Salivary Glands: Anatomy, Function, and Disorders

Salivary Glands Overview

• Salivary glands' positioning, histology, and function are important.
• It is important to list the major salivary glands.
• Describe each salivary gland’s positioning, associated duct, saliva production, and innervation.
• It is also important to describe the disorders that may affect salivary glands.

Formation of Salivary Glands

• The formation is covered in BMS lecture 'Embryology of the head, face, and oral cavity.'

Types of Salivary Glands

• There are 3 bilateral pairs of major salivary glands, the parotid, submandibular, and sublingual glands plus numerous minor salivary glands.
• Major salivary glands produce 90% of the total salivary volume.

Parotid Gland

• The parotid gland is the largest of the major glands.
• It produces 100% serous saliva and contributes 25% of the total saliva volume.
• It’s positioned below the external auditory meatus, and between the mastoid process and the posterior border of the ramus

Parotid Duct & Innervation

• The parotid duct is also known as Stensen’s duct.
• Stensen’s Duct is 5cm long
• The Duct runs from the gland outside the masseter muscle parallel to, and 1cm below, the zygomatic arch.
• It pierces the buccinator muscle, opening into the oral cavity via the Stensen’s papillae.
• Glossopharyngeal nerve provides autonomic innervation.
• Auriculotemporal nerve provides sensory innervation.
• It is intimately associated with the Facial nerve.

Submandibular Gland

• The submandibular gland produces mixed saliva secretions.
• It is half the size of the parotid gland (walnut size).
• It contributes 60-65% of total saliva volume.

Submandibular Gland Position & Innervation

• It is positioned between the body of the mandible and the mylohyoid muscle, in the submandibular fossa.
• Wharton's duct is 5cm long
• The Duct opens under the anterior part of the tongue, lateral to the lingual fraenum at the sublingual caruncle
• Nerve Innervation is the Chorda tympani, and Lingual branch of the inferior dental nerve

Sublingual Gland

• The sublingual gland produces 60% mucous saliva.
• It is the smallest of the major salivary glands (almond size).
• It contributes 5-10% of total saliva volume.
• Positioned on the floor of the mouth in the sublingual fossa.

Sublingual Ducts & Innervation

• Ducts include Bartholin’s duct and 10-20 smaller ducts (Rivinus ducts) which open along the sublingual fold.
• The Nerve Innervation is the same as the submandibular gland.

Tubarial Glands

• The tubarial glands are located in the nasopharynx.
• Literature suggests they may contain a large number of seromucous acini.
• They play a role in nasopharynx/oropharynx lubrication and swallowing.

Minor Salivary Glands

• Minor salivary glands produce mixed saliva, predominately mucous.
• They produce lots of salivary proteins.
• Minor salivary glands produce >10% of the total saliva volume.
• They're named according to location, e.g., buccal or labial salivary glands.

Salivary Gland Structure

• Epithelium lines the ducts, producing saliva.
• Connective tissue surrounds the epithelium, protecting and supporting the gland.
• The connective tissue divides into the capsule, which surrounds the outer portion of the gland, and the septum, which divides the inner portion of the gland into lobes and smaller lobules.
• The capsule and septa carry the nerve and blood supply to the cells.

Adenomeres

• Adenomeres are the working part of a salivary gland and are surrounded by connective tissue.

Acini

• Within the adenomere are secretory units (acini) made up of secretory cells.
• Their base rests against the surrounding connective tissue, supplying nerves and blood to the cells.
• Acini are classified into mucous acini, serous acini, or a mixture of both.

Serous Acini

• These are serous secretory cells.
• They produce a watery serous secretion (serous saliva).
• Functions include lubricating food, enzymatic action begins digestion, Removing epithelial debris and Diluting food

Mucous Acini

• These are mucous secretory cells with a wider lumen.
• Mucous acini produce a viscous, mucin-rich secretion (mucous saliva).
• Functions of mucous saliva include binding food into a bolus, protecting the oral cavity against frictional abrasion, and lubrication.

Serous-Mucous Acini

• In mixed serous-mucous acini, the serous secretory cell forms a serous demilune around the mucous secretory cell.

Myoepithelial Cells

• These cells embrace the acini secretory cells, contracting and squeezing, forcing the saliva out of the lumen and into the ducts.

Acinar Fluid

• Acinar fluid (not saliva yet) consists of water, inorganic ions, and small molecules and products synthesized by cells (mucoproteins and amylase).

Ducts

• Following the secretory end piece are ducts which, which the saliva travels and becomes further modified via resorption.
• Types of duct include Intercalated, Striated and Excretory.

Intercalated Ducts

• Intercalated Ducts are lined by a single layer of cuboidal epithelial cells

Striated Ducts

• Striated ducts make up the bulk of the duct system.
• They are lined with a single layer of columnar epithelial cells characterised by basal striations.
• And aids in the modification of the saliva.

Excretory Ducts

• These are terminal, or secretory ducts.
• Saliva exits into the oral cavity via this duct
• It is lined by pseudostratified columnar epithelium, changing to stratified cuboidal, and stratified squamous epithelium at its opening.

Blood Supply

• The glands are supplied by the external carotid artery (plus facial and lingual artery), with vessels (and nerves) entering at the hilum.
• There are two capillary networks, one for the secretory end piece and one for the ducts

Control of Salivation

• Salivary nuclei in the brain are stimulated by taste, smells, thoughts etc.
• These trigger neurotransmitter release from nerve endings of salivary glands.

Hyposalivation

• Hyposalivation can be caused by Medications or tablets, Radiotherapy, Autoimmune diseases, Diabetes, or Salivary stones (can cause severe pain when eaing).

Obstruction

• Caniculi are calcium deposits formation in the ducts.
• Common in the submandibular glands, obstruction can lead to infection or inflammation of the gland
• Cysts are caused dueTrauma to the salivary gland or duct causing an accumulation of saliva in the surrounding tissue.
• Mucocele are for minor glands while Ranulas are for major glands in the floor of the mouth (could be submandibular or sublingual).

Irradiation

• Head and neck irradiation destroys the secretory cells (atrophy) and leads to xerostomia.

Degenerative Disorders

• Sjögren’s syndrome, is an immunological disorder, with symptoms affecting both the body dry eyes, acini destroyed, change in lachrymal apparatus, rheumatoid arthritis is often associated, and Raynaud phenomenon, and the oral cavity including mild erythema and thinning of the mucosa, erythema, fissuring, coating and depapillation of the dorsum of the tongue, traumatic erosions and ulcers, angular chelitis and chapped lips, and frothy, ropey and thickened saliva.

Inflammation/Infection

• Mumps is an acute viral infection causing inflammation and painful swelling of the parotid glands
• Nicotine Stomatitis is caused by inflammation of the minor salivary glands located on the palate in response to heat from tobacco use.
• The duct openings become dilated and can appear as red dots.

Sialosis

• Sialosis is a painless swelling of the parotid glands, not caused by inflammation or infection.
• It can occur on its own but may also appear as a result of other medical conditions like liver cirrhosis, bulimia, diabetes, pregnancy, obesity and kidney failure.

Neoplasms

• These can Benign, e.g Warthin’s tumour or Pleomorphic adenoma, or Malignant, e.g Salivary gland carcinoma or Acinic cell carcinoma

Functional Disorders

• Dry mouth is caused by emotional disturbances e.g. anxiety, mouth breathing, smoking and drugs