submandibular gland

**Anatomy** - Location: Submandibular (digastric) triangle, wrapping around the posterior free edge of the mylohyoid muscle (superficial lobe inferior/lateral to mylohyoid; deep lobe superior/medial). - Duct: Submandibular (Wharton's) duct runs anteriorly, opening at the sublingual caruncle lateral to the lingual frenulum. - Relations: The lingual nerve loops under the duct (the "water under the bridge" mnemonic: the ureter passes under the uterine artery, and the lingual nerve passes under Wharton's duct). The hypoglossal nerve (CN XII) and the marginal mandibular branch of CN VII are also close, so they are at risk during gland excision. The facial artery and vein pass near or through the gland.

**Innervation** - Parasympathetic (secretomotor): The superior salivatory nucleus → CN VII → chorda tympani → joins the lingual nerve (V3) → submandibular ganglion → postganglionic fibers to the gland. This causes watery, copious saliva. - Sympathetic: Superior cervical ganglion → plexus along the facial artery. It causes scant, viscous, mucous-rich saliva. - Compare with the parotid gland, which is supplied by CN IX (glossopharyngeal) via the otic ganglion.

**Histology/Secretions** - Mixed seromucous gland, predominantly serous (~80% serous, ~20% mucous) with serous demilunes. - Contributes ~70% of unstimulated saliva (parotid ~25%, sublingual ~5%). The parotid dominates with stimulation. - Saliva contents: amylase (more from the parotid), lysozyme, lactoferrin, IgA, mucins, and bicarbonate. Saliva is hypotonic with high K⁺ and HCO₃⁻ and low Na⁺ and Cl⁻ relative to plasma, because the ducts reabsorb Na⁺/Cl⁻ and secrete K⁺/HCO₃⁻.

**Clinical Correlations** - Sialolithiasis (salivary stones): The submandibular gland is the most common site (~80%). Reasons: the duct is long and runs upward against gravity, and the saliva is alkaline, viscous, and mucous-rich with a high calcium and phosphate content. Presents with pain and swelling of the gland during meals (salivary colic). Treatment includes hydration, sialogogues, massage, and sialendoscopy or surgery. - Sialadenitis: Often secondary to obstruction or stasis, with bacterial infection (*Staphylococcus aureus* most common). Viral causes include mumps (usually the parotid). - Tumors: The submandibular gland has a higher proportion of malignant tumors than the parotid (about 50% malignant, versus ~80% benign in the parotid). Pleomorphic adenoma is the most common benign tumor overall. Adenoid cystic carcinoma shows perineural invasion. - Ludwig angina: A bilateral cellulitis of the submandibular, sublingual, and submental spaces, usually odontogenic (mandibular molars). It risks airway compromise. - Sjögren syndrome: Autoimmune lymphocytic infiltration causes xerostomia and keratoconjunctivitis sicca. It is associated with anti-Ro/SSA and anti-La/SSB, and carries an increased risk of MALT/B-cell lymphoma. - Surgical risk: During submandibular gland excision, the marginal mandibular branch of CN VII (lip depressor weakness), the lingual nerve (tongue sensation), and CN XII (tongue deviation toward the injured side) can be injured. - Embryology: The gland is endodermal in origin and arises as an epithelial bud from the floor of the primitive mouth. (The parotid gland is ectodermal.)

**High-Yield Pearls** - The chorda tympani carries taste from the anterior 2/3 of the tongue and the preganglionic parasympathetic fibers to the submandibular and sublingual glands. - The lesser petrosal nerve (CN IX) supplies the parotid gland, not the submandibular gland. - The submandibular and sublingual glands share the same parasympathetic pathway (CN VII).