EM 213 Capillary

Continuous Capillary

Capillaries are small blood vessels (5 to 10 µm in diameter) that form a network between arterioles and venules.The exchange of gasses (oxygen and carbon dioxide), fluids, nutrients, and waste products between blood and tissues occurs in capillaries.

Continuous capillaries have continuous endothelium and basal lamina. The endothelial cells are joined by tight junctions.

This micrograph shows the cross-section of a continuous capillary in smooth muscle.

• Endothelium (light green) - simple squamous epithelium
  • No nuclei of the endothelial cells are seen in this section
  • Tight Junctions (#1,#2) - abundant in the overlapping folds between endothelial cells
  • Molecules pass through the endothelium by several processes:
    • Gases, ions, and small molecules can pass between endothelial cells
    • Passive diffusion of lipid-soluble molecules
    • Pinocytosis - small pinocytotic vesicles (60-80 nm in diameter) transport larger molecules in both directions across endothelial cells
• Basal Lamina (purple) - surrounds the capillary and separates it from the surrounding tissue

Other Cells:

• Red Blood Cell (red) - often need to fold on themselves to allow passage through small capillaries
• Pericyte (dark green) - mesenchymal cells with long cytoplasmic processes that partly surround continuous capillaries
• Smooth Muscle Cells (tan)
• Schwann Cell (tan) / Nerves (orange) - multiple non-myelinated axons are ensheathed by the Schwann cell

Subcellular Structures:

• Nucleus (blue) / Nuclear Envelope (purple)
• Golgi Apparatus (yellow)
• Mitochondria (red)
• Endoplasmic Reticulum (cyan)