high after a night’s rest, low after meals. Their role is as yet imperfectly understood but it is the opinion of some investigators that they are phagocytic, reducing the bacterial ﬂora of the mouth.
The salivary glands are formed during fetal life as solid buds of oral epithelium with club-shaped ends pushing into the subjacent mesoderm. As the bud or anlage grows it proliferates distally, forming a cord of cells. The most distal portion forms the alveoli or fimctional elements of the gland. Cords and buds are at ﬁrst solid and are later hollowed out to form ducts and alveoli.
The bud of the parotid salivary gland appears as a shelﬂike outgrowth of epithelium during the fourth week of fetal life at the angle of the maxillary process and the mandibular arch (sulcus buccalis) ; the bud of the submaxillary appears in the sixth week, and that of the major sublingual (Bartholinian) during the eighth to ninth week from similar outgrowths located at the medial angle of the hollow between the tongue and mandibular arch (sulcus lingualis). The minor sublingual glands (Rivinian) arise as independent proliferations in the alveolingual region associated with the sulcus lingualis at the lateral margin of the plica sublingualis. Accessory and secondary lobes of the parotid and submaxillary glands become visible during the eighth to ninth weeks, as outgrowths arising from the cords of their respective glands. All the elements of the smaller sublingual, glossopalatine and palatine groups develop from the primitive oral epithelium. The anterior lingual glands are noticeable for the ﬁrst time at ten weeks. They start as epithelial proliferations located on the ventral surface near the tip of the tongue on both sides of the median line. Development of the labial glands takes place simultaneously with the anterior lingual glands. Lymphoid tissue is, frequently, found in the fetal salivary glands; this is especially common in the parotid. Occasionally, remnants of lymphatic tissue are found in the adult.
3. Classification of the Salivary Glands
The human salivary glands are usually classiﬁed either according to the type of cells or according to the location of the gland. Cells which liberate mucin are named mucous cells, and those Which secrete some form of protein (enzyme) are called albuminous or serous cells, but it is now quite evident that all mucous cells, as Well as all albuminous cells, do not produce identical products. In many cases the secretory granules of albuminous cells give a distinct reaction for mucin with mucicarmine stain. This would indicate that it is possible for these cells to secrete both mucin and protein substances. Although a simple classiﬁcation of the glands according to the chemical qualities of their secretion remains unsatisfactory, the glands are best classiﬁed as albuminous, mixed and mucous glands. The parotid gland of the adult is a pure albuminous gland. Glands with very few or no mucous cells are those of the vallate papillae. Glands in which both serous and mucous cells are present (true mixed glands) are referred to as predominantly serous or predominantly mucous, depending upon the ratio of the cell types. Those with a few mucous cells include the submaxillary gland (and the parotid gland of the newborn). Those predominantly of mucous character include the labial glands, small buccal glands, anterior lingual glands, and the sublingual gland. In man pure mucous glands are those at the base and border of the tongue, the glossopalatine glands and the palatine glands.
Classiﬁcation of the Oral Glands According to Location
A. Glands of the vestibule:
- 1. labial glands: a. superior labial glands b. inferior labial glands
- 2. buccal glands: a. minor buccal glands b. parotid gland
B. Glands of the oral cavity proper:
- 1. glands of the ﬂoor of the mouth (alveolingual complex)
- a. submaxillary (submandibular) gland
- b. major sublingual gland
- c. minor sublingual glands
- d. glossopalatine glands
- 2. glands of the tongue:
- a. anterior lingual glands b. posterior lingual glands (1) glands of the vallate papillae (2) glands of the base of the tongue
- 3. palatine glands
4. Secretory Cells of the Salivary Glands
Both albuminous and mucous cells vary in appearance with the flinctional changes of the gland.
The albuminous or serous cells of the parotid gland and other glands of the mouth probably do not perform an identical function; the cells, however, resemble each other closely. Their secretion is a thin watery ﬂuid containing a high percentage of organic and inorganic substances.
Albuminous cells are roughly pyramidal or polyhedral in shape, and form globular alveoli, the lumina of which are very narrow. The cells drain, for the most part, by intercellular secretory capillaries or canaliculi. In resting cells of a ﬁxed specimen the small highly refractive secretory granules, embedded in a closely reticulated cytoplasm, obscure the cell boundaries. These zymogen granules are the antecedents of the enzyme ptyalin. They accumulate between the nucleus and the free end of the cell. They are easily dissolved by chemical agents, but are more stable than the granules in the mucous cell. Following stimulation they diminish in number (Fig. 210).
In addition to the secretory granules the cytoplasm contains rod-shaped mitochondria, a Golgi net, and a cytocentrum which can be demonstrated only by special staining methods (Fig. 210). Intracellular fat droplets are common. The nucleus of the albuminous cell is large, spheroidal, and ﬁlled with abundant chromatin substance. Its size and location are somewhat dependent upon the stage of activity of the cell.
The mucous cell of the salivary glands secretes mucin, a glycoprotcin which, dissolved in water, becomes a lubricating solution called mucus. It makes the saliva highly viscid. In man, mucous cells are studied best in sublingual glands, the mucous glands of the tongue, the glossopalatine and palatine glands. They are also found in small mixed glands where they make up the greater number of alveoli; in the submaxillary gland they are few in number.
The mucous cells are irregularly cuboidal in form and aligned against a basement membrane (Fig. 211). Mucous alveoli vary from globular to long branching masses, their lumina forming large ovals or elongated tubules. In the ﬁxed preparation the nucleus is often deformed, shrunken; it is located at the base of the cell. The accumulation and removal of mucigen can be studied under favorable conditions. As the stimulated cell liberates its contents, the nucleus rises from the base and assumes an ovoid shape.
Fig. 209. Salivary glands of mad 1:1 muscle mug: ed.5°°?esi:11l1(-er a1;3&ﬂT:‘f1dlt:1:P;nudib1e and mylohyold
Fig. 210. A1buminoua gland. cycle is indicated by the letters 9. to g.
0" - Mucous cell Arrangement o1'_ cells in Glands
Mucigen granules cannot be observed because of their labile character except in fresh condition or by special methods of ﬁxing and staining, whereby they can be stained speciﬁcally with mucicarmine and mucihematin. Mucous cells which have lost their granules have an empty appearance and the remaining cytoplasm takes a faintly blue stain with hematoxylin. In properly prepared specimens a few irregular mitochondria, a Golgi net and a cytocentrum can be demonstrated; fat glob ules are a constant feature.
Fig. 212. Semi-diagrammatic drawing or a. section through a mixed alveolus in the submaxillary gland. Serous cells forming a. demllune around the mucous cells.
In mixed glands mucous and serous cells are combined in such a Way that either all the cells of some alveoli are serous, and all the cells of others mucous; or that within the same alveolus both serous and mucous cells are present. In a mixed alveolus the albuminous cells occupy a position at the terminal or peripheral region. They are found as small crescent-shaped clumps which cap the mucous cells: crescents or demilunes of Gianuzzi (Figs. 212 and 215, a). Crescent cells are somewhat smaller, more ﬁnely granular, and darker staining than mucous cells in ordinary preparations.
The secretory surfaces of the mucous cells form the lumen of a mixed alveolus. The cells of the crescents do not reach the lumen and discharge their secretion through ﬁne secretory capillaries which pass between the mucous cells (Fig. 212).
5. Myoepithelial Cells
In all salivary glands a syncytium of branching stellate cells surrounds the ducts and cells of the terminal secretory portions. They are in close contact with the bases of the glandular cells and lie between them and the basement membrane. They lie in a similar location in the ducts. Viewed from the periphery, they appear as spider—like structures embracing the alveoli (Fig. 213). Although probably of epithelial origin, these cells function as a part of the supporting structure of the glandular elements and are called basal or basket cells, or myoepithelial cells. The body of the myoepithelial cell is made up of a dark, angular nucleus with a scanty amount of cytoplasm containing ﬁne, straight ﬁbrils which continue into many tentacle-like processes that encircle the basal portion of the alveolar cells. In cross section only their nuclei are visible. The cells become especially prominent after treating fresh glandular tissue in the state of active secretion with osmic acid or by teasing fresh glandular substance in water.“
Fig. 213. Albuminous alveoli and striated duct or subma.xilla.ry gland with myoepithelial cells. (Modiﬁed after Zimmennannﬁ)
It is generally believed that myoepithelial cells are contractile cells which facilitate the movement of the secretion into and through the ducts. The phenomenon which is known as motor effect of the sympathetic nerves on the large salivary glands is probably caused by contraction of these cells under nervous stimulation.“ True muscular tissue is absent in the salivary glands.
Fig. 214. Diagrams of the duct system and terminal‘ secretory portions or salivary A. Parotid. B. SubmaxilIary. G’. Sublzlngual. (Modiﬁed after Brauaﬁ)
6. Duct Elements
The duct system of the salivary glands is complex and branching (Fig. 216). The smallest excretory channels are the intercalated ducts or the so-called necks or isthmuses. These connect the terminal alveoli with the excretory system. An outstanding characteristic of the intercalated ducts is their thin Wall and relatively small diameter. They are always surrounded by moyepithelial cells ‘(Fig 213). The cells are simple, low cuboidal in type, remain relatively undifferentiated, and take ordinary stains very poorly. They are of variable length depending on the type of gland which they drain. The parotid gland has long intercalated very short and inconspicuous (Fig. 214). In pure mucous glands the cells abut directly upon the distal tubules of the larger excretory ducts.
Fig . 216.—Reconstruction of a terminal portion and its duct or a salivary gland (a). (b) ross section through serous alveolus. (0) Cross section through mucous alveolus. (d) Qross section through lntercalated duct. (a) Cross section through striated duct. (Maximow and Bloom“)
In the parotid and submaxillary glands striated ducts (secretory ducts, salivary tubules) intervene between the intercalated ducts and the larger excretory ducts. These ducts are believed to secrete water and inorganic salts which act to dissolve the antecedents secreted by the alveolar cells. In the striated ducts the epithelial cells are regular and columnar in form and arranged in a single layer. The cytoplasm is ﬁnely granular and contains a nucleus which is centrally placed. The perpendicular striations from which the cells derive their name are conﬁned to the outer or basal zone near the basement membrane (Figs. 215, 217). In the larger ducts (parotid, submaxillary, major sublingual) the epithelium is columnar and pseudo-stratified; a basement membrane is distinct between epithelium and connective tissue wall. Where the ducts open into the oral cavity the walls fuse with the mucous membrane.
A common feature of compound glands in general is the presence of secretory capillaries or canaliculi which arise from the smallest excretory ducts and penetrate between the functional cells at their boundaries (Figs. 212, 215). The purpose of secretory capillaries is to increase the drainage capacity of alveoli composed of multiple layers of cells and, for that reason secretory capillaries are a constant feature of mixed alveoli. The capillaries are most effectively demonstrated with silver impregnation.
7. Interstitial Connective Tissue, Blood, Lymph and Nerve Supply
The interstitial substance of the salivary glands is loose connective tissue made up of a large number of ﬁbers. The ﬁbers run in all directions to form networks which surround and support the various elements. In it are ﬁbroblasts, macrophages, plasma and fat cells which vary in relative number with the type of gland. Around the terminal alveoli and ducts, located peripherally to the myoepithelial cells, the connective tissue forms a basement membrane.
The salivary glands possess a rich blood supply. The larger arteries follow the course of the excretory ducts, giving off branches which accompany the divisions of the ducts to the lobules; the capillaries form dense networks on the outer surface of the basement membrane of alveoli and ducts. The veins and lymph vessels follow the arteries in reverse order to drain the gland. The main branches of the nerves supplying the salivary glands also follow the course of the vessels to break up into terminal plexuses in the connective tissue adjacent to the alveoli. Both sympathetic and parasympathetic ﬁbers pass through the basement membrane and end in varicose ﬁlaments and budlike expansions between the secretory cells.
8. Major Salivary Glands
The parotid, submaxillary and sublingual glands are often classiﬁed as the salivary glands proper. Because of their size and the volume of saliva which they contribute they deserve special consideration. Physiologic investigations have been, for the most part, carried out on these glands but conclusions which have been drawn from their study can probably be applied with little change to the numerous smaller glands of the oral cavity. A comparison of the anatomic features of the three large salivary glands is presented in the accompanying table.
COMPARISON or rm: MAJOR Sanrvucr GLANDS (Amen Cownnv)
Size and Largest; main and ac- Intermediate; well lim-Smallest; major gland shape cessory parts both en- ited and encapsulated; and several minor
capsulated; compound, compound, branched, ones; no capsule; com branched, alveolar alveolar, partly tubular poxmd, b ranch e d, tubnlo-alveolar
Posiﬁon A r ound mandibular Beneath mandible (also In ﬂoor of mouth ramus anterior to ear called submandibular gland)
Ducts Parotid (Stenson’s)ductSubma.xi1lary (Whar- Major sublingual (Baropens opposite second ton’s) duct opens on tholin’s) duct opens upper molar; double either side of frenu- near submaxillary layer columnar cells on lum of tongue; struc- sometimes by common in a r k e d basement ture same aperture, also several membrane minor sublingual
(Rivinian) ducts; structure same
Secretory Single layer very con- Same but somewhat Rare or absent
ducts spicuously striated longer and may coneolumnar cells tain yellow pigment
Inter- Long, narrow, brancl1- Much shorter but similar Absent
calated ing made of single structure ducts layer of ﬂattened cells
59°79“?! 5610115 8-1V601i, 1111160115 Serons alveoli predom-Major gland: mucous
epithe- alveoli rare (in new- inate, some mucous al- alveoli predominate, hum born) veoli have serous cres- many serous crescents cents and alveoli. Minor glands all mucous Interstitial Fat cells most abundant Connective tissue septa ‘$188118 most abundant Ni’-"73 Sensory: ﬁfth nerve. Sens ﬁfth nerve. Sensory: ﬁfth nerve WPP1)’ Secretary: (1) sympa- Secretory: (1) sympa-Secretory: same as subthetic, superior cer- thetic, same; (2) maxillary gland
vical ganglion (vaso- parasympathetic, constriction); seventh‘ nerve, chords (2) parasympathetic, tympam, subrnamllary ninth nerve, ﬁtic gan- ganglion (vasod1laglion (vasodilation) tion)
The parotid gland (glandula parotis) is the largest of the salivary glands. Its superﬁcial portion is located in front of the external car on the lateral surface of the masseter muscle and extends slightly backward below the external auditory meatus. Its upper corner never transgresses the zygomatic arch, the lower corner reaches into the neck as cervical lobe (Fig. 209). The deep part of the parotid gland ﬁlls the retromandibular fossa. The gland is enclosed within a strong capsule which is tightly adherent and continuous with the connective tissue separating lobes and lobules. Accessory parotid glands are often found alongside the parotid duct.‘
The parotld gland empties by the parotid duct (ductus parotideus, Stenson’s duct) which is given off at the anterior corner of the gland, continues forward, turns around the anterior border of the masseter muscle, pierces the buccinator muscle and mucous membrane of the cheek to open opposite the upper second molar. Usually a small papilla marks the opening.
Fig. 216. Section through a human parotid gland. Intercalated duct Striated duct ,, new W4, A *-W’-r—‘ ' - - --— striated duct
Fig. 217. HIigher magniﬁcation of ﬁeld X in Fig. 216.
Fig. 218. Section through a human submaxillary gland.
Fig. 219. Higher magniﬁcation or ﬂeld X in Fig. 218.
The parotid gland of the adult is made up entirely of albuminous cells (Fig. 216). The alveoli which form small tightly packed oval masses are drained by long thin branching intercalated ducts; striated tubules are conspicuous (Fig. 217).
The parotid gland produces a thin and watery saliva which serves for the moistening and cleansing of the mouth cavity. It contains, besides salts and proteins, the enzyme ptyalin (amylase) which acts chemically to hydrolize starch into simpler compounds.
Fig. 220. Section through a. human major sublingual gland.
Fig. 221. Higher magniﬁcation of ﬁeld X in Fig. 220.
The submaxillary gland (submandibular gland; glandula submaxillaris) of man comprises one component of the group of glands in the ﬂoor of the mouth sometimes designated as the alveolingual complex.‘ It is ovoid in form, loosely encapsulated and about the size of a walnut. The greater part of the gland is located in the submaxillary triangle behind and below the free border of the mylohyoid muscle (Fig. 209). It is usually divided into several large lobes by deep incisures penetrating to the hylus. A tongue—like extension of the gland usually lies above the mylohyoid muscle close to the sublingual glands. It, occasionally, extends forward under cover of the lesser sublingual gland, nearly to the midline, and is designated as the secondary submaxillary gland proper.
The submaxillary gland including its accessory portions drains by the submaxillary duct (Wharton’s duct) which is composed of many smaller ducts arising in the lobules of the gland. The submaxillary duct is much thinner than the parotid duct. The supporting stroma contains a few longitudinal smooth muscle cells. It opens by a narrow oriﬁce on the summit of a small papilla, caruncula sublingualis, at the side of the lingual frenulum at the ﬂoor of the mouth.
In man, the submaxillary gland is of the mixed type with albuminous elements predominating (Fig. 218). Many purely serous alveoli are present; infrequently occurring mucous alveoli are usually capped by demilunes of serous cells. The intercalated ducts of the submaxillary gland are relatively short (Fig. 214), but similar in structure to those of the parotid gland (Fig. 219). The striated tubules are also structurally similar to those of the parotid but are somewhat longer (Fig. 214).
The secretion of the submaxillary gland contains mucin and is, consequently, more viscid than that of the parotid gland. It is described as clear and abundant. It varies, however, both in quantity and quality with the type of stimuli.
The sublingual glands form a composite of one larger and several smaller glands which open independently into the oral cavity. The larger or major sublingual gland (Bartholinian gland) is drained by a single duct, major sublingual duct, Bartholin’s duct. The smaller glands, Rivinian glands, are usually 8 to 20 in number and drain by separate openings, Rivinian ducts. The greater and lesser sublingual glands plus the supramylohyoid submaxillary gland sometimes carry the inclusive designation of “massa sublingualis.”‘
The sublingual gland or glands of the adult are the smallest of the units comprising the salivary glands proper. The greater sublingual is narrow, ﬂattened and elongated; it is situated in the ﬂoor of the mouth in the sublingual fold (Fig. 209). The course of the duct which drains it is roughly parallel to and a little lateral to the submaxillary duct. It opens into the mouth at the side of the frenulum of the tongue on the salivary caruncle with Wharton’s Qluct, in most cases; occasionally, however, the duct opens independently into the oral cavity near the submaxillary duct.
Some of the ducts of Rivini which do not take part in the formation of the larger sublingual duct, join the submaxillary duct, others open separately into the mouth on an elevated crest of the mucous membrane, plica sublingualis.
The large sublingual gland in man is a mixed gland in which the mucous elements predominate (Figs. 220, 221, 222). Most alveoli are purely mucous, the albuminous cells are mostly found as demilunes in mixed alveoli. Purely serous alveoli are rare. The smaller sublingual glands are, for the most part, mucous glands.
Fig. 222. Section thro h a human sublingual gland with long tubulo-alveolar terminal no ons. (Courtesy Army Medical Museum.)
10. Minor Salivary Glands
The labial glands, which are located in the inner surface of the lips, are of the mixed type. They are variable in size and closely packed in the submuoosa where they may be easily palpated. They are not encapsulated. The secretory portions may contain both serous and mucous cells lining the same lumen but more often typical demilunes are formed. A considerable number may contain only mucous cells (Fig. 223). The cells have a distinct muco-albuminous character, the intercalated ducts are short.
The buccal glands, which are a continuation of the labial glands, bear a marked resemblance to those of the lips. The glands which lie in the immediate vicinity of the parotid duct opening, and drain in the third molar region, are frequently designated as the molar glands (Fig. 224).
The glossopalatine (isthmian or faucial) glands are pure mucous glands; they are located in the isthmus region and are a continuation, posteriorly, of the lesser sublingual glands. They ascend in the mucosa of the glossopalatine fold. They may be conﬁned to the anterior faucial pillar or extend into the soft palate to fuse with the palatine glands pI‘0PeI‘- They may also be seen on the lingual side of the retromolar area of the mandible. The palatine glands which occupy the roof of the oral cavity can be topographically divided into ( 1) glands of the hard palate; (2) glands of the soft palate and uvula. They are composed of independent glandular aggregates numbering approximately 250 in the hard palate, 100 in the soft palate, and 12 in the uvula. In the posterior area of the hard palate the glands lie between the mucous membrane and bone supported by a dense framework of connective tissue characteristic of this region. Continuing backward, the lateral groups become arranged into compact rows and take on considerable size (Fig. 225). They merge with those of the soft palate and form a thick layer between the mucous membrane and palatal musculature (see chapter on Mucous Membrane).
Fig. 224. Section through a human retromolar gland. Palatine Glands
Fig. 225. The palatine glands. (Sicher and Tandlerﬁ)
The structure of the palatine glands is that of long branched tubulo-alveoli connecting with single ducts. The predominating cell produces only mucus. Cells of the so-called intercalated ducts are converted into mucous cells in the palatal glands, and function as part of the elongated alveoli.
The glands of the tongue are of three types: serous, mucous, and mixed, the mucous being the most numerous. The anterior lingual gland (gland of Blandin-Nuhn) is located close to the inferior surface of the tongue, one on each side of the frenulum near the apex. The structure is composed of a group of raccmose glands embedded deeply Within the structure of the tongue (Fig. 226). Approximately ﬁve small ducts open Imder the tongue on the plica ﬁmbriata. The gland is of the mixed type although chieﬂy mucous in its anterior part. In its posterior part are found mucous alveoli capped with delicate demilunes, with a distinctly serous character.
The glands of the base and border of the tongue are of the pure mucous variety. The glands which are located on the surface of the tongue -bear long mucous tubular alveoli and ill-deﬁned ducts. In the immediate region of the vallate and foliate papillae they are replaced by the serous glands of the gustatory papillae (glands of v. Ebner). These glands pour a watery secretion into and serve to wash out the furrows of the circumvallate papillae. (See chapter on Mucous Membrane.)
Fig. 226. Longitudinal section through the tip of the tongue of a. newborn child. Anterior lingual gland.
11. Clinical Considerations
Pathologic disturbances of the salivary glands are relatively infrequent. When they do occur the result may be either an increase in the ﬂow of saliva (sialism) or a decrease (xerostomia). Secretion is increased in mental and nervous affections, occasionally in acute fever and during attacks of generalized stomatitis. Injections of certain drugs, particularly mercury and iodine compounds, are likely to produce an abundance of saliva. Other than the discomfort. an abundance of saliva results in no known harm. Disturbances that cause a reduction of saliva, however. bring about loss of the protective action which this ﬂuid exerts upon the teeth and oral tissues. Atrophy of the secretory elements and their replacement by adipose tissue occurs in old age. The resulting xerostomia may cause discomfort to a. patient wearing artiﬁcial dentures. Through its loss the lubricating, cleansing and neutralizing power of the saliva is forfeited. Moreover, a normal ﬂow of saliva is a mechanical guard against infection.
Inﬂammation is frequently the cause of disturbances in the ﬂow of saliva. It is common in the parotid gland, less common in the submaxillary, sublingual and smaller glands. Pyogenic organisms are the chief offenders in acute infections. Most frequently in debilitated individuals suffering from infectious fever or general postoperative complications, the infection may be conﬁned to the ducts (sialodochitis) or, less frequently, spread through the parenchyma of the gland (sialadenitis). Inﬂammation of the glandular substance itself, when it occurs, is usually severe. When it progresses to suppuration, surgery is indicated.
Glass blowers and players of wind instruments are especially subject to infection of the salivary ducts. The heightened intraoral pressure tends to dilate the ducts, counteract the normal outﬂow of saliva, and bacteria are forced into the ducts.
Infection of the ducts of a salivary gland may cause a mass of dead cells or bacterial debris to become lodged in a constricted area of the ducts. If allowed to remain, such a mass acts as a nidus in which calcium salts are deposited. This leads to the formation of a salivary calculus. Salivary calculi occur most often in the submaxillary duct (90 per cent) where they vary in size from minute particles to deposits several centimeters in length. If they are retained their obstructive inﬂuence invites inﬂammatory exacerbations aﬁecting the parenchymatous tissues; or, if saliva is retained under pressure for any length of time, atrophy and ﬁbrosis of the gland may result. Salivary duct calculi are easily detected by palpation or roentgenologic examination, and are removed by gentle pressure or by excision. When calculi involve the glandular sub stance proper, total extirpation of the gland may be advisable.
Infectious parotitis (mumps) is the most common example of a virus infection of the salivary glands. This disease shows tender swelling of the parotid region, usually bilateral, with mild fever but no leukocytosis. Tuberculosis, syphilis, and actinomycosis may occasionally affect the salivary glands. The etiologic agents may be hematogenous or carried to the glandular substance through the ducts.
Mikulicz’ disease is a type of granulomatous inﬂammation, rare in occurrence, which affects both the salivary and lacrimal glands, and occasionally, the lips and eyelids. It makes its appearance as a symmetrical, indolent enlargement which may last several years. A dry mouth is one of the accompanying symptoms. Histologically, there is a lymphocytic inﬁltration of the interstitial connective tissue and, if persistent, ultimate destruction of the parenchymatous elements.“ The blood picture remains normal. It must be diﬂerentiated from Mikulicz’ syndrome which is associated with such general processes as leukemia, Hodgkin’s disease, and syphilis. A variety of tumors have been described in connection with the salivary glands: mixed tumors, carcinoma, sarcoma, and several other types are found of which about 75 per cent occur in the parotid. Of this number about 95 per cent are of the mixed variety.
Congenital malformations of the salivary glands may vary from atresia of the ducts to complete aplasia of the gland. Such disturbances are more common in the ﬂoor of the mouth in connection with the alveolingual complex, but they are not uncommon in the parotid area. Atresia is less common than aplasia, but when present causes disﬁguring cysts or tumorlike growths. The large sublingual gland is most frequently aﬁected, giving rise to the so-called ranula, in the ﬂoor of the mouth. The glands of Blandin-Nuhn, located in the anterior part of the tongue, are susceptible to cystic involvement as a result of closure of their ducts. These cysts are designated as mucous cysts or mucoceles. Mucoceles are quite commonly found in connection with the smaller glands of the oral cavity, where they probably result from trauma, a mild infection of the duets with consequent closure. They are, however, of little concern and usually disappear after rupture and discharge of their contents.
Aberrant glands are encountered occasionally in the alveolingual area. They are accessory glands which have become detached from the duct system. These glands remain functional but because they-lack an excretory duct, the secretion accumulates within their structure and causes distention with cyst formation.
The use of rubber dam or prolonged pressure by cotton rolls can occlude the opening of one of the salivary ducts. The resulting swelling occurs at the time the work is in progress, and disappears soon after the obstruction is removed and the saliva has an opportunity to discharge.
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