2.5

• Aorta


  Main artery which carries oxygenated blood from the heart in mammals
• Blood plasma


  The liquid part of the blood containing useful things like glucose, amino acids, minerals, vitamins (nutrients) and hormones, as well as waste materials such as urea
• Blood pressure


  A measure of the force that your heart uses to pump blood around your body
• Capillary


  Tiny blood vessels with walls one-cell thick where exchange of materials occurs
• Carbon dioxide


  A gaseous compound of carbon and oxygen, which is a by-product of respiration, and which is needed by plants for photosynthesis
• Diffuse


  When particles spread out from a region of higher concentration to a region of lower concentration
• Glucose


  A simple sugar used by cells for respiration
• Heart


  Muscular organ that pumps blood around the body
• Lumen


  The channel in the blood vessel that carries blood
• Lymph


  A colourless fluid containing white blood cells
• Oxygen


  Gaseous element making up about 20% of the air, which is needed by living organisms for respiration
• Pressure filtration


  Blood filtered due to pressure
• Pulmonary artery


  The artery which carries deoxygenated blood from the heart to the lungs
• Pulmonary vein


  One of the four veins that carries oxygenated blood to the heart from the lungs
• Tissue fluid


  Fluid which is derived from blood plasma that passes through the walls of capillaries
• Urea


  A nitrogenous waste product resulting from the breakdown of proteins. It is excreted in urine
• Vasodilation


  The dilation of blood vessels, decreasing blood pressure
• Vasoconstriction


  The constriction of blood vessels, increasing blood pressure
• Vein


  A blood vessel with valves that transports blood to the heart
• Vena cava


  One of the two veins that carries deoxygenated blood to the heart from the body systems
• Blood circulation


  Blood circulates from the heart through the arteries to the capillaries then to the veins and back to the heart
• As blood moves away from the heart

  There is a decrease in blood pressure
• Arteries


  • Carry oxygenated blood (except for the pulmonary artery)
  • Carry blood under high pressure
  • Have a narrow lumen
  • Have an outer layer of connective tissue containing elastic fibres and a middle layer containing smooth muscle with more elastic fibre
  • Have thick muscular and elastic walls which stretch and recoil to pump and accommodate the surge of blood after each contraction of the heart
• Veins


  • Carry deoxygenated blood (except for the pulmonary vein)
  • Carry blood under low or negative pressure
  • Have a wide lumen
  • Have less connective tissue containing elastic fibres than arteries
  • Have thin walls have less muscular tissue than arteries
• Arteries


  A for Away (carries blood away from the heart)
• Veins


  V for Valves (prevent blood flowing backwards on way back to the heart)
• Valves prevent blood backflow
• Controlling blood flow


  The smooth muscle surrounding the arteries can contract which causes vasoconstriction or they can relax which causes vasodilation
• Capillaries


  • Capillaries connect the smallest branches of arteries and veins
  • Capillaries allow exchange of substances between the blood and the body's cells by diffusion through their thin walls (one-cell thick)
• Exchange of molecules


  1. As blood travels at high pressure in the arteries towards the capillaries, pressure filtration occurs which causes plasma to pass through capillary walls into the tissue fluid surrounding the cells

  2. Tissue fluid and blood plasma are similar in composition, with the exception of plasma proteins, which are too large to be filtered through the capillary walls

  3. Tissue fluid supplies cells with useful substances such as glucose, oxygen and other substances

  4. Carbon dioxide and other metabolic wastes diffuse out of the cells and into the tissue fluid to be excreted

  5. Oxygen diffuses through the capillary wall, into the tissue fluid, and the cells

  6. Carbon dioxide diffuses from the cells into the tissue fluid, then across the capillary walls into the blood plasma

  7. Glucose diffuses from the blood plasma, across the capillary walls to the tissue fluid, and then to the cells

  8. The waste product, urea, diffuses from the cells of the liver to the tissue fluid, and then across the capillary walls into the blood plasma

  9. Much of the tissue fluid returns to the blood. Lymphatic vessels absorb excess tissue fluid and return it as lymph to the circulatory system