The submandibular gland is one of the three major salivary glands, responsible for producing and secreting saliva to aid in digestion and oral lubrication. It is the second largest salivary gland and contributes significantly to resting saliva production.
Location
The submandibular gland is located in the submandibular triangle of the neck, beneath the floor of the mouth. It lies posterior to the mylohyoid muscle, with its superficial part situated below the mandible and its deep part extending above the mylohyoid. The gland’s duct, known as Wharton’s duct, opens into the oral cavity near the lingual frenulum.
Anatomy
The submandibular gland is one of the three major salivary glands, playing a significant role in saliva production. It is a mixed gland composed of both serous and mucous acini, with a predominance of serous cells. Below is a detailed description of its anatomy:
Parts of the Gland
Superficial Part:
- The larger portion of the gland.
- Lies superficial to the mylohyoid muscle.
- Situated below the mandible, making it palpable under the jawline.
Deep Part:
Smaller and extends above the mylohyoid muscle.
Lies within the floor of the mouth, medial to the mandible and lateral to the hyoglossus muscle.
Duct
The gland’s excretory duct is known as Wharton’s duct:
- It is approximately 5 cm long.
- Originates from the deep part of the gland and runs anteriorly on the floor of the mouth.
- Opens into the oral cavity at the sublingual caruncle, located near the base of the lingual frenulum.
- The duct passes medially to the lingual nerve, which loops around it.
Blood supply
Arterial Supply
- The submandibular gland is primarily supplied by branches of the facial artery, including the submental artery.
- Additional supply comes from the lingual artery.
Venous Drainage
Drains into the facial vein and subsequently into the internal jugular vein.
Nerve Supply
Parasympathetic Innervation
Provided by the facial nerve (cranial nerve VII):
- Preganglionic fibers travel via the chorda tympani nerve, 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 secretion.
Sympathetic Innervation
Arises from the superior cervical ganglion, causing vasoconstriction and reducing saliva production.
Lymphatic Drainage
The lymphatic drainage of the submandibular gland is directed to:
- Submandibular lymph nodes for superficial drainage.
- Deep cervical lymph nodes for deeper drainage.
Relations
- Superficial Relations: Skin, platysma, and deep cervical fascia.
- Deep Relations: Mylohyoid muscle, hyoglossus muscle, and lingual nerve.
- Posterior Relations: Posterior belly of the digastric muscle and stylohyoid muscle.
- Medial Relations: Lingual nerve and sublingual gland.
Function
The submandibular gland is one of the major salivary glands responsible for producing and secreting saliva. Saliva plays a critical role in digestion, oral health, and lubrication. Below is a detailed explanation of its functions:
Saliva Production
The submandibular gland produces approximately 65-70% of the total saliva in the oral cavity during resting conditions.
The gland is classified as a mixed gland, meaning it produces both:
Serous Secretion:
- Rich in enzymes like salivary amylase, which initiates the digestion of carbohydrates by breaking down starch into maltose and dextrins.
- Provides a watery consistency that aids in lubrication and enzymatic activity.
Mucous Secretion:
- Contains mucins, glycoproteins that give saliva its viscous quality.
- Helps in lubricating the oral cavity and forming a cohesive bolus for swallowing.
Aiding in Digestion
Saliva from the submandibular gland contains enzymes and mucous that:
- Begin the chemical breakdown of carbohydrates through amylase.
- Moistens food, making it easier to chew and swallow.
- Facilitates the formation of a smooth bolus, aiding in its transport from the mouth to the esophagus.
Lubrication
Saliva produced by the submandibular gland ensures that:
- The oral mucosa remains moist, preventing dryness and irritation.
- The tongue and lips glide smoothly, aiding in speech and mastication.
- The bolus is lubricated for easier passage through the pharynx and esophagus.
Protection and Oral Hygiene
The saliva secreted by the submandibular gland contains several protective components:
Antibacterial Agents:
- Lysozymes: Enzymes that break down bacterial cell walls, protecting against infection.
- Immunoglobulin A (IgA): An antibody that provides immune defense against pathogens in the oral cavity.
Buffering:
Bicarbonates in the saliva neutralize acids produced by oral bacteria, protecting teeth from dental caries and maintaining a healthy pH in the mouth.
Washout Effect:
Continuous saliva flow helps to rinse away food particles and debris, reducing bacterial accumulation and plaque formation.
Facilitating Taste
Saliva dissolves food particles, allowing them to interact with the taste buds on the tongue:
- This enhances the perception of taste by enabling molecules to reach taste receptors.
Speech Facilitation
The lubrication provided by submandibular saliva aids in smooth tongue and lip movements during speech:
- It prevents dryness in the oral cavity, ensuring clear articulation of words.
Supporting Wound Healing
Components in saliva, such as epidermal growth factors (EGFs), promote the healing of oral mucosal injuries.
Parasympathetic Regulation
The submandibular gland plays a role in autonomic regulation:
- Parasympathetic stimulation (via the facial nerve) enhances the production of saliva in response to eating, chewing, or even the anticipation of food.
- Sympathetic stimulation reduces saliva flow during stress or dehydration.
Clinical significance
The submandibular gland plays a vital role in saliva production, and its dysfunction can lead to various clinical issues:
- Sialolithiasis (Salivary Stones): The submandibular gland is the most common site for salivary stone formation due to the viscous nature of its secretions and the long course of Wharton’s duct. Stones can obstruct the duct, causing pain and swelling, especially during meals.
- Infections: Bacterial or viral infections, such as sialadenitis or mumps, can affect the gland, leading to inflammation, pain, and swelling.
- Tumors: Both benign (e.g., pleomorphic adenomas) and malignant tumors (e.g., mucoepidermoid carcinoma) can arise in the gland, necessitating imaging and biopsy for diagnosis.
- Dry Mouth (Xerostomia): Dysfunction or damage to the submandibular gland, often due to radiation therapy or autoimmune conditions like Sjögren’s syndrome, can lead to reduced saliva production, resulting in dry mouth and difficulty in chewing, swallowing, and speaking.
- Surgical Relevance: The gland’s proximity to important structures like the lingual nerve and facial artery makes it a critical area in head and neck surgeries, including tumor excision or stone removal.
