Blood Vessels Overview

Structure of Blood Vessels

• Arteries and Veins:
  • Both consist of three layers (tunics):
    • Tunica Intima (Interna):
      • Innermost layer.
      • Composed of simple squamous epithelial cells.
      • Continuous with the endocardium of the heart.
      • Includes a basement membrane (visible as a blue layer in models).
    • Tunica Media:
      • Middle layer.
      • Composed mostly of smooth muscle arranged in a circular pattern.
      • Thicker in arteries than veins due to their role in blood propulsion and vasoconstriction.
    • Tunica Externa (Adventitia):
      • Outermost layer.
      • Made mostly of areolar connective tissue.
  • Vaso Vasorum:
    • Present in the tunica externa of large blood vessels.
    • Capillary bed supplies oxygen since the vessel is too big to rely solely on the blood within it.

Veins vs. Arteries

• Valves in Veins:
  • Present in veins to prevent backflow of blood, especially important in overcoming gravity when returning blood from lower body to the heart.
  • Absent in arteries due to higher blood pressure.
• Blood Pressure and Gravity:
  • Veins have lower blood pressure (<30 mm Hg) and must combat gravity, hence the presence of valves.
  • Blood flow in veins aided by skeletal muscle contractions.
  • Prolonged inactivity (e.g., sitting) can lead to pooling of blood and edema, especially in legs (feet swelling).