circulatory system

• humans have a double circulatory system
• first one - right ventricle pumps deoxygenated blood to the lungs to take oxygen. then blood then returns to the heart
• second one- the left ventricle pumps oxygenated blood around all the other organs of the body. the blood gives up its oxygen at the body cells and the deoxygenated blood returns to the heaty to be pumped to the lungs again
• the heart

  pumping organ that keeps blood flowing around the body

  walls made up of mostly muscles tissue

  heart has valves to make sure blood goes in the correct direction
• blood flows into the two atria from the vena cava and the pulmonary vein

  the atria contract pushing blood into the ventricles

  the ventricles contract forcing blood into the pulmonary artery and the aorta and out of the heart

  the blood then flows to the organs through arteritis and returns through veins

  the atria fill again and the cycle repeats
• resting heart rate controlled by a group of cells in the right atrium called a pacemaker - they produce small electric impulses which spreads to the surrounding muscle cells causing them to contract
• arteries

  carry blood under pressure

  carry blood away from heart

  strong and elastic walls
• capillaries 


  involved in the exchange of materials at the tissue

  thin wall- only one cell thick

  very small lumen

  permeable walls so substances can diffuse in and out

  supply oxygen and food and take away waste like CO2
• veins 


  carry blood to the heart

  capillaries join up to form veins

  carry blood at low pressure so walls are not as thick as arteries

  larger lumen than arteries

  have valves
• rate of blood flow = volume of blood flow / number of minutes
• red blood cells

  carry oxygen from lungs to all the body

  biconcave disc - large surface area for absorbing oxygen

  no nucleus - allows more room to carry oxygen

  contain haemoglobin
• white blood cells

  defeat against infection

  some change shapes

  other produce antibodies

  they have a nucleus
• platelets

  help blood to clot

  same fragments of cells

  have no nucleus

  lack of platelets causes excessive bleeding and bruising
• plasma 


  liquid that carries everything in the blood

  carry: red and white blood cells, platelets, nutrients, carbon dioxide, urea, hormones, proteins, antibodies and antitoxins