Saliva
Composition
- Water (99.5%)
- Electrolytes: Sodium (Na⁺), Potassium (K⁺), Calcium (Ca²⁺), Magnesium (Mg²⁺), Chloride (Cl⁻), Bicarbonate (HCO₃⁻)
- Mucus
- White Blood Cells
- Glycoproteins
- Enzymes: Amylase (digests starch), Lipase (digests fats)
- Antimicrobials: Immunoglobulin A (IgA), Lysozyme
Functions
- Digestion: Lubricates and dissolves food for chewing and swallowing.
- Protection: Irrigates mouth, flushes debris, prevents microbial infections.
- Enzymatic Action: Initiates digestion of carbohydrates and lipids.
- Speech & Taste: Aids in articulation and dissolves substances for taste reception.
- Wound Healing: Growth factors in saliva aid mucosal repair.
Neural Regulation
Saliva secretion is entirely under autonomic (neural) control, not hormonal.
Parasympathetic Stimulation (Dominant)
- Origin: Facial nerve (CN VII) & Glossopharyngeal nerve (CN IX)
- Neurotransmitter: Acetylcholine (ACh)
- Receptor: Muscarinic receptors on acinar cells
- Second Messenger: IP₃ → ↑ Intracellular Ca²⁺
- Effect: Profuse, watery saliva with low mucus content
- Stimulators: Food, smell, nausea, chewing
Sympathetic Stimulation
- Origin: T1–T3 spinal segments
- Neurotransmitter: Norepinephrine
- Receptor: β-adrenergic receptors
- Second Messenger: cAMP (via adenylyl cyclase)
- Effect: Low volume, viscous saliva with high mucus
- Inhibitors: Sleep, fear, dehydration