**5. Histology**

• **Interlobular ducts**: Those ducts which lie within the connective tissue within the lobules of

These are lined by single layer of cuboidal epithelium and are surrounded by myoepithelial cell bodies, and their processes typically are found along the basal surface of the duct. Under the light microscope, the intercalated ducts are difficult to identify as they are compressed between the secretory units. Under the electron microscope, the intercalated ducts have centrally placed nuclei and a small amount of cytoplasm containing some rough endoplasmic reticulum and a small Golgi complex. A few secretory granules may be found in the apical cytoplasm, especially in the cells located near the endpieces. The apical cell surface has a few short microvilli projecting into the lumen, and lateral surfaces are joined by junctional complexes. The macromolecule components, i.e., lysozyme and lactoferrin, are stored in the

The striated ducts receive the primary saliva from the intercalated ducts which constitute the largest portion of the duct system and are lined by columnar cells with a centrally placed large, spherical nucleus and pale, acidophilic cytoplasm. Under the electron microscope, the basal cytoplasm of the striated duct cells is partitioned by deep infoldings of the plasma membrane producing numerous sheetlike folds that extend beyond the lateral boundaries of the cell and interdigitate with similar folds of adjacent cells. Between the membrane infoldings, a large amount of radially oriented mitochondria are located in the portion of the cytoplasm. The combination of infoldings and mitochondria accounts for the striations seen in the light microscope. These ducts are involved in active transport and are considered as site of electrolyte reabsorption especially of sodium and chloride and secretion of potassium and bicarbonate. They also synthesize and secrete glycoproteins such as kallikrein and epidermal growth factor.

These ducts are located in the connective tissue septa between the lobules of the gland and are larger in diameter than striated duct. These ducts are lined by pseudostratified epithelium with columnar cells extending from the basal lamina to the ductal lumen and small basal cells that sit on the basal lamina. As the smaller ducts join to form large excretory ducts, the number of basal cell increases, and scattered mucous (goblet) cells may be present. The main excretory duct may become stratified near the oral opening. Tuft or brush cells with long stiff microvilli and apical vesicles are seen and are considered as receptor cells as they show nerve endings adjacent to the basal portion of the cell. Dendritic cells are also seen and play an

The cells that are found in the connective tissue of the salivary glands are similar to those in other connective tissues of the body and include fibroblasts, macrophages, mast cells,

the gland. The excretory ducts are interlobular ducts.

secretory granules of the intercalated duct and contribute to the saliva.

*4.3.1. Intercalated duct*

70 Histology

*4.3.2. Striated ducts*

*4.3.3. Excretory ducts*

important role in immune surveillance.

**4.4. Connective tissue elements**

#### **5.1. Major salivary glands**


**Figure 2.** Histology of serous gland [3].

well-being of mouth. The whole saliva that bathes the oral cavity is primarily a mixture of secretions from the paired major (parotid, submandibular, sublingual) glands and the numerous minor (labial, buccal, palatine, and lingual) glands. The formation of saliva occurs in two stages:

**1. Formation of macromolecular components:** The structure of acinar cells consists of abundant RER, prominent Golgi complexes, and numerous secretory vesicles. Synthesis of secretory proteins begins with gene transcription and manufacture of mRNA to carry the sequence information from the nucleus to ribosome in the cytoplasm. Protein synthesized in the RER is settled to the Golgi complexes in transport vesicles. After fusion of their unit membrane with surface cell membrane, they rupture and they are released to the external environment. Rupture and rearrangement of the lipid layer of both permit the continuity

**2. Formation of fluid components:** After appropriate stimulation it is thought that the free Ca++ is released from storage site within the endoplasmic reticulum. Free cytoplasmic Ca2+ concentration can increase five- to tenfold in a second after such a stimulation which brings out significant compensatory changes that include the opening of the two membrane ion

relocations is a flux of water into the lumen via the osmotic coupling of NaCl and H<sup>2</sup>

**a.** Many bacteria need a specific pH for growth; saliva prevents potential pathogens from colonizing in the mouth by denying them optimal environmental conditions.

**b.** Plaque microorganisms can produce acids from sugars, which if not rapidly buffered

• **Digestion:** It provides taste acuity, neutralizes esophageal contents, and forms the food

• **Taste:** It dissolves substances to be carried to taste buds and also contains a protein, called

**a.** Lactoferrin binds free iron and in doing so deprives bacteria of its essential element.

and Cl− occurs. The Cl− exits the cell between the channels at luminal sur-

enters the lumen through the paracellular pathway. The result of these ionic

is released from the cell, a compensatory

O.

Salivary Glands

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http://dx.doi.org/10.5772/intechopen.81213

and Cl−. When K<sup>+</sup>

• **Protection:** The protective functions of saliva is expressed as:

and cleared by saliva can demineralize enamel.

• **Antimicrobial action:** This occurs in various ways as:

**b.** Lysozyme hydrolyzes the cell wall.

gustin, which is necessary for growth and maturation of taste buds.

of the granule membrane and cell membrane.

channels for passage of K<sup>+</sup>

uptake of Na<sup>+</sup>

face, and Na<sup>+</sup>

**a.** Lubricant

bolus.

The functions of saliva are:

**b.** Mechanical washing

• **Buffering:** This occurs in two ways:

**Figure 3.** Histology of mixed gland [3].

demilunes and may be present at the blind ends of the tubules. The intercalated and striated ducts are poorly developed, and mucous tubules open directly into ducts lined with cuboidal or columnar cells without typical basal striations.

#### **5.2. Minor salivary glands**

