Lecture Notes on the Digestive System

Overview

• The digestive system is essential for:
  • Breaking down food
  • Absorbing nutrients
  • Eliminating waste
• Divided into:
  • The digestive tract (alimentary canal)
  • Accessory organs

The Digestive Tract (Alimentary Canal)

• Oral Cavity:
  • Digestion begins with teeth and tongue
• Pharynx:
  • Common passageway for food and air
• Esophagus:
  • Transports food to the stomach
• Stomach:
  • Further breaks down food
• Small Intestine:
  • Primary site of nutrient absorption
• Large Intestine:
  • Absorbs water and compacts waste

Accessory Organs

• Salivary Glands:
  • Produce enzymes for carbohydrate digestion
• Liver:
  • Produces bile for fat emulsification
• Gallbladder:
  • Stores and concentrates bile
• Pancreas:
  • Secretes digestive enzymes and bicarbonate

Functions of the Digestive System

• Ingestion: Taking in food and liquids
• Mechanical Processing: Physical breakdown via chewing
• Digestion: Chemical breakdown of food
  • Carbs to monosaccharides
  • Lipids to fatty acids/glycerol
  • Proteins to amino acids
  • Nucleic acids to nucleotides
• Secretion: Release of enzymes, acids, and buffers
• Absorption: Nutrients move into the bloodstream
• Excretion: Removal of waste products
• Compaction and Defecation: Formation and elimination of feces

Microscopic Structure of Digestive Tract

• Four Main Layers:
  • Mucosa: Directly lines the lumen
  • Submucosa: Connective tissue layer
  • Muscularis Externa: Movement of the tract
  • Serosa/Adventitia: Protective outer layer

Movement of Food

• Peristalsis: Wave-like muscle contractions
• Segmentation: Mixing and churning action
• Pace Setter Cells: Initiate muscle contractions

Peritoneum and Mesenteries

• Visceral Peritoneum (Serosa): Covers organs
• Parietal Peritoneum: Lines abdominal walls
• Peritoneal Cavity: Filled with serous fluid
• Mesenteries: Stabilize organ positions and provide passageways for vessels and nerves

Oral Cavity

• Salivary Glands: Produce saliva
• Teeth Structure: Crown, neck, and root
• Types of Teeth: Incisors, canines, premolars, molars

Esophagus

• Structure: Four layers (mucosa, submucosa, muscularis externa, adventitia)
• Swallowing Process: Buccal, pharyngeal, and esophageal phases

Stomach

• Regions: Fundus, cardia, body, pyloric part
• Rugae: Gastric folds that allow expansion
• Muscle Layers: Oblique, circular, longitudinal

Small Intestine

• Regions: Duodenum, jejunum, ileum
• Surface Area Adaptations: Plicae circulares, villi, microvilli

Large Intestine

• Regions: Cecum, colon, rectum
• Features: Haustra, teniae coli

Accessory Organs

• Liver: Produces bile, regulates blood composition
• Pancreas: Exocrine and endocrine functions

Effects of Aging on Digestive System

• Loss of teeth, toxin accumulation
• Declining stem cell production
• Decreased smooth muscle tone

Conclusion

• Review notes and redo quizzes
• Questions can be addressed by the lecturer