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SALIVA
DR NASRIN HABIB
MBBS,MPHIL(PHYSIOLOGY)
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Saliva
Saliva is a viscous, colourless,oplacent fluidwhich is secreted by three pairs of salivaryglands----the parotid,submandibular and
sublingual glands. There are also many smallbuccal glands from which salivation occurs.
Characters:
800-1500ml/day or1500ml/day. Slighlitly acidic.PH:6-7
Specific gravity:1.002-1.012
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Composition
Water:99.5% Solid:0.5%
Organic-O.3%
Enzyme:ptyline(salivary alpha-amylase),lingual lipse,corbonic
anhydrase phosphatase,lysozymes Other organics:Mucin,urea,cholesterol,amino acid.
Blood group subtances:Antigen of ABO blood group.
Inorganic(0.2%) NACL,KCL,acid and alkaline sodium
phosphate,calcium phosphate,CaCO3,KHC03 etc. Cellular Constituents: Yeast cell,bacteria,protozoa etc.
Gases:02,N2,C02.
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Function
Mechanical function:
keeps the mouth moist helps in speech.
Facilitates swallowing.
Helps in preparing food staffs into a bolus,suitable for digestion.
Dilutes hot and irritant food,thus prevents injuryto the mucosa
Acts as a lubricant. Washes down the food debris thereby prevent
bacterial growth.
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Function
Helps in taste by dissolving food stuff. Digestive function: It breaks down boiled starch into maltose in
presence of ptylin.Starch-Ptylin----Erythrodextrin---Achrodextrin-----Maltose.
Excretory function: It excretes urea, some heavymetals,thyocyanates,I2,penicillin.
Saliva helps in water balance: Saliva keeps the mouth moist, whenmoisture is reduced in the mouth, certain nerve ending at back ofthe tongue are stimulated the desire of thirst arises. The subjectthen take water thus water valance is maintained
Buffering function: due to presence of HCO3 and PO4 in saliva, itacts as buffer-NaHCO3,H2CO3 and Na2HPO4,NaH2PO4.
Bacteriolytic function: Cell membrane of bacteria containspolysaccharides,lysosome.The enzyme present in the saliva is apolysaccharide,thus it dissolves the cell membranes of manybacteria and finally kills them.
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Salivary Glands
3 pairs secrete into oral cavity
Each pair has distinctive cellular organization:
and produces saliva with different properties
Produce 1.01.5 liters of saliva each day:
submandibular gland: 70% by submandibular glands. Secrete both serous
and mucous type. The gland opens upon the floor ofthe mouth on the side of the frenulum of the tongue,
by duct of Wharton's duct.
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Salivary gland.Parotid gland
25% by parotids glands. Secrete mainly serous type,containing ptyelin.The gland opens upon the innersurface of the check, opposite the second uppermolar teeth, by duct of Stensen.
Sublingual gland
5% by sublingual glands-secrete both the serous andmucous types. The gland open by several fine
ducts, floor of the mouth on the frenulum of thetongue by duct of Rivinus.
There are small accessory buccal glands scatteredthroughout the mucous membrane and secrete
only mucous.
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Salivary gland
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Salivary glands
Nerve supply - Salivary glands are under the control of theautonomic nervous system-and receive efferent nerve fibersfrom both parasympathetic and sympathetic divisions(7th&9thcranial nerves)
Regulation of secretion-
1.Unconditional reflex-this is present since birth and is inborn(when any substance is put in the mouth)
2.Conditional reflex- That is by the sight, smell, hearing orthought of food. (Acquired-learnt after birth)
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Tractus solitarius &
salivation
Parasympathetic nervous regulation of
salivary secretion.
VII, IX & X cranial
nerves represent
parasympatheticdivision of ANS.
Secretomotor
functions.
From the tractus
solitarius, many taste
signals are
transmitted within the
brain stem itself
directly into
the super ior and
in fer ior sal ivatory
nucle i, and these areas transmit
signals to the
submandibular,
sublingual, and
parotid glands
to help control thesecretion of saliva
Taste Reflexes Integrated in the Brain Stem.
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Mechanism of saliva secretion
1)Neural control:Parasympathetic stimulation: superior and
inferior salivatory nuclei-causes--
vasodilatation-occurs and copious salivasecretion. Atropine and cholinergic blocking
agents reduce secretion. Acetylcholine
increase secretion.
Sympathetic stimulation: superior cervical
ganglioncauses vasoconstriction---
moderate amount of salivation.
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Mechanism..
2)Reflex:
Conditioned reflex: Here salivation occurs in presence of food
such as sight, vision and smell of food stimulate saliva
secretion reflexly although no food is actually given in mouth.
Unconditioned or inborn reflex: when food is actually given tothe mouth then the secretion of salivary gland occurs by
unconditioned reflex.
Salivation also occur in response to reflexes originating in the
stomach and upper intestines-particularly when veryirritating foods are swallowed or when a person is nauseated
because of some gastrointestinal abnormality. When a
person smells or eats favourite food ,salivation is greater than
when disliked food is smelled or eaten.
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Mechanism of saliva
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LEARING OUTCOME
1. Describe the mechanism for secretion of
saliva .
2.Explain the functions of each constituent of
the saliva.
3. State the functions of saliva.