Oral Physiology

Saliva

Why dentists should study oral

physiology?

• Knowing normal functions of mouth helps

to understand pathologies

• Better diagnosis & treatment

• More researches

• Impact on industry&marketing

Functions of mouth and oral cavity

• Ingestion (V, VII)

• Analysis of food by sensory systems:

- Taste

- Smell

- Touch

- Pain

- Temperature

• Mechanical (V, XII) and chemical digestion (VII, IX)

• Saliva production - Lubrication

- Other functions

• Chewing and swallowing (IX, X)

• Speech, hearing, breathing

Mechanical digestion = bolus

formation • Mastication is both voluntary and partly reflexive - the

tongue mixes the food with saliva to soften it, and the teeth cut and grind it into a bolus

• Neurological control – V, XII

Chemical digestion (VII, IX)

• Starch digestion – α-amylase - present in parotid saliva at conc. of 60-120 mg/ 100ml

- in submandibular saliva at approx. 25 mg/100 ml,

- very little amylase activity in the sublingual and minor glandular

secretions.

• Lipid digestion – lingual lipase

Neurohormonal control of oral

cavity

• Ingestion (voluntary) -

V,VII

• Mechanical digestion - V,

XII

• Chemical digestion - VII,

IX

• Swallowing (voluntary) -

IX,X

• NONE ????

• Sex hormones (pregnancy

vs. menopause)

• Aldosterone

• Gastrin

• CCK

• Melatonin

Cranial nerves Hormones

Saliva

Definition and site of production

• Fluid lubricating the mucosa and teeth of the oral cavity secreted by the salivary glands:

• Major glands – Secrete saliva

intermittently

• Minor glands – Secrete saliva

continuously

Saliva – general

characteristics

On the average about 1-2 liters of saliva are secreted /day

General characteristics

• pH (6.5-7.5) at rest,

• Resting salivary flow 0.5mL/min (less than

0.1mL/min = hyposalivation). High content

of K+ and HCO3-

• Response to the stimulus – 5.0 mL/min

(less than 0.7mL/min = hyposalivation)

• Hypotonic to plasma at rest; K+,HCO3-

higher than in plasma

Function of saliva

Functions of saliva

Fluid/lubricant Protect against mechanical, thermal and chemical irritation

and tooth wear.

Assists smooth air flow, speech and swallowing; it maintains

number of taste buds (trophic function)

Ion reservoir Facilitates remineralisation of the teeth

Buffer Helps to neutralise plaque pH after eating. Demineralisation

of enamel = pH of 5.5;

swallowed saliva protects esophageal wall from regurgitated

HCl

Antimicrobial

actions

Specific (e.g. sIgA) and non-specific (e.g. Lysozyme,

Lactoferrin and Myeloperoxidase) anti-microbial mechanisms

help to control the oral microflora; melatonin

Agglutination Agglutinins in saliva (mucins, glycoproteins) aggregate

bacteria, resulting in accelerated clearance of bacterial cells.

Functions of saliva

Digestion The enzyme α-amylase is the most abundant salivary

enzyme; it splits starchy foods into maltose, maltotriose and dextrins. Salivary lipase to start fat digestion. Role in cephalic

phase of digestion (pleasant taste)

Taste Saliva acts as a solvent, thus allowing interaction of foodstuff

with taste buds to facilitate taste. Trophic function.

Excretion As the oral cavity is technically outside the body, substances

which are secreted in saliva are excreted. This is a very

inefficient excretory pathway as reabsorption may occur

further down the intestinal tract. Possibly endocrine function.

Water balance Under conditions of dehydration, salivary flow is reduced,

dryness of the mouth and information from osmoreceptors

are translated into decreased urine production and increased

drinking

What to do when we are addicted

to sweets?

• Plaque pH stays below critical 5.5 for 15-20min and

does not return to normal until about 40 min after

ingestion of sucrose rinse

Social function

Salivary gland participation and

types of saliva

• Parotid – 20%

• Submandibular– 65-

70%

• Sublingual – 7-8%

• Small glands of mouth and pharynx – 5%

• Serous Saliva

• Mucus Saliva

• Mixed Saliva

Serous saliva = „watery saliva”

• Contains: - Amylase protein

- Polysaccharides

- Secreted by: - Parotid gl

- Von Ebner’s gl

Viscous saliva = „thick

mucus saliva”

• Contains: - Mucins

- Carbohydrates

- Secreted by: • Sublingual Gland

• Minor Salivary Glands (except Von

Ebner’s glands)

Mixed saliva

Secreted by: Sublingual and

Submandibular glands

Secretion of saliva

Spontaneous, resting and stimulated

secretion

• In humans, only the minor glands secrete saliva spontaneously

• In daytime and at rest, a nervous reflex drive—set up by low-grade mechanical stimuli due to movements of the tongue and lips, and mucosal dryness—acts on the secretory cells, particularly engaging the submandibular gland

• With respect to stimulated secretion, the parotid contribution becomes more dominant

Salivary response displays

circadian and circannual rhythms

• flow rate of resting as well as of stimulated saliva is

higher in the afternoon than in the morning

• salivary protein concentration follows this diurnal pattern

• the flow of the resting saliva is higher during winter than

during summer

23

CIRCAIDIAN RHYTHM OF SALIVA FLOW

Time of day

No sleep

sleep

12 am 6 am 12 pm 6 pm 12 am 6 am 12 pm 6 pm 12 am

30

20

10

Secretion of saliva

• The basic secretory units of

salivary glands, secretory

end pieces - Acini

• Parotid gland- serous gland

• Submandibular gland –

mixed

• Sublingual Gland - mucus

On average 1-2 liters of saliva are secreted /24h.

Afferent stimuli in response to food

intake:

• Taste receptors (activate PNS and SNS; SOUR AND SALT),

• Chewing by stim mechanorec in peridontal ligaments and gingival tissue (mastictory reflex, activate PNS)

• Olfaction – submandibular gl (olfactory reflex)

• Dry mouth reflex

• Pain, vomiting, esophgeal reflex

Taste activates both SNS and PNS

Mastication - PNS

26

Effect of feeding on salivary secretion

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10

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10 min collection periods

Meal

during

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Neural control – efferent stimuli

• Parasympathetic – constant stimulation,

watery saliva rich in enzymes

• Sympathetic – by vasoconstriction and

contraction of myoepithelial cells forces

the saliva into main ducts

• No opposite effects

Parasympathetic ---> large volume secretion (Ach),

enzymes, less protein conc.

Sympathetic ---> composition of saliva (adrenergic), more

macromolecules

Salivary centers

• Superior – connects (VII)

submandibular and sublingual

glands

• Inferior – connetcts (IX) parotid

gland

• Intermediate zone –

submandibular and parotid gl

• Upper thoracic segments of spinal

cord

Parasympathetic (medulla

oblongata)

The inhibitory influence of higher brain structures is illustrated by the reduced flow

of saliva associated with depression, fever, sleep, and emotional stress

Sympathetic

Mouth dryness in response to stress IS NOT CONSEQUENCE OF SNS ACTIVITY :

there are no inhibitory sympathetic fibers innervating the secretory cells !!!

Salivary reflexes Salivary secretion is enhanced by two different

types of salivary reflexes:

- simple or unconditioned reflex – chemo- and

pressure receptors (through salivary center in the

medulla; taste and mastication).

- acquired or conditioned reflex - learned

response based on previous experience (sight,

thought and smell of food).

- nausea

• When chemoreceptors and pressure receptors within the oral cavity respond to the presence of food.

• On activation these receptors initiate impulses in afferent nerve fibers that carry the information to the salivary center located in the medulla of the brain.

• The salivary center in turn sends impulses via extrinsic autonomic nerves to the salivary glands to promote salivation.

SIMPLE or UNCONDITIONED REFLEX

• In this case salivation occurs

without oral stimulation.

• Just thinking about, smelling, or hearing the preparation of pleasant food initiate salivation through this reflex.

• Also called mouth watering.

• This reflex is a learned response based on previous experience

ACQUIRED or CONDITIONED REFLEX

Salivary reflexes

• Gustatory-salivary

(sour > umami > salty

sweet > bitter)

• Masticatory-salivary

• Olfactory-salivary (not

from parotid gl)

• Visual and psychic

• Nociceptor-salivary

(V, parotid gl)

• Esophageal-salivary

(waterbrash

phenomenon

secondary to

gastroesophageal reflux )

The first step in stimulus-secretion

coupling

Release of neurotransmitter

Neurotransmitters

• Noradrenaline acts on α1- (fluid secretion) and β1- (protein

secretion) adrenoceptors,

• Acetylcholine acts on muscarinic M1 and M3 receptors (fluid

secretion)

• PNS uses other transmitters, i.e., peptidergic (vasoactive

intestinal peptide VIP, calcitoningene-related peptide,

substance P, neurokinin A, neuropeptide Y) and nitrergic

(nitric oxide, NO) mechanisms – to control protein secretion in

response to chewing and taste

Neurotransmitters and rec

Second messengers

Fluid secretion is activated by binding of ACh to muscarinic M1, M3, and NE to α1-adrenergic

receptors,

Macromolecule secretion by binding of NE to β1-adrenergic receptors and VIP

Fluid secretion

Macromolecule

secretion

The second step in stimulus-secretion coupling is binding of

neurotransmitter to receptor and activation of an intracellular enzyme

(1) the G-protein

binds GTP

instead of GDP and

is thus activated.

The α subunit of the

activated G-protein

dissociates

from the βγ subunits

(2) and

binds to and

activates a target

enzyme (3)

Fluid secretion

Phospholipase C;

Ca ions

The third step in fluid and electrolyte stimulus-

secretion coupling is an increase in

intracellular Ca2+ activity

Activated phospholipase C,

splits PIP2 into IP3 and

diacylglycerol

(DAG)(1).

IP3 binds to and activates IP3

receptors on the ER

(2).

Ca2+ diffuses from

the ER into the

cytoplasm.

Increased [Ca2+]i promotes

activation of the IP3

receptors and stimulutes further

Ca2+ mobilisation (3).

Macromolecule stimulus-secretion

coupling

Adenylate cyclase;

cAMP

The third step in macromolecule stimulus-

secretion coupling is production of cAMP

• When cAMP binds to protein kinase A (PKA) – PKA phosphorylates and

activates the cellular proteins responsible for the synthesis and secretion

of salivary macromolecules.

Blood flow

• The parasympathetic transmitter vasoactive intestinal peptide

VIP, besides acetylcholine, plays a major role in the

vasodilator response, which also involves the action of NO

• Vasoconstriction by α1 rec and neuropeptide Y rec in

response to SNS stimulation

Sympathetic innervation of the blood vessels of the gland is activated not

in response to a meal but in response to a profound fall in systemic

blood pressure in order to restore the blood pressure

THE SECRETORY UNIT The 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.

Fluid and protein secretion – active

process under neural control

• The acinar cells are responsible for the secretion of fluid and most of proteins

• The duct cells contribute to a minor proportion of the total protein output

• Water is transported to the lumen in response to osmotic force created by intraluminal NaCl

• The primary saliva is isotonic

a Acinar cells: water and protein secretion via vesicular and granular

pathways—primary secretion.

b Duct cells: modifications of saliva—secondary secretion

HCO3-

Basolateral channels for K

Apical channels for Cl

Interstitium

Cl-

• The salivary ducts reabsorb Na and Cl (without

H2O) from the saliva and add more K and HCO3

to it.

• Secondary saliva is hypotonic

• As a result the salivary NaCl concentration is

only 1/7 of that in the plasma.

The secretion of proteins is of two

types: vesicular and granular

• Vesicular – continues

• Granular (exocytosis) - stimulated

Stimulation of β1 rec (via cAMP) and vasoactive intestinal peptide VIP

receptors is associated with protein secretion by exocytosis and a small

volume response

Stimulation of M1, M3 and α1 rec (Ca ions as a II messenger) is associated

with fluid secretion—and particularly large volumes in response to muscarinic

agonists—and protein secretion via vesicular secretion and, with intense

stimulation, also via exocytosis

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

Other physiological factors affecting

secretion of saliva

Hormones, ageing

Hormones

• Aldosterone – little effect in humans

• Gastrin (gastric phase)

• Cholecystokinin and melatonin

• Sex hormones Gastrin, CCK and melatonin affect protein and amylase secretion

Melatonin

• Formed by pineal gland, made from tryptofan

• Released during the night

• Antioxidant

• Beneficial effects on

fibroblast activity and

bone regeneration • Ramelteon – melatonin receptor

agonist (long term use); helps falling asleep; „Supermelatonin”

Ageing – changes secondary to diseases?

• the secretory volumes of unstimulated and stimulated saliva are only slightly affected, if at all

• parotid saliva composition is considered unchanged

• the mucin secretion of the mucous/seromucous glands as well as the immunoglobulin secretion of the labial glands decrease

Ageing and oral health

• Dental caries

• Gingivitis

• Peridontosis

• Xerostomia

• Candidosis

• Denture stomatitis

• Oral cancer

Composition

of saliva

Composition of Saliva

Saliva is composed of 99.5% of water and 0.5% of electrolytes and proteins.

Like other exocrine glands the process of salivation occurs in two stages:

1.The glandular portion ,the acini produces a primary secretion with an electrolyte composition similar to plasma.

2.The primary secretion flows through the salivary ducts.

Salivary composition

1. Water content - 99.5%

2. Solids - 0.5%

Inorganic content - 0.2%

Organic content - 0.3%

Gases - 1ml oxygen/100ml

- 2.5ml nitrogen/100ml

- 50ml carbondioxide/100ml

Cellular elements

Saliva is a mixture of many

compounds:

• Water

• Lysozyme - is an enzyme found in egg white, tears, and other secretions.

It is responsible for breaking down the polysaccharide walls of many kinds of bacteria and thus it provides some protection against infection.

Saliva is a mixture of many

compounds:

• Lactoferrin -an iron-binding protein present in

neutrophil granules.

By combining with iron, lactoferrin prevents

microorganisms from combining with and using

iron for their growth and development. Also

present in milk, tears, mucus and bile.

Saliva is a mixture of many

compounds:

• Lactoperoxidase – Lactoperoxidase

catalyzes the oxidation of a number of

inorganic and organic substrates by

hydrogen peroxide.

• The oxidized products produced through

the action of this enzyme have potent

antibacterial activities.

Saliva is a mixture of many

compounds:

• Kallikrein – tissue and plasma kallikrein are

peptidases enzymes that cleave peptide bonds

in proteins. It causes the liberation of

bradykinin, which is a potent vasodilator.

• Histatins are human histidine-rich and mostly

cationic proteins identified as antimicrobial and

fungistatics in human parotid and

submandibular-sublingual gland secretions.

Saliva is a mixture of many

compounds:

• Cystatins - antibacterial/viral agents.

• Proline- rich proteins- these protect tooth

enamel and bind toxic tannins.

Saliva is a mixture of many

compounds:

• Salivary α-amylase

• Lingual lipase

• RNase

• DNase

• NaCl

• IgA

Saliva is a mixture of many

compounds:

• Bicarbonate

• Mucins

• Lactic acid

• Choline

• Ascorbic acid

• Urea

• Glucose

• Cholesterol

• Blood group substances (in some individuals).

Saliva is a mixture of many

compounds:

Electrolytes:

• Sodium (lower than blood plasma) Na

• Potassium (higher than plasma) K

• Calcium (similar to plasma) Ca

• Magnesium Mg

• Chloride (lower than plasma) Cl

• Bicarbonate (higher than plasma) HCO3

• Phosphate and iodine (usually higher than plasma, but

dependent variable according to dietary iodine intake)

Saliva is a mixture of many

compounds:

Mucus.

• Mucus in saliva mainly consists of

mucopolysaccharides and glycoproteins.

Pathology

samples

Pathology

• Three categories of problems

– 1. Altered saliva production

– 2. Painless swelling of saliva glands

– 3. Painful swelling of saliva glands

Pathology

• Increased or decreased stimulation • Medication, neurogenic, hormonal

• Obstruction of secretion • Sialadenitis, sialolithiasis

• Change of composition • Cystic fibrosis

• Nutrition

• Parenchymal damage • Irradiation, Sjogren’s syndrome, cystic fibrosis

Treatment of xerostomia

• Parasympathomimetics – cevimeline and pilocarpine (stimulate flow of saliva)

• Local treatment – cholinesterase physostigmine (Ach-esterase inhibitors)

Decreased stimulation

• Xerogenic drugs: antihistamines,

antidepressants, spasmolytics, diuretics, alpha

and beta blockers

• Dehydration

• Stress

• Radiotherapy

• Amphetamine, heroine

• AIDS

• Menopause

Increased stimulation, sialorrhea

• CNS disorders (eg. cerebral palsy, Parkinson disease, amyotrophic lateral sclerosis, stroke)

• treatment of Alzheimer disease and myasthenia gravis (Ach-esterase inhibitors)

• Side effect of clozapine

• Excessive starch intake

• Oral infections

• Toxins: mercury, copper, arsenic

• Pregnancy (hormonal profile)

Obstruction of secretion

• Acute tender swollen gland

• Fever

• Pain on salivation • Poor hygiene, dehydration,

trauma, immunosuppression

• Elderly and post-op patients

• May lead to abscess

• Culture saliva:

- S. aureus, S. pneumoniae, E. coli, H. influenza

Treatment: antiinflammatory

drugs, lime drinks, ensure good salivation

Sialadenitis (poor

hygiene?)

Obstruction of secretion

• 50% of all major salivary gland pathology, submandibular gland • disease of adults, typically between 30 and 60 years of age, males

• abnormalities in calcium metabolism, dehydration, altered pH (infecions), altered solubility of crystalloids

• food debris, bacteria or foreign bodies from the mouth enter the ducts of a salivary gland and are trapped by abnormalities in the sphincter mechanism of the duct opening

Sialolithiasis

Change of composition

• pH changes

• Inhibited Na reabsorbtion

• Higher amounts of Ca and P (stones formation)

• Defective mineralisation of enamel

• High/low caries prevalence?

• Antibiotics, diabetes and high carbohydrate diet side effects

CF - autosomal recessive disorder

Parenchymal damage

• Dry mouth and eyes

• Vaginal dryness

• Chronic bronchitis

Treatment:

- at-home topical fluoride application to

strengthen tooth enamel

- frequent teeth cleanings by a dental

hygienist

- water, artificial salivas

- saliva stimulants

Parenchymal damage

• Viral (paramyxovirus)

• Painful parotis

• Fever and headache

• Testicular swelling

• MMR (mumps, measles,

rubella); the first shot is given

between the ages of 12 and 15 months. A second vaccination is required for school-aged children between 4 and 6 years old.

Mumps

Salivary diagnostics

Caries risk assessment

• High levels of mutants streptococci more than 105 colony forming units (CFUs)/mL = increased risk for caries

• High levels of Lactobacilli (more than 105 CFUs/mL saliva)

• Buffering capacity (carbonic acid/bicarbonate system)

Measurment of drooling (salivation)

• For objective measurment of drooling, the Schrimer test strip was placed near submandibular gland of a patient and salivation was measured as the length of saliva permeation after 5 min.

Salivary variables measured for caries risk assessment

Saliva is easily available for non-invasive sampling

• It correlates gene expression with drug’s toxicity or efficacy (dose selection)

• Monitoring level of:

- Hormones and cytokines

- Drugs

- Antibodies (immunoglobulins)

- Microorganisms

… when venipuncture is uncomfortable or unacceptable…

Thank you!

Macromolecules secretion

cannot cross the plasma membrane

The secretory process may be divided into four stages.

Synthesis, segregation and packaging, storage and release.

• Proteins are synthesized inside secretory vesicles by ribosomes (R).

• Secretory vesicles mature and are stored until a secretory stimulus is received.

• Each of these stages is regulated by phosphorylation of target proteins by cAMP-dependent pKA

Increase in cAMP stimulates:

• Transcription of genes for salivary proteins (e.g. proline-rich

proteins).

• Post-translational modification (e.g. glycosylation)

• Maturation and translocation of secretory vesicles to the

apical membrane

• Exocytosis

Fluid secretion

Fluid secretion follows electrolyte

secretion

The Na+/K+ ATPase

makes direct use of ATP

to pump Na+ out of the

cell and create an

inwardly directed

Na+ gradient.

This energises the

Na+/K/2Cl- (NKCC1)

cotransport system (1)

which in turn

concentrates Cl above

its electrochemical

potential (2).

Increased [Ca2+]i opens

the Ca2+-dependent K+

and Cl- channels and

Cl- crosses the apical

membrane into the

lumen of the acinus (2).

Na+ follows Cl- across

the cell to maintain

electroneutrality and the

resultant osmotic

gradient moves water (3)

Bicarbonate secretion

• Carbon dioxide inside cells is converted to HCO3- and H+ by carbonic

anhydrase. HCO3 - is secreted across the apical membrane of the cell

through an anion channel (2).

• H+ are actively extruded across the basolateral membrane by Na+/H+

exchange energised by the Na+ gradient which is created by the action of

the Na+/K+ ATPase (1).

• If protons were not lost from the cell, carbonic anhydrase would be unable

to generate HCO3-.

Calcium and phosphate

secretion

A possible mechanism for

Ca2+ translocation. Ca2+

enters across the

basolateral membrane

through Orai1 Ca2+

channels (1) and tunnels

across the cell in the ER

(2) to be released at the

apical pole and extruded

by the PMCA (3). The

active step of phosphate

translocation is uptake

across the basolateral

membrane by the Na+-

coupled Pi transporter

NPT2b which utilizes the

inwardly directed Na+

gradient to concentrate Pi

inside the cells (4). Pi exits

across the apical

membrane down its

electrochemical gradient

through an as yet

unidentified mechanism

(5).

Control of saliva secretion

exclusively under nervous control

PNS stimulation - flow of watery saliva that is rich in enzymes

Afferent pathway:

• Taste&mastication

– V (chewing),

- VII, IX, X (taste)

- – salivary nuclei

• Higher brain centers influence

Efferent pathway:

• IX – otic ganglion - parotid gl

• VII - submandibular ganglion – sublingual and submandibular glands

SNS stimulation - smaller volume of thick saliva that is rich in mucus

• Sympathetic impulses are more likely to influence salivary

composition

• The relevant efferent sympathetic nerves originate in the

spinal cord, synapse in the superior cervical ganglia and then

travel along blood vessels to the salivary glands