Salivary gland anatomy and function

Types

Major

1) Parotid

2) Submandibular

3) Sublingual

Minor

1) Buccal

2) Labial

3) Palatal

4) Lingual

Serous Mucous

Mixed

Secretion

Parotid gland

1st to develop and last to be encapsulated Lymphatic's are entrapped in the parenchyma

of the gland Salivary epithelial cells are often entrapped in

these lymph node which may give rise to warthins tumor.

Other major salivary glands DON’T HAVE

intraparenchymal entrapments

Location

External features - pyramid

Surfaces - 4

1. Superior

2. Superficial

3. Anteromedial

4. Posteromedial

Borders -3

1. Anterior

2. Medial

3. Posterior

Parotid capsule

Investing layer of deep cervical fasciaSplits to enclose the glandSuperficial lamina thick and adherent attached to zygomatic arch

Deep lamina thin and attached to styloid

process, mandible below and tympanic plate above

Stylomandibular ligament

Relation - external

Apex –a) overlaps the posterior belly of digastric

b) cervical branch of facial and two division of retromolar

comes out through it

Superficial surface –

skin and fascia containing anterior branches of great auricular nerve and lymph nodes

Relation

Anteromedial – a) posterior border of mandible b)masseter, c)lateral surface of TMJ, d) emerging branches of facial nerve

Poseriomedial surface – a) mastoid process b)styloid process c)external carotid artery entry.

Anterior border – structure emerging through It are

a) duct

b) terminal branches of facial nerve

c) transverse facial vessel Posterior border separates superficial

and posteriomedial surface

Medial border is related to lateral wall of pharynx

Relations – internal

Facial nerve relation

Emerges out of stylomastoid foramen Almost immediately comes in relation

with parotid gland Enters through posteriomedial surface

divides into five branches and leaves through anteromedial surface

Folded or interwoven?

Branches of the Facial N

The nerve then gives rise to 2 divisions: 1) Temperofacial (upper)  2) Cervicofacial (lower) 

Followed by 5 terminal branches: 1) Temporal  2) Zygomatic  3) Buccal  4) Marginal Mandibular  5) Cervical 

Facial Nerve

Parotid gland duct -

Stensen’s duct is 5 cm long.

Arises from the anterior part of the gland and runs over the masseter one finger below the zygomatic arch to pierce the buccinator and open opposite the second upper molar tooth

Parotid Duct orifice

Clinical examination of the parotid gland should include examination of the duct orifice opposite the upper 2nd molar for signs of inflammation, and palpated for stone

Parotid Sialogram is performed by injecting a contrast through a canula placed in the orifice of the duct

Nerve supply

Parasympathetic nerves are secretomotor reach the gland through auriculotemporal nerve

Nerve supply

Symphathetic fibers are vasomtor and derived from plexus around external carotid artery

Sensory nerves come from auriculotemporal nerve but parotid fascia is innervated by greater auricular nerve c2

Frey syndrome, gustatory sweating

Usual after parotidectomy Caused by regeneration of secretory

fibers of parotid gland to sweat glands in its area of distribution

So the sweat glands respond to nerve impulses that should provoke the parotid secretion

starch-iodine test is used

Treatment

Medical - antiperspirants,, 3% scopolamine cream.

Surgical -tympanic neurectomy

Blood supply

Supplied by external carotid artery and its branches that arises near the gland

Drains into internal external jugular vein

Submandibular gland

Anterior part of digastric triangle

“J” shaped, indented by mylohyoid muscle

Large part superficial to muscle and small part deep to it

Capsule

Enclosed in capsule formed by deep cervical fascia

Loosely attached unlike parotid gland fascia hence can be shelled out

The superficial lamina is attached to base of the mandible and deep fascia is attached to mylohyoid line

Superficial and Deep Relations

Superficially: The skin, the platysma, the capsule (deep fascia), the cervical branch of Facial Nerve, and the Facial Vein

Deeply: the deep aspect lies against the mylohyoid for the most part. But posteriorly lies on the hyoglossus and comes in contact with the lingual and hypoglossal nerves.

Both nerves lie on the hyoglossus as they pass forward to the tongue

The facial Artery Arches over its

superior aspect to reach inferior border of the mandible and then ascends on to the face in front of the masseter

Submandibular duct

In its terminal course it may receive a major sublingual duct called bartholins duct

Sublingual papilla lateral to the freenum

Blood supply

Supplied by facial artery Veins drain into common facial and

lingual vein

Sublingual gland

Long flattened body situated in the shallow depression on the mandible called as sublingual fovea

Covered by thin mucous membrane and causes elevation called as salivary eminence

it is a glandular complex since there is no common duct for all the lobules

But the major part of the gland drains into Bartholins duct which latter drains into Warthons duct or opens close to it

Dozen or more small ducts called duct of Rivinus open directly in to the oral cavity from the upper border of the gland

Nerve supply - Parasympathetic

contd

Sensory from the lingual nerveParasympathetic from the plexus around

the facial artery

Effect of nerve stimulation

Superior salivatory nucleus for submandibular and sublingual

Inferior salivatory nucleus for parotid Parasympathetic Stimulation results in

abundant, watery saliva with a decrease in [amylase] in saliva

Stimulation by the sympathetic nervous system results in a scant, viscous saliva rich in solutes with an increase in [amylase] in the saliva

For all of the salivary glands, these fibers originate in the Superior Cervical ganglion and travel with arteries to reach the glands:

1) External Carotid artery for the Parotid 2) Lingual artery for the Submandibular, and 3) Facial artery in the case of the Sublingual. Parasympathetic Interruption to salivary

glands results in atrophy, while sympathetic interruption doesn’t cause a significant change.

Minor salivary glands - lingual

Anterior part of tongue near its inferior surface - gland of Blandin

Base of the tongue at the dorsal surface - the von Ebner gland –empties in into vallat papillae

saliva – composition and function

THE SECRETORY UNITThe basic building block of all salivary glands

ACINI - water and ions derived from plasma

Saliva formed in acini flows down DUCTS to empty into the oral cavity.

TWO STAGE HYPOTHESIS OF SALIVA FORMATION

Water & electrolytes

Isotonic primary saliva

Most proteins

Some proteins electrolytes

Na+ Cl- resorbed

K+ secreted

Hypotonic final saliva into mouth

contd

Resting condition – sodium and chloride ions are 1/10th of plasma concentration

potassium is 7 times more than in plasma

bicarbonate is 2 – 3 times more than in plasma

During maximal stimulation

sodium and chloride

potassium Effect of aldostoron Excess loss of saliva to the exterior of

body may lead to hypokalemia and paralysis

Composition

Inorganic components

Calcium and phosphate

Calcium sublingual > submandibular > parotis

Phosphate Help to prevent dissolution of dental

enamelpH around 6 - hydroxyapatite is unlikely to

dissolveIncrease of pH - precipitation of calcium

salts => dental calculus

Hydrogen carbonate

BufferLow in unstimulated saliva, increases with

flow ratePushes pH of stimulated saliva up to 8pH 5,6 critical for dissolution of enamelDefence against acids produced by

cariogenic bacteriaDerived actively from CO2 by carbonic

anhydrase

Other ions Fluoride

Low concentration, similar to plasma

Thiocyanate Antibacterial (oxidated to hypothiocyanite OSCN- by

active oxygen produced from bacterial peroxides by lactoperoxidase)

Higher conc. => lower incidence of caries Smokers - increased conc.

Sodium, potassium, chloride Lead, cadmium, copper

May reflect systemic concentrations - diagnostics

Organic components

Saliva composition

Organic components of saliva Mucins Proline-rich proteins Amylase Lipase Peroxidase Lysozyme Lactoferrin sIgA Histatins Statherin Blood group substances, sugars, steroid hormones,

amino acids, ammonia, urea

MultifunctionalityMultifunctionality

SalivarySalivaryFamiliesFamilies

Anti-Anti-BacterialBacterial

BufferingBuffering

DigestionDigestion

Mineral-Mineral-izationization

Lubricat-Lubricat-ion &Visco-ion &Visco-elasticityelasticity

TissueTissueCoatingCoating

Anti-Anti-FungalFungal

Anti-Anti-ViralViral

Carbonic anhydrases,Carbonic anhydrases,HistatinsHistatins

Amylases,Amylases,Mucins, LipaseMucins, Lipase

Cystatins,Cystatins,Histatins, Proline-Histatins, Proline-rich proteins,rich proteins,StatherinsStatherins

Mucins, StatherinsMucins, Statherins

Amylases,Amylases,Cystatins, Mucins, Cystatins, Mucins, Proline-rich proteins, StatherinsProline-rich proteins, Statherins

HistatinsHistatins

Cystatins,Cystatins,MucinsMucins

Amylases, Cystatins,Amylases, Cystatins,Histatins, Mucins,Histatins, Mucins,PeroxidasesPeroxidases

adapted from M.J. Levine, 1993adapted from M.J. Levine, 1993

Mucins

LubricationGlycoproteins - protein core with many

oligosaccharide side chains attached by O-glycosidic bond

More than 40% of carbohydratesHydrophillic, entraining water (resists

dehydration)Unique rheological properties (e.g., high

elasticity, adhesiveness, and low solubility)Two major mucins (MG1 and MG2)

Amylases – (ptyalin) Hydrolyzes (1-4) bonds of starches such as

amylose and amylopectin Maltose is the major end-product (20% is

glucose) Considered to be a good indicator of properly

functioning salivary glands Parotid gland saliva has highest content(80%) Its action is inactivated in the acid portions of the

gastrointestinal tract and is consequently limited to the mouth.

Provides disaccharides for acid-producing bacteria

Lingual Lipase

Secreted by lingual glands and parotisInvolved in first phase of fat digestionHydrolyzes medium- to long-chain

triglyceridesImportant in digestion of milk fat in

new-born

Statherins

Calcium phosphate salts of dental enamel are soluble under typical conditions of pH and ionic strength

Supersaturation of with calcium and phosphates maintain enamel integrity

Statherins prevent precipitation or crystallization of supersaturated calcium phosphate in ductal saliva and oral fluid

Also an effective lubricant

Proline-rich Proteins (PRPs)

40% of AAs is prolineInhibitors of calcium phosphate crystal

growth

Present in the initially formed Present in the initially formed enamel pellicle and in “mature” enamel pellicle and in “mature” pelliclespellicles

Lactoferrin

Iron-binding protein Links to free iron in the saliva causing

bactericidal or bacteriostatic effects on various microorganisms requiring iron for their survival such as the Streptococcus mutans group. 

Lysozyme

Present in numerous organs and most body fluids

Hydrolysis of (1-4) bond between N-acetylmuramic acid and N-acetylglucosamine in the peptidoglycan layer of bacteria.Gram negative bacteria generally more resistant

than gram positive because of outer LPS layeraggregation and inhibition of bacterial

adherence

Histatins

A group of small histidine-rich proteinsPotent inhibitors of Candida albicans

growthThe bactericidal and fungicidal effects

occur through  the destruction of their architecture and altering their permeability. 

Cystatins

Are inhibitors of cysteine-proteasesAre ubiquitous in many body fluidsConsidered to be protective against

unwanted proteolysisbacterial proteases

May inhibit proteases in periodontal tissues

Salivary peroxidase systems

Sialoperoxidase (SP, salivary peroxidase) Produced in acinar cells of parotid glands Also present in submandibular saliva Readily adsorbed to various surfaces of mouth

enamel, salivary sediment, bacteria, dental plaque

Myeloperoxidase (MP) From leukocytes entering via gingival crevice 15-20% of total peroxidase in whole saliva

Components of the peroxidase anti-microbial system

Peroxidase enzymes (SP or MP)Hydrogen peroxide (H2O2)

oral bacteria (facultative aerobes/catalase negative) produce large amounts of peroxide

S. sanguis, S. mitis, S. mutans

Thiocyanate ion (SCN-) which is converted to hypothiocyanite ion (OSCN-) by peroxidase

Thiocyanate reactions

More acid favors HOSCNDue to uncharged nature, HOSCN

penetrates bacterial cell envelope better

HH22OO22 + + SCNSCN-- OSCN-OSCN- + +HH22OOSP and/or MPSP and/or MP

HOSCN/OSCN--mediated cell damage

can oxidize sulfhydryl groups of enzymesblock glucose uptakeinhibit amino acid transportdamage inner membrane, leading to leakage

of celldisrupt electrochemical gradients

Immunoglobulin

Secretory immunoglobulin A (IgA) is the largest immunologic component of saliva. It can neutralize viruses, bacterial, and enzyme toxins

It serves as an antibody for bacterial antigens and is able to aggregate bacteria

IgG and IgM, occur in less quantity and probably originate from gingival fluid.

Tissue Repair

 Tissue repair function is attributed to saliva since clinically the bleeding time of oral tissues appears to be shorter than other tissues

Experimental studies in mice have shown wound contraction is significantly increased in the presence of saliva due to the epidermal growth factor it contains which is produced by the submandibular glands

Xerostomia – symptom not a disease

Temporary

1. Calculi

2. Psychological

3. Drugs

Permanent

1. Aplasia

2. Removal of gland

3. Sjogrens syndrome

Factors affecting flow of saliva

Individual Hydration Body Posture- Patients kept standing up or

lying down present higher and lower SF, respectively

The Circadian and Circannual Cycle Medications- antidepressants,, antipsychotics,

antihistaminics, and antihypertensives) Age Gender Lighting