A UK hospital is testing a home spit kit designed to help mums-to-be spot if they are at risk of pre-eclampsia. The test reads saliva for tell-tale markers of impending kidney problems. It is expected to be more reliable than traditional blood pressure and urine checks, according to the report in the Chemistry & Industry magazine. The preliminary trials showed that the saliva test accurately identified women with pre-eclampsia.
Nature's demands on saliva are extensive and diverse and range from the reptilian need for a venomous drop to incapacitate its prey to the 100 quarts that ruminants require to digest a day's grazing. Other species use the fluid for functions varying from grooming and cleansing to nest building.
As can be seen from the above report, saliva offers an alternative to serum as a biologic fluid that can be analyzed for diagnostic purposes. Whole saliva contains locally produced as well as serum-derived markers that have been found to be useful in the diagnosis of a variety of systemic disorders. Analysis of saliva can offer a cost-effective approach for the screening of large populations, and may represent an alternative for patients in whom blood drawing is difficult, or when compliance is a problem.
Hormones in saliva can be tested to assess pregnancy. Excessive testosterone in male saliva indicates testicular cancer. Amount of Immunoglobulin A and B in saliva indicates the health status of children. Certain substances such as lead, mercury, iodides, urea, arsenic, antibiotics, nitrates, chlorine, sulphates, acetates etc. and alkaloids and alkyl sulphides present in onion and garlic etc. are excreted through saliva.
Saliva can also be useful in the monitoring of therapeutic drug levels and the detection of illicit drug use. Further, analysis of saliva may provide valuable information regarding certain endocrine disorders.
Salivary Glands
Human saliva is secreted by the salivary glands. There are three pairs of salivary glands in human beings. These are the parotid, sublingual and sub maxillary glands. Parotids are the largest of the salivary glands and they are found lying one on each side of the face below and in front of the ears.
The secretion of each parotid gland passes via Stensen's duct, which opens in to the mouth opposite the site of the second upper molar tooth. The disease mumps is an infection of the parotid glands that causes swelling and irritation. The sub mandibular glands are found within the angles of the lower jaws. Their secretion passes via Wharton's duct into the floor of the mouth. Sublingual glands are found embedded in the mucous membrane on the floor of the buccal cavity and their ducts open under the tongue.
The secretion of saliva is generally coordinated by the intake of food. Olfactory and gustatory stimuli initiate the nervous reflex that results in the stimulation of salivary secretion. Secretion from the salivary gland cells is predominantly controlled by parasympathetic nerve fibres.
Alkaline reactions precipitate salivary constituents as tartar on teeth and calculus in salivary duct.
The complex mix of salivary constituents provides an effective set of systems for lubricating and protecting the soft and hard tissues. Protection of soft tissues is afforded against desiccation, penetration, ulceration, and potential carcinogens by mucin and anti-proteases. Saliva can encourage soft tissue repair by reducing clotting time and accelerating wound contraction.
In a state of fever the salivary out put decreases resulting in to accumulation of food debris at the base of teeth and upon the tongue. The taste buds can be stimulated only when the food substances are actually present in solution. By facilitating the movement of the tongue and lips it makes rapid articulation possible, thus deciding the features of our sound.
Saliva moistens dry food and facilitates swallowing by a lubricating action. Since water evaporates slowly from saliva it prevents desiccation of the oral mucosa. It helps in maintaining water balance, dissolves soluble substances such as sugar and salts, provides an enzyme called salivary amylase for the digestion of starch and brings about a buffering action through bicarbonate, phosphate and mucin. Saliva also possesses anti-fungal and anti-viral systems.
Properties of Saliva
The total amount of saliva secreted in an adult is 1200-1500ml/ day. It is slightly acidic in reaction with a pH ranging from 6.02 to 7.05. On boiling it looses CO2 and becomes alkaline.The specific gravity of saliva is 1.002-1.012 and its freezing point is 0.07 to 0.340C. About 99.5 percent of saliva is water and 0.5percent is solids. The cellular constituents include yeast, bacteria, protozoa, polymorphonuclear leucocytes and desquamated epithelial cells. The inorganic salts constitute 0.2% of the saliva and consist of sodium chloride, potassium chloride, sodium biphosphate, calcium carbonate, etc. The organic constituents of the saliva amount to 0.3% and they include amylase, maltase, esterase, lipases, carbonic, lysozymes, mucins, amino acids, cholesterol, urea, vitamins etc. The gases in saliva include oxygen (1.0ml), nitrogen (2.5ml), and carbon dioxide (50 ml) per 100ml of saliva.
The author is the Head, Dept of Zoology, Christ College.
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