Overview Saliva saliva is produced by salivary glands and secreted into mouth functions of saliva initial digestion of starches and lipids by salivary enzymes dilution and buffering of ingested foods lubrication of ingested foods with mucus to aid movement through esophagus Salivary Secretion Salivary glands parotid glands composed of serous cells that secrete an aqueous fluid composed of water, ions, and enzymes submandibular glands composed of serous cells that secrete an aqueous fluid composed of water, ions, and enzymes composed of mucous cells that secrete mucin glycoproteins sublingual glands composed of serous cells that secrete an aqueous fluid composed of water, ions, and enzymes composed of mucous cells that secrete mucin glycoproteins Formation of saliva acinar cells produce initial saliva composed of water, ions, enzymes, and mucus initial saliva is isotonic and has approximately same osmolarity as plasma initial saliva passes from acinus to duct ductal cells modify initial saliva to produce final saliva by altering various electrolyte concentrations ductal cells absorb Na+ and Cl-, decreasing ion concentrations in saliva ductal cells secrete K+ and HCO3-, increasing ion concentrations in saliva salivary HCO3- neutralizes oral bacterial acids maintains dental health final saliva is hypotonic and has lower osmolarity than plasma Salivary enzymes acinar cells secrete enzymes that include alpha-amylase, lingual lipase, and kallikrein α-amylase (ptyalin) begins initial digestion of carbohydrates lingual lipase begins initial digestion of lipids kallikrein catalyzes proteolytic cleavage of kininogen into bradykinin bradykinin is a potent vasodilator ↑ salivary gland activity → ↑ kallikrein → ↑ bradykinin → ↑ salivary blood flow acinar cells secrete immunoglobulin A (IgA) Flow rate and salivary composition ionic composition of saliva changes as salivary flow rate changes at highest flow rates, final saliva most closely resembles (most isotonic) plasma and initial saliva produced by acinar cells ductal cells have less time to modify saliva at lowest flow rates, final saliva is most dissimilar (most hypotonic) to plasma and initial saliva produced by acinar cells ductal cells have more time to modify saliva Regulatory Mechanisms Regulation of salivary secretion salivary secretion is stimulated by both sympathetic and parasympathetic nervous systems sympathetic nervous system sympathetic input to salivary glands originates in thoracic segments T1-T3 with preganglionic nerves that synapse in superior cervical ganglion postganglionic sympathetic neurons release norepinephrine (NE) ↑ NE → stimulates β-adrenergic receptors → stimulates adenylyl cyclase → ↑ cAMP → ↑ saliva secretion parasympathetic nervous system parasympathetic input to salivary glands originates in facial nerve (CN VII) and glossopharyngeal nerve (CN IX) facial nerve (CN VII) runs through parotid gland and may be damaged during surgery postganglionic parasympathetic neurons release ACh ↑ ACh → stimulates muscarinic receptors → ↑ IP3 and Ca2+ → ↑ saliva secretion parasympathetic activity stimulated by food, smell, nausea, and conditioning parasympathetic activity inhibited by dehydration, fear, and sleep