SALIVARY GLANDS

what provides defence for the oral cavity

• the mucosa - physical barrier

• palatine tonsils - lymphocyte and dendritic cells

• salivary glands

how do salivary glands provide defence for the oral cavity

• saliva washes away food particles that bacteria or viruses may use for metabolic support

• the glands are surrounded by the lymphatic system and therefore have good blood supply - efficient delivery of immune cells

what are the major salivary glands

• parotid

• submandibular

• sublingual

are the major salivary glands paired or unpaired

the major salivary glands are paired

what % of saliva do the major salivary glands collectively produce

the major salivary glands contributes to ≈ 80% of salivary flow

where are minor salivary glands located

• submucosa of oral mucosa

• lips

• cheeks

• hard palate

• soft palate

• tongue

what % of saliva do the minor salivary glands collectively produce

≈ 20%

which major salivary gland(s) are continuously active

• submandibular

• sublingual

UNSTIMULATED SECRETION

which major salivary gland(s) are not continuously active

• parotid

  • becomes the main source of saliva when stimulated - thinking about eating/ eating something

which gland is more dominant in unstimulated saliva secretion

submandibular gland

what does ‘whole saliva’ consist of (5)

• salivary gland secretions

• blood

• oral tissues

• microorganisms

• food remnants

between which structures does the parotid gland lie

superficial triangular outline between

• zygomatic arch

• sternocleidomastoid

• ramus of mandible

• masseter muscle

• medial pterygoid muscle

what is another term for the parotid duct

Stenson’s duct

describe the location of the parotid/ Stenson’s duct and state where it enters the oral cavity

• crosses masseter

• pierces buccinator and enters oral cavity at upper 7s

what structures pass through the parotid gland (3)

• external carotid artery and its terminal branches

• retromandibular vein

• facial nerve and its branches to the muscles of facial expression

which major salivary glands are encapsulated and which are not

• parotid + submandibular: encapsulated

• sublingual: non-encapsulated

what are acini

secretory units mostly found in exocrine glands that produce saliva

what type of acini are parotid glands made up of

parotid glands

• entirely serous acini

• with ducts interspersed (blue circle)

how is the submandibular gland divided

submandibular gland

• two lobes separated by mylohyoid muscle

  • larger superficial lobe

  • smaller deep lobe (in floor of mouth)

what is another term for the submandibular duct

Wharton’s duct

describe the course of the submandibular/ Wharton’s duct

• begins in superficial lobe

• wraps around free posterior border of mylohyoid muscle

• runs along the floor of the mouth

• the submandibular duct empties into the oral cavity at the sublingual papillae

diagram showing the lingual frenum, submandibular duct and sublingual papillae

what type of acini are submandibular glands made up of

• mixed gland

• serous and mucous acini

• referred to as seroumucous

describe the serous acini in submandibular glands

• the serous acini are arranged as crescent shaped groups of glandular cells at the base of mucous acini

  • serous demilunes

describe the location of the sublingual glands

in the floor of mouth between the mylohyoid muscle and oral mucosa of the FOM

what characteristic of the sublingual gland is variable

its size

what is another term for the sublingual duct

THE SUBLINGUAL GLAND DOES NOT HAVE A (LARGE) DUCT

if the sublingual gland has no duct, where does the saliva drain into?

the saliva drains into the submandibular duct/ Wharton’s duct and/ or small ducts that pierce the oral mucosa on the FOM

what is the result of the Wharton’s duct draining both submandibular and sublingual saliva

pure submandibular/ sublingual saliva cannot be collected because both come out of Wharton’s duct

what type of acini are sublingual glands made up of

• mixed gland

• serous and mucous acini

• mainly mucous acini

histological image of sublingual gland

where are minor salivary glands concentrated

minor salivary glands are concentrated in the:

• buccal

• labial

• palatal

• lingual

regions

where else are minor salivary glands also found

• superior pole of tonsils (Weber’s glands)

• tonsillar pillars i.e. palatoglossal and palatopharyngeal arches

• base of the tongue (von Ebner’s glands - underlying circumvallate papillae)

describe the acini of minor salivary glands

• all minor salivary glands are mucous

• except serous glands of von Ebner

histological image of taste buds and von Ebner’s glands

what structure do minor salivary glands lack and what is the result of this

• minor salivary glands lack a branching network of draining ducts

• each salivary unit has its own simple duct

what is the effect of parasympathetic stimulation on saliva production

stimulation of parasympathetic nerves causes the production of a copious flow of saliva

what does sympathetic stimulation cause production of

sympathetic stimulation selectively causes secretion of protein and glycoprotein

what is the basic structure of salivary glands

composed of two morphologically distinct epithelial tissue

• acinar cells

• ducts - collect to form large duct entering the mouth

what other features do salivary glands have

• equipped with channels and transporters in the apical and basolateral membranes

• this enables transport of fluid and electrolytes

describe serous acini

serous acini

• dark staining

• nucleus in basal third

• small central duct (orange circle in histological image)

• secrete water and alpha amylase

describe mucous acini

mucous acini

• pale staining - ‘foamy’

• nucleus at base

• large central duct

• secrete mucous and glycoproteins

identify the type of acini shown and state what the green circle represents

• serous acini

• green circle: large duct

what are intralobular ducts

intralobular ducts: small duct within an exocrine gland that drains the secretions from the acini and transport them towards the interlobular ducts

what are intralobular ducts divided into

• intercalated

• striated

outline intercalated ducts

intercalated ducts: short narrow duct segments with cuboidal cells that connect acini to larger striated ducts

outline striated ducts

• appear striated at the basal end because…

• basal membrane is highly folded into microvilli for active transport of HCO₃ against the concentration gradient

• microvilli are filled with mitochondria that produce energy to facilitate the active transport of salts

what is the function of striated ducts

striated ducts: major site for reabsorption of NaCl, this movement of salt alters the final composition of saliva

what is the composition of primary saliva

• NaCl rich

• isotonic

• plasma-like fluid secreted by acini

how does the composition of primary saliva change

• the composition of primary saliva changes as it moves down the striated duct

• K⁺ and HCO₃^- are secreted

• Na⁺ and Cl^- are reabsorbed

• the final saliva becomes hypotonic

why is the final saliva hypotonic

because the epithelium of the duct does not allow any water movement

what does this diagram show

the close proximity of the acinar cells to the lymphatic/ blood system

in what field are salivary glands a target tissue for

gene therapeutics - gene transfer technology

what are advantages of salivary glands (4)

• well-encapsulated - limits undesirable spread of vectors

• luminal membranes (membrane orientated towards the lumen) are easy to access in a relatively non-invasive manner

• one single salivary gland is not crucial for life and can therefore be removed with little morbidity

• salivary glands normally make large amounts of protein for export

less relevant and ? advantages of salivary glands (2)

• salivary epithelial cells are well differentiated and very slowly dividing, providing a stable cell population for non-integrating vectors

• ductal access of salivary glands use a limited fluid volume that is not diluted or disseminated following delivery, enabling use of low vector doses

how can salivary flow be restored

• use the AQP gene that codes for a water channel

• water channel is inserted into the membrane of the duct

• duct becomes more permeable therefore increased salivary flow

which salivary gland is the most affected (gland) by radiation and why

• parotid gland

• it is often in the radiation pathway

» dry mouth

what are the two general pathways for protein secretion

• regulated exocrine pathway

  • major regulated

  • minor regulated

• constitutive endocrine pathway

outline the regulated pathway

• external stimulus dependent

• proteins stored in secretory granules prior to stimulation with secretion being directed apically into saliva

what is exocrine secretion triggered by

• primarily triggered by sympathetic nervous system

• secondarily triggered by parasympathetic nervous system

outline the constitutive and constitutive-like pathway

• non-directional

• continuous secretion of protein

• not modulated by external stimuli

outline xerostomia

• dry mouth

• may be a consequence of cystic fibrosis or Sjogrens syndrome

• most common causes: medication and irradiation for head and neck cancers

• high prevalence of dental caries and candida infections in those with xerostomia

—

NOT A DISEASE MORE A CONSEQUENCE/ SYMPTOM

what are the types of salivary gland diseases and dysfunctions (4)

• obstructive

• inflammatory

• degenerative

• drug side effects

outline obstructive salivary gland disease

• saliva contains calcium and phosphate ions that can form salivary calculi (stones)

• most often found in submandibular glands (80%)

• block duct at the bend around the mylohyoid muscle (red X) OR the exit at the sublingual papillae (pink X)

what is the name given to the condition of having salivary stones

sialolithiasis

what are the treatment options for sialolithiasis

• laser directed at salivary calculi to break them into smaller pieces

• oral surgeons can excise the salivary gland stone

outline inflammatory salivary gland disease

• infection secondary to blockage i.e. on the other side of the blockage

• example of inflammatory salivary gland disease is mumps

  • viral infection

  • causes inflammation, swelling and pain - particularly the parotid gland

    • pain is due to the capsule

  • fever, malaise

outline degenerative salivary gland disease

• complication of radiotherapy to head and neck for cancer treatment

• example of degenerative salivary gland disease is Sjogren’s syndrome

  • mainly affects post-menopausal females

  • affects salivary and lacrimal glands » dry mouth + dry eyes

  • rheumatoid arthritis may also be present

outline drug side effects in relation to salivary gland disease

• ≈ 500 prescription drugs have a sympatheticomimetic effect

  • act on noradrenaline receptors

    OR

  • inhibit parasympathetic action at ACh receptors

» dry mouth

if salivary output falls to < __% of normal flow the patient will experience xerostomia

if salivary output falls to < 50% of normal flow the patient will experience xerostomia

what are the effects of salivary gland dysfunction (4)

• low lubrication

• low natural oral hygiene - poor pH control

• accumulation of plaque - rampant dental caries, gingivitis and periodontal disease

• opportunistic infections - esp. fungal infections e.g. oral thrush

what % of salivary gland neoplasms occur in the:

a) parotid gland

b) submandibular gland

c) sublingual and minor salivary glands

a) parotid gland: 80%

b) submandibular gland: 15%

c) sublingual and minor salivary glands: 5%

what % of salivary gland tumours are benign

• nearly 80% of salivary gland tumours are benign

• malignant salivary gland tumours are rare

  • 6% of all head and neck malignancies

  • < 0.5% of all cancers

what % of salivary gland tumours are malignant in the:

a) parotid gland

b) submandibular gland

c) sublingual and minor salivary glands

a) parotid gland: 20%

b) submandibular gland: nearly 50%

c) sublingual and minor salivary glands: > 60%

what are risk factors for salivary gland cancers (5)

• exposure to radiation

• low nutrition diet

• history of childhood benign salivary gland tumours

• infection

• genetics

what characteristics of salivary gland cancers makes them difficult to diagnose

• very heterogenous i.e. varied

• clinically diverse

• complex histology

histological sections of salivary gland cancers

what does the yellow circle indicate

cyst

what is a fusion gene

fusion gene: a part of two genes that inappropriately join together to create a new gene

relevancy of fusion genes to salivary gland cancers

• some benign and malignant tumours have the same fusion gene - abnormal

• fusion genes are expressed in 34-81% of salivary gland mucoepidermoid carcinomas (MEC) - most common malignant salivary gland tumour

• not all cells in a tumour will express the fusion gene associated with it

• fusion genes are associated with better survival rates in some studies

outline adenoid cystic carcinoma (ACC)

• relatively rare but life threatening cancer that occurs mainly in salivary glands

• can also occur in the breast, lacrimal gland, lung, vulva, skin

outline characteristics of salivary gland adenoid cystic carcinoma (SGACC)

• slow growing

• commonly grows down nerves

• absence of regional metastasis