DIGESTIVE SYSTEM
INCLUDES THE DIGESTIVE TRACT ( ALIMENTARY CANAL )
AND
THE ASSOCIATED ACCESORY ORGANS ( SALIVARY GLANDS, LIVER, GALLBLADDER, PANCREAS )
THE FUNCTIONS OF THE DIGESTIVE SYSTEM INCLUDE INGESTION, MECHANICAL PROCESSING, SECRETION, DIGESTION, ABSORPTION, COMPACTION, AND DEFECATION.
FOUR MAJOR TISSUE LAYERS COMPOSE THE DIGETIVE TRACT
MUCOSA
• THREE DISTINCT LAYERS CAN BE IDENTIFIED:
SUBMUCOSA
• LOOSE CONNECTIVE TISSUE LAYER CONTAINING LARGE BLOOD VESSELS, LYMPHATICS, AND NERVES.
• THE SUBMUCOSA PLEXUS ( between submucosa and muscularis externa ) CONTROL THE TONE OF THE MUSCULARIS MUCOSAE
MUSCULARIS EXTERNA
• ARE SEVERAL LAYERS OF SMOOTH MUSCLE TISSUE.
• THE INNER LAYER IS CIRCULAR, THE OUTER LAYER IS LONGITUDINAL.
• THE MUSCULARIS EXTERNA PRODUCES WAVES OF CONTRACTION CALLED PERISTALSIS.
SEROSA OR ADVENTITIA
LOOSE CONNECTIVE TISSUE COVERING THAT ATTACHES AND HOLDS THE TRACT IN POSITION
THE ORAL CAVITY
• FUNCTIONS OF THE ORAL CAVITY INCLUDE THE ANALYSIS OF POTENTIAL FOODS, MECHANICAL PROCESSING, LUBRICATION, AND INITIATING DIGESTION BY SALIVARY ENZYMES.
• ACCESORY STRUCTURES INCLUDE THE SALIVARY GLANDS AND THE TEETH.
• THE LINING OF THE ORAL CAVITY CONSISTS OF A STRATIFIED SQUAMOUS EPITHELIUM.
THE TONGUE
• ASSISTS IN MECHANICAL PROCESSING BY MANIPULATING MATERIALS IN THE MOUTH.
• A V-SHAPED LINE OF CIRCUMVALLATE PAPILLAE MARKS THE BOUNDARY BETWEEN THE BODY AND THE ROOT OF THE TONGUE.
THREE MAJOR PAIRS OF SALIVARY GLANDS PRODUCE THE MAJORITY OF THE SALIVA (1-1.5 lts/day ), ENZYMES AND MUCUS OF THE ORAL CAVITY
THE PAROTID
• LARGEST SALIVARY GLAND
• LOCATED IN FRONT OF THE EAR, BETWEEN THE SKIN AND MASSETER MUSCLE.
• SECRETION IS A CLEAR WATERY FLUID, IT CONTAINS THE DIGESTIVE ENZYME SALIVARY AMYLASE
THE SUBMANDIBULAR GLAND
• LOCATED UNDER THE MANDIBLE
• SECRETIONS ARE THICKER BECAUSE OF THE PRESENCE OF MUCIN ( help to keep food in a “bolus” for swallowing )
• THE DUCT OPENS NEAR THE LINGUAL FRENULUM.
THE SUBLINGUAL GLAND
• LOCATED UNDER THE TONGUE
• SALIVA IS SECRETED INTO NUMEROUS LESSER SUBLINGUAL DUCTS ALONG THE BASE THE TONGUE.
• IT IS PRIMARILY A MUCOUS GLAND
THERE ARE FOUR PRINCIPAL GROUPS OF SMALLER SALIVARY GLANDS IN THE MOUTH:
THE TEETH
• PERMIT MASTICATION OF MATERIALS IN THE MOUTH.
• HUMANS HAVE TWO SETS OF TEETH DURING THEIR LIFETIME, THE FIRST BEING THE DECIDUOUS WHICH ARE REPLACED BY THE PERMANENT DENTITION.
• DENTIN FORMS THE BASIC STRUCTURE OF A TOOTH.
• THE CROWN IS COATED WITH ENAMEL, AND THE ROOT WITH CEMENT.
• THE PERIODONTAL LIGAMENT ANCHORS THE TOOTH IN AN ALVEOLAR SOCKET.
• THERE ARE 20 “MILK” TEETH ( FIVE IN EACH CUADRANT )
• THE PERMANENT DENTITION CONSISTS OF 32 TEETH
THE PHARYNX
• IS A COMMON PASAGEWAY FOR NUTRIENTS AND AIR.
• IS DIVIDED IN : NASOPHARYNX, OROPHARYNX, AND LARYNGOPHARYNX.
• PROPULSION OF THE BOLUS RESULTS FROM THE CONTRACTIONS OF THE PHARYNGEAL CONSTRICTORS AND THE PALATAL MUSCLES.
THE ESOPHAGUS
• CONNECTS PHARYNX WITH STOMACH
• IT IS INFERIOR TO PHARYNX AND POSTERIOR TO THE TRACHEA.
• IT IS APROXIMATELY 25 CMS LONG.
• ESOPHAGEAL GLANDS PROVIDE ADDITIONAL LUBRICATION.
• IT PIERCES THE DIAPHRAGM AT THE ESOPHAGEA HIATUS TO CONNECT WITH THE STOMACH AT ABDOMINAL CAVITY.
• AT THE STOMACH THE ESOPHAGUS TERMINATES IN A LOWER ESOPHAGEAL SPHINCTER
THE STOMACH
SERVES AS A BULK STORAGE AREA, AND BREAKS DOWN INGESTED FOODS WITH A COMBINATION OF MECHANICAL STRESS, ACID SECRETION, AND ENZYMATIC DGESTION
IMPORTANT LANDMARKS
• LESSER AND GREATER CURVATURES
• THE CARDIA
• THE FUNDUS
• THE BODY
• THE PYLORUS
• THE PYLORIC SPHINCTER
• IS HIGHLY DISTENSIBLE, AND IN THE RELAXED STATE THE LINING IS THROWN INTO FOLDS CALLED RUGAE
• A PAIR OF MESENTERIES SUPPORT THE STOMACH: THE GREATER OMENTUM AND THE LESSER OMENTUM
THE MUSCULARIS EXTERNA OF THE STOMACH CONTAIN THREE LAYERS OF SMOOTH MUSCLE INSTEAD OF TWO. ( ONE OBLIQUE LAYER, ONE CIRCULAR, AND ONE LONGITUDINAL LAYER )
THEY CONTRACT AND CHURN STOMACH CONTENS
• PARIETAL CELLS SECRETE INTRINSIC FACTOR AND HYDROCHLORIC ACID.
• CHIEF CELLS SECRETE PEPSINOGEN
• ENTEROENDOCRINE CELLS SECRETE SEVERAL COMPOUNDS, NOTABLY THE HORMONE GASTRIN
THE SMALL INTESTINE
• INCLUDES THE DUODENUM, THE JEJUNUM, AND THE ILEUM.
• IS APROXIMATELY 21 FT. LONG.
• THE INTESTINAL LINING IN THESE AREAS BEARS PERMANENT TRANSVERSE FOLDS, CALLED PLICAE, THAT INCREASE THE SURFACE AREA FOR ABSORPTION.
SMALL INTESTINE IS THE SITE OF MOST DIGESTIVE AND ABSORPTIVE ACTIVITIES
THE SMALL INTESTINE JOIN THE LARGE INTESTINE AT THE ILEOCECAL VALVE, THAT EMPTIES INTO THE CECUM OF THE LARGE INTESTINE.
THE LARGE INTESTINE
THE LARGE INTESTINE REABSORBS WATER, AND SOME VITAMINS AND NUTRIENTS, COMPACTS THE FECES, AND STORES FECAL MATERIALES.
• IS DIVIDED INTO THE COLON AND THE RECTUM.
• IT IS APROXIMATELY 5 FT LONG
• IS ALSO DISTINGUISHED BY BEARING PROMINENT HAUSTRA AND MUSCULAR TAENIA COLI
IMPORTANT LANDMARKS
• CECUM
• APPENDIX
• ASCENDING, TRANSVERSE, AND DESCENDING COLON
• SIGMOID COLON
• RECTUM AND ANUS
THE LIVER
• LOCATED MOSTLY IN THE RIGHT HYPOCHONDRATIC REGION, INFERIOR TO THE DIAPHRAGM.
• PERFORMS METABOLIC AND HEMATOLOGICAL REGULATION. IT ALSO SYNTHESIZES AND EXCRETES BILE
THE LIVER HAS FOUR MAJOR LOBES
EACH LOBE IS DIVIDED INTO THOUSANDS OF SMALLER LOBULES LIVER CELLS ( HEPATOCYTES ) MANUFACTURE AND SECRETE BILE INTO SMALL DUCTS (bile canaliculi) WHICH THE EMPTY INTO bile ductules, AND TO HEPATIC DUCTS, AND FINALLY INTO THE SINGLE
HEPATIC DUCT
THE GALLBLADDER
• LOCATED INFERIOR TO THE RIGHT LOBE OF THE LIVER.
• IT IS A SMALL, MUSCULAR SAC THAT STORES AND CONCENTRATE BILE SALTS.
THE PANCREAS
• LIES BETWEEN STOMACH AND DUODENUM.
• HAS A HEAD, BODY AND TAIL.
• A SINGLE PANCREATIC DUCT ENTERS THE DUODENAL WALL.
• EXOCRINE PANCREAS PRODUCES LIPASES, CARBOHYDRASES, AND PROTEOLYTIC ENZYMES.
• THE PANCREATIC DUCT BEGIN AT THE PACREATIC ACINI. THE ENDOCRINE PANCREATIC ISLETS ARE SCATTERED BETWEEN THE ACINI