The salivary glands are the small glands responsible for the production of saliva, a highly important link in the digestive chain. They are considered to be accessory digestive glands. Saliva serves a dual function. It is chemically designed to break down the molecular structure of food, which in turn gives food its taste. Additionally, it cleanses the teeth and helps to keep the mucous membranes inside the mouth moist. Saliva has been proven to maintain starch digesting enzymes and a lubricating enzyme, both of which aid in the process of digestion and swallowing. Saliva is continuously secreted, however it is only secreted in amounts that are suitable for maintaining moisture in the mouth when there is a lack of food to break apart. The average human secretes between 1 to 1.5 liters of saliva in a 24 hours period.
There are several minor salivary glands within the oral cavity, positioned within the mucous membranes of the palatal area. The greatest amount of saliva comes from three pairs of glands outside the oral cavity altogether. From these glands, the saliva ends up in the mouth via ducts that run into the oral cavity. The parotid, the submandibular, and the sublingual glands are considered the three main glands, despite the fact that they are extrinsic glands. The largest of all the salivary glands is the parotid gland.
The parotid gland can be located just under and anterior of the auricle of the ear, where it lies sandwiched in between the skin and the masseter muscle. The vast amounts (in comparison) of saliva that this gland creates enters the oral cavity via the parotid duct, or the Stensen’s duct. The parotid duct and the zygomatic arch run even with each other until the parotid duct crosses the masseter muscle, running through the buccinator muscle until it finally follows the line to the second upper molar. Here, the duct empties into the mouth, keeping the saliva amounts up to par. When the mumps attack the glands and the immune system, the parotid gland is the gland which swells.
The submandibular gland is found just under the mandible, as the name implies, along the inside of the jaw about the mid line. The mylohoid muscle creates a superficial encasement to the gland. The submandibular duct drains saliva produced by the submandibular gland into the floor of the oral cavity, just lateral to the lingual frenulum. The submandibular duct is also known as the Wharton’s duct. Just under the mucous membrane of the floor of the oral cavity, one can find the sublingual gland. The sublingual glands have numerous ducts that drain the saliva produced into the oral cavity. These ducts are known interchangeably as sublingual ducts or Rivinus’ ducts. These ducts empty just behind the papilla of the submandibular duct.
There are two distinctive varieties of secretory cells. Each variety exists within every salivary gland, but not all glands have the same number of each type. There are serous cells which are responsible for the secretions that are reminiscent of water with a powerful enzyme for digestion. Mucous cells are able to produce a thicker, stringier liquid, called mucous. The lumina of all salivary ducts are coated with cuboidal epithelial cells. Both divisions of the autonomic nervous system innervate the salivary glands. Moderate amounts of viscous saliva can be initiated via the stimulation of the sympathetic impulses. Alternatively, vast quantities of the watery saliva can be initiated via stimulation from the parasympathetic impulses. When a person becomes stimulated by food, either due to thought, smell, visual sensations, taste, or even dreams, saliva is generated in greater quantities through a physiological response that triggers the parasympathetic impulses.