Salivary glands and saliva play a vital role in our digestive system. We really don’t give great importance to Saliva. However, in absence of saliva, we will not be able to digest the food we eat. In this article on saliva and salivary glands facts, let us take a quick look into these important organs of human body and find out the role they play in digestion of the food we consume. Let’s begin…
Saliva and Salivary Glands Facts: 1-5 | What Are Salivary Glands and Types
1. The salivary glands are the exocrine glands (glands which release their secretions on the epithelium’s surface with the help of ducts). They produce saliva.
2. There are three major pairs of salivary glands which are – parotid glands (cheek), submandibular glands which are also called as submaxillary glands (lower jaw) and sublingual glands (below the tongue). Along with these three major glands, there are many minor glands which release saliva.
3. These glands are usually divided into serous, seromucous (mixed) or mucous secreting glands. The salivary glands which come under serous secretions have ptyalin or alpha-amylase, which is an enzyme which breaks starch to glucose and maltose.
4. In mucous secretions, the salivary glands secrete mucin which helps in lubrication. In seromucous secretions, the salivary glands secrete both alpha-amylase and mucin.
5. 500 ml to 1500 ml of saliva is secreted every day in an adult human being. Salivation or secretion of saliva is controlled by the parasympathetic nervous system. Acetylcholine is the neurotransmitter which stimulates the secretion of saliva.
Saliva and Salivary Glands Facts: 6-10 | Position and Role of Salivary Glands
6. Parotid glands are situated in the cheeks. They are the largest of all glands present in the salivary glands. The saliva secreted by parotid glands helps in mastication or chewing and swallowing. It is serous type of gland which releases amylase which starts the breakdown of starches.
7. Parotid glands open into the oral cavity through parotid ducts or Stenson ducts. Nearly 20% of the saliva is produced by the parotid glands. Parotid glands are infected with Mumps virus and cause Mumps disease.
8. Submandibular glands (submaxillary glands) are present below the lower jaw. This is a seromucous type of gland and hence releases both alpha-amylase and mucin. It opens into the oral cavity through submandibular duct or Wharton duct.
9. Though they are smaller than Parotid glands, they secrete 65-70% of saliva. It can be felt through palpation (usage of one’s hands to examine the body). It feels like a rounded ball. It is located approximately two fingers above the Adam’s apple.
10. Sublingual glands are situated below the tongue. They mostly release mucous or mucin, however they are considered as the seromucous secreting glands because they also release alpha-amylase. Saliva is secreted through 8-20 ducts (known as Rivinus ducts) directly. Nearly 5% of the saliva is secreted by the sublingual glands.
Saliva and Salivary Glands Facts: 11-15 | Position and Role of Salivary Glands
11. Minor salivary glands are almost 800 to 1,000 in number. They are present in the submucosa layer which supports the mucosa layer of the oral cavity i.e. in the buccal region, soft palate, hard palate’s lateral parts, regions between the tongue’s muscle fibers.
12. They measure 1-2 mm in size and are surrounded by a connective tissue. They usually have few acini (group of cells) in a tiny lobule (a small part of the gland). These glands either may have their own excretory duct or release their secretions through a common duct. They usually secrete mucous and coat the buccal cavity with saliva.
13. Von Ebner’s glands are present on the tongue’s dorsal side. They release or secrete a serous fluid which starts hydrolysis of lipids. They help us in tasting the food by releasing proteins and enzymes. The positioning of these glands is such that most of the taste buds are drenched with the secretions of Von Ebner’s glands. It plays an important role in dissolving the food particles to be tasted by the tongue.
14. Salivary glands are controlled by both the parasympathetic and sympathetic nervous system, the arms of autonomic nervous system. Parasympathetic system stimulates the secretion of saliva whereas the sympathetic system inhibits the secretion of saliva or stimulates small amount of saliva which is rich in proteins.
15. Some structural changes take place in the salivary glands as a person age. Some of the changes are: ducts dilate and there is increase in adipose tissue and fibrous tissue in the salivary glands. The amount of mucin secreted also decreases. But the amount of saliva secreted remains more or less same.
Saliva and Salivary Glands Facts: 16-20 | Saliva Facts
16. Saliva is thick liquid which is mostly made up of water (98-99%). The presence of mucus gives it a glistering look and makes the saliva thick. Saliva also consists of proteins, enzymes, buffering agents etc.
18. Saliva contains chemicals like immunoglobulin A1, lysozyme2, etc. which help in fighting against the bacteria.
19. Most of the saliva is produced during the afternoons. The least amount of the saliva is produced during the evenings.
20. 25,000 quarts or 23,659 liters of saliva is produced in a person’s lifetime. This amount is sufficient to fill two swimming pools!
Saliva and Salivary Glands Facts: 21-25 | Functions of Saliva
21. The proteins, like mucins, secreted by saliva, lubricate and keep oral cavity’s soft and hard tissue protected. Saliva decreases the clotting time and helps in healing a wound or repairing soft tissue.
22. Saliva protects the teeth from tooth decay and other dental issues. This happens because of the presence of buffering agents like sodium bicarbonate. They neutralize the acids present in the food and protects the teeth and gums.
23. Saliva forms a thin membrane on our teeth. This helps in reducing loss of minerals from the teeth and attracts calcium ions and helps teeth to be healthy and strong.
24. Needless to say, saliva helps in digestion of starches. Lipids also starts breaking down first due to saliva.
25. It prevents the growth of bacteria and other microbes. For example: antimicrobial peptides like histatins stop the growth of Streptococcus mutans and Candida albicans.
Saliva and Salivary Glands Facts: 26-30 | Functions of Salivary Glands
26. Another major but underrated function of the saliva is that it helps in keeping the mouth moist and thereby the food or the bolus enters the esophagus without damaging any tissue or organ.
27. The moisture which the saliva gives helps in moving our tongues and lips flexibly to make sounds.
28. Did you know that food cannot be tasted if saliva is not present? If it were not for saliva, we wouldn’t differentiate a bitter gourd from chicken!
29. Saliva maintains the water level in our body. When the water content is less in body, less saliva is produced which ultimately results in dry mouth. This stimulates us to drink more water.
30. Did you know our saliva is produced more when we are about to throw up? Yes, it is a simple mechanism of our body. Our body tries to digest whatever passes through esophagus. When we are about to vomit, the food from the stomach enters esophagus. This is when the body releases more saliva hoping that the digestive enzymes in saliva will digest the bolus.
Saliva and Salivary Glands Facts: 31-35 | Diseases Related to Salivary Glands
31. Sometimes stones may appear in salivary glands or salivary ducts. These are formed by the crystallized lumps of chemicals present in saliva.
32. Calcium is the major constituent of all the chemicals. Most of the stones are formed in submandibular glands.
33. Formation of stones in salivary glands is technically known as Sialolithiasis. Symptoms include dry mouth, swelling, and pain. Swelling may spread to the face as well. Infection in the affected area is also a possibility.
34. When the stones are formed, they obstruct the passage of saliva which causes swelling and pain. The symptoms are less severe if the stones are located in glands but if the stones are present in the salivary ducts, it causes immense pain.
35. Causes for Sialolithiasis are not known but thick saliva is considered to increase the risk. Staying hydrated is the best shot that one can give to stay away from this disease. For small stones, sucking a piece of any citric fruit may stimulate the secretion of saliva and eventually dissolve the stone. But consulting a doctor is always best.
Saliva and Salivary Glands Facts: 36-40 | Diseases Related to Salivary Glands
36. Another disease is Sjogren’s Syndrome. It is an autoimmune disorder (a disorder where a person’s immune system attacks the body’s cells mistakenly). In Sjogren’s Syndrome, the immune system attacks the tear and salivary glands. These glands in turn produce very less liquid.
37. Common symptoms are dry mouth (known as xerostomia), increased tooth decay and increased gum related problems, bacterial infections etc.
38. Salivary glands are also susceptible to cancer as well. The three major glands and hundreds of minor glands can be affected by cancer.
39. Doctors divide the tumors of salivary glands into three grades which are
- Grade 1: The cells appear to grow normally. It is also known as well differentiated or low grade. If the tumor is detected at this stage and surgically removed, outcomes are mostly positive.
- Grade 2: Not much of difference is seen in cell structure or growth. This grade is also known as intermediate grade or moderately differentiated.
- Grade 3: Cells appear abnormal and grow rapidly. This grade is usually termed as poorly differentiated or high grade. Doctors use radiation therapy along with the surgery.
40. The causes of cancer in salivary glands is still not known. However, there are few factors which may increase the risk of getting cancer like working for long with silica dust or nickel alloy, eating food which contains very less vegetables and high fat etc.
Bonus Fact: When we yawn, the sublingual glands get pushed when a muscle near the glands gets contracted and release saliva in streams.
Glossary of Terms
Immunoglobulin A1: It is an antibody with a very crucial role in mucous membrane’s immune functions.
Lysozyme2: It is an enzyme that specifically targets the chemical bonds present in the outer cell walls of bacteria.
Image Credit:By BruceBlaus. When using this image in external sources it can be cited as:Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014“. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. – Own work, CC BY 3.0, Link