M01.10.17 Colon

The colon, a vital component of the large intestine, is specialized for the absorption of water, and electrolytes, and the formation of feces. Its histological features reflect these functions. Below is an overview of its histological structure:

Layers of the Colon Wall

1. Mucosa

• Epithelium:
  • Type: Simple columnar epithelium.
  • Cells:
    • Absorptive cells (enterocytes): Specialized for water and electrolyte absorption.
    • Goblet cells: Secrete mucus for lubrication.
  • Crypts of Lieberkühn: Straight, unbranched tubular glands that open into the lumen; no villi are present.
• Lamina propria:
  • Contains connective tissue with immune cells (lymphocytes, plasma cells).
  • Houses blood vessels and lymphatics.
• Muscularis mucosae: Thin layer of smooth muscle separating mucosa from submucosa.

2. Submucosa

• Contains loose connective tissue.
• Rich in blood vessels, lymphatics, and nerves.
• May have lymphoid follicles, particularly in the appendix region.

3. Muscularis Externa

• Two layers of smooth muscle:
  • Inner circular layer: Facilitates segmentation.
  • Outer longitudinal layer: Organized into three distinct bands called taeniae coli, which aid in peristalsis.

4. Serosa/Adventitia

• Serosa: Covers intraperitoneal portions of the colon; consists of mesothelium and connective tissue.
• Adventitia: Covers retroperitoneal portions of the colon.

Key Features and Functions

Points to Remember

• The colon lacks villi, distinguishing it from the small intestine.
• The number of goblet cells increases as you move distally.
• The Taeniae coli and haustra are gross anatomical features unique to the colon.
• Immune defense in the lamina propria is crucial due to the high bacterial load in the lumen.

Bibliography

1. Junqueira, L. C., & Carneiro, J. (2021). Basic Histology: Text and Atlas. McGraw-Hill.
2. Ross, M. H., & Pawlina, W. (2020). Histology: A Text and Atlas. Wolters Kluwer.