**2. Overview of salivary glands**

The salivary glands can be classified as major and minor salivary glands. The major salivary glands, located outside the oral cavity include the parotid salivary gland, submandibular/ submaxillary salivary gland and sublingual salivary gland. The minor salivary glands are

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

classified based on their location in the oral cavity as labial/buccal glands, glossopalatine glands, palatine glands, lingual glands which are further classified as anterior lingual (glands of Blandin and Nuhn) and posterior lingual glands (Von Ebner's) [1, 2]. The following diagram (**Figure 1**) shows the anatomical location of major and minor salivary glands. The salivary glands consists of a secretory part and ducts (**Table 1**).

**S. no Salivary gland Salivary gland duct Location of salivary duct orifice**

2. Submandibular Wharton's duct Opens at sublingual papillae

**Table 1.** Location and names of salivary gland ducts.

1. Intercalated duct Connect the terminal secretory

2. Striated duct Intercalated ducts drain into

3. Interlobular duct/ excretory duct

**Table 2.** Description of salivary ducts.

**Figure 2.** Architecture of salivary ducts and acini.

ducts

ducts

**S. no Duct Description Epithelium**

striated duct

unit with the next system of

Formed by joining of striated

3. Sublingual Bartholin's duct Opens with or near submandibular duct

4. Minor salivary glands Short ducts Open directly via short ducts into mouth

1. Parotid Stensen's duct Opens at papilla in buccal mucosa opposite maxillary

second molar

Duct of Rivinus Opens independently along sublingual fold

Single layer of low cuboidal cells

outer connective tissue adventitia

under light microscope

Tall columnar epithelial cells with centrally placed nucleus. Cells are partitioned by deep sheet like foldings of membrane, which appear as striations

Secretions of Human Salivary Gland http://dx.doi.org/10.5772/intechopen.75538 5

Pseudo-stratified columnar epithelial cells with

#### **2.1. Parenchymal elements of salivary gland**

The salivary glands are made of secretory units called acini, which are made up of acinar cells which could be serous or mucous. The serous cells are pyramidal or triangular in shape while the mucous cells are columnar in shape. The serous cells are occasionally seen capped by structures called demilunes. The acini cells are surrounded by contractile cells called as myoepithelial cells/basket cells, which are responsible for the flow of secretions of saliva by contraction of the cell. The acini of salivary glands are connected to hollow tubular structures which are called salivary ducts. The lining of the duct changes with the type of duct and its location within the salivary gland [1–3]. A description of the ducts observed is given in **Table 2** and the parenchymal elements are shown in **Figure 2**.

#### **2.2. Development of salivary gland**

Salivary glands arise from the ectoderm of oral cavity. The minor salivary gland arise from the oral and nasopharyngeal ectoderm. The chronology of the development of salivary gland is mentioned in **Table 3**. Each gland develops at a specific location in the oral cavity by the inward growth of an epithelial bud into the underlying mesenchyme. These epithelial buds then grow and later branch into a system of cords of cells. These get canalized and develop

**Figure 1.** Anatomical locations of major and minor salivary glands.


**Table 1.** Location and names of salivary gland ducts.

classified based on their location in the oral cavity as labial/buccal glands, glossopalatine glands, palatine glands, lingual glands which are further classified as anterior lingual (glands of Blandin and Nuhn) and posterior lingual glands (Von Ebner's) [1, 2]. The following diagram (**Figure 1**) shows the anatomical location of major and minor salivary glands. The sali-

The salivary glands are made of secretory units called acini, which are made up of acinar cells which could be serous or mucous. The serous cells are pyramidal or triangular in shape while the mucous cells are columnar in shape. The serous cells are occasionally seen capped by structures called demilunes. The acini cells are surrounded by contractile cells called as myoepithelial cells/basket cells, which are responsible for the flow of secretions of saliva by contraction of the cell. The acini of salivary glands are connected to hollow tubular structures which are called salivary ducts. The lining of the duct changes with the type of duct and its location within the salivary gland [1–3]. A description of the ducts observed is given in **Table 2**

Salivary glands arise from the ectoderm of oral cavity. The minor salivary gland arise from the oral and nasopharyngeal ectoderm. The chronology of the development of salivary gland is mentioned in **Table 3**. Each gland develops at a specific location in the oral cavity by the inward growth of an epithelial bud into the underlying mesenchyme. These epithelial buds then grow and later branch into a system of cords of cells. These get canalized and develop

vary glands consists of a secretory part and ducts (**Table 1**).

and the parenchymal elements are shown in **Figure 2**.

**Figure 1.** Anatomical locations of major and minor salivary glands.

**2.2. Development of salivary gland**

**2.1. Parenchymal elements of salivary gland**

4 Salivary Glands - New Approaches in Diagnostics and Treatment


**Table 2.** Description of salivary ducts.

**Figure 2.** Architecture of salivary ducts and acini.


which is followed by the packaging of the proteins by the golgi complex. The secretions are stored as granules and later released into the lumen by the process of exocytosis or by vesicular mechanism. Exocytosis involves fusion of the secretory granules with the membrane allowing release of the contents into the lumen. Vesicular mechanism involves transport of vesicles filled with secretions from golgi complex to plasma membrane. Transcytosis involves passage of substances like immunoglobulin A through the acini. Water is taken up by the cells from the bloodstream and the resulting saliva secreted is isotonic. The serous cells produce serous saliva which is thin, watery and is composed of zymogen granules and contains more proteins, while mucous cells produce thick, viscous saliva containing mucopolysaccharides and mucin. Parotid gland and von Ebner's gland is purely serous gland, while sublingual, glossopalatine and palatine glands have more of mucous secretions. Submandibular gland and other minor salivary gland have both serous and mucous acini, resulting in mixed saliva [2–6].

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In the second stage the saliva undergoes changes as it passes through the salivary ductal system into the oral cavity. Saliva secreted from the acini is isotonic or slightly hypertonic when it reaches the intercalated ducts. The intercalated duct cells also release lysozymes and lactoferrin. Striated and excretory ducts are impermeable to water. In the striated duct, reabsorption of sodium and chloride occurs more as compared to the secretion of potassium and bicarbonate ions, which makes saliva hypotonic (**Figure 3**). Striated duct cells also secrete kallikrein and epidermal growth factor. Thus, saliva secreted into the oral cavity is hypotonic

The myoepithelial cells are responsible for the contraction of the acini cells, aiding in the flow and secretion of saliva. In health, the total volume of saliva produced is 750–1000 ml

as compared to serum [1–6].

**Figure 3.** Modification of saliva.

*3.1.3. Saliva secretion in health and disease*

**Table 3.** Chronology of salivary gland development.

a lumen by the action of microfilaments at apical areas of cell to become ducts. The secretory part develops later by repeated branching and budding of finer cell cords, to form pregland cells which give rise to acini [1].
