Biology B3 Unit 2

• Humans have a circulatory system which consists of blood vessels, the heart, and blood.
• The right side of the heart forced deoxygenated blood to the lungs where it picks up oxygen and loses carbon dioxide
• After returning to the heart, the oxygenated blood is then pumped around the rest of the body by the left pump
• The heart has 4 chambers. The upper ones called atria recieve blood from the vena cava on the right and the pulmonary vein on the left. The atria contract to move blood into the lower chambers, the ventricles. When the ventricles contract they force blood into the pulmonary artery in the right side and the aorta in the left. Valves prevent blood flowing in the wrong direction. The heart muscle is supplied with oxygenated blood via the coronary arteries. 
• veins -> atria -> ventricles -> arteries

Blood flows around the body in 3 main types of blood vessel: the arteries, veins and capillaries.    Arteries:

• carry blood away from the heart 
• have thick walls containing muscle and elastic tissue
• have a small lumen

Veins:

• have thinner walls than arteries 
• often have valves along their length to prevent the backflow of blood
• have a large lumen

Capillaries:

• are narrow, thin-walled vessels
• carry the blood through the organs and allow the exchange of substances with all the living cells in the body  
• have a narrow lumen

• Blood plasma transports many substances including:
  • carbon dioxide from the organs to the lungs
  • soluble products of digestion from the small intestine to the other organs 
  • urea from the liver to the kidneys where urine is made
• Red blood cells:
  • are biconcave disks which do not have a nucleus 
  • contain the red pigment haemoglobin
  • use their haemoglobin which combines with oxygen to form oxyhaemoglobin in the lungs
  • carry the oxygen to all the organs where the oxyhaemoglobin splits into haemoglobin and oxygen.
• White blood cells:
  • have a nucleus 
  • form part of the body's defence system
• Platelets:
  • are small fragments of cells
  • do not have a nucleus
  • help blood to clot at the site of a wound

• The blood plasma can be given to patients in a transfusion to increase blood volume
• Artificial blood such as perfluorocarbons (PFCs) may be used which doesn't need to be refrigerated. It doesn't contain cells so blood matching is not necessary
• Artificial blood is expensive and doesn't carry as much oxygen as whole blood. Some types are insoluble in water so do not mix well with blood.
• Heart donors are also greatly lacking
• Advantages of artificial hearts are that they do not need to match the person's tissue and there is no need for immunosuppressant drugs
• Disadvantages of artificial hearts are problems with blood clotting, long stays in hospital and expense