*1.3.2 Secretory epithelium*

There are two types of glands—endocrine and exocrine.


There are irregular tight connective tissue sheath around the macroscopic glands which are parotid, submandibular, and sublingual gland. The connective tissue enters into the glands in the form of septa. The septa divide the gland into compartments. In the compartments, there may be acinus or tubules or both according to the type of the gland. Intralobulated duct channels are also included within the lobule. In the septa of connective tissue, interlobular channels are located. From these visible glands, the serous glands consist of acinus (alveolus), and the mucous glands are mucous tubules (**Figure 11a**–**d**). Exocrine glands can be subdivided into serous, mucous, and mixed glands according to the nature of the secretion they produce. Both serous- and mucous-secreting endpieces are covered with cubic epithelial cells which form intercalated (initial) ducts. Intercalated ducts combine to form the striated (intralobular) ducts. The intralobular ducts merge together to form the interlobular duct. These ducts are joined together and form "Stenson" in the parotid gland, "Wharton" in the submandibular gland, and "major sublingual" channels in the sublingual gland and open into the oral cavity. The most important features of intralobular ducts are the membrane folds extending from the cell basal to the nuclei. A large number of mitochondria were placed on the long axis of these folds. Such a location is particularly important for the salivary gland, which is functionally intense and consumes relatively more energy during its work. The parotid and the exocrine glands part of the pancreas are pure serous. The submandibular and sublingual glands are mixed glands [4–9].

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*Morphology of Salivary and Lacrimal Glands DOI: http://dx.doi.org/10.5772/intechopen.84380*

apical portion is stained with eosin [4–8, 10] (**Figure 11c**).

The abundant zymogen granules in the serous glands are found in the upper part of the cell cytoplasm. Serous glands produce a smooth flow and protein secretion. The duct channels are narrower than the mucous glands. The nuclei of the cells are located in the middle and are round in shape. In the sections stained with hematoxylin–eosin, the basal part of the cell is stained with hematoxylin, and the

Mucous glands secrete carbohydrate properties. Since these granules are lost when preparing hematoxylin–eosin stained sections, these parts of the cells are often seen as empty. Therefore, these glands secrete in dense consistency and are lightly colored, and the discharge ducts are wider than the serous glands (**Figure 11d**) [4–9]. The epithelial cells of the gland are divided into three types according to the type

1.Merocrine secretion: The secretory product is transported to the apical surface of the cell by vesicles. The vesicles are combined with the cell membrane and give their contents to the external environment by exocytosis. As in the pancreas, the most common form of secretion in the body is the merocrine type.

2.Apocrine secretion: While the secretory product is separated from the apical part of the cell membrane, it takes some cell membrane with it. This secretion occurs in the mammary glands, the apocrine of the skin, the ciliary (Moll's) of

3.Holocrine secretion: Secretion product accumulates in the cell that continues to mature; then the secretory product is excreted into the outer environment together with the cell in which it is contained. The ovaries, the fat in the skin, and the Meibomian glands in the eyelid are the examples [4–8].

a.The parotid gland is surrounded by irregular tight connective tissue called a capsule. The parts separated from the capsule move into the gland and are called septa. The septa separate the gland into lobules (**Figure 12a**). Each lobule is composed of spherical acini, which empty their serous secretion into intercalated ducts, from where it flows into striated (intralobular) ducts. We will see these ducts in the lobule. The intralobular ducts combine to form interlobular ducts. The interlobular ducts are located in the septa. Interlobular ducts leave the lobule and together with muscular arteries, veins, nerve, and lymphatic vessels. The interlobular duct channels are also known as excretory duct. Excretory ducts are emerged to form the main duct, "the Stenson." Round-shaped acinus is a part of the serous gland. The acinus (acinar cell) is formed by laying a single-layer cubic or prismatic epithelium on the basal lamina (**Figure 12b**). Fat cells which are one of the connective tissue cells are located between acini. Myoepithelial cells are located between epithelial cells and basal lamina. Contraction of myoepithelial cells accelerates the flow of saliva. Acinar secretion with serous content and secretion passes to intercalated ducts. Several intercalated ducts form an intralobular (striated) duct.

the eyelid, and the seromusin glands of the outer ear canal.

**2. Structure of major salivary glands**

*1.3.3 Serous glands*

*1.3.4 Mucous glands*

of secretion:
