Clinical Nutrition: The salivary glands

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The salivary glands are derivatives of the cranial portion of the embryonic foregut, and thus are intimately associated with the physiology of digestion. They are commonly associated with carbohydrate digestion because it is well known the parotid glands secrete salivary amylase. But, there is much more to them than that.

Previously, I spoke about carbohydrate ingestion being intimately linked to the production of the neurotransmitter serotonin -- the symptoms of serotonin deficiency primarily being increased feelings of stress and tension, an exaggerated reaction to being easily startled, decreased ability to concentrate, and loss of appetite.

I thought in light of the increased use of Prozac and Ritalin by the medical profession, it might be helpful to review how incredibly important the salivary glands are to the process of digestion and your patients nutritional status in general.

Background

The secretion of the salivary glands is minimal at birth and does not contain salivary amylase, since only lactose is being ingested. The volume increases until it becomes sufficiently copious to cause drooling by two or three months. Salivary amylase does not appear in the saliva until the infant is given more complex carbohydrates, such as the starch in cereals.

This is a major theme of this column: digestion does not just automatically occur, the body responds specifically to what you put in it.

There are three pairs of salivary glands: parotid; submaxillary; and sublingual. The sublingual and submaxillary glands are easily palpated when they are stressed and hypertrophied. This can be an important consideration for a chiropractor attempting to determine the patient's tolerance of the carbohydrates in his or her diet and possible need for increased serotonin production. Without using chiropractic palpation as a diagnostic tool, how else could you make such a determination?

The purpose of the salivary glands is to continuously secrete saliva for lubrication and to initiate digestion. Salivary secretions are of two types: a) Serous secretion, a clear solution containing the digestive enzymes; and b) Mucous secretion, a thick, viscous solution containing mucus. The binding and lubricating properties of mucus facilitate mastication, the formation of the bolus, and swallowing.

The secretion of the parotid glands is serous and contains amylase. The sublingual secretion is serous and mucous and contains lipase. The submaxillary secretion is both serous and mucous. Saliva also contains several factors that actually destroy bacteria. Among these are thiocyanate ions as well as several proteolytic enzymes, most importantly, lysozyme.

The secretion of the watery elements and the salts found in saliva is increased by stimulation of the parasympathetics. Secretion of the organic substances depends upon stimulation of the sympathetics. Saliva is also stimulated by the thought of, the sight of, and odor of food.

Salivation also occurs in response to reflexes originating in the stomach and upper intestines -- particularly when very irritating foods are swallowed or when a person is nauseated because of some gastrointestinal abnormality. The swallowed saliva presumably helps to remove the irritating factor in the gastrointestinal tract by diluting or neutralizing (enzymatic action) the irritant substances.

Digestive difficulties

Salivary secretion is reduced during periods of emotional stress. Such psychic conditions as fear and anger are usually accompanied by a salivary secretion far below normal.

About 1-to-1.5 liters of saliva is secreted daily, and it has a pH between 6.0 and 7.4, a favorable range for the digestive action of the salivary enzymes. The characteristics and the actual volume of saliva are related to the type of food ingested. For example:

- A dietary practice of high protein meals decreases amylase production in the saliva, whereas a practice of high carbohydrate intake gradually increases the amylase content.

- Acid substances and dry foods produce a large volume of thin, watery saliva. The enzyme content is greater with meat than with weak acids.

- Milk or cold water produces a smaller volume of viscous saliva.

Another function of saliva is to supply a fluid medium in which enzymes, contained in the food which is being chewed, can be activated.

An excellent example of this occurs with raw vegetables. They are covered with a thin, transparent layer of cellulose which acts as a protective layer. Without the removal of the cellulose, neither the salivary nor pancreatic enzymes can penetrate the cellulose and digest the vegetable. The result is the well-known complaint of raw foods causing gas.

The body does not make an enzyme to digest cellulose, but the vegetable does! If the food is chewed properly, the cellulose in the vegetable will digest the cellulose, allowing the enzymes in the food, as well as the salivary enzymes to initiate digestion in the upper stomach.

Cooking also removes the cellulose layer. This is why cooking is regarded as a digestive aid in most nutrition textbooks. However, cooking destroys all the enzymes in the vegetable, and they are not available to assist in digestion as nature intended.

Thus, it can be seen that inappropriate salivary gland function is not just an often-overlooked condition affecting carbohydrate digestion, but can be a key diagnostic factor in your patients' overall health picture.

The Chiropractic Journal.

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By Howard F. Loomis

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