Salivary Secretions

Introduction  The glandular secretion of fluids and compounds that have important functions in GIT are : * Salivary glands secretion. * Gastric glands secretion. * Exocrine pancreas secretion. * Liver secretion.

.  These digestive secretions are released from glands by the action of specific effector ( regulatory) substances on the secretory glands.  These substances are called secretagogues.  These secretagogues may be classified as: * neurocrine * endocrine * paracrine

Objectives  Types, amount and composition.  Digestive functions.  Regulation of secretory processes (events or mechanism and regulation) for:  salivary secretions.

Salivary Glands 3 pairs of extrinsic salivary glands Parotid glands Submandibular glands Sublingual glands

Salivary secretion *Introduction:  Saliva is a mixture of all salivary glands secretion.  Salivary glands produce about 1 liter of saliva / day ( ml/day).  Main function of saliva :-  lubricates food to make swallowing easier + facilitates speaking.

Salivary glands Sublingual gland Submandibular and buccal glands Parotid glands 5% viscous viscous saliva that contains mainly mucin. facial nerve 75% mixed moderately viscous saliva that contains mucin + enzymes+ ions. facial nerve 20% serous watery secretion that lacks mucin but contains enzymes and ions. glossopharyngeal nerve

Types of salivary secretion  1-Parotid glands ( largest s. glands)  secretions are serous [= produce watery secretion that lacks mucin but contains enzymes and ions]. * amount = 20% of total secretion /day.  2-Sublingual gland  secretions are viscous [= produce a more viscous saliva that contains mainly mucin]. * amount = 5% of total secretion /day. 3- Submandibular and buccal glands secretions are mixed [= produce a moderately viscous saliva that contains mucins] + enzymes+ ions). * amount = 70 % for subm. and 5% for buccal.

Physical characteristics of saliva  Amount= ml/day.  Colorless.  Moderately viscous.  Hypotonic to plasma ( le ss N a+, Cl- ) = 70% of that of plasma.  The pH of saliva from resting gland i s s lightly acidic (average= 6.7), but it become s basic during activity of gland s ( average = 8) due to increasing in bicarbonate concentration with increasing flow rate.

Chemical composition s of saliva 1-Water = 97% % 2- S olids : * organic ( protein, carbohydrate, lipid) * inorganic ( electrolyte s ).

. Organic composition : * mucin * digestive enzyme s =ptyalin, lingual lipase. * ly s ozyme, lactoferrin and IgA. * proline rich protein.

.  Inorganic  1-Buffers(e.g.H 2 CO 3 :NaHCO 3, …..)  2- Soluble Calcium salts: Ca(HCO 3 ) 2, Ca(H 2 PO 4 ) 2, which saturate saliva to prevent decalcification of teeth.  3- Some electrolyte s As Na+,CL-, HCO3&-K+.

Mechanism of saliva secretion Acinar cells Ducts Secretory portion Produce Primary secretion By active process Like plasma ( isotonic ) Modify primary secretion by Reabsorption secretion Na+ actively K+ actively Cl- passively Hco3- actively Note:* This modification is controlled by aldosterone H.

Functions of saliva  1-Facilitation of swallowing and speech.  2-Cleaning(hygien) :of the mouth and teeth by washing and antibacterial effect of lysozymes &IgA.  3-Buffer function: by bicarbonate &phosphate.  4-Digestion: By salivary amylase to start digestion of cooked starch &by salivary lipase initiate lipid digestion.  5-Excretory function: for waste product, lead, mercury, iodide, fluoride, some drugs &alcohol.  6-Facilitate taste sensation.  7-Regulation of water balance (decrease in dehydration and give thirst sensation). Others …….

Functions of saliva *Mechanical function( by water +mucin ): * Moister, hydration, lubrication, solvent, washing To help :mastication digestion swallowing, to prevent dysphagia wash : mouth and teeth to prevent decay. help: taste sensation * Chemical function (digestion): *By salivary amylase to start digestion of cooked starch *by salivary lipase initiate lipid digestion * buffer function: * by electrolyte for neutralization * Excretory function: for waste product, heavy metal, drug,

functions * protective function: Keep oral hygiene against infection by: - it s w ater content for w ashing. - IgA, lyozyme, defensin, lactoferrin, nitric oxide, HCO3-, proline rich protein. * Temp. regulation by w ater evaporation. * W ater balance by stimulate thirst center

Regulation of salivary secretion *The primary physiological control of s. glands is by the parasympathetic N.S. * Excitation of either parasympathetic or sympathetic nerves to s. glands stimulates salivary secretion, but the effects of parasympathetic are stronger and more long lasting. If parasympathetic supply is interrupted, salivation severely impaired and the glands atrophy. But the sympathetic interruption does not disrupt salivary gland function.

. Preganglionic fibers come via branches of facial and glossopharyngeal nerves that form synapse with postganglionic neurons in ganglia in or near s. glands. Origin of sympathetic from superior cervical ganglion.

Parasympathetic effects *Parasympathetic effects:- -Profuse secretion of watery saliva with a relatively low content of organic material -Vasodilation due to VIP that act as cotransmitter for acetylcholine. + increases blood flow - stimulates glandular metabolism and growth.

Sympathetic effects *Sympathetic effects:- -The increase in saliva secretion by it is transient (secretion of small amount of saliva rich in organic material). -Stimulate contraction of myoepithelial cells that surround acini to empty its contents into ducts.

. *Salivation is controlled mainly by neural ( conditioned& unconditioned reflexes ) *Salivary center is salivatory nuclei ( superior and inferior ) that lies at junction between pons and medulla. *This center receives many signals ( conditioned & unconditioned ) to control autonomic activities to glands.

. *Factors (or signals) increase secretion: Acid food, smooth objects., liked food, irritating food, overhydration. *Factors (or signals) decrease secretion Rough objects, disliked food, dehydration, anticholinergic drugs ( atropine)

Unconditioned reflex  Inborn reflex (not need previous learning).  a-Stimuli: direct contact of the food, chewing &Irritation of G.I.T.  b-Receptors: taste receptors& receptors of G.I.T. wall.  c-Afferent:  Chorda tympani (from ant.2/3 of tongue).  Glossopharyngeal nerve (from post.1/3of tongue).  Lingual nerve (movement of tongue).  Vagus nerve (from epiglottis).  d-Center: superior and inferior salivatory nuclei.  e-Efferent: Chorda tympani &Glossopharyngeal nerve.  f- Response: increase salivary glands secretion.

Conditioned reflex  Acquired reflex & need previous learning.  a-Stimuli: seeing, smelling, hearing about of food or even thinking of food.  b-Receptors: special sense receptors.  c-Afferent:  Optic olfactory& auditory nerves.  d-Center: cerebral cortex then to salivatory nuclei.  e-Efferent: Chorda tympani &Glossopharyngeal nerve.  F-Response: increase salivary glands secretion.

 Mechanical digestion Chewing (mastication) Food mixed with saliva Shaped into a bolus  Chemical digestion  salivary amylase breaks down and converts polysaccharides (starches) to disaccharides (maltose) and monosaccharides (glucose)  [no enzymatic action with cellulose which is also a polymer of glucose] Physiology of Digestion in Mouth