digestive tract

• Digestive System


  System responsible for the ingestion, digestion, and absorption of food and elimination of waste

  
• Digestive Tract (Alimentary Canal)

  • Oral cavity (mouth)
  • Pharynx
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine
• Accessory Organs


  • Teeth
  • Tongue
  • Salivary glands
  • Liver
  • Gallbladder
  • Pancreas

  
• Functions of the Digestive Tract


  • Ingestion – food/liquid enter digestive tract
  • Mechanical processing – chewing, churning, mixing
  • Digestion – chemical, enzymatic breakdown of food
  • Secretion – by glandular accessory organs
  • Absorption – organic molecules, electrolytes, vitamins
  • Compaction – dehydration of indigestible materials, waste
  • Excretion – waste products secreted into digestive tract
  • Defecation – elimination of fecal material from body

  
• Layers of the Digestive Tract Wall


  • Mucosa
  • Submucosa
  • Muscularis externa
  • Serosa

  
• Mucosa


  • Mucosal epithelium
  • Lamina propria
  • Muscularis mucosa
• Circularis Plica


  Folds in the mucosa that function to increase surface area for absorption
• Villi


  Little bumps covered in epithelial cells that increase surface area for absorption
• Submucosa


  • Areolar tissue surrounding the muscularis mucosa
  • Contains blood vessels, lymphatics, exocrine glands, submucosal plexus
• Muscularis Externa


  • Circumferentially oriented smooth muscle fibers (inner layer)
  • Longitudinally oriented smooth muscle fibers (outer layer)
• Movement of Digestive Materials

  1. Muscularis layers contract in waves (peristalsis and segmentation) to propel and mix contents

  2. Pacesetter cells trigger muscle contraction patterns

  
• Peristalsis


  Wavelike contractions of the muscularis externa that propel a bolus along the digestive tract

  
• Segmentation


  Contractions of the circular layer of the muscularis externa that churn and mix the contents of the digestive tract

  
• Mesenteries


  • Lesser omentum
  • Greater omentum
  • Mesentery proper
  • Mesocolon
• Mesenteries


  • Double sheets of peritoneal membrane that suspend regions of the digestive tract
  • Provide access route for blood vessels, nerves, and lymph
  • Stabilize the relative positions of the organs

  
• Intraperitoneal organs


  Covered by visceral peritoneum and suspended by mesentery from the body wall

  
• Retroperitoneal organs


  Mesentery has fused with the posterior abdominal wall, organs lie posterior to the peritoneal cavity

  
• Oral Cavity


  • Analysis of ingested material
  • Mechanical processing/bolus formation
  • Lubrication
  • Digestion of carbohydrates
• Accessory Organs of the Oral Cavity


  • Tongue
  • Teeth
  • Salivary glands

  
• Salivary Glands


  • Parotid
  • Submandibular
  • Sublingual
• Saliva


  Composed of 99.4% water with ions, buffers, metabolites, and enzymes
• Pharynx


  Muscular structure with an epithelial lining that functions in both respiration and digestion

  
• Swallowing


  1. Buccal Phase – compression of bolus, elevation of soft palate, retraction of tongue

  2. Pharyngeal Phase – bolus contacts posterior pharyngeal wall, elevation of larynx, folding of epiglottis

  3. Esophageal Phase – opening of upper esophageal sphincter, peristalsis, opening of lower esophageal sphincter
• Esophagus


  Flat muscular tube that transports foods and liquids to the stomach

  
• Landmarks of the Stomach


  • Lesser curvature
  • Greater curvature
• Regions of the Stomach


  • Cardia
  • Fundus
  • Body
  • Pylorus (& sphincter)

  
• Functions of the Stomach


  • Bulk storage of ingested food
  • Mechanical breakdown of ingested food
  • Chemical digestion of ingested food via acids and enzymes
  • Beginning absorption of water, aspirin, alcohol

  
• Chyme


  Mixture of ingested substances and gastric juices
• Stomach Wall


  • Rugae – longitudinal folds in the mucosa
  • Extra inner oblique layer of smooth muscle in the muscularis externa
• Gastric Gland Secretions


  • Mucous cells: mucous
  • Parietal cells: HCl & gastric intrinsic factor
  • Chief cells: pepsinogen
  • Enteroendocrine cells (G cells): gastrin
• Acid Reflux Disease (GERD)


  Relief: 1. Neutralize acid (Tums, Rolaids) 2. Slow down parietal cell secretions (Zantac 75)
• Small Intestine


  20ft tube that functions in enzymatic digestion and absorption of water, nutrients, and electrolytes
• Chemical digestion of ingested food


  Disruption of chemical bonds by acids and enzymes
• Beginning Absorption


  1. Water

  2. Aspirin

  3. Alcohol
• Chyme


  The mixing of ingested substances with the gastric juices (secreted by gastric glands)
• Rugae


  • Longitudinal folds in the mucosa of the stomach wall that permit the expansion of the gastric lumen
• Muscularis externa of the stomach


  • Extra inner oblique layer of smooth muscle
• Gastric Gland Secretions


  • Mucous cells: mucous
  • Parietal cells: HCl & gastric intrinsic factor
  • Chief cells: pepsinogen
  • Enteroendocrine cells (G cells): gastrin = hormone
• Acid Reflux Disease


  Gastroesophageal reflex Disease – GERD
• Relief for Acid Reflux Disease


  • Neutralize acid (Tums, Rolaids)
  • Slow down the Parietal cell secretions (Zantac 75)