LEC 24: intestines

• Deep circular folds


  • Force chyme to spiral
  • Increase mixing for nutrient absorption
• Villi & microvilli


  • Finger-like projection
  • Increase surface area
• Intestinal crypts


  • Tubular glands
  • Produce mucus, hormones, antimicrobial compounds that can destroy invasive bacteria (paneth cells)
• Villus epithelium


  • Contains rapidly dividing cells
• Goblet cells


  • Secrete mucous
  • Protect intestinal lining
• Enterocytes


  • Absorb nutrients from chyme into bloodstream
  • Primary absorptive cells
• Paneth cells


  • Produce antimicrobial compounds
  • Maintain gut health
• Roles of cell types in the intestinal mucosa

  • Enterocytes - absorb nutrients from chyme into bloodstream
  • Goblet cells - secrete mucous, protect intestinal lining
  • Enteroendocrine cells - produce hormones involved in digestion & gut function
  • Paneth cells - produce antimicrobial compounds, maintain gut health
  • Stem cells - replace other cell types, regenerate intestinal epithelium
• Major functions of large intestine

  • Absorbs water from ingestible food residues
  • Forms and stores feces
  • Houses bacteria that ferment indigestible carbohydrates
  • Synthesizes B complex vitamines and vitamin K
  • Influences the behaviour of the immune system
  • Protects against ingested pathogens
• Diarrhoea


  Watery stool - large intestine does not have enough time to absorb remaining water in chyme
• Causes of diarrhoea


  Irritation of the colon by bacteria or jostling of digestive viscera
• Constipation


  • Difficulty passing stool
  • Hard and dry stool
  • Infrequent bowel movements
• Causes of constipation

  • Food remaining in the colon for extended periods of time
  • Excessive water reabsorption
• Components of bowel transit time

  • Stomach transit time - influenced by food volume, composition, gastric emptying rate
  • Small intestine transit time - affected by motility, presence of food particles, absorption rate
  • Colon transit time - determined by peristaltic contractions, water absorption, stool consistency
• Intestinal juice


  Secreted in response to acidic chyme
• Between meals, migrating motor complexes move remnants toward the large intestine in waves
• The large intestine (also known as the colon) absorbs water from indigestible food residues and eliminates the latter as faeces
• what transit time is influenced by food volume, composition, and emptying rate?

  stomach
• what transit time is affected by motility, presence of food particles, and absorption rate?

  small intestine
• what transit time is determined by peristaltic contractions, water reabsorption, and stool consistency?

  colon