circulatory system structure

• circulatory can be open like in insects or closed like in mammals
• a double form of the circulatory system means that the heart has four chambers and blood passes through the heart twice for every circuit of the body, this is more efficient as it increases pressure and therefore speed of oxygenated blood the tissues
• arteries branch into arterioles which are a smaller network throughout the body, they can contract to restrict blood flow and relax to increase blood flow
• arterioles branch into capillaries which form capillary beds
• smooth muscle layer - contracts to control the blood flow in arteries, arterioles and veins
• elastic layer - allows the vessel to stretch and recoil in arteries, arterioles and veins
• endothelium - thin inner lining which is smooth to avoid friction in all vessels
• Artery:

  • narrow lumen to help maintain pressure
  • carries blood away from the heart
  • thick muscular walls and elastic layer to stretch and recoil maintaining high pressure
  • endothelium is folded to allow stretching maintaining high pressure
• Vein:

  • carry blood towards the heart
  • wider lumen means lower pressure
  • thinner layers of muscle and elastic tissue
  • valves to avoid backflow of blood
• Capillary:

  • same diameter as a red blood cell
  • close to cells so short diffusion pathway
  • walls are one cell thick so shorter diffusion distance
  • fenestrations ( gaps ) between endothelial cells allowing substances to diffuse out between
  • large number of capillaries to increase surface area for diffusion
• blood pressure is highest in the aorta immediately after ventricular contractions