The sublingual gland is the smallest of the three major salivary glands. It is primarily responsible for producing saliva that keeps the mouth moist and aids in digestion. The gland predominantly secretes mucous saliva and contributes a smaller portion of the overall salivary output compared to the submandibular and parotid glands.
Location
The sublingual gland is located in the floor of the mouth, beneath the mucosa of the oral cavity. It lies anterior to the submandibular gland and is situated above the mylohyoid muscle. The gland is medial to the mandible and lateral to the genioglossus muscle, with its multiple small ducts opening into the oral cavity through the sublingual fold or joining Wharton’s duct from the submandibular gland.
Anatomy
The sublingual gland is the smallest of the three major salivary glands. It is almond-shaped and primarily contributes to mucous saliva production. Below is a detailed anatomical description:
Shape and Size
- Almond-shaped and flattened.
- Measures approximately 3-5 cm in length.
- The smallest among the major salivary glands.
Capsule
- The gland is encapsulated by the oral mucosa, which acts as its covering layer.
- Unlike the parotid and submandibular glands, it does not have a distinct fibrous capsule.
Ducts
The sublingual gland has multiple small ducts called ducts of Rivinus:
- These ducts open into the floor of the mouth along the sublingual fold.
- Some of the ducts may unite to form a larger duct called the Bartholin’s duct, which joins the Wharton’s duct (submandibular duct) before opening at the sublingual caruncle near the base of the lingual frenulum.
Histology
- The sublingual gland is classified as a mixed gland, but it predominantly produces mucous secretions.
- Composed of:
- Mucous Acini:
- Make up the majority of the gland.
- Secrete viscous, mucin-rich saliva.
- Serous Acini:
- Found in smaller numbers and secrete watery saliva.
- Ductal System:
- Intercalated and striated ducts are shorter and less prominent compared to the other major salivary glands.
- Mucous Acini:
Blood Supply
Arterial Supply:
- The gland is primarily supplied by branches of the lingual artery, a branch of the external carotid artery.
- Additional supply may come from the facial artery and submental artery.
Venous Drainage:
Blood is drained via the sublingual vein, which eventually empties into the internal jugular vein.
Nerve Supply
- Parasympathetic Innervation:
- Provided by the facial nerve (cranial nerve VII):
- Preganglionic fibers travel via the chorda tympani, which joins the lingual nerve (a branch of the mandibular nerve, CN V3).
- Synapse occurs at the submandibular ganglion, from which postganglionic fibers innervate the gland, stimulating saliva production.
- Provided by the facial nerve (cranial nerve VII):
- Sympathetic Innervation:
- Derived from the superior cervical ganglion, causing vasoconstriction and modulating saliva production.
Lymphatic Drainage
The lymphatic drainage of the sublingual gland is directed to:
- Submandibular lymph nodes.
- Deep cervical lymph nodes for deeper drainage.
Relations
- Superior Relation: Oral mucosa of the floor of the mouth.
- Inferior Relation: Mylohyoid muscle.
- Medial Relation: Genioglossus muscle and submandibular duct.
- Lateral Relation: Mandible.
Function
The sublingual gland is one of the three major salivary glands, and its primary function is to produce and secrete saliva into the oral cavity. While it contributes the smallest amount of saliva among the major glands, its mucous-rich secretions play a vital role in maintaining oral health and facilitating digestion. Below is a detailed explanation of its functions:
Saliva Production
The sublingual gland produces primarily mucous saliva, with a minor contribution from serous components:
Mucous Secretion
The gland’s acini are predominantly mucous-secreting, which results in a viscous, lubricating saliva.
Serous Secretion
A smaller proportion of serous acini contribute watery saliva containing digestive enzymes like amylase, though in lesser amounts than the submandibular and parotid glands.
Lubrication
The mucous secretions from the sublingual gland ensure:
- The oral mucosa remains moist, preventing dryness and irritation.
- Smooth movements of the tongue and lips, which are essential for speech and mastication.
- Formation of a lubricated bolus of food, easing its transport through the pharynx and esophagus during swallowing.
Protection and Oral Hygiene
The sublingual gland contributes to oral defense mechanisms by secreting saliva rich in:
- Mucins: Form a protective layer over the oral mucosa, shielding it from mechanical damage, dehydration, and microbial invasion.
- Antibacterial Agents: Saliva contains lysozymes, lactoferrin, and immunoglobulin A (IgA), which help control bacterial growth and prevent infections.
- Buffering Capacity: Saliva neutralizes acids in the mouth, protecting teeth from enamel erosion and preventing conditions like dental caries.
Facilitating Digestion
Although primarily mucous in nature, sublingual saliva aids in the digestive process by:
- Mixing with food to initiate its breakdown and facilitate swallowing.
- Activating taste receptors by dissolving food particles, enhancing the sense of taste.
Speech Facilitation
The sublingual gland contributes to saliva production that prevents dryness in the oral cavity:
- Ensuring proper articulation and fluidity of speech.
- Maintaining a comfortable environment for tongue and lip movements.
Role in Reflexive and Autonomic Control
The gland’s secretion is modulated by:
Parasympathetic Stimulation:
Stimulates saliva production during eating or chewing to aid in digestion and oral lubrication.
Sympathetic Stimulation:
Modulates the viscosity of saliva, producing a thicker secretion during stress or dehydration.
Supporting Taste Perception
Saliva produced by the sublingual gland dissolves food particles, enabling them to interact with taste buds on the tongue:
- Enhances the perception of flavors.
Contribution to Continuous Saliva Flow
The sublingual gland contributes to the basal (resting) salivary flow:
- Ensures the oral cavity remains hydrated even during periods of rest or fasting.
Clinical significance
The sublingual gland plays an important role in oral health and digestion, and its dysfunction or pathology can lead to various clinical conditions:
- Sialolithiasis (Salivary Stones): Although less common than in the submandibular gland, stones can form in the ducts of the sublingual gland, causing swelling and discomfort.
- Ranula Formation: Blockage or rupture of the sublingual ducts can result in a mucous retention cyst called a ranula, presenting as a swelling in the floor of the mouth.
- Infections and Sialadenitis: Bacterial or viral infections may cause inflammation, leading to pain and swelling.
- Tumors: Both benign (e.g., pleomorphic adenoma) and malignant tumors (e.g., adenocarcinoma) can occur, although these are rare.
- Dry Mouth (Xerostomia): Reduced function of the sublingual gland, often due to autoimmune conditions like Sjögren’s syndrome or radiation therapy, can lead to dryness, difficulty in swallowing, and increased risk of oral infections.
