Structure
The three major glands differ in size, secretion and the course of their ducts. Hundreds of minor salivary glands in the lips, cheeks, palate and tongue add to the total.
| Feature | Parotid | Submandibular | Sublingual |
|---|---|---|---|
| Size | Largest | Intermediate | Smallest |
| Secretion | Serous | Mixed, mainly serous | Mixed, mainly mucous |
| Duct | Parotid (Stensen's) duct | Submandibular (Wharton's) duct | Many small ducts, some joining the submandibular duct |
| Opening | Cheek, opposite the upper second molar | Sublingual papilla beside the lingual frenulum | Along the sublingual fold |
| Secretomotor nerve | Glossopharyngeal (IX) | Facial (VII) | Facial (VII) |
The submandibular glands produce most of the resting saliva, while the parotids contribute most of the watery saliva produced in response to eating.
Position and ducts
Parotid gland
The parotid gland fills the retromandibular region between the ramus of the mandible, the mastoid process and the external acoustic meatus, and extends forwards over masseter. It is enclosed in a tough capsule derived from the investing layer of deep cervical fascia. Its duct runs forwards across masseter about a fingerbreadth below the zygomatic arch, turns sharply around the anterior border of the muscle, pierces buccinator and opens on a small papilla opposite the upper second molar.
Submandibular gland
The submandibular gland lies in the submandibular triangle, between the body of the mandible and the two bellies of digastric. It hooks around the free posterior border of mylohyoid, giving a large superficial part below the muscle and a small deep part above it. The duct leaves the deep part and runs forwards on hyoglossus and then genioglossus to open at the sublingual papilla.
Sublingual gland
The sublingual gland lies in the floor of the mouth, above mylohyoid and lateral to genioglossus, raising the sublingual fold. It drains by numerous short ducts directly into the mouth along the fold, and some ducts join the submandibular duct.
Relations
The parotid gland is surgically important because three structures pass through it. From superficial to deep these are the facial nerve and its branches, the retromandibular vein, and the external carotid artery, which divides within the gland into the maxillary and superficial temporal arteries. The facial nerve plexus separates a larger superficial lobe from a smaller deep lobe, which is a surgical rather than an anatomical division. The auriculotemporal nerve emerges from the upper border, and intraparotid lymph nodes lie within the gland.
The submandibular gland has three key relations. The marginal mandibular branch of the facial nerve runs superficial to it, deep to platysma. The facial artery grooves the deep and upper surface of the gland before hooking over the mandible, while the facial vein lies superficial to the gland. In the floor of the mouth, the lingual nerve crosses the submandibular duct: it starts lateral to the duct, passes beneath it and ends on its medial side.
Blood supply and innervation
All three glands are supplied by branches of the external carotid artery. The parotid receives the superficial temporal and transverse facial arteries, and drains to the retromandibular vein. The submandibular gland receives the facial and submental arteries; the sublingual gland the sublingual branch of the lingual artery and the submental artery.
Secretomotor pathways
- Parotid: inferior salivatory nucleus, glossopharyngeal nerve, tympanic nerve and tympanic plexus, lesser petrosal nerve, synapse in the otic ganglion, then postganglionic fibres carried to the gland by the auriculotemporal nerve.
- Submandibular and sublingual: superior salivatory nucleus, facial nerve, chorda tympani, which joins the lingual nerve, synapse in the submandibular ganglion suspended from the lingual nerve, then postganglionic fibres to the glands.
Sympathetic fibres reach all three glands along the arteries from the superior cervical ganglion and are mainly vasomotor. Sensation from the parotid capsule is carried by the great auricular and auriculotemporal nerves.
Clinical relevance
Most salivary calculi form in the submandibular gland. Its saliva is more alkaline and mucoid, and its long duct runs upwards against gravity to its opening. A stone causes painful swelling at mealtimes and can often be felt bimanually in the floor of the mouth. When the duct is opened to remove a stone, the lingual nerve lies close beneath it.
Most salivary gland tumours arise in the parotid, and most parotid tumours are benign, pleomorphic adenoma being the commonest. Facial nerve palsy with a parotid mass suggests malignancy. After parotidectomy, severed parasympathetic fibres can regrow into sweat glands in the overlying skin, causing gustatory sweating and flushing when eating (Frey syndrome). Mumps typically causes painful bilateral parotid swelling, made worse by the tight fascial capsule.
Excision of the submandibular gland risks the marginal mandibular nerve, the lingual nerve and the hypoglossal nerve. A ranula is a mucous retention cyst of the sublingual gland; a plunging ranula passes through or behind mylohyoid into the neck.