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 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 . 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 UNIT The basic building block of all salivary glands ( Acini) Saliva formed in acini flows down DUCTS to empty into the oral cavity. ACINI - water and ions derived from plasma

THE SECRETORY UNIT

Hypotonic final saliva into mouth TWO STAGE HYPOTHESIS OF SALIVA FORMATION Most proteins Na+ Cl- resorbed Hypotonic final saliva into mouth Water & electrolytes Some proteins electrolytes K+ secreted Isotonic primary saliva

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 Amylases, Cystatins, Carbonic anhydrases, Histatins, Mucins, Peroxidases Carbonic anhydrases, Histatins Anti- Bacterial Buffering Amylases, Mucins, Lipase Cystatins, Mucins Anti- Viral Digestion Salivary Functions Mineral- ization Anti- Fungal Cystatins, Histatins, Proline- rich proteins, Statherins Histatins Lubricat- ion &Visco- elasticity Tissue Coating Amylases, Cystatins, Mucins, Proline-rich proteins, Statherins Mucins, Statherins adapted from M.J. Levine, 1993

Salivary Protein Functions (cont’d)

Function of saliva

Salivary Protein Functions