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    Lec30 Lec30 Presentation Transcript

    • The GI tract is a muscular tube that begins at the mouth (oral cavity) and ends at the anus.
      Accessory organs
      Organs of the digestive system
    • Organs of the Alimentary Canal
      • Mouth
      • Pharynx
      • Esophagus
      • Stomach
      • Small intestine
      • Large intestine
      • Anus
    • Accessory organs includes:
      Digestive glands
      Organs of the digestive system
    • Upper GI Tract from Mouth to Stomach
      Receive food
      Mechanical action of teeth and tongue (Chewing) breaks the foods and mix it with saliva which contains salivary amylase.
      Enzyme that can catalyze the partial digestion of starch.
      • Initiation of swallowing by the tongue
    • Motility in the mouth is chewing
      Mechanical breakdown of food particles
      Mixing food with saliva
    • Pharynx
      Moves bolus of foods to esophagus (swallowing)
      Food is propelled to the esophagus by two muscle layers
      Longitudinal inner layer
      Circular outer layer
      Epiglottis covers the entrance to respiratory tract
      The epithelium lining the mouth and pharynx is stratified squamous (flattened) cells
      Upper GI Tract from Mouth to Stomach
    • Pharynx Anatomy
      • Nasopharynx – not part of the digestive system
      • Oropharynx – posterior to oral cavity
      • Laryngopharynx – below the oropharynx and connected to the esophagus
    • Upper GI Tract from Mouth to Stomach
      No digestive or absorption functions
      Connects pharynx to the stomach.
      Upper third contains skeletal muscle.
      Middle third contains a mixture of skeletal and smooth muscle.
      Terminal portion contains only smooth muscle.
    • Upper GI Tract from Mouth to Stomach
      Produced by a series of localized reflexes in response to distention of wall by bolus.
      Wave-like muscular contractions:
      Circular smooth muscle contract behind, relaxes in front of the bolus.
      Followed by longitudinal contraction (shortening) of smooth muscle.
      Insert 18.4a
    • Esophagus
      Motility in the esophagus is peristalsis
      Function: propel bolus of food to the stomach
    • Stomach
      Functions of the stomach:
      Stores and digests food.
      Its movement mixes gastric secretion with the food
      Initiates digestion of proteins.
      Moves food (chyme) into intestine.
      Empties into the duodenum
    • Stomach
      Compose of four regions:
      Cardia: The region surrounding the opening through which foods enters the stomach
      Fundus: The dome shape part of the stomach beneath the diaphragm
      Body: the mid portion of the stomach
      Pyloric region: Funnel shaped region, contains the antrum and the pylorus
      Pyloric antrum is the largest part of pyloric region
      Pylorus is the constricted terminal portion
    • Stomach
      The interior of the stomach consist of folds called Rugae
      Consist of longitudinal, circular and oblique muscle layer
      Pyloric sphincter thick muscle that controls the rate of gastric emptying
      Strong contractions in the pyloric region are important for mixing ingested food with gastric juice and emptying chyme into the small intestine
    • Stomach
      Contractions and movement of the stomach:
      Mix chyme with gastric secretions.
      Push food into intestine.
      Insert fig. 18.5
    • Lower GI Tract includes small and large intestine
      Most digestion and absorption occurs in the small intestine
      Juices in the small intestine neutralize the acidic chyme, restore normal osmolarity and continue digestion of macromolecule
      Breakdown products of macromolecules are absorbed across the intestinal epithelium into blood or lymph
    • The small intestine has three regions:
      The duodenum 8 – 11 inch long
      The jejunum and ileum 8 – 13 feet
      Lower GI Tract includes small and large intestine
    • Folds of the Small Intestine
      • The interior of the small intestine contains many circular folds called plicae circulares
      • Deep folds of the mucosa and submucosa
      • Do not disappear when filled with food
      • The submucosa has Peyer’s patches (collections of lymphatic tissue)
    • Villi of the Small Intestine
      • Fingerlike structures formed by the mucosa
      • Give the small intestine more surface area
    • Microvilli of the Small Intestine
      • Small projections of the plasma membrane
      • Found on absorptive cells
    • Structures Involved in Absorption of Nutrients
      • Absorptive cells
      • Blood capillaries
      • Lacteals (specialized lymphatic capillaries)
    • Large Intestine
      Small intestine delivers chyme to the large intestine
      Water and electrolyte absorbed from the chyme
    • Large Intestine
      The large intestine subdivision includes:
      Cecum: A blind end pouch at the beginning of the large intestine
      Appendix: A blind wormlike tube attached to the cecum
      Colon: Is the longest region of the large intestine includes, ascending, transverse, descending and sigmoid portions
      Rectum: The distal 5 cm of the digestive tract
      Anal canal: Last segment of the large intestine, consist of stratified squamous
    • Anus: Is the outlet of the GI tract
      The feces eliminated from the GI tract are primarily indigestible food combined with bacteria, inorganic material and sloughed off epithelial cells
      Large Intestine
    • Sphincters
      Separates the organs of the GI tract
      Controls the entrance of food into the tract
      Prevent reflux of material
      Control elimination of feces
      Such as:
      Upper esophageal sphincter
      Lower esophageal sphincter
      Pyloric sphincter
      Ileocecal sphincter
      Anal sphincter