SALIVA

Oral Physiology

Dent 207

Saliva Functions

Lubrication Mucin Physical protection of oral mucosa

Taste Antibacterial and immunity

Lysozyme IgA – produced by plasma cells

Digestion Amylase

Buffering Minerals Helps in maintaining the integrity of enamel

Wound healing and upper GI mucosal integrity Epidermal Growth Factor – produced and secreted by the

submandibular salivary glands Blood coagulation

Kallikrein

The process of secretion

Stimuli to secretion Formation of initial acinar fluid Ductal modification of acinar secretion

Stimuli to secretion

Three phases of stimulating saliva secretion Cephalic Intra-organ Inter-organ

Cephalic phase

Psychological phase (thinking of food) Visual phase (sight of food) Olfactory phase (smelling food)

*increasing salivary secretion vs. enhanced awareness of saliva

Intra-organ phase

Most important phase Mechanical stimulation

Stimulation of touch & pressure receptors leading to…. Mandibular movement & activation of masticatory

muscles Chemical stimulation

Stimulation of taste receptors More effect than mechanical stimulation, esp., acids

Direct olfactory stimulation?

Taste – salivary secretion (neural association) Afferent taste fibers within chorda tympanic –

efferent secretomotor fibers to SL & SM glands

Afferent taste fibers within glossopharyngeal – efferent secretomotor fibers to Parotid, lower labial & lower buccal glands

Inter-organ phase

Irritation to the esophagus Vomiting reflex

Control of salivary secretion

Not hormonal Although circulation aldosterone can effect

composition Neural

Dual innervation for major glands Sympathetic & parasympathetic

Parasympathetic control

Cell bodies of postganglionic fibers Peripheral ganglia

PPG, SM, Otic, Ciliary Cell bodies of preganglionic fibers

Superior salivatory nucleus Related to nucleus of facial nerve SM, SL major glands

Inferior salivatory nucleus Related to nucleus of glossopharyngeal Parotid gland

Stimulation of salivatory nuclei – salivation on ipsilateral side

Sympathetic control

Cell bodies of preganglionic fibers Level of 2nd thoracic nerve

Cell bodies of postganglionic fibers Superior cervical sympatheitc nucleus

Higher control of salivation

Excitement or inhibition Patterned reflexes – preparatory stimulation of

salivatory flow before vomiting Stimulation of regional parts of the cortex – increased

flow Decreased salivation during sleep Progressive reduction in unstimulated flow rate of

infants between birth – 5 years Control of hypothalamus

Over-riding control Direct connection with sympathetic system

Fear, rage, excitement – Dryness of the mouth Excess salivation in certain circumstances

Formation of initial acinar fluid

Parasympathetic stimulation Sympathetic stimulation

Parasympathetic stimulation

A cascade of biochemical reactions leads to releasing calcium from calcium stores

Intracellular calcium has 3 functions Opening of basal K channels Opening of apical Cl channels Movement of secretory granules towards the

apical membrane & exocytosis Protein & mucoprotein

Opening of basal K channels

Outward diffusion of K High [K] in 1st few drops of saliva collected after

stimulation [K] is raised in basal extracellular fluids

Activation of Na-K-Cl transporter Carrying these ions intracellularly For each Na ion: 2 K & 3 Cl ions K influx replaces K lost by outward diffusion Increased intracellular [Cl] brings water down an

osmotic gradient – cell swells Na is excreted from the cell by Na-K pump [Cl] in acinar lumen –Na is dragged to the acinar

lumen to balance the –ve charge of Cl

Sympathetic stimulation

A cascade of biochemical reactions leads to mobilization of Ca ions

A proportion of intracellular increase in [Ca] is due to opening of Ca channels

Rapid opening of K channels Fluid secretion is initiated Major result of sympathetic stimulation is

Secretion of protein & mucoprotein, giving… Thick viscous saliva

Ductal modification of acinar secretion

Composition of primary acinar fluid (table) Modification at intercalated ducts

Short in Humans No significant organelles like those seen in

acinar cells Possible modifications

Protein secretion similar to acinar cells? Site of Kallikrein section?

Ductal modification (non-specific site)

Addition of IgA From lymphoid plasma cell follicles dispersed

throughout the gland’s stroma Lysozymes & lactoferrin Carbonic anhydrase Serum albumin Salivary amylase

Passes across ductal epithelium in opposite direction Salivary duct obstructed – intraluminal pressure rises –

ductal epithelium becomes leaky – [amylase] rises when this happens

Modification at striated ducts

Main sites of modification of ionic composition Striated ducts are absent in SL & minor

glands No hypotonic secretion (except some labial

glands) Reabsorption pf Na Addition of K Reabsorption of Cl Hydrogen ion pass out to the lumen

Reabsorption of Na

Na passes from luminal fluids into cells and then out across the basal folded membranes of intercalated ducts

Cells impermeable to water – lumen becomes hypotonic

Possibility of reducing Na to zero if saliva stays in the duct for a long period

[Na] in saliva is thus related to the flow rate Rises when flow is increased

Modification at remainder of ductal system Some addition of K Not known whether any of ductal-derived

proteins are added through these parts of the ductal system

Composition of saliva

Saliva vs. oral fluid (whole saliva) Whole saliva (oral fluid) = saliva + crevicular fluid +

sloughed epithelial cells + WBC + food debris + bacterial + dental plaque …etc

Saliva A mixture of secretions Substantial component from minor glands Fluids near ductal orifices are very close to pure saliva

Greater information about secretions of parotid Easy collection of large amounts of pure saliva through Method of Lashley (Carlson-Crittenden) cannula / cup

Ionic composition of saliva

Calcium & phosphate Hydrogen carbonate Fluoride

Protection of enamel against acidic dissolution Thiocyanate – antibacterial Na, K & Cl

Role in forming & secretion of saliva No important roles in the mouth

Lead Cadmium, copper Iodine

Calcium & phosphate

Prevent dissolution of enamel High Ca secretion from SM gland

Stones Calculus on lingual surfaces of lower anterior

teeth Increase in pH – formation of calculus

(precipitation of calcium on tooth surfaces) Common site of calculus formation

Hydrogen carbonate

Buffer pH of resting saliva is 6 pH can be pushed to 8 Critical pH is 5.6 where enamel starts to

dissolve Thus saliva acts in reducing dental decay &

periodontal disease

Organic composition of saliva

Proteins with lubricating properties Mucin Proline-rich proteins (little lubrication)

Digestive proteins – amylase Proteins with antimicrobial properties

Sialoperoxidase Lysozyme IgA Lactoferrin

Proteins binding calcium Statherin

Prevents precipitation pf calcium phosphates in the ducts Reduces calculus formation

Salivary amylase

Breaks down starch into maltase & longer chain polysaccharides

Active above pH 6 (inactivated in stomach) Short time of action in the mouth Mainly secreted from parotid gland

Other organic components

Blood group substances Sugar Lipids Aminoacids, ammonia, urea, sialin

Composition of whole saliva

Composition of parotid gland saliva

Composition of SM gland saliva

Composition of SL gland saliva

Composition of minor labial gland saliva

Normal variation in salivary composition Flow during sleep

SM (72%) SL + minors (14%) No measurable secretion from P

Unstimulated flow SM (70%) P (20%) Minor (7%) SL (<2%) in stimulated or unstimulated flow

Acid stimulation P + SM (45% each)

Chewing stimulation P : SM = 2 : 1

Factors affecting composition

Rate of salivary flow Na & Cl HCO3 rises in high flow rates Amylase rises in high flow rates (esp. stimulated) Urea, IgA fall in high flow rates

Diffused through the ductal system

Duration of stimulation Flow rate falls slightly with time Protein content falls

Slow synthesis HCO3 rises and Cl falls

Saliva slow during the day

Early morning 4-6 am (lowest) Afternoon 16-20 pm (peak) Late afternoon (highest protein)

Summary of secretion of saliva Throughout the day

Low level in general Periodic large addition from major glands

Average flow rate (90% from Major SG) 0.3 ml/min 500-700 ml/day

Contribution of gingival fluids Secretion

Spontaneous Small amounts from sublingual and minor SGs

Stimulated (nerve-mediated) The bulk of saliva from all glands Parotid and Submandibular SGs do not secret spontaneously

Anaesthesia ceases secretion as it is nerve-mediated

Saliva vs. blood plasma

Saliva is an active secretion Not ultrafiltrate of plasma Little effect of plasma on saliva composition Correlation between the two media through

Glucose & urea concentrations Fluoride & iodide

Adult saliva vs. infant saliva

Unstimulated rate in infants is higher than in adults

Ca, Mg, K are higher in infant’s Phosphate are low in infant’s but rises to

adult level over the first year Rate of parotid gland is not significantly

affected by age SL + SM show some decreased flow with age

Salivary change in disease

Immunological reactions Reduce flow

Cystic fibrosis Defective chloride transporting proteins Decreased salivary secretion

Adrenal cortex abnormality Aldosterone reduces Na levels, & increases K level

Hyperparathyroidism Raise Ca & phosphate

Radiotherapy Sialadenitis Sjogren’s syndrome

Clinical Considerations

Dry Mouth (xerostomia) Causes

Ageing – Parenchymal tissue < Stroma Drugs

Central action on the salivary centre Diuretics, sedatives, hypnotics, antihistamines,

antihypertensives, antipsychotics, antidepressants, anticholinergics, and appetite suppressants

Loss / destruction of salivary tissue Radiotherapy Autoimmune disorders

Sjogren’s syndrome – destruction by lymphoid tissue (autoimmune disease)

Salivary gland surgery Endocrine disorders

Diabetes Hyperthyroidism

Clinical Considerations

Dry mouth (xerostomia) Signs and symptoms

Dry, red, glossy atrophic mucosa Difficulty chewing, swallowing, or speaking Altered / diminished taste ability Dental caries

Saliva contains re-mineralising minerals Periodontal disease Candidal infection

Treatment Consider stopping offending medication Commercial saliva substitute Fluoride Supplementation Scrupulous dental care

Clinical considerations

Obstructive disorders Sialolithiasis (salivary calculi)

80% in submandibular SG Mucoceles and cysts Minor SGs

Retention of mucous outside the duct Ranula

Submandibular and sublingual SGs Inflammatory disorders (Sialadenitis)

Viral Mumps

Bacterial – uncommon Suppurative parotitis

Autoimmune diseases Sjogren’s syndrome

Salivary gland tumours

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