Submandibular gland

The submandibular gland is the second largest of the three major paired salivary glands and is approximately the size of a walnut with an irregular shape.

Location

It lies mainly within the submandibular triangle of the neck, extending anteriorly toward the anterior belly of the digastric muscle and posteriorly to the stylomandibular ligament, which separates it from the parotid gland. Superiorly, the gland lies against the submandibular fossa on the medial surface of the mandible, while inferiorly it commonly overlaps the intermediate tendon of the digastric and the insertion of the stylohyoid muscle.

Superficial and deep lobes

The submandibular gland is enclosed by a capsule derived from the investing layer of the deep cervical fascia and is divided by the mylohyoid muscle into a large superficial lobe and a smaller tongue-like deep process (deep lobe) that curves around the posterior border of the mylohyoid into the floor of the mouth.

Relations

• The superficial surface of the gland is related to the skin, superficial fascia, platysma, and deep cervical fascia, and is crossed by the facial vein and cervical branches of the facial nerve. Submandibular lymph nodes lie in close relation to its superficial aspect near the mandible.

• The deep surface of the submandibular gland is related to the mylohyoid, hyoglossus, styloglossus, stylohyoid, and posterior belly of digastric muscles, together with the mylohyoid nerve and accompanying vessels.

• The facial artery grooves the posterior part of the gland before winding around the inferior border of the mandible.

• The deep part of the gland lies between the mylohyoid laterally and the hyoglossus and styloglossus medially.

• Superiorly it is related to the lingual nerve and submandibular ganglion, while inferiorly it is related to the hypoglossal nerve and accompanying vein.

Histology and submandibular duct

The gland is a mixed tubulo-acinar gland containing both serous and mucous acini, although serous elements predominate structurally. It produces approximately 70% of resting (unstimulated) saliva. The principal excretory duct is the submandibular duct (Whartons duct), which is approximately 5 cm long and thinner-walled than the parotid duct. It arises from numerous branches on the deep surface of the gland and passes forwards between the mylohyoid laterally and the hyoglossus and genioglossus medially. It then runs between the sublingual gland and genioglossus before opening at the sublingual caruncle, a small papilla situated on either side of the lingual frenulum. Along its course, the duct is closely related to the lingual and hypoglossal nerves; notably, the lingual nerve loops beneath it (from lateral to medial) and then ascends medially near its termination at the caruncle.

Blood supply

Arterial supply to the gland is mainly from branches of the facial and lingual arteries (branches of external carotid artery), while venous drainage follows corresponding veins into the internal jugular system.

Lymph drains to the submandibular lymph nodes, which are clinically important in the spread of oral and salivary gland malignancies.

Innervation

Parasympathetic secretomotor innervation is supplied by fibres from the facial nerve (CN VII) via the chorda tympani, lingual nerve, and submandibular ganglion, whereas sympathetic fibres arise from the superior cervical ganglion along peri-arterial plexuses.

Clinical correlates

Clinically, the submandibular gland is the most common site of sialolithiasis, largely because its saliva is relatively mucous and its duct follows a long ascending course that predisposes to salivary stasis and stone formation.