The salivary glands

The salivary glands

I-INTRODUCTION:

The salivary glands are exocrine digestive glands that discharge their secretion products into the oral cavity, the mixture of which constitutes: saliva which ensures the permanent humidification of the oral cavity. 

Properties of saliva:

• Average volume is 750 ml per 24 hours; 
• PH varies between 6.7 to 8.5 in humans;
• Composition : 

• 99% water 
• The remaining 1% is formed by organic and mineral elements (Organic constituents: 

• Enzymes, lysozyme, salivary mucins, salivary IgA. 
• Inorganic constituents (examples: Na+, Ka+, Ca++, H+ ions, phosphates, bicarbonates, thiocyanates, iodine, fluorine, iron and copper) 

II-ANATOMY OF THE SALIVARY GLANDS: 

-Main (major) salivary glands:   

• Parotid gland
• Submaxillary gland
• Sublingual gland

They are: Pairs; Symmetrical; Bilateral; Large volume.

-Accessory (minor) salivary glands:   

Small glands. Scattered in the chorion of the oral mucosa: jugal, lingual, labial, pharyngeal.

1-THE MAIN SALIVARY GLANDS:

1-1.THE PAROTID:

Parotid, comes from the Greek word “PARA” which means “near”, and “GENITIFOTOS” which means “ear”.

It is the largest of the major salivary glands, weighing about 25 to 30 grams and lobulated in appearance. It occupies a compartment located in front of the ear, between the sternocleidomastoid muscle and the ascending ramus of the mandible.

-Anatomical situation:

Inverted pyramidal shape; it is located below the zygomatic arch, below and in front of the external acoustic meatus, in front of the mastoid process, on the masseter, and behind the ascending branch of the mandible (RAMUS).

Its lower end, or apex, is located behind and below the angle of the mandible.

The secretion from each parotid gland opens into the oral cavity through the Steno duct , a collecting duct 5 cm long and approximately 3 mm in diameter, it opens opposite the second upper molar, its orifice may be marked by an elevation called the parotid papilla.

1-2. THE SUBMAXILLARY GLAND:

It has the size of a large almond weighing 6 to 8 grams, of firm consistency with a lobulated and encapsulated appearance. It is located in the submandibular triangle, a triangular-shaped osteofibrous cavity.

Its main collector is the Wharton canal, which opens below the frenulum of the tongue.

1-3. THE SUBLINGUAL GLAND:

It is the smallest of the major glands, it weighs about 2 to 3 grams, it is elongated in shape, flattened transversely. It is located in the sublingual fossa of the mandible, on either side of the lingual frenulum.

Its secretion is collected at the level of the Rivinius and Walther canals which open under the tongue.

2-ACCESSORY SALIVARY GLANDS:

There are about 750 accessory glands scattered beneath the mucous membranes of the oral cavity except the gingiva and the anterior part of the bony palate.

They are most often small clusters of unencapsulated secretory units opening into the mouth via short canaliculi.

III-HISTOLOGY OF THE SALIVARY GLANDS:

The salivary glands are composed of morphological and functional units called “ADENOMERE”, it is a tubuloacinar structure these include connective tissue formations and a glandular parenchyma. The connective tissue part is represented by the envelope capsule which emits trabeculae dividing the parenchyma into lobules themselves formed of several acini which are the salivary secretion units. 

1-THE CONNECTIVE PART (THE CAPSULE): 

It is fibrous in nature and emits trabeculae dividing the parenchyma into lobules themselves formed of several acini which are the salivary secretion units. The trabeculae serve as a passageway for vessels and nerves. 

2- THE GLANDULAR PARENCHYMA: 

It includes secretory units and excretory pathway systems.

2-1 THE SECRETORY UNITS OR THE ACINI: 

The acinus consists of a cluster of secretory cells grouped around a collecting duct called the intercalated duct.

There are several types of acini depending on their secretion product and their morphology (serous, mucous and mixed acini).

.

A-THE SEROUS ACINUS: 

Composed of serous secretory cells, rich in neutral polysaccharides and secreting a “watery” saliva. They are roughly pyramidal cells with a rounded nucleus pushed back to the basal third (apical) of the cell and with basophilic cytoplasm (blue coloration) and rich in secretory granules; the secretory granules are rich in proteins.                         

The parotid glands and the lingual accessory glands of Von Ebner are purely serous glands.

B- THE MUCOSAL ACINUS: 

Mucous cells (muciparous) are rich in acidic mucopolysaccharides (sialic or neuraminic acid) and secrete a very viscous saliva (mucus), they are large pyramidal cells with clear cytoplasm, whose nucleus is small, dense and flattened in the basal region of the cell.

The cells produce glycoproteins that make up salivary mucin.

Muciparous cells are found in the submaxillary, sublingual and accessory glands excluding Von Ebner’s glands.

C-THE MIXED ACINUS:

The mixed acinus brings together the serous and mucous cells arranged in the following way: the mucous cells form a tube which ends with a crescent of serous cells called “GIANUZZI”, these cells communicate with the lumen of the acini by fine secretory canaliculi. The submaxillary, sublingual and accessory glands except the Von Ebner glands are mixed salivary glands 

Noticed :

• The parotid is a pure serous gland.
• The submaxilla is a mixed gland with a predominantly serous gland.
• The sublingual: is a mixed gland with a predominantly mucous membrane.
• Excreto-secretory ducts: or striated ducts or Pfuger ducts, are wider than the previous ones, they are largely intralobular, their cells have striations at the basal pole due to the presence and arrangement of mitochondria. They actively participate in the production of saliva.

2-2- THE EXCRETORY TRACTS

The saliva secreted by the acini is collected by a network of canals differentiated into an intercalated canal for the acini and a striated canal for the lobule; the striated canals join excretory canals.

A- INTERCALATED CANALS OR BOLL PASSAGE:

Is an intralobular canal, with a narrow lumen. The secretions of their cells are rich in bicarbonate allowing to neutralize the chlorides of saliva.

B- THE INTRA-LOBULAR CANALS OR PFLUGER’S STRIA CANALS:

Or excretory-secretory ducts, are wider than the previous ones, they are largely intralobular, their cells have striations at the basal pole due to the presence and arrangement of mitochondria.  

Striated cells have an important function of absorption-secretion of water and ions. They actively participate in the production of saliva.

C-EXCRETORY CHANNELS ( COLLECTOR CHANNEL) :

Interlobular in location, they form the junction between the striated canals and the oral cavity. We distinguish: the STENON canal for the parotid, the WHARTON canal for the submaxilla and the RIVINUS and WALTHER canals for the sublingual.

3-MYOEPITHELIAL CELLS:

These are stellate cells located between the basement membrane and the base of the glandular cells and the intercalated duct cells. These cells of epithelial origin, whose morphological and functional resemblance to smooth muscle cells is great, have a contractile function that is probably important in the mechanism of expulsion of acinar secretion products. They participate in the regulation of secretory flow;

IV-VASCULARIZATION AND INNERVATION:

1-Blood vascularization: is ensured by: 

• The facial artery and the external carotid artery the parotid gland
• The arteries: facial and lingual the submandibular gland
• The arteries: sublingual and submental the sublingual gland

The capillaries are arranged in two networks joined by portal veins. The first network is arranged around the ducts and the second around the acini. The blood flow therefore circulates in the opposite direction to the salivary flow, which allows a concentration of saliva.

2-Innervation:

1. The sensory innervation of the main salivary glands is provided by the trigeminal nerve. 

b-Effective innervation is provided by the autonomic system via the glossopharyngeal nerve and the otic ganglion for the parotid gland and via the chorda tympani and the mandibular ganglion for the submandibular and sublingual glands.

The salivary glands

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The salivary glands