When you look down beautiful meal, you may have experienced the strange fluid taking over your mouth. That fluid is called saliva, and it comes from structures called salivary glands. A salivary gland is a secretory gland that secretes tasteless and clear saliva. It has many essential functions in the body, such as keeping the mucous membrane of the mouth moist. Salivary glands help us lubricate food. It also prevents tooth decay and is involved in the initial steps of digestion.
The salivary glands play an important role in the body. There are both major glands and minor glands. The minor glands are located in and around the world cavity. It is estimated that there are 800 to a thousand minor salivary glands located within the mucous membrane lining of the mouth and tongue. However, these glands contribute less than 5% of the total saliva produced.
How does saliva work?
Saliva is a complex fluid that facilitates lots of necessary functions. It lubricates our mouths, moistens food, assists digestion, protects teeth, and even defends mouths from microorganisms. A group makes saliva of cells called salivary glands that deliver it into mouths through ducts. The body secretes between one and one and a half liters of saliva a day, and saliva is composed of about 99.5% water. Other components of saliva include electrolytes, digestive enzymes, metabolic wastes, and antibacterial elements.
There are three major salivary glands:
- The parotid glands.
- The submandibular glands.
- The sublingual glands.
There are four types of minor glands:
- Buccal glands are located in the cheeks.
- Lingual glands located on the tongue.
- Palatine glands located in the roof of the mouth.
- Labial glands located in the lips.
One essential minor salivary gland is von Ebner’s glands located around the tongue’s circumvallate and foliate papillae. They release lingual lipase, an enzyme that begins the digestion or breakdown of fats.
Parotid glands: The parotid gland is the largest of the major salivary glands. It is located in front of the ear in a place known as the preauricular region. These secrete a thin liquid that’s full of rich antibacterial proteins and compounds that remineralize the teeth. They don’t care whether or not you’re chewing on bread or plastic. They will work on anything in the mouth and produce 25 to 30% of saliva transported through the parotid duct to the oral cavity.
The parotid gland has a rich blood supply due to its constant saliva production, especially during mealtimes. It has an irregular-shaped parotid bed or nest, otherwise described as the surrounding and touching the parotid gland. The blood supply to the parotid gland comes from three external carotid artery branches, the superficial temporal artery. The parotid gland is drained mainly by the retromandibular vein in terms of venous drainage.
Sublingual gland: The sublingual gland is an almond-shaped gland which is also the smallest gland out of the major salivary glands. It also secretes the smallest amount of saliva per day. The sublingual glands lie bilaterally on the floor of the mouth. They produce 3-5% of saliva and release it through many ducks under the tongue. There are two types of secretory cells within these large glands.
- Serous cells and mucous cells.
The mucous cells secrete mucin, and the serous cells secrete a fluid containing water electrolytes and salivary amylase. It is an enzyme that digests or breaks down larger carbohydrates into smaller carbohydrates.
So you have one on each side, and these glands have several ductal openings that run along the margin of the sublingual folds. They’re embedded below the floor of the mouth, above the throat. These produce a more viscous fluid used to lubricate the throat and mouth.
As for the arterial blood supply of the sublingual gland, two separate arteries supply it. These are the sublingual artery, and the sublingual gland’s other artery is the submental artery. It is a branch of the facial artery. The veins are responsible for draining the sublingual gland.
Submandibular glands: These glands are located inferiorly to the inner aspect of the mandible of the neck. These glands share the same arterial blood supply as the sublingual gland. They produced about 60 to 70% of saliva and transported it through the submandibular dock, releasing it under the front of the tongue. It is supplied by the submental artery, a branch of the facial artery. The sublingual artery is then a branch of the lingual artery.
The submental vein mainly drains the submandibular gland in terms of venous drainage. Anastomosis, in other words, connects with then the sublingual vein.
Finally, a fourth salivary gland covers the tongue and the lining of mouths with hundreds of smaller glands. While they lubricate the mouth, they also protect it against infections.
Saliva is produced and secreted into the mouth, producing an alkali substance. The functional unit of the saliva glands is called Sullivan. It consists of acinar cells, which produce this isotonic secretion, and this is the first part of saliva production.
Surrounding these Asuna cells are myoepithelial, which can contract, moving the fluid produced by the asana cells towards the duct. These duct cells reabsorb sodium chloride. But it will not reabsorb the water making the saliva more hypotonic.
Saliva has three main functions.
Saliva contains lysosomes that attack the bacterial cell walls. Lactoferrin which kills aids many bacteria normally needs iron and iron for replication. Also, it can contain IgA, which is immunoglobulin and helps in the immune response. Saliva contains amylase and lingual lipase, which help break down carbohydrates and fats.
Salivation is stimulated by thought, sight, smell, and taste. Sleep dehydration, fatigue, and fear all inhibit salivation. The saliva gland has different nerves which supply it. In the brain stem, there have a medulla region and a superior celebratory nucleus. The nervous system is responsible for the rest and digest response.
So saliva production is the parasympathetic nervous system. The salivatory nucleus has parasympathetic neurons targeting the saliva glands via the glossopharyngeal nerve. The facial nerve originates from the salivary nucleus in the pons.
Importance of saliva
Each saliva gland has hollow tubes called ducts that open into the mouth. The saliva or spit flows from the salivary glands through the ducts into the mouth. Sometimes a salivary gland, usually the sublingual gland, may be injured or its ducts become blocked. As a result, saliva can’t get into the mouth. Instead, it leaks into the surrounding tissue forming a ranula. A ranula is saliva filled bubble or sack that forms on the floor of the mouth.
A simple ranula stays under the tongue. If a ranula extends down into the neck, it’s called a plunging ranula. A new interventional radiology treatment for ranulas called salivary gland ablation involves injecting medicine into the injured salivary gland to help the gland heal. First, ultrasound imaging is used to guide the placement of a needle into the ranula.
Fluid is drained from the ranula through the needle then imaging is used to guide injection of absolute alcohol into the abnormal salivary gland. The gland then makes much less saliva and gets smaller. The injured gland heals and stops leaking saliva, and the ranula is gone.
The saliva produced by the salivary glands has many important functions in the body.
- Saliva moistens food making it easier to swallow. It starts the chemical breakdown of some carbohydrates and fats through the enzymes contained in saliva.
- By dissolving food molecules, saliva stimulates taste receptors on the tongue.
- As saliva contains some antibacterial elements, it helps to inhibit bacterial growth in the oral cavity.
Saliva is mostly made of water, but it also contains enzymes that break down food for digestion and do the whole “protection from infection” thing. So, when it’s not digesting and making things taste great, it kills the germs! Spit is so good at cleaning. Some art conservators use it on fragile surfaces instead of chemical solutions.
Mother saliva spits into her infant’s mouth to teach their immune systems how to produce antibodies and destroy pathogens. All the antibodies already in the mother’s saliva introduce the infant to bacteria without getting them sick.
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Nosek, Thomas M, Essentials of Human Physiology.
Fejerskov, O, Dental Caries: The Disease and Its Clinical Management (2nd ed.).
Edgar, M, Saliva, and Oral Health (3 ed.). British Dental Association.