Presentation on theme: "Mastication (Chewing) Salivary Secretion"— Presentation transcript:
1 Mastication (Chewing) Salivary Secretion To grind & break food into small parts.FunctionFacilitate swallowingMix food with salivaStimulate tastebuds that affect secretion of saliva, stomach & pancreasMechanism:Can be done voluntary.Most chewing is reflex in response to the present of food in mouth.Salivary Secretion3 pairs of glands2 parotids20%Serous sec.Rich in enzymes2 submandibular70%Mixed secretion(mucous + enzymes)2 sublingual5%MucousBuccal glands5%MucousNerve supply:Symp. 1st & 2nd thoracic seg. relay in cervical gangliaParasymp. 7th & 9th cranial cranial nerve facial glosso-phary.
2 K+ & HCO3- more than plasm. Mucous to lubricate food Composition of Saliva:Volume lit/daypH i.e. acidicTonicity Hypotonic than plasma99.5% Water0.5% SolidsOrganicInorganicNa & cl less than plasm.K+ & HCO3- more than plasm.Mucous to lubricate foodEnzymesPtylin (S.amylase)Lingual lipaseLysozymes (antibacterial)
3 Functions of Saliva:Swallowing moisten food particles lubrication by mucous.Speech help movement of tongue & lips.Solvent for substance to stimulate taste bicarbonate.Antibacterial due to presence of lysozymes.Buffer action due to presence of bicarbonate to prevent dental caries.Excretion of drugs as Hg & I2.Regulation of osmolality by sensation of thirst.Digestion Saliva is not essential for digestion Starch amylase maltose
4 Na+ K+ actively actively Na+ in Saliva K+ in Saliva Xerostomia: or arrested salivary secretionDry mouth.Bad odor.Dysphagia (difficult swallowing).Dental caries.Difficulty in speech.Mechanism of Salivary Secretion: Primary sec. = (Acini stage) contains enzymes mucous electrolytes very near to ECF Secondary sec.= (Duct stage)Na K actively activelyreabsorbed secreted Na+ in Saliva K+ in SalivaNa reab. > K+ secretion -ve 70 mv. inside duct.HCO3- are secreted by duct into lumen.HCO3- is exchanged with cl-.Duct is impermeable to H2O hypotonic.
5 Saliva Characters of Saliva under Resting condition: HypotonicRich in K+ & HCO3-Poor in Na+ & cl-Characters of Saliva under Activity:Salivary flow is rapid time for electrolyte exchangeSalivaHypotonic(closer to isotonic)Less K+ & HCO3- that of plasmaHigh Na+ & cl- but still less than plasmaAldosterone hormone: Na+ & cl- K+ secretion reab.N.B.: If rate of salivary flow is rapid K+ loss. K+ in plasma. Hypokalemia. Muscle weakness & paralysis.
6 Control of Salivary Secretion: Under nervous control Only why there is No hormonal controlThe hormonal control needsTime, while food in mouthStay for very short timeBasal Secretion of Saliva:Continuous & spontaneous.Occurs even in absence of stimuli.Is due to parasymp. ToneControl of secretionUnconditioned reflex (simple)Conditioned reflex (acquired)
7 Unconditioned reflex: Food in mouth stimulateChemoreceptorsPressure receptorsAfferent 7, 9, 10 cranial nerves.Centre M.O.Efferent 7 & 9 cranial nerves.Response salivary secretion.N.B.: During dental procedures, salivary secretion is due to stimulation of pressure receptors.
8 Conditioned Reflex (Acquired): Before food enters mouth.Sight, smell, odor, hearing thinking.Centre: Cerebral cortex+++ superior & inferiorSalivary nucleiAfferent: 7th & 9th cranial nervesResponse: Salivary secretionThis reflex needs previous experience.Removal of cortex Loss of Cond. Re.
9 Role of Autonomic Nerves: Cause dry mouth during stressRich in mucousRich in enzymesSmall volumeHigh volume ( water)ConcentratedTrue secretionVisicidDominant roleSymp.Parasymp.N.B.: VIP is cotransmitter with ac. ch.VIP V.D not blocked by atropine
10 is divided into The smooth muscles of G.I.T. are arranged in bundles. AutonomousRegulationThe smooth muscles of G.I.T. are arranged in bundles.They are electrically connected with one another through gap junctions that allow low-resistance movement of ions from one cell to the next.So, each muscle layer functions as functional a syncytium.The pace maker cells of G.I.T smooth muscle are present in the circular muscle layer.These cells are called:Interstitial cells of CajalThese Cajal cells are self excitable like SA-nodeElectrical activity of G.I.Tis divided intoBasic electric rhythm= Slow wave potential= Resting membrane potential
11 It is the passage of food from mouth to stomach. Deglutition(Swallowing)It is the passage of food from mouth to stomach.Started: Voluntary (Buccal phase)Completed: Involuntary (Pharyngeal & oesoph.)Controlled by: Deglutition Centre in M.O.Involves 3 phasesBuccal (oral) 1 sec.Pharyngeal phase 2 sec.Oesophageal phase 8-10 sec.
12 Buccal phase (Oral phase): Voluntary lasts for 1 sec.Passage of food from mouth to phary. by contraction of myelohyoid muscle.The bolus is on the dorsum of tongueThe tip of tongue is in contact to hard palate.Tongue moves upward & backwardsTo push bolus into pharynx.We can stop deglutition in this buccal phase (bec. it voluntary).Hard palateBolusTongue
13 Pharyngeal phase: Involuntary lasts 2 sec. Passage of food from pharynx to oesoph.When bolus is at oropharyngeal junctionIt stimulates: Pressure receptorsAfferent : 5 & 9 cranial nerves.Centre : Deglutition centre in M.O.Efferent : 5, 9, 10 & 12 cranial n.
14 Events: Palatopharyngeal folds: Soft palate (uvula): Respiration: Approximate to prevent passage of large bolus into pharynx.Soft palate (uvula):Moves upwards to close posterior nasal cavity to prevent food entrance into nasal cavity.Respiration:Is inhibitedi.e. reflex apnea for 2 sec.Vocal cords:Approximated.Larynx:Moves upwards & anterior to be covered by epiglottis.Anterior movement will open upper oesoph. sphincter.Pharyngeal muscles:Fast pharyngeal peristalsis to intrapharyngeal pressure to move bolus into oesophagus.It is Primary Peristalsis.Upper oesophageal sphincter:Is relaxed by the anterior movement of larynx.
15 Secondary Peristalsis Oesophageal phase:Involuntary.Passage of food from oesophagus into stomach.2 types of peristalsis.Primary PeristalsisSecondary PeristalsisContinuation of peristaltic wave initiated in pharynx.Takes 8-10 sec.Occurs with each swallowingControlled by swallowing centre in M.O.If food is remained in oesoph. wall.Food attached to oesph. wall will stimulate.Pressure receptorsLocal reflex from oesophageal myenteric plexusVery strong Powerful peristalsis to push food till reached to stomach.Sec. peristalsis occurs when primary fails to move food into stomach.
16 To protect wall of esoph. from Hcl of stomach Lower esophageal sphincter LES:Formed of circular muscle.It is Tonically contracted to prevent reflux of Hcl from stomach into oesoph.When peristalsis reaches lower end of esophagus, LES is relaxed to allow bolus to pass into stomach.Esophageal secretion:OnlyTo lubricate foodmucousTo protect wall of esoph. from Hcl of stomachNo enzymes.
17 Motor disorders of esophagus: (1) Achalasia(2) LES incompetenceFailure of relaxation of LES.Due to:Damage of myenteric plexus.Accumulation of food in esophagus.Distension of esoph.Treatment:Antispasmotics to relax sphincterSurgical myotomy to dilate sphincter.If LES is incompetent Hcl reflux from stomach to esoph.Heart burn.(3) Dysphagia:i.e. difficulty in swallowingEx.Myasthenia gravisParalysis of 5, 9, 10 cranial nerves.