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Submandibular gland

The submandibular glands are small, paired exocrine glands, each located within the submandibular (digastric) triangle of the neck. Together with the parotid and sublingual glands, they make a set of major salivary glands that are the components of the accessory digestive system. In addition, there are many minor salivary glands scattered throughout the oral cavity.

The main function of the submandibular glands is to contribute to the production of saliva, which helps to lubricate the oral cavity and aids in the chemical digestion of food. The saliva also coats the food bolus, which makes it easier to swallow.

This article will review the anatomy, neurovascular supply and physiology of submandibular glands.

Key facts about the submandibular gland
Parts Two parts: superficial and deep
One duct: submandibular duct (Wharton’s duct)
Type Seromucous gland
Innervation Submandibular ganglion – parasympathetic secretomotor supply
Superior cervical ganglion – vasomotor supply
Blood supply External carotid artery via facial and lingual arteries
Function Production and secretion of saliva
Contents
  1. Structure
    1. Superficial part
    2. Deep part
    3. Submandibular duct (Wharton's duct)
  2. Innervation
  3. Blood supply
  4. Function
  5. Salivary stone
  6. Sources
+ Show all

Structure

The submandibular glands are relatively small, paired, irregular structures each situated in their ipsilateral submandibular fossa. Remember that the submandibular fossas are triangular depressions found bilaterally on the medial surfaces of the body of mandible. Each fossa is located within the submandibular (digastric) triangle on the same side. Respectively, they are formed by the mylohyoid line superiorly, the base of mandible inferiorly and the inferior part of ramus of mandible posteriorly.

On average, the submandibular glands measure about 3 – 4 cm along its long axis and weigh roughly 10 – 15 grams each. Anteriorly, each gland is unevenly divided into a larger superficial and a smaller deep component by the mylohyoid muscle. However, the superficial and deep portions are confluent beyond the posterior border of the mylohyoid muscle. Each gland has its own excretory duct – called submandibular or Wharton’s duct – that excretes the contents of the gland onto the floor of the oral cavity.

From a histological perspective, the submandibular glands are mixed glands, made up of serous and mucous acini, as well as seromucous glands called serous demilunes.

Superficial part

The superficial part of the submandibular gland is separated from its deep counterpart by the mylohyoid muscle. It is nestled in the digastric triangle and is limited anteriorly by the anterior belly of digastric muscle and posteriorly by the stylomandibular ligament. Laterally, it is bounded by the medial surface of the posterior half of the body of mandible.

This part of the gland is enclosed in the superficial and deep layers of the deep cervical fascia. The superficial layer covers the inferior surface of the gland, as it attaches to the lower border of the mandible. The deep layer covers the medial surface and attaches to the mylohyoid line on the medial surface of the mandible.

Deep part

The smaller, deep part of the submandibular gland is continuous with the superficial part and continues anteriorly to meet the posterior end of sublingual gland. It is surrounded by numerous muscular and neurovascular structures. The mylohyoid is superomedial to the gland, while hyoglossus and styloglossus are medial to the structure. The lingual nerve passes superiorly over this part of the gland, while the deep lingual vein and hypoglossal nerve pass inferiorly.

Submandibular duct (Wharton's duct)

Submandibular duct or Wharton’s duct is a relatively short conduit that drains the contents of the submandibular gland into the buccal cavity. It is roughly 5 cm long but has a convoluted course with several important structures nearby.

The duct starts on the medial surface of the superficial part of the submandibular gland behind the posterior border of the mylohyoid muscle. Initially, the duct continues upward and slightly posteriorly to form the genu of the duct which curves around the free edge of mylohyoid. Subsequently, the duct continues anteriorly to pass between hyoglossus and mylohyoid, then between genioglossus and sublingual gland. It eventually emerges from the sublingual papilla, adjacent to the lingual frenulum on either side of the floor of the mouth.

Another important fact about the submandibular duct is that it is crossed twice by the lingual nerve along its course. While this is more important for ENT surgeons, it is still a relatively common question in anatomy exams.

Take this opportunity to review the structures of the oral cavity with these videos and quizzes.

Innervation

While the anatomy of the submandibular gland is relatively straightforward, understanding the innervation of these glands can be challenging. 

The preganglionic parasympathetic fibers originating from the superior salivatory nucleus travel first through the facial nerve (CN VII) then to chorda tympani. They then join the lingual nerve (branch of mandibular division of trigeminal nerve [CN V3]) and pass through the posterior filament, which then enters the submandibular ganglion. They form synapses with the postganglionic secretomotor fibers, which then leave the ganglion to innervate submandibular (and sublingual) glands.

The vasomotor activity is regulated by the postganglionic sympathetic fibers arising from the plexus of the facial artery (cell bodies located in superior cervical ganglion). These fibers pass through submandibular ganglion without synapsing.

Note that chorda tympani (not the lingual nerve) gives parasympathetic supply to the gland. The lingual nerve only functions as a conduit for these parasympathetic fibers and is not directly responsible for this form of innervation.

Blood supply

The glands are supplied indirectly by the external carotid artery through the branches of the facial and lingual arteries.

Venous drainage follows a similar pattern.

Note also that the lymphatic drainage of the glands occurs by way of the submandibular nodes to the deep group of cervical lymph nodes; specifically jugulo-omohyoid nodes.

Function

The primary role of the submandibular gland is to contribute to the production and secretion of saliva. Saliva is an extracellular fluid that is made up mostly of water along with few enzymes, electrolytes and antimicrobial entities. Saliva may also contain varying amounts of two specific types of proteins that will determine its classification. If the mixture contains mostly ptyalin, which is an alpha-amylase enzyme (breaks down starch), then it is considered a serous secretion. On the other hand, if it contains mostly mucin, which is a lubricating protein, then it is considered a mucous secretion. The submandibular gland produces both serous and mucous secretions and is therefore considered a seromucous gland. In contrast, parotid gland is exclusively serous and the sublingual gland is also seromucous.

Consequently, this gland not only helps to lubricate the tongue, buccal cavity and oropharynx, but it also aids in the early stage of digestion of starches. Additionally, it lubricates the food bolus during mastication to allow for easier deglutition.

Another important role of saliva is the neutralization of bacteria in the buccal cavity. Additionally, saliva helps to wash away bacteria from buccal surfaces thus reducing their destructive effects.

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