Digestive 2

• Secretion and Regulation of HCl in the Stomach & Overview of Stomach Digestion


  1. Food enters mouth

  2. Peristalsis moves food over stomach every 15-25s

  3. Peristalsis moves food towards next region of stomach

  4. Retropulsion keeps moving food back to body of stomach to be further broken down

  5. Bolus becomes chyme

  6. Gastric emptying - movements of chyme from stomach into small intestine
• Mechanical Digestion: Stomach Peristalsis


  • Interactions Animation: Mechanical Digestion in the Gastrointestinal Tract
  • Stomach Peristalsis and Enterogastric Reflex: Animation sections 5.1 and 6.1
• Summary of Digestive Activities in the Stomach


  • Surface mucous cells and mucous neck cells secrete mucus to form protective barrier
  • Absorption of small quantity of water, ions, short-chain fatty acids, and some drugs
  • Parietal cells secrete intrinsic factor needed for absorption of vitamin B12 and hydrochloric acid to kill microbes, denature proteins, and convert pepsinogen into pepsin
  • Chief cells secrete pepsinogen and gastric lipase
  • G cells secrete gastrin to stimulate parietal and chief cells, contract lower esophageal sphincter, increase motility of stomach, and relax pyloric sphincter
  • Muscular layer has mixing waves to churn and physically break down food, mix with gastric juice, and force chyme through pyloric sphincter
  • Pyloric sphincter opens to permit passage of chyme into duodenum and regulates flow
• Bariatric Surgery


  Procedures to limit amount of food that can enter stomach to promote weight loss
• Bariatric Surgery Methods


  • Gastric banding
  • Sleeve gastrectomy
  • Gastric bypass
• Pancreas


  • Lies posterior to stomach
  • Produces enzymes that digest carbohydrates, proteins, fats, and nucleic acids
  • Produces sodium bicarbonate to buffer stomach acid
  • Empties contents into duodenum
  • Consists of head, neck, tail, and body
• Major Digestive Enzymes in Pancreatic Juice

  • Pancreatic amylase - breaks down carbs
  • Trypsin - breaks down proteins
  • Pancreatic lipase - breaks down fats
• Pancreatic Juice


  Secreted into small intestine to buffer gastric juices in chyme
• Liver


  Makes bile, important for emulsification of fats
• Gallbladder


  Stores bile until needed
• Gallstones


  • Form due to insufficient bile salts or excessive cholesterol that crystallizes
  • Range in size from grain of sand to golf ball
  • Treated with stone dissolving drugs, lithotripsy, or surgical removal
• Histology of the Liver


  • Hepatocytes secrete bile
  • Bile canaliculi collect bile and pass to bile ducts
  • Hepatic sinusoids are highly permeable blood capillaries that receive oxygenated blood
  • Together they form the portal triad
• Hepatic Acinus


  Functional unit of the liver via combination of hepatocytes, canaliculi, and sinusoids
• Blood Supply of the Liver: Hepatic Portal System
• Functions of the Liver and Gallbladder


  • Carbohydrate, lipid, and protein metabolism
  • Processing/detoxifying of drugs and hormones
  • Bilirubin excretion via feces
  • Bile salt synthesis to break down and absorb fats
  • Storage of vitamins and minerals
  • Phagocytosis of aged WBC's, RBC's, and bacteria
  • Vitamin D activation
• Small Intestine (SI)


  • Majority of digestion and absorption occur here
  • Averages about 16ft
  • Begins at pyloric sphincter and ends at large intestine
  • Broken down into duodenum, jejunum, and ileum
• Functions of the Small Intestine


  • Segmentations mix chyme with digestive juices and bring food into contact with mucosa for absorption; peristalsis propels chyme
  • Completes digestion of carbohydrates, proteins, lipids; begins and completes digestion of nucleic acids
  • Absorbs about 90% of nutrients and water that pass through digestive system
• Circular Folds in the SI

  • Increase surface area for digestion and absorption