Saliva

SALIVA

• Principal secretory event in mouth – Salivary secretion.
• About 1 – 1.5 L/day, by three salivary glands.
• Parotid – 250-400 ml.
• Submandibular – 700-1000 ml.
• Sublingual – 50-100 ml.

SALIVARY ACINAR CELL:

• Categorized into 2 types –
• Serous & Mucous.

Serous cells:

• Secrete watery saliva (> than 90% water).

Mucous cells:

• Secrete more viscous fluid.
• Contains glycoprotein mucin.
• Parotid gland – Purely serous.
• Sub-lingual gland – Predominately mucous.
• Submandibular glands – Mixed gland.

COMPOSITION:

• Consists of 99% of water & only 1% solid.
• Important inorganic constituents – Na2+, K+, Cl–, HCO–3, Ca2+.
• Organic components – Mucus & enzyme amylase.
• Salivary pH: 6.5 – 7.
• Under resting conditions:
• Na2+ & Cl– concentrations are always lower than in plasma.
• Hence, saliva is always hypotonic.
• K+ & HCO–3 concentrations are higher than in plasma.

FUNCTIONS:

1.  Digestive functions:

1a. Starch hydroxylation:

• By Salivary amylase/Tylin.
• Hydrolyses starch into disaccharide maltose & oligosaccharides mixture.
• Very short-lasting action.
• Gets inactivated by acidic gastric pH (<3).
• Salivary amylase active at pH 6.9 (6.5 – 7).
• Inactive at pH below 4.5.

1b. Lingual lipase:

• Secreted by Ebner’s glands, on dorsum of tongue.

2. Other functions:

• Partially liquefies solid food.
• Salivary mucus content lubricates food bolus assisting in deglutition.
• Helps maintain oral hygiene.
• Contains thiocyanate ions – Bactericidal.
• IgA antibodies – Confers protection.
• Serves as molecular solvent reaching taste receptors in taste buds.