Lecture on Capillaries

Overview

• Focus on capillaries and their unique properties within the vascular network
• Previous discussions centered on arteries and veins

Capillary Bed Imaging

• Arterial End:

  • Arterioles bring fluids and materials
  • Muscle layer is not continuous, featuring smooth muscle ringlets
  • Diameter: ~20 micrometers

• Venous End:

  • Venules feed into veins
  • Sparse muscle association

Capillary Networks

• Structure:
  • Made mainly of endothelial cells (simple squamous epithelium)
  • Single cell layer thick walls with light connective tissue
• Diameter:
  • 5-9 micrometers, smaller than red blood cells (~7 micrometers)

Red Blood Cells

• Size: 7 micrometers across (biological yardstick)
• Pliable, can squeeze through capillaries

Smooth Muscle Ringlets

• Control fluid movement based on local tissue conditions

Types of Capillaries

Continuous Capillaries

• Cells form continuous wall
• Materials pass through bilipid membranes
• Intercellular gaps for small molecules

Fenestrated Capillaries

• Contain pores (fenestrations) for channels
• Allow passage of small molecules like sodium, potassium, glucose

Lipid Soluble Substances

• Fatty acids, steroids, O2, and CO2 can move easily due to lipid solubility

Permeability and Transport

• Water: Used as reference point for permeability (set as 1)
• Sodium Chloride: Permeability 0.96
• Urea, Glucose, Sucrose: Varying permeability
• Proteins: Larger proteins (e.g., hemoglobin) have low permeability
• Albumin: Standard marker for permeability, cannot cross capillary walls

Importance of Permeability

• Understanding molecule movement across capillary walls is crucial
• Future discussions will cover forces affecting molecule transport

Conclusion

• Capillaries use concentration gradients to transport materials
• Essential for tissue nutrition, oxygenation, and waste removal

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Next lecture will delve into forces and concentration gradients in capillary transport.