Saliva and salivary glands

Question 1

Functions of saliva

Answer 1

Lubricant for mastication, swallowing and speech
Oral hygiene - Wash
- Immunity – Antibacterial/antiviral/antifungal
- Buffer
Oral pH needs to be maintained at about pH 7.2
- bicarbonate/carbonate buffer system for rapid neutralisation of acids
Digestive enzyme
- Aqueous solvent necessary for taste
Dysfunction associated with oral pain, infections and increased risk of dental caries

Question 2

saliva statistics

Answer 2

• Flow rate from 0.3 to 7ml per minute
• Daily secretion of 800 – 1500ml in adults from major and minor glands.
• pH ranges from 6.2 to 7.4
• Serous secretion – α amylase – starch digestion
• Mucus secretion – mucins for lubrication of mucosal surfaces
• Parotid gland = serous
• Submandibular and sublingual both mucous and serous
• Minor glands mainly mucous

Question 3

Factors affecting composition and amount of saliva produced

Answer 3

• Flow rate
• Circadian rhythm
• Type and size of gland
• Duration and type of stimulus
• Diet
• Drugs
• Age
• Gender

Question 4

Defence provided by

Answer 4

a) The mucosa - physical barrier
b) Palatine tonsils – lymphocyte subsets + dendritic cells – immune surveillance and resistance to infection
c) Salivary glands – saliva washes away food particles bacteria or viruses might use for metabolic support

Question 5

Immunity

Answer 5

• Salivary glands are surrounded by lymphatic system
– linked to thoracic duct and blood
• Broad range of functional immune cells
• Oral mucosa and glands have high blood flow rate
• Submandibular, sublingual and minor glands are continuously active
• Parotid – no measurable unstimulated secretion but becomes main source of saliva when stimulated
• Unstimulated saliva is dominated by SMG components
• Stimulated has composition resembling parotid secretion
• Whole saliva = salivary gland secretions, blood, oral tissues, microorganisms and food remnants

Question 6

Structure of salivary glands

Answer 6

Composed of two morphologically and distinct epithelial tissue
– acinar cells around
– ducts - collect to form large duct entering the mouth
Equipped with channels and transporters in the apical and basolateral membranes enabling transport of fluid and electrolytes
i.e. just like any other secretory or reabsorbing epithelia

Question 7

Intralobular ducts and main excretory duct

Answer 7

• Intralobular ducts divided into intercalated and striated
• Intercalated – short narrow duct segments with cuboidal cells that connect acini to larger striated ducts
• Striated ducts – striated like a thick lawn. Major site for reabsorption of NaCl

Question 8

Striated ducts

Answer 8

 Appear striated at basal end
 Basal membrane highly folded into microvilli for active transport of HCO3 against concentration gradient
 Microvilli filled with mitochondria for energy to facilitate active transport

• The ducts are NOT just a plumbing system.
• Primary saliva – NaCl rich isotonic plasma-like fluid secreted by acini.
• Electrolyte composition is modified in duct system.
• Ducts secrete K+ and HCO3- and reabsorb Na+ and Cl-.
• Epithelium of duct doesn’t allow any water movement so final saliva becomes hypotonic.

Question 9

Advantages of salivary glands (SG)

Answer 9

• Well-encapsulated, limiting undesirable spread of vector.
• Luminal membranes of virtually every epithelial cell in SGs are easy to access in a relatively non-invasive manner.
• Ductal access of SGs uses a limited fluid volume that is not diluted or disseminated following delivery, enabling use of low vector doses.
• Salivary epithelial cells are well differentiated and very slowly dividing, providing a relatively stable cell population for non-integrating vectors.
• SGs normally make large amounts of protein for export, both exocrine and endocrine
• A single SG is not crucial for life and can be removed in event of unexpected adverse effect with relatively little morbidity, cf liver or lung!!!

Question 10

2 general pathways for protein secretion

Answer 10

• Predominant (larger arrow) leading to saliva (mucosal; across apical membrane).
• Constitutive leading mainly towards interstitium and bloodstream (serosal; across basolateral membrane).
• Entry into regulated can be saturated by overexpression of transgene product and “overflow” can exit via constitutive into bloodstream.

Question 11

composition of salivary glands

Answer 11

80% major

20% minor

Question 12

Parotid glands

Answer 12

Superficial triangular outline between Zygomatic arch
Sternocleidomastoid, Ramus of mandible + masseter and med pterygoid
Parotid duct: Stenson’s duct -crosses masseter, pierces buccinator and enters oral cavity at 7/7
Palpate a finger’s breadth below zygomatic arch
Horizontally it has a triangular outline with apex on carotid sheath
Structures passing through parotid -
• External carotid artery + terminal branches
• Retromandibular vein
• Facial nerve + branches to muscles of facial expression (MFE)
• Parotid capsule very tough

Question 13

Submandibular gland

Answer 13

• Two lobes separated by mylohyoid muscle: Larger superficial lobe, Smaller deep lobe in floor of mouth
• Submandibular duct (Wharton’s duct) begins in superficial lobe, wraps round free posterior border of mylohyoid, runs along floor of mouth and empties into oral cavity at sublingual papillae.

Question 14

Minor salivary glands

Answer 14

Concentrated in the buccal labial, palatal and lingual regions.
Also found at
• superior pole of tonsils (Weber’s glands),
• tonsillar pillars
• base of the tongue (von Ebner’s glands - underlying circumvallate papillae).

Question 15

Salivary gland disease and dysfunction

Answer 15

• Obstructive
• Inflammatory
• Degenerative
• Drug side effects

Question 16

Xerostomia – dry mouth

Answer 16

• May be a consequence of cystic fibrosis or Sjogrens syndrome
• Most common causes – medication and irradiation for head and neck cancers
• High prevalence of caries and Candida infections

Question 17

Obstruction

Answer 17

• Saliva contains calcium and phosphate ions that can form salivary calculi (stones)
• Most often in submandibular gland (c 80%)
• Block duct at bend round mylohyoid [X] or at exit at sublingual papillae [X]

Question 18

Inflammatory

Answer 18

Infection secondary to blockage
Mumps (viral infection)
•	Fever, malaise
•	Swelling of glands 
•	Pain especially over parotid because capsule
•	does not allow much enlargement

Question 19

Degenerative

Answer 19

Complication of radiotherapy to head and neck for cancer treatment
Sjogren’s syndrome
• Mainly post-menopausal females
• Also affects lacrimal glands
• Rheumatoid arthritis may also be present

Question 20

Drug side effects

Answer 20

The most common dysfunction you will encounter
About 500 prescription drugs have a sympatheticomimetic effect
• Act on NA receptors or
• inhibit parasympathetic action at ACh receptors

Question 21

effects of salivary gland dysfunction

Answer 21

If salivary output falls to < 50% of normal flow – patient experiences xerostomia (dry mouth)
Low lubrication – oral function difficult
Low (natural) oral hygiene – poor pH control
• Accumulation of plaque =>Rampant dental caries, gingivitis and periodontal disease
• Opportunistic infections esp. fungal infections (candida = thrush)