Saliva• 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.

• 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.

• 2-submaxillary (mandibular) glands ; which produces a mixed serous and mucous secretion.

• 3-sublingual glands; which secretes a saliva that is predominantly mucous in character.

The primary secretion isproduced by acinar cells.The composition of salivais modified in the striatedand excretory ducts. Athigh rates of secretin,saliva compositionapproached that ofplasma, indicating thatmodification has lowereffect.

Saliva glands

Saliva glands• The basic secretory units of salivary glands are clusters of cells called an

acini .

• 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.

- Appearance ; a clear colourless fluid.

- pH = 6 – 7.4 (to suit the digestive action of the α- amylase ) .

- Specific gravity 1.002 1.008 .

Saliva secretion• The secretion of saliva is a two stage operation ;

• 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.

• 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 UNITThe basic building block of all salivary glands ( Acini)

ACINI - water and ions derived from plasma

Saliva formed in acini flows down DUCTS to empty into the oral cavity.

THE SECRETORY UNIT

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

Saliva• Secretion of saliva is under control of the nervous system, which controls both the

volume and type of saliva secreted .

• Potent stimuli for increased salivation include the presence of food or irritating substances in the mouth, and thoughts of or the smell of food.

• 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• 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 OSCN-

by active oxygen produced from bacterial peroxides by lactoperoxidase).– -iodine (mmol/L variable according to dietary iodine intake)

Composition of Saliva• 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• 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 anti-microbial 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.

• 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

SalivaryFunctions

Anti-Bacterial

Buffering

Digestion

Mineral-ization

Lubricat-ion &Visco-elasticity

TissueCoating

Anti-Fungal

Anti-Viral

Carbonic anhydrases,Histatins

Amylases,Mucins, Lipase

Cystatins,Histatins, Proline-rich proteins,Statherins

Mucins, Statherins

Amylases,Cystatins, Mucins, Proline-rich proteins, Statherins

Histatins

Cystatins,Mucins

Amylases, Cystatins,Histatins, Mucins,Peroxidases

adapted from M.J. Levine, 1993

Salivary Protein Functions (cont’d)

Oral function Problem Protein function• Control of in-

digenous & in-vading bacteria,fungi and viruses

• Colonization &infection

• Controllingpathogens andcommensals

• Adhesion of bac-teria versus theirdetection

• Anti-bacterialsystems

• Immunoglobu-lins, histatins,glycoproteins,lysozyme, sia-loperoxidase,lactoferrin

• Adhesion-modulating pro-teins

Function of saliva

Salivary Protein FunctionsOral function Problem Protein function

• Acts as an airway • Air-born organisms• Dehydration

• Anti-bacterialsystems

• Water-retainingglycoproteins

• Speech • Need for lubrication • Lubrication system

• Taste -- • Gustin

• Entry-point for foodmastication,swallowing

• Food-bornorganisms

• Soft and hard tissueabrasion

• Food toxins

• Anti-bacterialsystems

• Lubrication;mucins, statherin

• Toxin-neutralization