Vessels

BLOOD VESSELS

FACTS

• Three major types of blood vessels: arteries, veins, and capillaries.
• Blood vessels extend over 60,000 miles in the human body.

VESSEL STRUCTURE

• Except capillaries, blood vessels have three layers (tunics):
  • Tunica intima (endothelium, subendothelial layer, internal elastic membrane)
  • Tunica media (smooth muscle, elastic fibers)
  • Tunica externa (collagen fibers, vasa vasorum)

ARTERIES

• Conduct blood away from the heart.
• Walls are thick and rounded; high pressure, with valves not present.
• Types:
  • Elastic arteries (conducting arteries)
  • Muscular arteries (distributing arteries)
  • Arterioles (resistance vessels)

ARTERIAL BLOOD PRESSURE

• Arterial BP is the force on vessel walls, measured in mmHg.
• Factors affecting BP:
  • Cardiac output
  • Peripheral resistance (influenced by vessel diameter and length)
  • Blood volume/viscosity

CAPILLARIES

• Sites of exchange, consist of only tunica intima.
• Fluid movement determined by hydrostatic and osmotic pressure.
  • Net filtration pressure (NFP) drives fluid exchange.

VEINS

• Conduct blood toward the heart; walls are thin and often collapsed.
• Contain valves to prevent backflow; lower pressure than arteries.
• Major types: venules and larger veins.

VENOUS BLOOD PRESSURE

• Influenced by the muscular pump (skeletal muscle contractions) and respiratory pump (pressure changes in thoracic cavity).