Saliva
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It is the watery fluid produced in the mouths of humans that is produced by the
salivary glands , and is made up mainly of water, electrolytes, mucus and enzymes.
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Saliva glands; Humans have three major pairs of salivary glands that differ in the
type of secretion they produce ;
1- parotid glands ; which produces a serous, watery secretion.
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2-submaxillary (mandibular) glands ; which produces a mixed serous and mucous
secretion.
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3-sublingual glands; which secretes a saliva that is predominantly mucous in
character.
The primary secretion is
produced by acinar cells.
The composition of saliva
is modified in the striated
and excretory ducts. At
high rates of secretin,
saliva composition
approached that of
plasma, indicating that
modification has lower
effect.
Saliva glands
Saliva glands
• The basic secretory units of salivary glands are clusters of cells called an
acini .
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These cells secrete a fluid that contains water, electrolytes, mucus and
enzymes, all of which flow out of the acinus into collecting ducts.
• Within the ducts, the composition of the secretion is altered. Much of the
sodium is actively reabsorbed, potassium is secreted, and large quantities
of bicarbonate ion are secreted .
• Small collecting ducts within salivary glands lead into larger ducts,
eventually forming a single large duct that empties into the oral cavity.
Saliva
• Physical properties;
- Volume ;daily secretion is about 800 -1500ml.
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Appearance ; a clear colourless fluid.
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pH = 6 – 7.4 (to suit the digestive action of the α- amylase ) .
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Specific gravity 1.002 1.008 .
Saliva secretion
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The secretion of saliva is a two stage operation ;
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The first stage involves the production of the primary secretion which is an isotonic
fluid that contains water, eletrolytes, mucus,and enzymes by the acini gland cells.
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In the second stage the fluid secreted by the acini cells will flow out to the
collecting ducts , and within the ducts the composition of the primary secretion is
altered by ;
• - the active reabsorbtion of Na+ .
• - the active secretion of K+ .
• Cl- passive reabsorption.
• - HCO3 - secretion.
Small collecting ducts within salivary glands will carry the saliva to larger ducts,
eventually forming a single large duct that empties into the oral cavity.
THE SECRETORY UNIT
The basic building block of all salivary glands ( Acini)

ACINI - water and
ions derived from
plasma
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Saliva formed in acini flows
down DUCTS to empty into
the oral cavity.
THE SECRETORY UNIT
TWO STAGE HYPOTHESIS
OF SALIVA FORMATION
Most proteins
Water &
electrolytes
Na+ Cl- resorbed
Some proteins
Isotonic
primary saliva
electrolytes
K+ secreted
Hypotonic
final saliva
into mouth
Saliva
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Secretion of saliva is under control of the nervous system, which controls both the
volume and type of saliva secreted .
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Potent stimuli for increased salivation include the presence of food or irritating
substances in the mouth, and thoughts of or the smell of food.
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The composition of saliva is affected by the salvation rate , during maximal
salvation , the rate of formation of the primary secretion increases to about 20
folds , which makes it flow through the ducts rapidly thus the chemical changes
that occur in the ducts is reduced leading to the production of a saliva of higher
Na+ and lower K+ concentrations.
Composition of Saliva
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Human saliva is composed of 98% water while the other 2% consists of other
compounds.
Inorganic components;
– 2-21 mmol/L sodium (lower than blood plasma)
– 10-36 mmol/L potassium (higher than plasma)
– 1.2-2.8 mmol/L calcium , 1.4-39 mmol/L phosphate both help to prevent
dissolution of dental enamel.
– 0.08-0.5 mmol/Lmagnesium.
– 5-40 mmol/L chloride (lower than plasma)
– 25 mmol/L bicarbonate (higher than plasma) , acts as a buffer thus is
important in the defence against acids produced by cariogenic bacteria.
– Flouride .
– -Thiocyanate, it has an antibacterial role (oxidated to hypothiocyanite OSCNby active oxygen produced from bacterial peroxides by lactoperoxidase).
– -iodine (mmol/L variable according to dietary iodine intake)
Composition of Saliva
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Organic components;
Mucins
Proline-rich proteins
Amylase
Lipase
Peroxidase
Lysozyme
Lactoferrin
sIgA
Histatins
Statherin
Blood group substances, sugars, steroid hormones, amino acids, ammonia, urea
Composition of Saliva
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Mucins ; They are glycoproteins, that are important in;
– 1-Tissue Coating (providing protective coating around hard and soft
tissues,plays primary role in formation of acquired pellicle,concentrates antimicrobial molecules at mucosal interface).
– 2-Lubrication .
Amylases; It is an enzyme that Hydrolyzes (1-4) glycosidic bonds of starches such as
amylose and amylopectin, producing Maltose as its major end-product.
It has a digestive function .
It represents 30% of total the protein in parotid saliva .
Lingual Lipase ;
Secreted by lingual and parotid glands.
Involved in first phase of fat digestion ( has a pH optimum ~4.0 so it is not activated until
entering the acidic environment of the stomach) .
Hydrolyzes medium- to long-chain triglycerides.
Important in digestion of milk fat in new-born.
Statherins;
It is a salivary protein that prevents precipitation or crystallization of supersaturated
calcium phosphate in ductal saliva and oral fluid.
It also has a lubricating role.
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Lactoferrin ;
It is an iron binding protein( it can deprive microorganisms from iron acting as
playing an antimicrobial role).
Lysozyme;
It has an antimicrobial effect( can disrupt the cell wall of some bacterial cells)
Histatins ;
A group of small histidine-rich proteins that have an a antimicrobial effect.
Multifunctionality
Amylases, Cystatins,
Carbonic anhydrases,
Histatins, Mucins,
Histatins
AntiPeroxidases
Buffering
Bacterial
Amylases,
Cystatins,
Mucins, Lipase
AntiMucins
Digestion
Viral
Salivary
Functions MineralAntiization
Fungal
Cystatins,
Histatins
Histatins, ProlineLubricatTissue ion &Viscorich proteins,
Coating elasticity
Statherins
Amylases,
Cystatins, Mucins,
Mucins, Statherins
Proline-rich proteins, Statherins
adapted from M.J. Levine, 1993
Salivary Protein Functions (cont’d)
Oral function
Problem
Protein function
• Control of in• Colonization &
• Anti-bacterial
digenous & i ninfection
systems
vading bacteria, • Controlling
• Immunoglob ufungi and v iruses
pathogens and
lins, histatins,
commensals
glycoproteins,
• Adhesion of ba clysozyme, siateria versus their
loperoxidase,
detection
lactoferrin
• Adhesionmodulating pr oteins
Function of saliva
Salivary Protein Functions
Oral function
Problem
• Acts as an airway
• Air-born organisms
• Dehydration
• Speech
• Taste
Protein function
• Anti-bacterial
systems
• Water-retaining
glycopr oteins
• Need for lubrication • Lubrication system
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• Gustin
• Entry-point for food • Food-born
• Anti-bacterial
mastication,
organisms
systems
swallowing
• Soft and hard tissue • Lubrication;
abrasion
mucins, statherin
• Food toxins
• Toxin-neutralization