Digestive System (Chapter 03)

Jul 17, 2024

Digestive System (Chapter 03)

Overview

  • The digestive system consists of two main groups: the alimentary canal (gastro-intestinal tract) and accessory organs.
  • Alimentary Canal: A muscular tube from mouth to anus. Functions: digestion, absorption, elimination.
  • Accessory Organs: Participate in digestion but are not part of the alimentary canal. Examples: liver, pancreas, gallbladder.

Alimentary Canal (Gastro-Intestinal Tract)

Main Sections:

  • Mouth
  • Esophagus
  • Stomach
  • Small Intestine
  • Large Intestine

Functions:

  • Ingestion: Putting food in the mouth.
  • Mechanical Digestion: Physical breakdown (e.g., chewing, segmentation).
  • Chemical Digestion: Breakdown of food into molecules by enzymes.
  • Absorption: Nutrients into the blood.
  • Elimination: Waste removal.

Movement of Food:

  • Peristalsis: Muscle contractions move food forward.
  • Segmentation: Mixing food with digestive enzymes.

Peritoneum

  • Double-layered membrane lining abdominal cavity.
  • Visceral Peritoneum: Covers organs.
  • Parietal Peritoneum: Lines cavity wall.

Functions:

  • Provides routes for blood vessels and nerves.
  • Holds organs in place.
  • Stores fat.

Types:

  • Retroperitoneal Organs: Behind peritoneum (e.g., kidneys, parts of large intestine).
  • Intraperitoneal Organs: Within peritoneum (e.g., stomach).

Histology of Alimentary Canal

Layers from Inside to Outside:

  1. Mucosa
    • Epithelium: Absorption, secretion (e.g., enzymes, hormones).
    • Lamina Propria: Connective tissue with blood capillaries.
    • Muscularis Mucosae: Local movement of mucosa.
  2. Submucosa
    • Dense connective tissue with blood, lymph, nerves.
  3. Muscularis Externa
    • Circular Layer: Constriction.
    • Longitudinal Layer: Shortening.
    • Functions: Peristalsis, segmentation.
  4. Serosa (Visceral Peritoneum)
    • Outer connective tissue layer.

Nervous System Control

  • Enteric Nervous System: Autonomous control via neurons in the digestive tract.
    • Intrinsic Control: Short reflexes.
  • Central Nervous System Involvement: Long reflexes.
    • Sympathetic Nervous System: Slows down digestion.
    • Parasympathetic Nervous System: Enhances digestion.

Oral Cavity

  • Components: Lips, cheeks, palate, tongue (assists in speech, taste, swallowing).
  • Lined with Stratified Squamous Epithelium: Protection against mechanical and chemical damage.

Summary

  • The digestive system is a complex network that transforms food into essential nutrients and energy while eliminating waste. Various organs and tissues work together, regulated by intricate neural controls, to maintain overall health.