The salivary glands consist of two parotid glands, two submandibular glands, two principal sublingual glands, and a large number of minor salivary glands. Combined, the salivary glands produce serous secretions, mucous secretions, or both. The serous saliva of the parotid gland and the predominantly mucous secretions of the submandibular, sublingual, and minor salivary glands provide digestive enzymes, bacteriostatic functions, lubrication, and hygienic activities. The secretions of the parotid and submandibular glands are primarily stimulated by the autonomic nervous system.
The salivary glands consist of multiple secretory units that include an acinus at the proximal end and a distal ductal unit. The ductal unit combines a sequential array of ductal elements extending away from the acinus: the intercalated duct, the striated duct, and the excretory duct. Myoepithelial cells surround the acinus and extend to the intercalated duct. These myoepithelial cells contract, enabling the glandular cells to expel their secretions. Benign disorders of the salivary glands involve abnormalities of saliva production and secretion.
Saliva is produced by the clustered acinar cells and contains electrolytes, enzymes (eg, ptyalin and maltase), carbohydrates, proteins, inorganic salts, and even some antimicrobial factors. Approximately 500–1500 mL of saliva is produced by the acinar cells daily and transported through the ductal elements at an average rate of 1 mL per minute. Human saliva is generally alkaline.
Benign diseases of the major and minor salivary glands can often be classified as nonneoplastic and neoplastic. Most clinically significant benign diseases involve primarily the parotid and submandibular glands and less frequently the paired principal sublingual and widely distributed minor salivary glands.
The parotid gland is the largest of the paired major salivary glands, with an average weight of 25 grams. Each gland is located lateral to the masseter muscle anteriorly and extends posteriorly over the sternocleidomastoid muscle behind the angle of the mandible. The dermis lies laterally to the gland, and the lateral parapharyngeal space lies medially. Each encapsulated gland is artificially divided into a superficial lobe and a deep lobe by the branches of the seventh cranial nerve. The parotid duct, or Stensen duct, courses anteriorly from the parotid gland over the masseter muscle and pierces the buccinator muscle to enter through the buccal mucosa, usually opposite the second maxillary molar. The Stensen duct can be found approximately 1.5 cm below the zygoma.
The parotid gland has two layers of draining lymph nodes. The superficial layer lies beneath the capsule, and the deeper layer lies within the parotid parenchyma.
The paired submandibular glands are the second largest salivary glands in the body, each weighing approximately 10–15 grams. Each submandibular gland is divided into superficial and deep lobes by the posterior edge of the mylohyoid muscle and occupies the submandibular triangle. The submandibular duct, also known as ...