blood vessels

• what are the three layers of arteries?

  Tunica intima

  Tunica media

  Tunica advenitia
• what do arteries do?


  Arteries carry oxygenated blood away from the heart, so the pressure is high.
• Why is the lumen of arteries so small?


  Helps maintain high blood pressure
• describe the tunica intima of the arteries?


  It consists of a thin layer of elastic tissue which allows the walls to stretch and recoil to maintain blood pressure
• describe the tunica media?


  It consists of a thick layer of smooth muscle
• Describe the tunica adventitia?


  A relatively thick layer of collagen and elastic tissue, it provides strength to withstand high pressure and recoils to maintain pressure.
• what is the purpose of the arterioles?


  they are small bloodvessels that distribute blood from an artery to the capillaries
• Describe the structure of arterioles?


  Thier walls contain a layerof smooth muscle, the contraction of this muscle will constrict the diameter of the arteriole increasing the resistance to flow and reducing the rate of flow of blood. the contraction of the walls can divert the flow of blood to regions of the body# that demand more oxygen.
• what are the main adaptations of capillaries?


  Narrow lumen

  Leaky walls

  Walls consist of a single layer of endothelial cells
• what is the importance of capillaries having a narrow lumen?


  Erythrocytes may be squeezed against the walls of the capillary as they pass along, this helps the transfer of oxygen as it reduces the diffusion path to the tissues, increasing the resistance and reducing the rate of flow.
• what is the importance of capillaries having a wall made of asingle layer of flattened endothelial cells?


  Reduces diffusion distance for the materials being exchanged
• what is the importance of capillaries having leaky walls?

  Allows blood plasma and dissolved substances to leave the blood.
• what is the purpose of veins?


  carry blood back to heart at low pressure
• What are the adaptations of the veins?

  Large lumen

  Walls are thin

  Valves
• why do veins need a large lumen?

  ease flow of blood
• Why are the walls of veins thin?


  They have less collagen, smooth muscle and elastic tissues than arteries. they don't need to stretch and recoil and are not actively constricted to reduce blood flow.
• whydo veins have valves?


  help prevent the backflow of blood going back to the heart. As the walls are thin, the veins can be flattened by the action of surrounding skeletal muscle. Contraction of the surrounding muscle applies pressure to the blood which forces it to move in a direction determined by the veins.