The human mouth contains a complex network of glands responsible for producing saliva, including the accessory salivary glands, often called minor salivary glands. These thousands of tiny glands are physically and structurally distinct from the three large, paired major salivary glands: the parotid, the submandibular, and the sublingual glands. Unlike their larger counterparts, which are encapsulated and can be several centimeters in size, accessory glands are small, measuring 1 to 5 millimeters in diameter, and are dispersed throughout the mucosal lining of the upper aerodigestive tract. They are embedded directly within the connective tissue of the oral lining, each possessing its own small duct that opens onto the surface.
Widespread Anatomical Distribution
Accessory salivary glands are found in nearly every part of the oral cavity and surrounding structures, creating a diffuse network of moisture. They are highly concentrated in the lips, particularly the lower lip, and across the buccal mucosa (inner lining of the cheeks). Their presence extends throughout the roof of the mouth, including the soft palate and the lateral parts of the hard palate.
The tongue also hosts several groups of minor glands, such as the lingual glands near the tip and the specialized von Ebner glands beneath the circumvallate papillae. This widespread distribution ensures that a consistent layer of saliva is maintained over all mucosal surfaces, not just those covered by the secretions of the major glands. These glands also continue into the pharynx, nasal cavity, paranasal sinuses, and the supraglottis, supporting the entire upper respiratory and digestive tract.
Essential Roles of Minor Salivary Glands
The primary function of accessory salivary glands is to provide continuous, localized secretion, unlike major glands that produce large volumes primarily stimulated by eating. This constant, low-level output is predominantly mucous, meaning it is thick and rich in mucins. This mucous secretion serves the important purpose of lubricating and hydrating the mucosal surfaces of the mouth and throat, preventing the delicate tissues from drying out.
Localized hydration is important for maintaining the integrity of the oral lining and facilitating comfortable speech and swallowing. The secretions of the accessory glands also contribute to the mouth’s innate immune defense system. They contain various antimicrobial components, including secretory immunoglobulin A (IgA), which acts as a first line of defense against pathogens.
The saliva from these glands includes specialized antimicrobial peptides like histatins and defensins, which help regulate the oral microbiome. These substances possess broad-spectrum activity against bacteria and fungi, complementing the physical barrier of the mucous layer. This continuous surveillance helps prevent localized infections and maintains the health of the oral environment.
Common Issues Affecting Accessory Glands
The small size and superficial location of the accessory salivary glands make them susceptible to complications, ranging from simple blockages to tumor formation. The most common issue is the formation of an oral mucocele, a benign lesion resulting from trauma to the gland’s excretory duct. When the duct is severed or ruptured, mucus leaks into the surrounding connective tissue, forming a localized, fluid-filled swelling called an extravasation mucocele.
Mucoceles typically appear as soft, dome-shaped swellings. They can range from the color of the surrounding mucosa to a bluish or translucent hue due to pooled fluid. These lesions are most frequently observed on the inner surface of the lower lip, often following a minor injury such as biting the lip. While most mucoceles are small (2 to 10 millimeters in diameter), they can sometimes spontaneously rupture and heal, or require minor surgical removal if persistent or interfere with daily activities.
A less common mucocele type, the retention mucocele, occurs when the duct becomes obstructed, causing saliva to accumulate within the ductal system. When a mucocele develops specifically on the floor of the mouth, originating from glands in that area, it is given the specialized name of a ranula. These can grow larger and interfere with speech or swallowing, necessitating careful management.
Accessory glands can also be the site of neoplastic growth (tumors), although salivary gland tumors overall are rare. Tumors arising in the accessory glands are disproportionately more likely to be malignant compared to those found in the parotid gland. While the parotid gland accounts for the majority of all salivary gland tumors, roughly 50 to 75 percent of those found in the minor glands are cancerous.
The most common benign tumor is the pleomorphic adenoma, a slow-growing, generally painless mass. The most frequent malignancy is mucoepidermoid carcinoma, followed by adenoid cystic carcinoma. Tumors of the accessory glands occur most often in the palate, and any persistent, firm mass in the oral mucosa warrants immediate evaluation. Accessory glands can also be affected by inflammation (sialadenitis), and their dysfunction can contribute to xerostomia (chronic dry mouth), especially when systemic diseases impact salivary tissue function.