The salivary glands exist to produce saliva, a fluid that plays important roles in digestion, pH balance and hygiene. Salivary glands also play an important role in thermoregulation for some other animals, such as dogs. According to About.com, most species possess three distinct pairs of salivary glands, known as the parotid, sublingual and submaxillary glands.
Salivary glands are primarily composed of one of two types of cells. Serous cells secrete watery fluids, while mucous cells secret thick, mucous-like fluids. About.com states that the parotid glands are primarily comprised of serous cells, while the sublingual glands are primarily composed of mucous cells. The submaxillary glands, which produce a saliva with characteristics of both water and mucous, are made from both types of cells.
According to About.com, the autonomic nervous system controls both the quantity of saliva produced and the relative mixture of the two types. The body can alter the consistency and composition of the saliva in response to stimuli. For example, dogs that are fed dry food tend to produce serous saliva. By contrast, when dogs eat meat-based, wet food, their saliva is predominately mucous-based.
Saliva is very important for digestion, as it is the first step in the process of digesting starches. Additionally, according to About.com, saliva helps to keep the mouth clean.