1. 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.

2. 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.

3. Saliva glands

4. 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.

5. Saliva Physical properties;
Volume ;daily secretion is about ml.
Appearance ; a clear colourless fluid.
pH = 6 – 7.4 (to suit the digestive action of the α- amylase ) .
Specific gravity

6. 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.

7. 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

8. THE SECRETORY UNIT

9. 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

10. 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.

11. 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)
 mmol/L calcium ,  mmol/L phosphate both help to prevent dissolution of dental enamel.
 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)

12. 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

13. 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.

14. 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.

15. 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

16. Salivary Protein Functions (cont’d)

17. Function of saliva

18. Salivary Protein Functions