Biology 3 Part 2

B3.2
1. The Heart
  1. The heart is divided into two sides, right and left. Each side consists of two chambers; and upper atrium and a lower ventricle. Each side has a valve that allows blood to flow from the atrium into the ventricle, but preventss backflow. Blood is returned to the heart by two veins: the Vena Cava and the Pulmonary Vein. Blood is pumped out of the heart though two arteries; the Aorta and the Pulmonary Artery. Valves at the base of the pulmonary artety and the aorta prevent the backflow of blood into the heart.
  2. Double Circulation
    1. Blood from the right ventricle is pumped through the pulmonary artery to the lungs.
      1. In the lung tissue, oxygen diffuses into the blood and carbon dioxide diffuses out. This is nownoxygenated blood.
        Oxygenated blood from the lungs then returns via the pulmonary vein to the left atrium.
        Oxygenated blood is pumped through the aorta and arteries to the rest of the body.
        In respiring tissues, oxygen diffuses fro the blood into the body cells, and carbon dioxide diffuses from body cells into the blood. The blood has become deoxygenated.
        Deoxygenated blood is returned to by the vena cava to the right atrium.
        This is called a double circulatory system because blood travels through the heart twice as it flows around the body. By having a double circulation, oxygenated blood is separated from deoxygenated blood.
2. Blood Vessels
  1. Arteries
    1. These carry blood away from the heart and the tissues.
      1. Therefore the blood is at a high pressure.
        The artery walls are thick, muscular and elastic to withstand the pressure surges.
        The elastic tissue can recoil to maintain blood pressure between heart beats.
        The arterial blood is oxygenated except in the pulmonary artery.
  2. Veins
    1. These return the blood from the tissues back to the heart.
      1. The blood is at low pressure
        Therefore the walls are much thinner than the artery walls, the lumen is much bigger, there are semi-lunar valves to ensure the blood moves the right way.
        Veins carry deoxygenated blood except for the pulmonary vein
  3. Capillaries
    1. These join the arterioles to the venules at the tissues.
      1. There are many narrow vessels which are the site for exchange of substances. Oxygen and glucose will leave the blood while carbon dioxide and other waste is picked up and removed.
        Therefore a capillary wall is only one cells thick.
  4. Composition of Blood
    1. Liquid
      1. Plasma
        Glucose, Minerals, Vitamins, Amino Acids, Fatty Acids, Carbon Dioxide, Urea, Hormones, Salt
        Water
    2. Cells
      1. Platelets (clotting blood)
      2. Red (containing haemoglobin to carry oxygen)
      3. White
        Phagocytes (to engulf pathogens)
        Lymphocyte (to make antibodies)
3. Assisting Circulation
  1. Artificial Blood
    1. This is useful because it can be steralised.
      1. It also doesn't need a blood group match.
  2. Haemolgobin Based Oxygen Carrier
    1. HBOC is haemoglobin bound to a synthetic polymer molecule
      1. It is commonly used in places where there is a shortage of blood for transfusion.
        South Africa, where there is a shortage due to the high incidence of HIV
        Its usefulness is short lasting and a blood transfusion is needed eventually
  3. PolyFluoroCarbons
    1. Fully synthetic oxygen carriers
      1. They are 20 to 30% better than just plasma.
        They can only be used if extra oxygen is supplied.
        Being small, they can deliver oxygen to regions where HBOCs and red blood cells cannot reach.
  4. Dealing with Atheroma
    1. This is a build up of cholesterol and fatty material under the endothelium of an artery
      1. It bulges into the lumen of an artery to block or narrow it.
        If it is a coronary artery, the heart muscles will receive less blood.
        There is less oxygen so there may be tissue death leading to a heart attack
    2. A by-pass operation may be performed
      1. A piece of vein from a leg is attached to the coronary artery across the blockage in order to by-pass it.
        This requires surgery under full anaesthetic and recovery time up to 3 months.
    3. A stent is a collapsed mesh tube surrounded by a balloon and inserted into the blocked region by a catheter.
      1. The balloon is inflated allowing the mesh to expand and forming a supporting scaffold to keep the artery open. The catheter is then removes.
        Insertion takes 1 or 2 hours with local anaesthetic but the fatty material can build again in the future.

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Biology 3 Part 2

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