**Abstract**

Generally, the tissues consist of stroma and parenchyma. The epithelial tissue, which forms the basis of exocrine glands, is rich in parenchyma. The secretions of salivary glands are functionally related to the digestion, and the secretions of the lacrimal glands protect the eye surface and allow to maintain a proper vision. The parotid is a pure serous gland and consists of serous acinus. The submandibular gland is a mixed gland consisting of serous acini and mucous tubules, and the acinus is predominant. The sublingual gland is a mixed gland composed of serous acini and mucous tubules, such as the submandibular gland, but the mucous tubules are predominant. The secretions of salivary glands reach the oral cavity with the intercalated canal, the intralobular canal, the interlobular canal, and the main duct channel. "Stenon duct" in the parotid gland, "Wharton duct" in the submandibular gland, and "major sublingual" duct in the sublingual gland open into the oral cavity. The lacrimal gland is structurally similar to salivary glands. This gland was divided into lobules by irregular tight connective tissue. In the lobules, acinar cells and mucus tubules are located together.

**Keywords:** salivary glands, lacrimal glands, morphology, functions

## **1. Introduction**

The smallest unit of a living organism is the cell and cells congregate to form tissues. The cells that make up the tissues do not only have similar shapes but also form a community to perform specified functions. Basically, the tissues consist of two parts: parenchyma and stroma. Stroma forms the skeleton of the structure. The parenchyma is the tissue's functional part and is located inside the stroma. Therefore, the tissue as a whole performs specific tasks and functions. In normal conditions, stroma and parenchyma are in certain ratios in each tissue. In some tissues parenchyma is predominant, as in epithelial tissue, while in a connective tissue, it makes up its minority. Basically, according to the rate of parenchyma and stroma, there are four kinds of tissues: epithelial tissue (epithelium), connective tissue, muscle tissue, and nerve tissue. In the second week of embryonic development, the bilaminar embryo disc forms, while the trilaminar embryo disc emerges at its third week. Tissues take origin from the different layers of this embryonic disc. The epithelial tissue originates from all of the embryonic germ leaves [1–3].

Ectoderm-derived epithelial structures are as follows: sweat glands and ducts, oral cavity, and vaginal and anal canal epithelium [1–3].

Mesoderm-derived epithelial structures include blood vessel endothelium, mesothelium that lines up body cavities, and epithelium covering genitourinary system and tubules [1–3].

The epithelial tissue originating from endoderm is located on the inner surface of the esophagus, as an epithelium covering the stomach-intestinal tract, an epithelium surrounding the gallstones, large glandules such as in the liver and pancreas, and an epithelium located in the respiratory system [1–3].

### **1.1 Features of epithelial tissues**


The lateral surface of the epithelium, there are intercellular binding complexes: non-permeable connections, anchor connections, and gap junction. Zonula occludens are non-permeable; zonula adherens, hemidesmosomes, and desmosome are anchors; and gap junction is the intercellular connections that provide communication.

Basal invagination is present in the epithelium. These are the finger in folds that the cell membrane makes at baseline and parallel to each other; there are abundant mitochondria in these recesses. Basal invaginations are known as ductus striata of salivary gland's duct channels. Basal invaginations are also present in the epithelium

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**Figure 1.**

**Figure 2.**

*staining (Dr. Alpaslan Gokcimen).*

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

that forms the proximal and distal tubule, which allow the transport of the water and minerals. A rich capillary network exists around the basal invaginations. The cells pump the ions, glucose, sodium, potassium, and calcium through active transport from lumens of the tubes to the recesses. Thus, the water passes from the cytoplasm to the spaces that become hypertrophic and swell and expand, and then

*Light microscopic image of the epidermis, skin. Keratinized stratified epithelium can be seen in the brackets.* 

*(a, b) In the section taken from the testis, the basement membrane is seen as a red-pink line. Hematoxylin–eosin* 

e.Avascularity: The epithelium is fed by diffusion through the blood vessels in the connective tissue below. In the feeding of multilamellar epithelium such as the skin, lip, esophagus, and vagina, the underlying connective tissue sends finger extensions into the epithelium. This is the name given to the "papilla"

f. Layer: The epithelial tissue can be classified according to the number of cell layers and the shape of cells. Different kinds/forms of epithelium are present in

the collected water and ions pass into the veins [4, 9].

*Hematoxylin–eosin staining (Dr. Alpaslan Gokcimen).*

and thus feeding the epithelium [4, 5, 8].

various organs, as shown in **Table 1**.

#### **Figure 1.**

*Chronic Autoimmune Epithelitis - Sjogren's Syndrome and Other Autoimmune Diseases...*

and an epithelium located in the respiratory system [1–3].

cells, mesangial cells, and macula densa [4, 5].

**1.1 Features of epithelial tissues**

The epithelial tissue originating from endoderm is located on the inner surface of the esophagus, as an epithelium covering the stomach-intestinal tract, an epithelium surrounding the gallstones, large glandules such as in the liver and pancreas,

a.Basal membrane: The epithelium is never found in space but is located on the basal membrane as single or multiple layers (**Figure 1a**, **b**). All cells are arranged on the basement membrane but with the exception of ependymal

b.Diversity: We can summarize the main function of epithelial tissue as covering, protection, secretion, and absorption. It varies according to these functional differences. The epidermis covers the outer surface of our body and protects it (**Figure 2**). The covering function protects not only the body's external surface but also the inner part of the lumen structures such as the small intestine and colon, the trachea, and the urinary system (**Figures 3**–**6**). The epithelial cells progress in the lower connective tissue and form different gland structures such as tubular and simple branched tubular. In this way, mucous tubules and serous acini are formed. Therefore, suitable serous, mucous, or mixed secretions are produced. These glands give out their secretions through duct channels [4, 6].

c.Polarity: The epithelium has three surfaces. These include apical, lateral, and basal surface. There are membrane extensions on the apical surface such as cilia, microvillus, flagella, and stereocilia. Microvillus is especially important for these structures in food exchange. The small intestine is the best example of it (**Figure 3**). In particular, the microvillus is located in the proximal part of the kidney where the absorption occurs (**Figure 7**). The microvillus in the epithelial cells provides reabsorption of important substances. Reabsorption is also provided by basal invaginations. Basal invaginations can be observed in the ductus striata of the salivary glands and proximal and distal tubules of the kidney at best. The substances taken with the apical surface of the epithelial

d.The cilia are mobile and they are located in the respiratory system (**Figure 5**). Cilia make the sweeping movement from the trachea to the oral cavity. In this way, harmful substances such as microorganisms and carbon particles are thrown out of the body. The cilia are also found in the uterus and tuba uterina of female genital system (**Figures 8**, **9a**, **b**). Cilia in the female genital system sweep the secretion to pass the zygote from the uterus into the uterine cavity. Flagella is seen in the spermium, and it provides the spermium moves in this way (**Figure 10a**, **b**) [4–8]. Stereocilia are a non-movement structure (**Figure 11**). Stereocilia increase the surface area of the epididymis and allow absorption of testicular fluid and phagocytosis of pathological sperm. Stereocilia which reside in the hair cells of

The lateral surface of the epithelium, there are intercellular binding complexes: non-permeable connections, anchor connections, and gap junction. Zonula occludens are non-permeable; zonula adherens, hemidesmosomes, and desmosome are anchors;

Basal invagination is present in the epithelium. These are the finger in folds that the cell membrane makes at baseline and parallel to each other; there are abundant mitochondria in these recesses. Basal invaginations are known as ductus striata of salivary gland's duct channels. Basal invaginations are also present in the epithelium

and gap junction is the intercellular connections that provide communication.

cell are given to the basal part by active transport [4, 6].

the inner ear are involved in signal generation [4–8].

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*(a, b) In the section taken from the testis, the basement membrane is seen as a red-pink line. Hematoxylin–eosin staining (Dr. Alpaslan Gokcimen).*

#### **Figure 2.**

*Light microscopic image of the epidermis, skin. Keratinized stratified epithelium can be seen in the brackets. Hematoxylin–eosin staining (Dr. Alpaslan Gokcimen).*

that forms the proximal and distal tubule, which allow the transport of the water and minerals. A rich capillary network exists around the basal invaginations. The cells pump the ions, glucose, sodium, potassium, and calcium through active transport from lumens of the tubes to the recesses. Thus, the water passes from the cytoplasm to the spaces that become hypertrophic and swell and expand, and then the collected water and ions pass into the veins [4, 9].


#### **Figure 3.**

*Simple columnar epithelium with microvilli of the small intestine. Hematoxylin–eosin staining (Dr. Alpaslan Gokcimen).*

#### **Figure 4.**

*Simple columnar epithelium of the large intestine can be seen between the lines. Hematoxylin–eosin staining (Dr. Alpaslan Gokcimen).*
