Principles of Human Physiology - Gastrointestinal System

PowerPoint® Lecture Presentation on Principles of Human Physiology

Chapter: The Gastrointestinal System

Author: Cindy L. Stanfield, 6th Edition, © 2017 Pearson Education, Inc.

Chapter Outline

  • 20.3 Digestion and Absorption of Nutrients and Water

Learning Outcomes

  • Describe the fundamental mechanisms involved in the absorption of carbohydrate, protein, and lipid digestion products.
  • Explain how the mechanism of lipid absorption is related to the hydrophobic nature of fats.

20.3 Digestion and Absorption of Nutrients and Water

  • Macronutrients Involved:
    • Carbohydrates
    • Proteins
    • Lipids
  • Other Absorption Processes:
    • Absorption of vitamins
    • Absorption of minerals
    • Absorption of water

Carbohydrates

  • Typical Diet Composition:
    • Approximately 500 grams/day of carbohydrates
    • Most consumed as di- or polysaccharides
  • Types of Carbohydrates:
    • Sucrose
    • Lactose
    • Maltose
    • Starch
    • Glycogen
    • Cellulose (Fiber): Cannot be digested

Digestion of Carbohydrates

  • Location: Small intestine
  • Enzymes (Brush Border Enzymes):
    • Dextrinase: Converts limit dextrins to glucose
    • Glucoamylase: Converts polysaccharides to glucose
    • Sucrase: Converts sucrose to fructose + glucose
    • Lactase: Converts lactose to galactose + glucose
    • Maltase: Converts maltose to 2 glucose

Proteins

  • Protein Digestion Process:
    • Begins in the stomach
    • Key Enzyme: Pepsin
    • Secretion and Activation:
      • Secreted as zymogen pepsinogen by chief cells
      • Activated by HCl secreted from parietal cells, converting pepsinogen to functional pepsin
    • Positive Feedback Mechanism

Protein Digestion Details

  • Mechanism:
    • Pepsin breaks down proteins into smaller peptide fragments
  • Absorption of Amino Acids:
    • Apical Membrane:
    • Sodium-linked secondary active transport or facilitated diffusion
    • Basolateral Membrane:
    • Facilitated diffusion of amino acids
    • Dipeptides and Tripeptides Absorption:
    • Apical Membrane: Hydrogen linked secondary active transport
    • Inside Cells: Broken down to amino acids
    • Basolateral Membrane: Facilitated diffusion of amino acids

Lipids

  • Typical Diet Composition:
    • Approximately 50 grams/day of lipids
    • Main Component: 90% triglycerides
  • Challenge in Digestion and Absorption:
    • Lipids are hydrophobic and do not mix with aqueous stomach or intestinal contents, forming fat globules and large droplets
    • Emulsification: First step in lipid digestion

Lipid Digestion Process

  • Role of Bile Salts:
    • Digestive Aid:
    • Synthesized from