The salivary glands, of which there are three pairs known as the parotid, submandibular, and sublingual glands, play a crucial role in maintaining oral health and initiating the digestive process. Positioned near the ears, beneath the masseter muscle, the parotid glands secrete saliva into the oral cavity through the parotid duct of Stensen. Meanwhile, the submandibular glands, located on the floor of the mouth, secrete saliva through channels named submandibular ducts. The sublingual glands, found underneath the tongue, release their secretions via the lesser sublingual ducts.
Saliva, predominantly water (99.5%), also contains 0.5% solutes. These include a variety of ions, such as sodium, potassium, chloride, bicarbonate, and phosphate. Furthermore, saliva contains dissolved gases, and organic substances, including urea, uric acid, mucus, immunoglobulin A, lysozyme, and salivary amylase, a digestive enzyme that works on starch. However, not all glands contribute the same components. The parotid glands, for example, secrete a serous solution heavy with salivary amylase, while the submandibular glands contribute a mucus-laden liquid with a smaller proportion of amylase. The sublingual glands, rich with mucous cells, secrete a thicker fluid with minimal amylase.
Saliva's water component acts as a solvent for food particles, facilitating taste perception and initiating digestion. Salivary amylase breaks down starch into maltose, maltotriose, and α-dextrin. Buffers in the saliva, specifically bicarbonate and phosphate ions, neutralize incoming acidic foods. Saliva has a pH that ranges from 6.2 to 7.6 with 6.7 being the average pH. Mucus lubricates food in the mouth, assisting in swallowing, while immunoglobulin A and lysozyme work to hinder bacterial attachment and proliferation, although they are not present in sufficient quantities to obliterate all oral bacteria.
Salivation is regulated by the autonomic nervous system. The level of salivary secretion changes significantly, ranging from 1000–1500 mL daily on average. Under normal conditions, parasympathetic stimulation ensures a continuous moderate flow of saliva, aiding in speech and moistening the mucous membranes. However, during times of stress or dehydration, salivary secretion decreases. The subsequent dry mouth sensation prompts the desire to drink, restoring both oral moisture and overall bodily hydration. The taste and texture of food can strongly stimulate salivary secretion. This response is mediated by taste receptors on the tongue, which send signals to the salivary nuclei in the brain stem. The ensuing parasympathetic impulses stimulate further saliva production, ensuring the mouth is cleansed, and any residual food particles or irritants are diluted and buffered. Even the mere anticipation of food, incited by its smell, sight, or sound, can trigger saliva secretion.
Saliva is composed of 97 to 99.5% water. The remaining proportion includes enzymes such as lipases and amylases, electrolytes, dissolved gasses, IgA, mucin, lysozymes, and metabolic wastes like urea and uric acid.
Saliva primarily functions to dissolve food and initiate the digestion of carbohydrates through salivary amylases.
Additionally, it neutralizes acidic foods and hinders bacterial proliferation in the oral cavity.
The glands that produce saliva are called the salivary glands.
The intrinsic salivary glands, scattered throughout the mouth, produce minimal saliva.
The extrinsic salivary glands — parotid, submandibular, and sublingual — produce most of the saliva.
These extrinsic glands release their secretions through their independent ducts.
The parotid glands, located near the ears, secrete a serous solution rich in salivary amylase.
The submandibular glands, located on the floor of the mouth, release a mucus-heavy liquid with amylase.
Finally, the sublingual glands, situated beneath the tongue, release a thick fluid with minimal amylase.
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