L4_Salivary secretions.pdf

Salivary Secretion  Saliva is secreted by three pairs of glands: (Parotid, submandibular and sublingual glands; and many small buccal glands).  Structure of the glands: Each salivary gland is formed of: A. Acini: secrete a primary secretion (1) Serous cells: secrete serous (watery) secretion con...

Salivary Secretion  Saliva is secreted by three pairs of glands: (Parotid, submandibular and sublingual glands; and many small buccal glands).  Structure of the glands: Each salivary gland is formed of: A. Acini: secrete a primary secretion (1) Serous cells: secrete serous (watery) secretion containing ptyalin (α amylase enzyme). (2) Mucous cells: secrete mucous (viscous) secretion containing mucin. B. Salivary ducts: open into oral cavity. N.B: 1. Parotid glands acini are serous. 25% of saliva. 2. Sublingual glands acini are mucous. 5% of saliva. 3. Submandibular glands acini are mixed. 70% of saliva. 4. Buccal glands secrete only mucous.  Salivary secretion: Volume 1500 ml / day PH Resting glands is about 7.0. Composition  Proteins (enzymes as ptyalin and mucin)  Electrolytes (K+, HCO 3-, Na+ and Cl- Tonicity Hypotonic (Aldosterone) Control Nervous Only (ANS)  Mechanism of salivary secretion: consists of 2 stages: A. First stage: involves acini, which secrete a primary secretion that contains ptyalin and/or mucin in a solution of ions similar to ECF. B. Secondary stage: in ducts, saliva is markedly modified by Aldosterone: 1. Sodium ions (Na+) are actively reabsorbed, and potassium ions (K+) are actively secreted. 2. Na+ reabsorption is higher than K+ secretion in the salivary ducts. 3. Chloride ions (Cl-) to be passively reabsorbed. 4. Na+ & Cl- concentrations are markedly reduced whereas K+ concentration becomes increased during passage through ducts. 5. Bicarbonate ions (HCO3-) are actively secreted into duct lumen. 6. Ducts are relatively impermeable to water. Therefore, saliva that reaches mouth is hypotonic.  Innervation of salivary glands: both parasympathetic cholinergic, and sympathetic adrenergic fibers: Parasympathetic Sympathetic Origin a) Sublingual and submaxillary glands: Origin: lateral horn cells & Origin: superior salivary nucleus of the first and second Relay (medulla). thoracic segments Nerve: chorda tympani (facial nerve) Relay: superior cervical Relay: submandibular ganglion. ganglion. Supply: both salivary glands. Postganglionic fibers b) Parotid gland: arising reach all the Origin: inferior salivary nucleus in salivary glands along wall medulla of their blood vessels. Nerve: glossapharangeal nerve Relay: otic ganglion. Supply: parotid gland Function 1. Profuse secretion of watery saliva. 1. Vasoconstriction 2. High in electrolytes with a relatively 2. Secretion of a small low content of organic material. amount of saliva rich 3. Marked vasodilatation by VIP. in organic constituents. 4. VIP is a cotransmitter with acetylcholine in some postganglionic parasympathetic neurons. 5. Atropine and other cholinergic blocking agents reduce salivary secretion.  Control of Salivary secretion: (neural control) Saliva secretion occur in response to conditioned or unconditioned stimuli: 1- Unconditioned reflexes: A. Food in mouth causes reflex secretion of saliva: Taste, tactile, and thermal stimuli from mouth will excite superior and inferior salivary nuclei, resulting in reflex increase in salivary secretion. B. Reflexes originating in stomach and upper intestine: swallowing of very irritating foods, or due to some GIT abnormality. Swallowed saliva helps to remove the irritating factor in the GIT by diluting or neutralizing it. 2- Conditioned reflexes: A. From cerebral cortex: Sight, smell, hearing, preparation of food and even thinking of food, results in reflex increase in secretion of saliva. B. Appetite area in hypothalamus receives signals from taste and smell areas of cerebral cortex or amygdala. It excites salivary nuclei to increase salivary secretion.  Functions of Saliva: A) Protection of oral mucosa: 1. Cooling hot foods. 2. Neutralizing acid: Buffers in saliva help maintain oral pH at about 7.0. Neutralize gastric acid, and relieve heartburn. 3. Maintaining healthy oral mucosa by: A. Washing away pathogenic bacteria, and any food remnants. B. Lysozyme attacks walls of bacteria. C. Antibodies (immune globulin lgA) destroy oral pathogenic bacteria. D. Lactoferrin is a bacteriostatic. B) Teeth protection: A. Buffers in saliva help to keep oral pH at about 7.0. At this pH, teeth do not lose calcium. Loss of ca+2 from teeth enamel leads to dental caries. B. Fluoride protects teeth enamel. N.B: In absence of salivation (xerostomia), dry oral-mucosa becomes ulcerated and infected, with a higher incidence of dental caries C) Digestion:  Saliva contains ptyalin that digests starch into a-limit dextrins, maltriose, and maltose. D) Lubrication and Wetting: 1. Swallowing: Saliva contains mucins (glycoproteins) that lubricates food, facilitating its swallowing. 2. Speech: Keeping mouth moist facilitates movements of lips and tongue during speech. 3. Taste: Saliva acts as (a solvent for molecules that stimulate taste receptors).