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Overview of the Digestive System

May 2, 2025

Digestive System Lecture Notes

Functions of the Digestive System

  • Ingestion: Act of placing food into the mouth.
  • Mechanical Breakdown: Begins in the mouth (teeth and tongue) and continues in the stomach.
  • Chemical Breakdown: Enzymes and acids break down large molecules into smaller ones for absorption.
  • Secretion: Glands secrete fluids, enzymes, and molecules throughout the digestive tract.
  • Absorption: Nutrients absorbed into the bloodstream.
  • Excretion: Waste exits the body.

Structure of the Digestive Tract

  • Alimentary Canal: Also known as the digestive tract or GI tract, from mouth to anus.
  • Accessory Organs: Liver, pancreas, etc., assist digestion.

Digestive Process

  1. Mouth

    • Salivary glands produce saliva containing water, enzymes, and antibodies.
    • Types of Salivary Glands:
      • Parotid
      • Sublingual
      • Submandibular
    • Enzymes:
      • Amylase: Breaks down carbohydrates.
      • Lysozyme: Keeps bacterial populations in check.
    • Teeth and Tongue: Assist in mechanical digestion.

  2. Esophagus

    • Hollow muscular tube moving food to the stomach through peristalsis.
    • No absorption occurs; lubricating secretions aid movement.

  3. Stomach

    • Functions: Storage, mechanical/chemical breakdown, and chyme emptying.
    • Regions: Cardia, fundus, body, and pylorus.
    • Layers: Mucosa, submucosa, muscular layer, serosa.
    • Mechanism: Churning and gastric juice production.
    • Gastric Glands:
      • Parietal cells (HCl production)
      • Chief cells (Pepsinogen secretion)
    • Hormone: Gastrin regulates hunger.

  4. Small Intestine

    • Key player in digestion and absorption.
    • Length: 18-20 feet.
    • Segments: Duodenum, jejunum, ileum.
    • Structures: Villi and microvilli increase surface area for absorption.

  5. Large Intestine

    • Includes cecum and colon.
    • Function: Reabsorption of water, nutrient absorption, formation of solid feces.
    • Sections: Ascending, transverse, descending, sigmoid colon.

  6. Rectum and Anus

    • Rectum: Stores feces.
    • Anus: Exit point; two sphincters control release.

Accessory Organs

  • Liver
    • Largest internal organ, key in metabolism and detoxification.
    • Produces bile for fat emulsification.
    • Stores vitamins and glycogen.
  • Gallbladder
    • Stores bile produced by the liver.
    • Releases bile into the duodenum via the common bile duct.
  • Pancreas
    • Produces digestive enzymes and buffers.
    • Exocrine function contributes to digestion.

Digestive Disorders

  • Gastritis: Stomach irritation.
  • Ulcers: Caused by H. pylori bacteria, stress-related exacerbation.
  • Gallstones: Bile salt buildup.
  • Cholera: Causes severe diarrhea.
  • Hepatitis: Liver infection.
  • Jaundice: Excess bilirubin causing yellowing.
  • Cirrhosis: Liver damage from toxins.
  • Constipation/Diarrhea: Imbalance in water absorption.
  • Lactose Intolerance: Insufficient lactase enzyme.
  • Gingivitis: Gum inflammation from poor oral hygiene.

Conclusion: The digestive system is complex, involving various organs and processes to effectively ingest, digest, absorb nutrients, and excrete waste.

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