Lecture on Digestive System Histology

Overview

• Focus on histology of the esophagus, stomach, small intestine, and large intestine.
• Key distinguishing features and specialized structures of each part.
• All digestive organs have four main histological layers: mucosa, submucosa, muscularis externa, and an outer layer (adventitia or serosa).

Esophagus

• Unique feature: Stratified squamous epithelium with a darker border at the bottom.
• Layers:
  • Mucosa: Stratified squamous epithelium, lamina propria, muscularis mucosa.
  • Submucosa: Connective tissue (type varies).
  • Muscularis externa: Inner circular and outer longitudinal layer; top portion has skeletal muscle, middle is mixed, and bottom is smooth muscle.
  • Adventitia: Connects to surrounding structures.

Stomach

• Distinguishing features: Ridges resembling knuckles, gastric pits (openings) and glands (deeper structures).
• Layers:
  • Mucosa: Simple columnar epithelium, lamina propria between gastric pits and glands, muscularis mucosa.
  • Submucosa: Connective tissue.
  • Muscularis externa: Inner oblique, middle circular, outer longitudinal layer.
  • Serosa: Because the stomach is highly mobile and located within the peritoneum.

Small Intestine

• Main function: Absorption of nutrients.
• Distinguishing features: Villi (finger-like projections) and microvilli (increase surface area).
• Layers:
  • Mucosa: Simple columnar epithelium with goblet cells (secrete mucus), lamina propria.
  • Submucosa: Connective tissue.
  • Muscularis externa: Circular and longitudinal layers.
  • Serosa or Adventitia: Duodenum has adventitia due to its fixed position; jejunum and ileum have serosa.

Large Intestine

• Distinguishing features: No villi, numerous goblet cells.
• Layers:
  • Mucosa: Organized, smaller in proportion than in the stomach.
  • Submucosa: Connective tissue.
  • Muscularis externa: Circular and longitudinal layers.
  • Serosa or Adventitia: Depending on the segment, e.g., ascending/descending colon have adventitia, transverse colon has serosa.

Practice Questions

• Identify organs based on histological slides.
• Recognize sub-layers and specific features.