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.