GASTROINTESTINAL SYSTEM

• Functions of Digestive System are Ingestion, Digestion, Absorption, and Defecation
• Ingestion — taking in food
• Digestion — breaking food into nutrient molecules
• Absorption — movement of nutrients into the bloodstream
• Defecation — excretes to rid the body of indigestible waste
• TWO MAIN GROUP OF ORGANS

  • Alimentary canal
  • Accessory digestive organs
• Alimentary canal

  • gastrointestinal, or GI, tract
  • continuous, coiled, hollow tube
• These organs ingest, digest, absorb, defecate:

  • Mouth
  • Pharynx
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine
  • Anus
• Accessory digestive organs

  • Include teeth, tongue, and several large digestive organs
  • Assist digestion in various ways
• Mouth (oral cavity) — mucous membrane–lined cavity
• Lips (labia) — protect the anterior opening
• Cheeks — form the lateral walls
• Hard palate — forms the anterior roof
• Soft palate — forms the posterior roof
• Uvula — fleshy projection of the soft palate
• Vestibule — space between lips externally and teeth and gums internally
• Oral cavity proper — area contained by the teeth
• Tongue — attached at hyoid bone and styloid processes of the skull, and by the lingual frenulum to the floor of the mouth
• Palatine — located at posterior end of oral cavity
• Lingual — located at the base of the tongue
• Tonsils

  • Palatine
  • Lingual
• Functions of Mouth:

  • Mastication (chewing) of food
  • Tongue mixes masticated food with saliva
  • Tongue initiates swallowing
  • Taste buds on the tongue allow for taste
• Pharynx - Serves as a passageway for foods, fluids, and air
• Food passes from the mouth posteriorly into the Oropharynx and Laryngopharynx
• Oropharynx — posterior to oral cavity
• Laryngopharynx — below the oropharynx and continuous with the esophagus
• Food is propelled to the esophagus by two skeletal muscle layers in the pharynx:

  • Longitudinal outer layer
  • Circular inner layer
• Alternating contractions of the muscle layers (peristalsis) propel the food
• Esophagus (Anatomy) - About 10 inches long and runs from pharynx to stomach through the diaphragm
• Esphagus (Physiology) - Conducts food by peristalsis (slow rhythmic squeezing) to the stomach and passageway for food only (respiratory system branches off after the pharynx)
• Layers of Tissue in the Alimentary Canal Organs:

  • Mucosa
  • Submucosa
  • Muscularis Externa
  • Serosa
• Mucosa

  Innermost, moist membrane consisting of:

  - Surface epithelium that is mostly simple columnar epithelium (except for esophagus—stratified squamous epithelium) - Small amount of connective tissue (lamina propria) - Scanty smooth muscle layer - Lines the cavity (known as the lumen)
• Submucosa

  - Just beneath the mucosa - Soft connective tissue with blood vessels, nerve endings, mucosa-associated lymphoid tissue, and lymphatic vessels
• Muscularis Externa

  - Made up of smooth muscle - Inner circular layer - Outer longitudinal layer
• Serosa - outermost layer of the wall; contains fluid-producing cells
• Visceral peritoneum — innermost layer that is continuous with the outermost layer
• Parietal peritoneum — outermost layer that lines the abdominopelvic cavity by way of the mesentery
• Alimentary canal wall contains two intrinsic nerve plexuses that are part of the autonomic nervous system

  • Submucosal nerve plexus
  • Myenteric nerve plexus
• Alimentary Canal Nerve Plexuses - Regulate mobility and secretory activity of the GI tract organs
• Anatomy of the Stomach

  • C-shaped organ located on the left side of the abdominal cavity
  • Food enters at the cardioesophageal sphincter from the esophagus
  • Food empties into the small intestine at the pyloric sphincter (valve)