1 DIGESTION OF ORAL CAVITY AND STOMACH. 2 ORAL CAVITY PHYSIOLOGICAL EVENTS 1. Ingestion 2....

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DIGESTION OF DIGESTION OF ORAL CAVITY ORAL CAVITY

AND STOMACHAND STOMACH

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ORAL CAVITYORAL CAVITY

PHYSIOLOGICAL EVENTSPHYSIOLOGICAL EVENTS

1.1. IngestionIngestion

2. Mechanical digestion2. Mechanical digestion

3. Chemical digestion3. Chemical digestion

4. Propulsion voluntary stage of 4. Propulsion voluntary stage of swallowingswallowing

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1. 1. IngestionIngestion of food is of food is simply voluntarily taking simply voluntarily taking food into the digestive food into the digestive tract through the oral tract through the oral cavity.cavity.

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ORAL CAVITYORAL CAVITY2. 2. MECHANICAL PROCESSESMECHANICAL PROCESSES

MasticationMasticationAs food enters the oral cavity the As food enters the oral cavity the

cheeks and the closed lips hold cheeks and the closed lips hold food between the teeth, the food between the teeth, the tongue mixes the food with saliva tongue mixes the food with saliva to soften it, and the teeth cut and to soften it, and the teeth cut and grind it into a grind it into a bolusbolus. Suitable for . Suitable for swallowingswallowing

Mastication is both voluntary and Mastication is both voluntary and partly reflexive.partly reflexive.

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ORAL CAVITYORAL CAVITY3. 3. Chemical processesChemical processesChemical digestion of starch is begun by salivary amylase present Chemical digestion of starch is begun by salivary amylase present

in saliva. in saliva.

SalivaSaliva (1-1,5 liters per day) is a slightly acid solution of salts and organic (1-1,5 liters per day) is a slightly acid solution of salts and organic substances secreted mainly by 3 pairs of salivary glands (substances secreted mainly by 3 pairs of salivary glands (parotid, parotid, buccal, submandibular glands).buccal, submandibular glands).

Basic saliva components:Basic saliva components:• • Water 99.5%Water 99.5%• • Ions: NaIons: Na++, K, K++, Ca, Ca2+2+, , ClCl––, , HCOHCO33

–– • • Proline-rich proteins for protection of teeth enamel: Proline-rich proteins for protection of teeth enamel: - Enzymes: ptyalin (from salivary glands), - Enzymes: ptyalin (from salivary glands), **lingual lipase (secreted from glands on the tongue).**lingual lipase (secreted from glands on the tongue).

- Immunoglobolins: IgA- Immunoglobolins: IgA- Mucin: glycoproteins for lubrication of food and protection of oral mucosa- Mucin: glycoproteins for lubrication of food and protection of oral mucosa- Lysozyme, lactoferrin, thiocyanate ions- Lysozyme, lactoferrin, thiocyanate ions pH of saliva is about 7pH of saliva is about 7

Salivary flow ranges between 0.5 ml/min during basal flow and 5ml/min during Salivary flow ranges between 0.5 ml/min during basal flow and 5ml/min during maximum flowmaximum flow

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Other important (non-digestive) functions of saliva:Other important (non-digestive) functions of saliva: Cleansing Cleansing – Mouth and teeth kept free of debris, ect.– Mouth and teeth kept free of debris, ect. ProtectionProtection – Leucocytes, the enzyme lysozyme and – Leucocytes, the enzyme lysozyme and

antibodies act against some bacteria.antibodies act against some bacteria. Moistening and LubricatingMoistening and Lubricating – soft parts of mouth – soft parts of mouth

kept pliable for speech. Cells of oral mucosa kept pliable for speech. Cells of oral mucosa protected from drying. protected from drying.

ExcretoryExcretory – many organic substance (e.g. urea, – many organic substance (e.g. urea, sugar) and inorganic substance (e.g. mercury, lead) sugar) and inorganic substance (e.g. mercury, lead) can be excreted in saliva.can be excreted in saliva.

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4. 4. PROPULSIONPROPULSION

The voluntary phase of The voluntary phase of deglutition is initiated deglutition is initiated by the tongue. The tip by the tongue. The tip of the tongue is place of the tongue is place on the hard palate, and on the hard palate, and then contracts which then contracts which forces the forces the bolusbolus into into the oropharynx.the oropharynx.

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Cerebral cortex Other inputs

Salivary centerin medulla

Conditionedreflex

Pressure receptorsand chemoreceptorsin mouth

Autonomic nerves

Autonomic nerves

Salivary glands

Salivary secretions

Simple reflex

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PHARYNXPHARYNX

PHYSIOLOGICAL EVENTSPHYSIOLOGICAL EVENTS

11. . Chemical digestionChemical digestion

Carbohydrate digestion continues. This is due Carbohydrate digestion continues. This is due to fact that the pH of the pharynx is slightly to fact that the pH of the pharynx is slightly acid to neutral as is the oral cavity. acid to neutral as is the oral cavity.

No other marcomolecule begins chemical No other marcomolecule begins chemical digestion. digestion.

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PHARYNXPHARYNX

2. 2. PROPULSIONPROPULSION

The pharyngeal phase of deglutition The pharyngeal phase of deglutition is initiated by food in the is initiated by food in the oropharynx. The presence of food oropharynx. The presence of food causes the tongue to blocks off causes the tongue to blocks off the oral cavity, the soft palate to the oral cavity, the soft palate to rise and close off the rise and close off the nasopharynx. nasopharynx.

In addition, the larynx to rise so that In addition, the larynx to rise so that the epiglottis covers the opening the epiglottis covers the opening into the respiratory system, and into the respiratory system, and the upper esophageal sphincter to the upper esophageal sphincter to relax and open.relax and open.

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EsophagusEsophagus

Bolus (moistened ball of chewed up Bolus (moistened ball of chewed up food) is forced into the pharynx. food) is forced into the pharynx.

The epiglottis prevents food from The epiglottis prevents food from entering the trachea during entering the trachea during swallowing, and passes bolus into the swallowing, and passes bolus into the esophagus esophagus

The esophagus is a muscular tube The esophagus is a muscular tube that connect pharynx to the stomach. that connect pharynx to the stomach.

The series of rhythmic contractions & The series of rhythmic contractions & relaxations is called peristalsis. relaxations is called peristalsis. Peristalsis pushes the bolus through Peristalsis pushes the bolus through the esophagus into the stomach.the esophagus into the stomach.

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The Swallowing ProcessThe Swallowing Process

Is also called deglutitionCan be initiated voluntarily, Proceeds automaticallyIs divided in 3 phases:

buccal phase – Compression of bolus against hard palate, Retraction of tongue forces bolus into oropharynx:pharyngeal phase – Bolus contacts: arches and posterior pharyngeal wall esophageal phase - Contraction of pharyngeal muscles forces bolus through entrance to esophagus Primary Peristaltic Waves

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STOMACHSTOMACH 3 muscle layers: oblique, circular, longitudinal3 muscle layers: oblique, circular, longitudinal Regions:Regions:

Cardiac sphincterCardiac sphincter FundusFundus Antrum (pylorus)Antrum (pylorus) Pyloric sphincterPyloric sphincter

VascularVascular Inner surface thrown into folds – RugaeInner surface thrown into folds – Rugae Contains enzymes that work best at pH 1-2Contains enzymes that work best at pH 1-2

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Functions of stomachFunctions of stomach Mix foodMix food ReservoirReservoir Start digestion ofStart digestion of

- Protein- Protein

- Nucleic acids- Nucleic acids

- Fats- Fats Activates some enzymesActivates some enzymes Destroy some bacteriaDestroy some bacteria Makes intrinsic factor – BMakes intrinsic factor – B1212 absorption absorption AbsorbsAbsorbs

- Alcohol- Alcohol

- Water- Water

- Lipophilic acid- Lipophilic acid

- B- B1212

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Exocrine gastric glandsExocrine gastric glands

Golbet cellsGolbet cells mucus mucus;; Pariental cellsPariental cells hydrochloric acid (HCl);hydrochloric acid (HCl); Chief (or zymogenic) cellsChief (or zymogenic) cells pepsinogenpepsinogen,,

an inactive form of the protein-digestive enzime pepsin;an inactive form of the protein-digestive enzime pepsin; Enterochromaffin-like (ECL) cells Enterochromaffin-like (ECL) cells histamine and serotoninhistamine and serotonin

as paracrine regulalators of the GI tract;as paracrine regulalators of the GI tract; G cells gastrin into the blood;G cells gastrin into the blood; D cells hormone somatostatin.D cells hormone somatostatin.

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STOMACHSTOMACH

Mechanical digestionMechanical digestion The walls of the stomach have several muscle The walls of the stomach have several muscle

layers. These muscles work together to churn layers. These muscles work together to churn the food, breaking up food particles and mixing the food, breaking up food particles and mixing them with gastric fluid. This results in a mixture them with gastric fluid. This results in a mixture called chyme. Chyme moves from the stomach called chyme. Chyme moves from the stomach to the small intestine.to the small intestine.

Gastric glands release gastric juice, a mixture of Gastric glands release gastric juice, a mixture of mucus, digestive enzymes, and hydrochloric acid.mucus, digestive enzymes, and hydrochloric acid.

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STOMACHSTOMACH Gastric fluid carries out Gastric fluid carries out chemical chemical

digestiondigestion in the stomach in the stomach Hydrochloric acid ensures a low pH Hydrochloric acid ensures a low pH

in the stomach, dissolves minerals in the stomach, dissolves minerals and kills bacteriaand kills bacteria

An enzyme called pepsin begins the An enzyme called pepsin begins the break down of proteins into peptide break down of proteins into peptide chains (chains of amino acids). chains (chains of amino acids). Pepsin functions in a pH of about 2.Pepsin functions in a pH of about 2.

Mucus coats the stomach and Mucus coats the stomach and protects it from HCl & digestive protects it from HCl & digestive enzymesenzymes

• When the mucus coating breaks down When the mucus coating breaks down allowing digestive enzymes to eat allowing digestive enzymes to eat through part of the stomach lining, the through part of the stomach lining, the result is called an ulcer.result is called an ulcer.

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STOMACHSTOMACH

PROPULSIONPROPULSION

After a meal, peristalsis begins After a meal, peristalsis begins near the cardiac region and near the cardiac region and moves toward the pyloric moves toward the pyloric sphincter. The intensity of the sphincter. The intensity of the movements are due to the movements are due to the increase in the number of increase in the number of muscle layers of the stomach.muscle layers of the stomach.

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STOMACHSTOMACHThe pyloric region of theThe pyloric region of thestomach holds about 30 ml ofstomach holds about 30 ml ofchyme. It allows only liquidschyme. It allows only liquidsand small particles of chyme,and small particles of chyme,about 3 ml, to pass throughabout 3 ml, to pass throughthe valve for each peristalticthe valve for each peristalticwave. The contractions ofwave. The contractions ofthe pylorus decrease thethe pylorus decrease theopening of the valve. Thisopening of the valve. Thisresults in the remainingresults in the remainingchyme being remixed againchyme being remixed againand again.and again.

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STOMACHSTOMACH

The rate of peristaltic wavesThe rate of peristaltic wavesis constant 3/min., however,is constant 3/min., however,the intensity can be modified.the intensity can be modified.This contractile rhythm is setThis contractile rhythm is setby the spontaneous activity ofby the spontaneous activity ofpacemaker cells located in thepacemaker cells located in thelongitudinal smooth musclelongitudinal smooth musclelayer. This cells establisheslayer. This cells establishesthe basic electrical rhythm ofthe basic electrical rhythm ofthe stomach.the stomach.

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STOMACHSTOMACH

The stomach usually The stomach usually empties completelyempties completelywithin 4 hours after awithin 4 hours after ameal. The rate ofmeal. The rate ofgastric emplyinggastric emplyingdepends on thedepends on thecontents of thecontents of theduodenum as on whatduodenum as on whatis happening in theis happening in thestomach.stomach.

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Mechanism for secretion of Mechanism for secretion of hydrochloric acidhydrochloric acid

Extracellularfluid

Pariental cell Lumen of canaliculus

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Stomach neurological controlStomach neurological control

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1. CEPHALIC PHASE1. CEPHALIC PHASE

Slight, thought, taste, or Slight, thought, taste, or smell of food causes smell of food causes stimulation of the vagus. stimulation of the vagus. The vagus stimulates The vagus stimulates the production of gastric the production of gastric juice.juice.

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2. GASTRIC PHASE2. GASTRIC PHASE

Stomach distention Stomach distention will act locally or will act locally or evoke the evoke the vagovagal reflex.vagovagal reflex.

VAGOVAGALREFLEX

Vagovagalreflex

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3. INTESTINAL PHASE

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Stomach hormonal controlStomach hormonal control

MECHANICAL DIGESTIONMECHANICAL DIGESTION

1. Gastrin--stimulate gastric emptying1. Gastrin--stimulate gastric emptying

2. Serotonin--contraction ofsmooth muscle2. Serotonin--contraction ofsmooth muscle

3. Somatostatin--inhibits motility and emptying3. Somatostatin--inhibits motility and emptying

4. Secretin--inhibits gastric motility4. Secretin--inhibits gastric motility

5. Gastric Inhibitory Peptide--inhibits gastric 5. Gastric Inhibitory Peptide--inhibits gastric motilitymotility

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CHEMICAL DIGESTIONCHEMICAL DIGESTION

1. Gastrin--stimulates gastric secretions1. Gastrin--stimulates gastric secretions

2. Histamine--stimulates HCl formation2. Histamine--stimulates HCl formation3. Somatostatin—inhibits gastric secretions3. Somatostatin—inhibits gastric secretions4. Secretin--inhibits gastric secretions4. Secretin--inhibits gastric secretions5. Gastric inhibiory peptide--inhibits gastric 5. Gastric inhibiory peptide--inhibits gastric secretionssecretions6. Vasoactive intestinal peptide-inhibits HCl 6. Vasoactive intestinal peptide-inhibits HCl productionproduction

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PROPULSIONPROPULSION1. Gastrin--stimulates emptying1. Gastrin--stimulates emptying2. Somatostatin--inhibits gastric motility and 2. Somatostatin--inhibits gastric motility and emptyingemptying3. Secretin--inhibits gastric motility and 3. Secretin--inhibits gastric motility and emptyingemptying4. Gastric Inhibitory Peptide—inhibits gastric 4. Gastric Inhibitory Peptide—inhibits gastric motility motility and emptyingand emptying

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Mouthbreak up fooddigest starchkill germsmoisten food

Stomachbreak up fooddigest proteinkill germsstore food

1 DIGESTION OF ORAL CAVITY AND STOMACH. 2 ORAL CAVITY PHYSIOLOGICAL EVENTS 1. Ingestion 2....

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Transcript of 1 DIGESTION OF ORAL CAVITY AND STOMACH. 2 ORAL CAVITY PHYSIOLOGICAL EVENTS 1. Ingestion 2....