Lecture Notes: The Digestive System and Lactose Intolerance

Introduction

• Discussion of topics: heart failure, respiratory gas exchange, digestive system with a humorous intro about nachos.
• Focus on lactose intolerance: affects digestion of dairy products due to lack of lactase enzyme.

Lactose Intolerance

• Lactose: a milk sugar digested by lactase enzyme.
• Genetic mutation for lactase persistence occurred ~7500 years ago in central Europe.
• Distribution:
  • High persistence: 90% in Britain and Scandinavia.
  • Low persistence: 40% around the Mediterranean, <10% in Africa and Asia.
• Consequences of lactose intolerance involve bacteria in large intestine digesting lactose, leading to gas, bloating, diarrhea.

Digestive System Overview

• Stomach: Breaks down food but minimal chemical digestion or absorption.
• Small Intestine:
  • Length: 6-7 meters with high surface area due to villi and microvilli.
  • Main role: Nutrient absorption.
  • Subdivisions:
    • Duodenum: Chemical digestion, receives chyme, bile, and enzymes.
    • Jejunum: Primary site of absorption.
    • Ileum: Absorbs vitamins A, B12, E, D, K.

Role of Accessory Organs

• Liver:
  • Produces bile that emulsifies fats for digestion.
  • Can regenerate from 25% of its tissue.
• Gallbladder:
  • Stores and concentrates bile.
  • Releases bile into duodenum when triggered by hormones.
• Pancreas:
  • Produces a cocktail of digestive enzymes:
    • Trypsin and peptidase: Break down proteins.
    • Lipases: Process fats.
    • Amylase: Digests carbohydrates.
    • Nuclease: Breaks down nucleic acids.

Large Intestine Function

• Shorter than small intestine.
• Functions:
  • Absorbs remaining water.
  • Hosts bacteria that produce vitamins and gas.
• Bacteria digest leftover chyme, releasing gases like CO2, methane, mercaptans, and hydrogen sulfide.

Process of Defecation

• Fecal matter moves through haustral contractions and peristalsis.
• Rectum stores feces until voluntary defecation occurs.

Conclusion

• Key Points:
  • Small intestine is primary site of digestion and absorption.
  • Accessory organs support digestion with enzymes and bile.
  • Large intestine finalizes nutrient absorption and prepares waste for elimination.
• Mention of Crash Course contributors and production team.