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Tongue & Salivary glands.
Taste is a chemical sense which is detected by special structures called taste buds, of which we all have about 10,000, mainly on the tongue with a few at the back of the throat and on the palate. Taste buds surround pores within the protuberances on the tongue's surface and elsewhere. There are four types of taste buds: these are sensitive to sweet, salty, sour and bitter chemicals. All tastes are formed from a mixture of these basic elements.
Many different tastes can be distinguished because of the combination of taste and the more discriminating sense of smell. The sense of smell is estimated to be about 10,000 times more sensitive than the sense of taste. The two senses are very closely related. It is usually correct to say that one smells more flavours than one tastes. When the nose fails, from a bad cold for instance, 80% of the taste ability is lost. Loss of taste without loss of smell is pretty rare, but "dry mouth" can contribute because taste buds can only detect flavour when food is dissolved in saliva. Taste can also be lost as a result of damage to the taste buds themselves or damage to the cranial nerves that carry taste sensations to the brain. Full sensory appreciation of food also involves its appearance, its consistency, and its temperature.
The picture of the tongue shows the areas where different types of taste are detected.
Green represents the area where sweet taste is interpreted.
Blue interprets salty tastes.
Red detects sour tastes and yellow picks out the bitter tastes.
The majority of oral secretions are contributed by the sub-mandibular and parotid glands, which equally provide 80 to 90 per cent of the saliva. The remainder is formed by sublingual and minor salivary glands. One thousand to 1500 ml of saliva is produced daily. Saliva contributes to the digestion of food and to the maintenance of oral hygiene. Without normal salivary function the frequency of dental caries , gum disease (gingivitis), and other oral problems increases significantly.
These glands may contain mucous secreting cells, serous cells or a mixture of both.
Serous cells produce a watery saliva that contains the enzymes amylase and lysozyme, IgA (immunoglobulin A), and lactoferrin (an iron binding compound).
Saliva has important functions :
The submandibular salivary gland secretes a mixed product containing both serous and mucous secretions although the serous component is the larger. They are roughly ovoid in shape and are situated below the mandible (jaw bone) to the left and right. Their ducts open into the floor of the mouth on either side of the tongue's frenulum.
The parotid salivary glands secrete a serous product only. They are situated on either side of the head in front of the ears. They have long ducts which open into the mouth opposite the second molar tooth on either side.
The sublingual glands produce a mainly mucous product. They are situated just uner the back of the tongue again in a left and right pair. Their ducts open close to those of the submandibular glands.
In addition there are numerous smaller groups of salivary gland tissue scattered diffusely in the submucosa.
The most important are:
Both the sympathetic and the parasympathetic nervous systems innervate the salivary glands. It is evident that the sympathetic nervous system, although its role in salivation is still controversial, influences the blood flow to the salivary glands and activates myoepithelial cells within the salivary ducts. These myoepithelial cells expedite the flow of saliva by squeezing saliva out of the salivary glands.
During infancy drooling is accepted as a normal part of development. After this period salivary incontinence is culturally unacceptable.
For the child with cerebral palsy drooling not only is a social burden but also may further handicap his already difficult task of acquiring speech. Some reports have stressed the role of hyper-salivation in the genesis of drooling, but in most cases it is believed that drooling results from failure to swallow salivary secretions or from inability to retain the accumulated secretions within the mouth because of a seventh-nerve palsy or facial disfigurement.
Hyper-salivation may be associated with many disorders such as herpetic stomatitis, irritation by dentures and pregnancy, but drooling does not occur in these cases unless the ability to hold secretions within the mouth or the ability to swallow secretions is impaired. Patients with hyper-salivation may expectorate repeatedly, but this is not drooling. It is the difference between salivary production and the ability to swallow saliva that results in drooling rather than the absolute production of saliva.
Difficulty in swallowing saliva is encountered at three levels of function: the oral, pharyngeal and oesophageal components of deglutition. Some of the common disorders associated with drooling, classified according to the presumable level of malfunction, are as follows: oral (cerebral palsy, Parkinson's disease, motor-neurone disease, seventh-nerve palsy, facial disfigurement and radical cancer surgery); pharyngeal (motor-neurone disease, myasthenia gravis and polymyositis); and oesophageal (carcinoma or stricture).
Mumps is a disease caused by a virus that can infect many parts of the body, especially the parotid salivary glands. The parotid salivary glands, which produce saliva for the mouth, are found toward the back of each cheek, in the area between the ear and jaw. In mumps, the parotid glands become increasingly swollen and painful over a period of one to three days. Pain gets worse when the sufferer swallows, talks, chews, or drinks juices that are acidic (like orange juice). As the glands swell, there is often a fever of up to 103°F (39.4°C), with headache and loss of appetite.
In two out of three cases, both left and right parotid glands are affected, and the second gland usually swells about four to five days after the first. In rare cases, mumps will attack other groups of salivary glands instead of the parotids. If this happens, the swelling and pain may be under the tongue, under the jaw, or all the way down to the front of the chest. Mumps can also involve the brain, pancreas and other organs.
Mumps in young adult males (and older) may result in the development of orchiditis, an inflammation of the testicles - a condition that ultimately can lead to a decreased sperm count. Usually one testicle becomes swollen and painful about seven to 10 days after the parotids swell. There is a high fever (often to 106°F or 41.1°C), with shaking chills, headache, nausea and vomiting. After three to seven days, testicular pain and swelling subside, usually about the same time as the fever passes. In some cases, both testicles are involved.
Mumps may also lead to encephalitis or meningitis (inflammation of the brain or the lining of the central nervous system). Symptoms appear three to seven days after parotid swelling begins and may include: high fever, stiff neck, headache, nausea and vomiting, drowsiness, convulsions, and other signs of brain involvement.
Mumps may also affect the pancreas or, in females, the ovaries, causing pain and tenderness in the parts of the abdomen.
This page last updated Friday, 30 April 1999 10:45 +0100
