Saliva and its functions NOTES

Composition of Saliva

• Volume secreted – 600-1000ml/day
• Electrolytes – Na+, K+, Cl-, HCO3-, Ca+2, Mg+2, HPO42-, SCN-, F-
• Secretory proteins – amylase, proline-rich proteins, mucins, histatin, cystatin, peroxidase, lysozyme, lactoferrin, defensins and cathelicidin-LL37
• Immunoglobulins – secretory immunoglobulin A, immunoglobulins G and M
• Small organic – glucose, amino acids, urea, uric acid and lipid molecules
• Other components – epidermal growth factor, insulin, cyclic adenosine monophosphate-binding proteins and serum albumin

	Parotid gland	Submandibular gland	Sublingual gland	Mixed or whole saliva
Saliva characteristics	Watery saliva rich in enzymes such as amylase, proteins such as proline-rich proteins and glycoproteins.	Watery saliva rich in enzymes such as amylase, proteins such as proline-rich proteins and glycoproteins including mucins	Viscous saliva rich in mucins	Secretions of all major gland, minor glands,  desquamated oral epithelial cells, microbes and their products, food debris, serum components, and inflammatory cells from the gingival crevice. (Many of the proteins maybe removed as they adhere to tooth surface, mucosa, microbes or are degraded)

Functions

1. Protection

• Washing action that flushes away non-adherent bacteria and other debris.
• Clearance of sugars from the oral cavity to limit the invasion of microbes.
• Lubrication by mucins and other glycoproteins.
• Barrier formation(thermal/chemical insulation) by mucins against noxious stimuli, microbial toxins, and minor trauma.
• Pellicle formation by proteins, glycoproteins, mucins.
• Tannin binding by basic proline-rich proteins and histatin.

2. Buffering

• Mainly bicarbonates and phosphate ions, some salivary proteins protect the teeth from demineralization caused by bacterial acids produced during sugar metabolism.
• Neutralization of acids (increase in pH) is brought about by metabolism of salivary proteins and bacterial peptides such as urea and ammonia

3. Maintenance of Tooth Integrity

• Supersaturated saliva with calcium and phosphate ions (including statherin and acidic proline-rich proteins)at the surface of the tooth results in posteruptive maturation of the enamel, increasing the surface hardness and resistance to demineralization.
• Remineralization of initial carious lesions can occur and is enhanced by the presence of fluoride ions in saliva.

4. Antimicrobial Action

• A physical barrier is formed by mucins.
• Immune defense by secretory immunoglobulin A.
• Non-Immune defense is provided by proteins such as histatin, peroxidase, lysozyme, lactoferrin, defensins, mucins, agglutinins, secretory protease inhibitor and cathelicidin-LL37
• Peptides which disrupt cellular or mitochondrial functions present in saliva are alpha and beta defensins, cathelicidin-LL37 and histatins.
• Agglutination of specific microbes preventing their adherence to oral tissues and inturn forming clumps which can be swallowed is done by salivary immunoglobulin, secretory immunoglobulin A, mucins and specific agglutinins.

5. Tissue Reapir

• Growth factors, trefoil proteins and peptides under experimental conditions promote tissue growth and differentiation, wound healing and regeneration.

6. Digestion

• Amylase and lipase in saliva begins the digestion process of starch and triglyceride digestion respectively.
• Water and mucin content allows the formation of bolus.

7. Taste

• Water and lipocalins helps in the disolution of food particles so that taste receptors can sense them.
• Maintainance of taste buds is done by epidermal growth factor and carbonic anhydrase VI present in saliva.
• Saliva produced by minor gladds of circumvallate papillae binds the taste substances and presents them to taste receptors.
• Saliva has proteind which have trophic effect (growth effect) on taste receptors