Circulatory System

• • Human cells' needs are met by our circulatory system
  • Our system is described as a closed system.
  • Blood circulates from the heart through the arteries to the capillaries then to the veins and back to the heart.
  • There is a decrease in blood pressure as blood moves away from the heart.
• The five major functions of the cardiovascular system are:

  1. Transporting oxygen and removing carbon dioxide
  2. Transporting nutrients and removing wastes
  3. Fighting disease
  4. Transporting hormones
  5. Regulating body temperature
• The blood vessels carry the blood around the body to supply organs with the nutrients they need and remove CO2 waste.
• There are 3 types of blood vessel:

  • arteries (and arterioles)
  • capillaries
  • veins (and venules)
• The endothelium lining in the central lumen of the blood vessels is surrounded by layers of tissue. These surrounding layers differ in each type of blood vessel.
• Arteries:

  • Carry blood away from the heart
  • Under high pressure, therefore walls more muscular
  • Have an outer layer of connective tissue containing elastic fibers and a middle layer containing smooth muscle with more elastic fibers.
  • The elastic walls stretch and recoil to accommodate the surge of blood after each contraction of the heart.
• The largest arteries, e.g. the aorta, have thick elastic walls which can stretch to accommodate the surge of blood after each contraction of the heart.
• To control blood flow, the smooth muscle surrounding arteries can contract causing vasoconstriction or relax causing vasodilation.
• Veins:

  • Return blood to the heart from tissues
  • Lower pressure, therefore less muscular
  • They have an outer layer of connective tissue containing elastic fibres but a much thinner muscular wall than arteries.
  • Contain valves to prevent back flow of blood.
• Vein structure:

  • Thin outer wall -
  • Collagen, elastic fibres
  • Thin middle muscle layer
  • Low pressure of blood
  • Wide lumen
  • Blood flow slow
  • Valves present, prevent back flow of blood
• Artery structure:

  • Thick outer wall -
  • Collagen, elastic fibres
  • Thick middle muscle layer
  • Able to withstand high pressure
  • Narrow lumen
  • Blood flow rapid