Salivary glands are exocrine glands present in the oral cavity which release saliva. If we study their classification, salivary glands have been classified according to their size, as major salivary glands and minor salivary glands or according to the type of saliva they secrete, serous salivary glands, mucous salivary glands and mixed salivary glands. Development. Salivary glands are ectodermal in origin. During embryogenesis, the epithelial cells proliferate into the underlying ectomesenchyme. This epithelial bud grows with development of clefts, which results in the formation of branches. This process of growth, clefting and branching continues and is called 'branching morphogenesis' which requires the epithelial mesenchymal interaction. The central cells of this solid epithelial structure, then undergoes degeneration for lumen formation. The central cell degeneration occurs first in the distal and proximal portion of the chords and then in the middle portion. Finally, the central cells of the acini undergo degeneration for completing the lumen formation. The first salivary gland to initiate development is parotid gland around 5 weeks in utero, then submandibular gland around 6 weeks in utero, sublingual gland at 8 weeks in utero and all minor salivary glands initiate development during the 3rd month of fetal life. Histologically speaking, salivary glands have two main components, first component is the secreting end pieces or acini, which are small sac-like cavity. And second component is the duct system. The acini produces the saliva and the duct system carries the saliva from the acini to the oral cavity. These secreting end pieces or acini can be serous acini, mucus acini or a serous demilune, which is a combination of both. Whereas the duct system includes the intercalated ducts, striated ducts and excretory ducts. Apart from these, there are some cells located adjacent the acini and intercalated ducts called the Myoepithelial cells. The whole salivary structure is lined by a basement membrane. Let us start with the serous acini. Serous acini are spherical in shape. On looking inside we see, 8 to 12 serous cells, which are pyramidal in shape, with their broad bases at the basement membrane and apex towards the lumen. Now the lumen is small and has finger like extensions between the adjacent cells called intercellular canaliculi. Serious cells are connected to each other by various intracellular junctions and to the basement membrane by hemidesmosomes. If we take a closer look, the cell membrane of these cells towards the lumen is not smooth but shows numerous short microvilli. On looking inside the cells we see a spherical nucleus placed at the basal region, with most of the cell organelles, like rough endoplasmic reticulum and gogli complex, in the apical part. There is accumulation of secretory granules, which are rich in proteins. During routine staining these granules take up stains strongly, making the cytoplasm appear dark. Serous acini are seen in parotid glands, von Ebner glands and submandibular gland. Next, mucus acini. Mucous acini are usually tubular in shape. On looking inside we see 10 to 16 mucous cells. The lumen is larger in size but lacks the intercellular canaliculi. Mucous cells are connected to each other by various intercellular junctions and to the based membrane by hemidesmosomes. If we look closely, we see the cell membrane towards the lumen shows numerous short microvilli. On looking inside the cell, the major part of the cell is filled with accumulation of secretory products. This secretary product is mucus, which is rich in carbohydrates and it pushes the nucleus in the basal part against the cell membrane. Where it is oval and flattened in shape, along with the rest of the cell organelles. During routine staining mucuos does not take up stain, as a result of which the cytoplasm appears empty. Mucuos acini are seen in sub-mandibular gland, sublingual gland and all minor salivary glands, except the von Ebner glands. Serous demilune. Serous demilune is formed when serious acini and mucous acini are present together. Serous demilune consist of a mucous acini which is capped by a crescent-shaped serous acini. It is always mucous acini capped by a serious acini and never the serous acini capped by a mucous acini. The mucous acini in serous demilune, have intercellular canaliculi, which are not normally seen in mucous acini. The saliva from the serious acini passes through these intracellular canaliculi and enters the lumen of mucous acini, from where it enters the ducts. They are predominantly seen in mixed salivary glands like submandibular gland. So that was about the various types of secretory end pieces or acini. Now about the duct system. The duct system of salivary glands is a varied network of hollow tubules which connects the lumen of secretary end pieces to the oral cavity. Let's begin with the intercalated ducts. Intercalated ducts are present just adjacent to the secretary end pieces and are first to receive the saliva. Their lumen is just wider than that of the acini. In histology they sometimes appear pressed between the acini, hence the name intercalated. These ducts are lined by simple cuboidal epithelium. That is, a single layer of cuboidal cells. Though myoepithelial cells may be present adjacent to these cells. The ductal cells have intercellular junctions and desmosomes with myoepithelial cells. On looking closely the apical surface or the surface towards the lumen has few short microvilli. On looking inside the cells we see a large rounded nucleus in the center, with cell organelles around it. Few secretory granules are present in the apical part of the cell which plays a role in saliva modification. Striated ducts. Saliva from the intercalated ducts drains into these striated ducts and form the largest portion of the duct system. The lumen is larger than that of the intercalated ducts and are lined by simple columnar epithelium. That is, a single layer of tall columnar cells. They are joined together by intercellular junctions and have short microvilli on the apical surface of the cells. On looking inside the cells the nucleus is spherical and centrally placed with cell organelles around it. Few secretory granules are present in the apical part of the cell. The basal part of the cell shows numerous elongated infoldings of cell membranes. These cytoplasmic partitions are full of elongated mitochondria, giving the cell an appearance of having striations, hence the name striated duct. Excretory ducts. Saliva from striated ducts drains into the excretory ducts which then open into the oral cavity. The overall diameter of the ducts and the lumen is largest. These ducts are lined by pseudostratified epithelium. That is, a single layer of tall columnar cells, which reach the lumen and basal cells, which do not reach the lumen. They are joined together by intercellular junctions and have short microvilli in the apical surface. On looking inside, the nucleus is spherical and centrally placed, with cell organelles around it. The infoldings of basal cell membrane is less pronounced. Some other types of cells are also present in the excreted ducts. Like, goblet cells, which contain mucin. Tuft cells or brush cells with long stiff microvilli and a nerve ending near its base. As the excretory duct reaches the oral cavity, the pseudostratified epithelium transforms into stratified epithelium and merges with the oral epithelium. So that was about the various types of ducts in the duct system. Now about the myoepithelial cells. These cells are closely related to the secretary cells and intercalated duct cells. They lie between the acini or duct cells and the basement membrane and are attached by desmosomes. Adjacent the acini the myoepithelial cells are stellate shaped, that is, they have long processes. If we take a look at the acini from the outside, the myoepithelial cells are present around it. Imagine a player's hand around a ball. Due to this shape they are sometimes also called as the basket cells. Myoepithelial cells that are present adjacent to the intercallated ducts are fusiform. If we take a look inside the myoepithelial cells, we see a flattened nucleus surrounded by most of the organelles. The cytoplasm has actin filaments just like smooth muscles and cytokeratin filaments just like epithelial cells. These actin filaments give myoepithelial cells the ability to contract. Myoepithelial cells support the acini and prevent any backflow of saliva. And when required, by their contractile movement, squeeze the secretary acini to increase the outflow of saliva.