Salivary Glands and Saliva

The three extrinsic salivary glands are the parotid glands, located near the ears; the submandibular glands, positioned on the floor of the mouth; and the sublingual glands, situated beneath the tongue. These glands produce most of the saliva and release secretions through independent ducts into the oral cavity.

Salivary amylase is a digestive enzyme that initiates carbohydrate digestion by breaking down starch into maltose, maltotriose, and α-dextrin. This enzyme is secreted primarily by parotid and submandibular glands, beginning the chemical digestion process in the mouth before food enters the gastrointestinal tract.

Saliva is 97 to 99.5% water, which dissolves food particles and facilitates taste perception. The remaining 0.5% includes enzymes like amylase and lipase, electrolytes such as bicarbonate and phosphate ions that buffer acidic foods, mucin for lubrication, immunoglobulin A and lysozyme for antimicrobial defense, and metabolic wastes like urea and uric acid.

The parotid glands secrete a serous solution rich in salivary amylase for starch digestion. The submandibular glands release a mucus-heavy liquid containing amylase. The sublingual glands, rich with mucous cells, secrete a thick fluid with minimal amylase, primarily providing lubrication rather than enzymatic digestion.

The autonomic nervous system controls salivary secretion through parasympathetic stimulation, which maintains a continuous moderate flow averaging 1000–1500 mL daily. Taste receptors on the tongue, food smell, sight, or even anticipation trigger increased saliva production. Conversely, stress and dehydration decrease secretion, causing dry mouth.

Saliva contains immunoglobulin A and lysozyme, which hinder bacterial attachment and proliferation in the mouth. Additionally, bicarbonate and phosphate ions buffer acidic foods, creating an environment less favorable for bacterial growth. However, these antimicrobial components are not present in sufficient quantities to eliminate all oral bacteria.

Saliva has a pH ranging from 6.2 to 7.6, with an average of 6.7, making it slightly acidic to neutral. This pH range, maintained by bicarbonate and phosphate buffers, neutralizes acidic foods entering the mouth and creates optimal conditions for salivary amylase to function effectively during initial carbohydrate digestion.