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.

Learn about the composition of saliva, including the ratio of protein to carbohydrate, and the rate of saliva secretion throughout the day.