anatomy of submandibular gland

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Anatomy of Submandibular Gland

Fuad Ridha Mahabot

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Introduction• a major salivary gland• situated in the anterior part of digastric triangle in

submandibular region• about the size of walnut• roughly ‘J’- shaped - being indented by posterior border

of mylohyoid muscle which divides into• superficial part• deep part

• composed of a mixture of serous and mucous acini

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Embryology• during sixth and seventh weeks of embryonic period• begins as solid epithelial buds from the primordial oral

cavity• the club-shaped ends of these epithelial buds grow into

the underlying mesenchyme• connective tissue - derived from neural crest cells• all parenchymal (secretory) tissue arises by proliferation

of the oral epithelium

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Development of Submandibular Glands

• appear late in sixth week• develop from endodermal buds in the floor of

stomodeum• grow posteriorly, lateral to developing tongue• later they branch and differentiate• acini - begin to form at 12 weeks; secretory activity at 16

weeks• growth continues after birth with formation of mucous

acini• lateral to the tongue - a linear groove forms soon

closes over submandibular duct

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Histology• branched tubuloacinar glands• lobes lobules adenomeres (secretory unit)• each adenomere contains one or more acini - small

clusters of cells that secrete their products into a duct• acini - either serous or mucous cells, with serous

adenomeres predominating (mixed gland)• mucous adenomeres may also be capped with a serous

demilune, a layer of lysozyme-secreting serous cells resembling a half moon

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group of mucous alveoli

group of serous alveoli

8Submandibular gland - histology slide

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Superficial Part• this part fills the digastric triangle• extends upwards deep to the mandible up to the

mylohyoid muscle• has inferior, lateral and medial surfaces• partially enclosed between two layers of deep cervical

fascia• superficial layer of fascia covers the inferior surface of

the gland and is attached to the base of mandible• deep layer covers the medial surface of the gland and is

attached to the mylohyoid line of mandible

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Relations

• inferior surface is covered by skin platysma muscle cervical branch of facial nerve deep fascia facial vein submandibular lymph nodes

• lateral surface is related to submandibular fossa on the mandible insertion of pterygoid facial artery

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• medial surface maybe divided into three parts anterior part - related to mylohyoid muscles, nerve and vessels middle part - related to hyoglossus, styloglossus, lingual nerve,

submandibular ganglion and hypoglossal nerve posterior part - related to styloglossus, stylohyoid ligament, the

ninth nerve, and the wall of pharynx. Inferiorly it overlaps stylohyoid and posterior belly of digastric

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Deep Part• small in size• lies deep to mylohyoid, and superficial to hyoglossus and

styloglossus• posteriorly continuous with superficial part around the

posterior border of mylohyoid• anteriorly extends up to posterior end of sublingual

gland

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Submandibular Duct• a.k.a Wharton’s duct• thin walled, about 5cm long• emerges at anterior end of deep part of gland • runs forwards on the hyoglossus, between lingual and

hypoglossal nerves• at the anterior border of hyoglossus, the duct is crossed

by lingual nerve• it opens on the floor of the mouth, on the summit of

subligual papilla, at the side of frenulum of the tongue

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Blood Supply and Lymphatic Drainage

• supplied by facial artery• veins drain into common facial or lingual vein• lymph passes to submandibular lymph nodes

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Nerve Supply• supplied by branches from the submandibular ganglion• these branches convey:

secretomotor fibressensory fibres from lingual nervevasomotor fibres from plexus on facial artery

• secretomotor pathway (parasympathetic) - begins in the superior salivary nucleus preganglionic fibres pass through sensory root of facial nerve,

geniculate ganglion, facial nerve, chorda tympani, lingual nerve, to reach submandibular ganglion

post ganglionic fibres emerges from the ganglion and enter submandibular gland

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• vasomotor function (sympathetic) regulates submandibular secretions through

vasoconstriction of the arteries that supply it increased sympathetic activity reduces glandular

bloodflow decreasing salivary secretions producing an enzyme rich serous saliva.

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Functions of Submandibular Gland

• mainly production of saliva• contents of saliva

water (98%)electrolytes:

• 2-21 mmol/L sodium (lower than blood plasma) • 10-36 mmol/L potassium (higher than plasma) • 1.2-2.8 mmol/L calcium (similar to plasma) • 0.08-0.5 mmol/L magnesium • 5-40 mmol/L chloride (lower than plasma) • 25 mmol/L bicarbonate (higher than plasma) • 1.4-39 mmol/L phosphate

mucus - mainly consists of mucopoly-saccharides and glycoproteins

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antibacterial compounds (thiocyanate, hydrogen peroxide, and secretory immunoglobulin A)

various enzymes:• α-amylase - starts the digestion of starch and lipase fat

before the food is swallowed. It has a pH optima of 7.4. • lingual lipase• antimicrobial enzymes that kill bacteria - lysozyme, salivary

lactoperoxidase, lactoferrin, immunoglobulin Acells - possibly as much as 8 million human and 500

million bacterial cells per mL. opiorphin - a newly researched pain-killing substance

found in human saliva.

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Applied Anatomy1. Excision of the submandibular gland for calculus of tumour is done

by an incision below the angle of jaw. Since the mandibular branch of facial nerve passes posteroinferior to the angle of jaw before crossing it, the incision must be placed more then one inch below the angle to preserve the nerve.

2. In differentiating between an enlarged submandibular gland and a mass of submandibular lymph nodes, one remembers that the gland lies not only below the mandible but also extends into the floor of mouth; it can therefore be palpated bimanually between a finger in a mouth and a fingerbelow the angle of the jaw. Enlarged lymph nodes are felt only at latter site.

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3. A stone in Wharton’s duct can be felt bimanually in the floor of the mouth and can be seen if sufficiently large.

4. Presence of small lymph nodes actually within the substance of the gland makes removal of the gland an important part of block dissection of the neck.

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