01 Introduction to the GI system

Introduction to the GI System

• The gastrointestinal (GI) system, also known as the alimentary canal, is a complex tube responsible for digestion, absorption, secretion, excretion, and host defense.
• Key functions include digestion (breaking down food), secretion (releasing fluids and enzymes), absorption (taking in nutrients), excretion (removing waste), and host defense (protecting against pathogens).
• Gastrointestinal "Jabberwocky" uses analogies to simplify the system's function.

Learning Objectives

• Describe the gross anatomy of the GI system.
• Describe the functions of the GI tract and its organs.
• Identify the accessory organs associated with the GI system.

Key Concepts and Definitions

• Concept 1: Gastrointestinal Functions
  • Digestion: Mechanical and chemical breakdown of food into smaller molecules.
  • Secretion: Release of enzymes and fluids to aid digestion.
  • Absorption: Nutrients extracted and absorbed into the bloodstream.
  • Excretion: Removal of indigestible materials as feces.
  • Host Defense: GI tract acts as a barrier against harmful pathogens.
• Concept 2: Gastrointestinal "Jabberwocky"
  • Analogies simplify functions:
    • Chopper and Grinder (Mouth): Mechanical digestion, lubrication (saliva).
    • Garage Door and Gear Shifter (Pharynx/Esophagus): Movement to stomach via peristalsis.
    • Acid Bath Grinder and Reservoir (Stomach): Mixing food with acid and enzymes, creating chyme.
    • Reaction Vessel (Small Intestine): Main site of chemical digestion and nutrient absorption.
    • Agitator and Conveyor Belt (Small/Large Intestine): Movement through intestines, water/electrolyte absorption, and waste formation.
    • Spreader and Emission Control Device (Rectum/Anus): Fecal storage and excretion control.
• Concept 3: Accessory Organs
  • Salivary Glands: Produce saliva to moisten food and begin carbohydrate digestion.
  • Liver: Produces bile to aid in fat digestion.
  • Gallbladder: Stores and releases bile into the small intestine.
  • Pancreas: Secretes digestive enzymes and bicarbonate to neutralize stomach acid.

Clinical Applications

• Case Study: Difficulty swallowing due to lack of saliva production impacts carbohydrate digestion and food transport through the esophagus.
• Diagnostic Approach: Assessing salivary gland function using imaging and saliva tests.
• Treatment Options: Using artificial saliva or medications to stimulate saliva production.

Pathophysiology

• Mechanism of Digestion in the Stomach: Stomach secretes hydrochloric acid, pepsin, and lipase to break down proteins and fats. Muscular contractions create chyme.
• Pancreatic Secretion: Pancreas releases enzymes (amylase, lipase, proteases) and bicarbonate into the duodenum aiding in carbohydrate, fat, and protein breakdown, and neutralizing stomach acid.

Pharmacology

• Pancreatic Enzyme Supplements: Replace enzymes for patients with pancreatic insufficiency (e.g., chronic pancreatitis, cystic fibrosis).
• Antacids: Neutralize stomach acid to relieve indigestion or heartburn (e.g., GERD, peptic ulcer disease).

Differential Diagnosis

• GERD (Gastroesophageal Reflux Disease): Heartburn, regurgitation; diagnosed via endoscopy.
• Peptic Ulcer Disease: Epigastric pain, nausea; diagnosed via endoscopy.

Investigations

• Endoscopy: Visualization of the upper GI tract for diagnoses like GERD, ulcers or malignancies.
• Abdominal Ultrasound: Evaluation of the gallbladder, liver, and pancreas for stones, tumors or inflammation.