Lecture Notes: Digestive System

Introduction

• Lecture Focus: Digestive System
• Main Topic: Small Intestine
• Lab Structure: Experiment on Chemical Digestion

Digestive System

Stomach Recap

• Prevents backward movement of food
• Conditions for vomiting:
  • Opening sphincters (gastroesophageal, upper esophageal)
  • Blood pH change when vomiting (more basic due to acid loss)
  • Vomiting involves diaphragm contraction

Small Intestine

• Role: Continuation of digestion, site of absorption
• Functions:
  • Peristalsis and segmentation for propulsion and mixing
  • Main site for digestion and absorption

Anatomical Features

Structural Adaptations

• Circular Folds: Increase surface area, slow down chyme
• Villi and Microvilli: Further surface area increase for absorption

Cellular Makeup

• Enterocytes: Absorb nutrients, secrete intestinal juices
• Goblet Cells: Secrete protective mucus
• Paneth Cells: Secrete antimicrobial compounds
• Duodenal Glands: Secrete alkaline mucus to neutralize stomach acid

Digestive Enzymes and Accessory Organs

Liver and Gallbladder

• Liver: Produces bile (bile salts, lipids, bilirubin)
• Gallbladder: Stores and concentrates bile
• Bile's Role: Lipid digestion, recycling of bile salts

Pancreas

• Secretes digestive enzymes (proteases, amylase, lipases, nucleases)
• Produces bicarbonate to neutralize stomach acid
• Enzyme Activation in Small Intestine

Physiological Implications

Gallbladder Removal

• Liver still produces bile
• Immediate aftermath: Bile less concentrated, avoid fatty foods
• Long-term adaptation: Cystic duct assumes role of gallbladder

Digestion and Absorption

Mechanisms

• Segmentation: Mixing through contraction and relaxation of circular muscles
• Carbohydrates: Amylase and brush border enzymes break down starch into monosaccharides
• Proteins: Proteases break down into amino acids
• Water: Follows nutrient absorption by osmosis

Conclusion

• Small intestine is crucial for nutrient absorption
• Next session: Focus on lipids and their digestion