Saliva and Salivary Glands: Interesting Facts and Three Disorders
A Very Useful Liquid
Saliva is the watery liquid in our mouths. It has important functions, including destroying bacteria, helping to prevent tooth decay, beginning the digestion of food, helping us to speak, and enabling us to swallow food. Problems with saliva production can interfere with our lives. Three of these problems are blocked salivary glands, infected glands, and Sjogren's syndrome. The latter problem is an autoimmune condition in which the salivary glands make an insufficient amount of saliva.
Saliva contains many chemicals in addition to water, including mucus, salts, antibacterial substances, enzymes, and chemicals that control the pH in the mouth. It also contains bacterial cells, since bacteria live in our mouths, as well as human cells shed by the lining of the mouth, the tongue, and the gums. The salivary glands continuously release their secretion into the mouth, although the amount varies during the day. The quantity of saliva increases when we taste, smell, or even think of food. It decreases when we go to sleep.
Composition of Saliva
- Saliva is a thick, colorless, and glistening liquid consisting of about 98% to 99% water. Mucus produces the glistening appearance and causes the liquid to have a thicker texture than pure water. Saliva also contains enzymes and other proteins as well as salts and buffering agents to keep the pH at the correct level.
- The water in saliva is obtained from blood. The water leaves the capillaries in the salivary glands to become part of the saliva.
- Saliva contains an enzyme called salivary amylase or ptyalin, which digests starch into a sugar called maltose. (Maltose is later broken up into glucose molecules in the small intestine.) If we chew a starchy food like a piece of bread or a cracker for a long time, it will start to taste sweet as the starch molecules break up into maltose molecules.
- Saliva also contains chemicals that fight bacteria, including lysozyme, lactoferrin, peroxidase, and immunoglobulin A.
- Sodium bicarbonate in saliva helps to neutralize acids in foods and drinks. These acids can damage tooth enamel.
The salivary glands generally make between one and two liters of liquid a day (between two and four pints). During an average lifetime they produce about 10,000 gallons of saliva.
More Facts About Saliva
- Saliva keeps the mouth moist and comfortable and lubricates food so that it's easy to swallow. It also prevents the swallowed food, or bolus, from damaging the wall of the esophagus.
- The moisture in the mouth helps us to manipulate the tongue and lips to make speech sounds. The liquid also moistens food and enables us to taste it.
- Saliva reduces tooth decay and infection in the mouth by washing away food particles, bacteria, and dead cells.
- We make much less saliva when we sleep than when we are awake. This allows bacteria to build up and can cause bad breath in the morning.
- Saliva helps us to maintain the correct amount of water in our bodies. When we become dehydrated, less saliva is made and the mouth becomes drier. This stimulates us to drink.
Saliva is made by salivary glands. The parotid glands are located on the insides of the cheeks, the submandibular ones are found under the floor of the mouth, and the sublingual ones are situated under the tongue. In addition, there are between six hundred and a thousand minor salivary glands located in the mouth, throat, and lips.
- The parotid glands are the largest salivary glands. A parotid gland is located in each cheek, in front of the ear. It produces a watery liquid containing proteins.
- The two submandibular or submaxillary glands are located under the floor of the mouth. They produce a liquid that is a mixture of water and mucus.
- The two sublingual glands are located under the tongue in front of the submandibular ones. They produce a liquid that contains more mucus than the secretions of the other salivary glands.
- Saliva leaves the glands in tubes called salivary ducts.
- More saliva is made when the mouth contains spicy, sour, or acidic foods. When taste buds are stimulated by these chemicals, they trigger the release of saliva.
The saliva of other animals is also interesting. In the case of birds known as cave swiftlets, it's useful for us as well.
Bird's Nest Soup
Many other animals have saliva and salivary glands, although sometimes the glands are modified for a particular function, such as producing venom. The saliva of some animals has an interesting feature not shared by the human version. In the case of cave swiftlets, the different feature is useful for us.
Cave swiftlets roost in dark caves, where they navigate by echolocation. During the day the birds hunt for insects outside the caves. They produce a protein-rich and sticky saliva which helps them build their nests. The saliva is used to stick nest materials together. It's a gummy substance and hardens when exposed to air.
The hardened saliva is the basis for bird's nest soup, which is popular in Asia and is thought to have many health benefits by the local people. The soup is very expensive. The nest is washed before use to remove unwanted material and has a gelatinous texture when added to water. It's often cooked in chicken broth to give it taste.
Three of the more common disorders involving human salivary glands are sialolithiasis (stones), sialadenitis (infection), and Sjogren's Syndrome (an autoimmune disorder). All of them require a visit to a doctor.
Stones in a Salivary Gland or Duct
Salivary glands and ducts may contain "stones". These are small, solid lumps made from crystallized chemicals in the saliva. Most stones contain calcium and form in the submandibular glands or ducts. The presence of the stones is known as sialolithiasis.
Stones in a duct can block the passageway and cause saliva to build up behind the blockage. This can result in swelling and pain, especially when a person is trying to open their mouth or swallow. The pain may begin suddenly just after a person has begun to eat and may be intense. The swelling may extend over the face and even down into the neck. The mouth may be dry and the area may become infected as well. Symptoms of a stone will probably be less severe if the stone stays in the salivary gland and doesn't enter the duct or if it only partially blocks the duct.
The cause of salivary gland stones isn't known for certain, but thickened saliva is believed to increase the risk. It's important to stay well hydrated, which may reduce the chance of stone formation.
Someone who may have a stone in a salivary gland needs to visit a doctor in order to obtain a diagnosis. The doctor may suggest drinking a lot of water to help remove a stone. A warm compress or a gentle massage may also help. Sucking on a small piece of lemon will stimulate saliva flow and may help to remove a stone if it isn't very large. Increased saliva flow in a blocked salivary duct that stays blocked may worsen the pain, however, which is one reason why it's important to visit a doctor. A doctor or dentist may be able to remove a stone inside their office. Surgical techniques can also remove it.
Infection of Salivary Glands
Salivary glands may become infected by microorganisms. Most commonly, these are bacteria. The disorder is known as sialadenitis and may be very painful. The infected gland may be swollen and may release bad-tasting pus into the mouth. Pus is a thick liquid released from an infected area. It contains dead white bloods, tissue debris, and bacteria as well as liquid serum. The white blood cells are killed while fighting the infection.
Sialadenitis is most common in elderly people who have salivary gland stones, but it can also occur in children shortly after birth. Fortunately, it can be treated by doctors. If it isn't treated, it may lead to a severe infection, especially in people who are already weakened by another condition.
Our immune system normally fights bacteria and viruses. In an autoimmune disease, the immune system mistakenly attacks the body's own cells instead. Sjogren's syndrome is an autoimmune disease in which the glands that produce saliva and tears are attacked by the immune system. The glands become inflamed and don't produce enough liquid. As a result, the person has dry eyes and a dry mouth.
A dry mouth is technically known as xerostomia. Besides being uncomfortable, xerostomia can lead to increased tooth decay and an increased risk of gum disease, bacterial infections, yeast infections, and bad breath. Dry mouth isn't necessarily a sign of Sjogren's syndrome, however. Many medications can cause the condition, and so can other illnesses, such as fibromyalgia.
In some patients, only the eyes and mouth are affected. A person may also experiences other health problems, such as painful and swollen joints. The lungs, digestive organs, and kidneys may be affected as well.
Sjogren's syndrome usually affects women over the age of forty, but it may also affect men and younger people—even children.
Classification and Cause
Sjogren's syndrome is sometimes classified as primary and secondary. The primary form develops in a patient who has no other autoimmune disease. If the patient already has another autoimmune disease when Sjogren's syndrome develops, the condition is known as a secondary one. The other disease is often rheumatoid arthritis or lupus.
Scientists don't know the exact cause of the syndrome. There appears to be a genetic basis to the disorder, but an environmental stimulus seems to be required in order to trigger the development of the disease in susceptible people. The stimulus might be certain bacteria or viruses.
Someone who may have or has Sjogren's syndrome should visit a doctor for a diagnosis and treatment recommendations. Other saliva or gland problems should also be checked by a doctor if they persist. These problems include a change in saliva texture or pain that may be coming from a salivary gland or duct.
Relieving the Discomfort
A doctor and a dentist should be consulted about the best treatments for Sjogren's syndrome. The doctor may prescribe specific medications and will probably suggest other helpful steps to relieve symptoms. Sucking sugarless candies or chewing sugarless gum may be recommended because they can stimulate saliva flow and decrease dry mouth symptoms. Someone with a dry mouth should drink lots of water, preferably in frequent sips.
Drinking dilute lemon juice or sucking a small slice of lemon may increase saliva flow temporarily. Lemon juice is acidic and can damage tooth enamel, though. Concentrated lemon juice may cause rapid saliva release followed by an even drier mouth than before.
The choice of toothpaste and mouthwash is important for someone with Sjogren's syndrome. Some products are less drying than others. Some manufacturers claim that their products actually help a dry mouth.
The Cycle of Saliva Production and Removal
Most of us rarely think about our saliva unless a problem arises. The cycle of saliva secretion into our oral cavity followed by the act of swallowing to remove it takes place continuously, yet we are rarely aware of the process. It's interesting that the liquid has so many functions in our lives. It's possible that there are even more that we haven't yet discovered.
Salivary glands and saliva information from Colorado State University
Information about saliva from WebMD
How bird's nest soup is made from Business Insider
Salivary gland disorders from the Merck Manual
Information about salivary gland stones from WebMD
Sjogren's syndrome facts from the U.S. National Library of Medicine
Sjogren's syndrome causes, symptoms, and treatments from the Mayo Clinic
Questions & Answers
Why is water not reabsorbed with Na?
A complete explanation of sodium ion and water movement related to saliva in the glands and ducts would be very long. In addition, the production of saliva isn’t completely understood. One factor that is important is that the ducts of the salivary glands are relatively impermeable to water. This reduces the amount of water that leaves the ducts and allows a hypotonic saliva to be produced.
Could swollen salivary glands be caused by mumps?
It’s possible, but it’s not very likely. Mumps is an uncommon disease today. Most people in North America were vaccinated against the disease as children. The vaccine is known as the MMR vaccine and protects against measles, mumps, and rubella. Outbreaks of mumps sometimes occur, however. The disease is more common in children than adults.
Mumps is caused by a virus that affects the parotid glands as well as other parts of the body. The virus is spread in droplets of infected saliva that have been released by someone coughing or sneezing or obtained by sharing cups, plates, and utensils. Symptoms appear two to three weeks after the virus enters the body.
Some people have no or only minor symptoms from the viral infection. Others have an unpleasant experience with the disorder. Swollen parotid glands may cause puffing up of the cheek and jaw on one or both sides of the face. The person may also have a headache, muscle aches, a fever, loss of appetite, and fatigue.
If someone suspects that they or their child has mumps, a doctor should be consulted. The condition can sometimes cause complications. These complications are rare, but they may be serious. Possible effects include inflammation of the brain (encephalitis) and loss of hearing.
If you’re waiting for a doctor’s appointment for a child or teenager who may have mumps and want to give them a pain reliever, make sure that the medicine isn’t aspirin. The combination of aspirin and a recent viral infection can cause Reye’s syndrome in children. This syndrome includes dangerous swelling of the liver and brain.
© 2012 Linda Crampton