The oral cavity is home to a great variety of primitive organisms. It is the gateway to two of the most imperative body systems, the gastrointestinal and the respiratory systems. The oral cavity is the drainage to secretory glands called the salivary glands of which there is between 600-1000 small glands located throughout the mouth. They are exocrine glands that release their secretions through tiny ducts that open into the mouth. There are three major pairs of salivary glands however that contribute the most to the oral secretion and these are; the parotid gland, which is the largest and it is located at the back of the jaw, the submandibular gland, located in the lower jaw, and the sublingual glands, located under the tongue ( "Composition of Saliva 2010"). All salivary glands release the substance Saliva, which not only moistens the mouth, but it has a myriad of components that carry out differentiated functions within the mouth.
As insignificant as it may seem, Saliva is an expression of the status of many of the body's tissues, organs or even systems. It consists of 98% water and only 2% of it are substances whose concentrations and contents as secreted into the mouth are effective biological indicators ( " Saliva"). They change with illness, they change with a change in diet and they change periodically. The periodical change in the salivary secretions takes many forms and rhythms, monitored by internal biological clocks. These biological clocks are simply groupings of interacting molecules in cells and they are responsible for a great variety of oscillations in physiological processes in animals, plants, and even prokaryotes. In humans, all the biological clocks in the body are controlled by a "Master clock" in the brain. This Master clock consists of a group of around 20,000 nerve cells called the suprachiasmatic nucleus (SCN) found in the hypothalamus of the brain, and it coordinates all the body clocks ( " Brain SCN is the master clock").
The biological clock controlling the salivary secretions gives rise to various cyclic changes in the salivary component such as changes corresponding with change in phases of females menstrual cycles, or corresponding to daily, monthly or seasonal changes. Rhythms in physiological oscillations that repeat every 24 hours are known as circadian rhythms. They are rhythms that mainly correspond with the time it takes the Earth to complete one full rotation around its axis and with one day and night. Salivary glands exhibit such circadian rhythms and the salivary secretions experience cyclic changes both quantitatively and qualitatively.
The salivary flow rate is amongst the aspects exhibiting a circadian rhythm. Although researchers have identified genes that direct the circadian rhythms of the body, commonly known as the "clock genes", external factors can also affect the salivary flow rate and desynchronize the circadian rhythm ("The Journal of Neuroscience Society for Neuroscience."...