Digestive Processes of the Intestines

Small Intestines

• No Ingestion or Defecation
  • Propulsion through peristalsis (wave-like contraction to push food)
• Mechanical Digestion
  • Segmental contractions help evenly distribute nutrients and enzymes
  • Food is referred to as chyme (smoothie-like consistency)
• Chemical Digestion
  • Pancreatic secretions break down polypeptides, carbohydrates, fats
  • Enzymes involved to be discussed
• Absorption
  • Absorbs amino acids, monosaccharides, fatty acids, water, vitamins, minerals, ions
  • Focus on simple units and smaller molecules

Secretions in the Small Intestines

• Liver and Gallbladder
  • Secrete bile (90% water, 2% bile salts)
  • Bile salts emulsify fats (amphipathic: hydrophilic and hydrophobic parts)
  • Emulsification increases surface area for enzyme action
• Pancreatic Secretions
  • Bicarbonate ions neutralize acidic chyme (raise pH)
  • Enzymes: proteases, amylases, lipases, nucleases
  • Enzymes secreted as inactive zymogens
  • Activation via trypsinogen and enteropeptidase on intestinal mucosa

Defense Mechanisms

• Peyer’s Patches
  • Lymph nodules in mucosa
  • Fight against pathogens with lymphocytes

Large Intestines

• Digestive Actions
  • Propulsion and mechanical digestion via peristalsis and segmental contractions
  • Chemical digestion by gut flora (e.g., fiber digestion)
• Absorption
  • Absorbs water, ions, minerals, and byproducts of gut flora
  • Relationship with gut flora for nutrient absorption
• Defecation Process
  • Happens in the rectum, involves a reflex loop

Defecation Reflex

1. Feces distend the rectum
   • Stretch receptors activated
   • Sensory neurons send signals to spinal cord
2. Spinal cord reflex
   • Parasympathetic motor nerves induce rectum contractions
   • Internal anal sphincter relaxes
3. Voluntary control
   • External anal sphincter relaxation allows feces to pass

Future Topics

• Next video will cover digestion and absorption of macromolecules