Saliva Composition and Secretion

Salivary Glands

• There are two main types of salivary glands: mucous and serous.
• Mucous glands produce a viscous, mucin-rich product.
• Serous glands produce a watery secretion.

Saliva Flow Rate

• Average salivary flow rate is 0.3ml/min.
• 500-750ml of saliva is secreted each day, with 90% derived from major salivary glands.

Mechanism of Secretion

• There are two main regulated pathways: constitutive and main regulated.
• Constitutive pathway is always active, whereas main regulated pathway requires stimuli.
• Proteins are stored in granules in the constitutive pathway and vesicles in the main regulated pathway.

Parotid Gland

• The largest salivary gland, producing 25% of saliva, mainly serous in adults.
• In newborns, it produces mixed saliva, predominantly serous.
• Duct: Stenson's duct.
• Has a capsule with fat cells and lymph nodes on the surface and within the gland.

Types of Salivary Glands

• Compound: has more than one tubule entering the main duct.
• Tubuloacinar: describes the morphology of the secreting cells.
• Merocrine: only the secretion of the cell is released.
• Exocrine: secretes fluid onto a free surface.
• Major salivary glands: parotid, submandibular, and sublingual.
• Minor salivary glands: scattered throughout the oral mucosa, including labial, buccal, palatoglossal, palatal, and lingual glands.

Composition of Saliva

• Over 99% water.
• Small amounts of inorganic and organic compounds, including proteins, glycoproteins, and enzymes.

Functions of Saliva

• Lubricates during mastication, swallowing, and speech.
• Protects the mucosa and keeps it moist.
• Brings substances into solution for tasting.
• Limits bacterial activity by causing aggregation.
• Contains minerals and acts as a buffer to maintain dental enamel integrity.
• Produces peptide growth factors, such as epidermal growth factor and nerve growth factor.
• Contains immunoglobulins, mainly IgA, for mucosal immunity.
• Aids digestion with amylase.

Structure of Salivary Glands

• Consists of glandular secretory tissue (parenchyma) and supporting connective tissue (stroma).
• The stroma of the capsule surrounding the gland passes septa that subdivide the gland into major lobes.
• Lobes are further subdivided into lobules, each containing secretory units with clusters of grape-like structures (acini) around a lumen.
• Acini produce saliva, which empties into intercalated ducts, then striated ducts, and finally collecting ducts.
• Striated ducts affect the composition of the secretion passing through them.

Stroma of Capsules

• Septa carry blood supply and nerve into the parenchyma.
• Septa contain fibroblasts, collagen, fat cells, and plasma cells.