Blood Vessel Adaptations

• Parts of circulatory system


  • heart
  • blood vessels (arteries, arterioles, blood capillaries, venules, veins)
• Arteries


  • thick, muscular and elastic walls to withstand the high blood pressure of blood flowing within
  • elasticity helps the artery wall to stretch and recoil
  • contraction and relaxation of the arterial walls divert blood to certain organs at certain times (e.g. dilation of arterioles of skin to divert blood to skin capillaries during thermoregulation)
• Veins


  • transports blood back to the heart
  • blood in the veins has lower pressure and speed, so it has a tendency to backflow
  • veins have valves to prevent backflow of blood
  • thinner walls than arteries since blood flows more slowly and smoothly compared to the blood in the arteries
• Poor blood circulation


  • when we sit for too long without much movement, pressure can build in the veins of the lower limbs, causing poor blood circulation and blood to pool in the legs
  • skeletal muscles and movement are important to ensure blood returns to the heart
• Blood capillaries


  • Facilitate exchange of substances between blood and tissue cells in the body
  • walls of blood capillaries partially permeable and made up of a single layer of flattened cells, decreasing diffusion distance
  • vessels tiny and numerously branched, increasing surface area for exchange of substances, and increasing total cross sectional area of blood vessels, lowering blood pressure and slowing blood flow, increasing time for exchange of substances
  • Continuous blood flow through capillaries allow for steep concentration gradient
• Tissue fluid


  • colourless fluid that filled the spaces between cells in tissue
  • transport dissolved substances between blood capillaries and tissue cells