Circulation

2.2 Respiration

undefined Digestion

Circulation

  1. Overview

    1. The circulatory system transports substances from where they enter the body to the cells, or from the cells to where they exit the body, by blood pumped by the heart through blood vessels
    2. Humans have a double circulatory systems: one for the lungs and one for the rest of the body

  2. Heart

    1. Structure

      1. The heart is an organ that pumps blood around the body
      2. Much of the wall of the heart is made of (cardiac) muscule tissue
      3. The heart has four main chambers: the left & right atria & ventricles
      4. Pacemaker cells are a group of cells in the wall of the right atrium1 that control the natural resting heart rate

    2. Action

      1. Blood enters the atria of the heart
      2. The atria contract, forcing blood into the ventricles
      3. The ventricles contract, forcing blood out of the heart
      4. Valves in the heart ensures that blood flows in the correct direction2

  3. Blood vessels

    1. Structure

      1. Blood flows from the heart to the organs through the arteries and returns through veins
      2. Arteries have thick walls containing muscle and elastic fibres
      3. Veins have thinner walls and often valves to prevent backflow of blood
      4. Capillaries are thin-walled blood vessels in organs where, through the walls, substances needed by the cells pass out of the bloodstream and substances produced by the cells pass into the bloodstream

    2. Around the heart

      1. The aorta is the artery that carries oxygenated blood from the left ventricle to the rest of the body
      2. The venae cavae are two veins that carry deoxygenated blood to the right atrium from the rest of the body: the superior vena cava, from the upper half of the body, and the inferior vena cava, from the lower half of the body
      3. The pulmonary artery is the artery that carries deoxygenated blood from the right ventricle to the lungs
      4. The pulmonary veins are four veins that carries oxygenated blood to the left atrium from the lungs: two from each lung

  4. Blood

    1. Blood is a tissue consisting of a fluid called plasma, in which the red & white blood cells and platelets are suspended:

      Component Properties
      Plasma Transports carbon dioxide from the organs to the lungs
      Transports soluble products of digestion from the small intestine to other organs
      Transports urea from the liver to the kidneys
      Red blood cells Have no nucleus
      Are packed with a red pigment known as haemoglobin
      Transport oxygen from the lungs to the organs
      In the lungs, haemoglobin combines with oxygen to form oxyhaemoglobin
      In the organs, oxyhaemoglobin splits up into haemoglobin and oxygen
      White blood cells Have a nucleus
      Form part of the body’s defence system against microorganism
      Platelets Are small fragments of cells
      Have no nucleus
      Help blood clot at the site of a wound
    2. Blood clotting is a series of enzyme-controlled reactions that convert fibrinogen into fibrin, forming a network of fibres that trap blood cells, forming a clot

  5. Antigens

    1. Antigens are proteins on the surface of cells that identify the cell

    2. Organ transplant

      1. In organ transplants, a diseased organ is replaced with a healthy one from a donor
      2. The recipient’s antibodies may attack the antigens on the donor organ as they do not recognise them as part of the recipient’s body
      3. To prevent rejection, a donor organ with a “tissue-type” similar to that of the recipient is used and the recipient is treated with drugs that suppress their immune system

    3. Blood group3

      1. There are four main types of human blood, which correspond with the antigens on the red blood cells and the antibodies in the plasma

        Blood group Antigen on red blood cell Antibody in plasma
        A A Anti-B
        B B Anti-A
        AB A & B None
        O None Anti-A & Anti-B
      2. In blood transfusions, it is essential that the antigens on the donor red blood cells are not the same letter as the antibodies in the recipient’s plasma otherwise they will react, causing agglutination, which can be fatal

      3. Therefore, the ABO compatibility table is used to determine whether a blood transfusion will be successful:

        Donor Recipient
        A B AB O
        A ✓ ✗ ✓ ✗
        B ✗ ✓ ✓ ✗
        AB ✗ ✗ ✓ ✗
        O ✓ ✓ ✓ ✓
      4. Every type can donate to their own type, but additionally, AB can receive from every type and O can donate to every type

  6. Circulation problems

    1. Pacemakers

      1. Artificial pacemakers are electrical devices used to correct irregularities in heart rate by periodically sending an electric pulse through electrodes into the heart

    2. Valves

      1. Heart valves can become faulty in two main ways: the valve tissues can stiffen, preventing the valve from opening fully, or the heart valve can develop a leak
      2. Faulty heart valves can be replaced with biological or mechanical ones

    3. Heart

      1. Artificial hearts are occasionally used to keep patients alive whilst waiting for a heart transplant or to allow the heart to rest as an aid to recovery

    4. Coronary arteries

      1. Coronary arteries supply oxygen to the heart muscle
      2. Coronary heart disease occurs when fatty material builds up on the lining of the arteries and narrow them, reducing blood flow through them until there is not enough oxygen for the heart muscle4
      3. Stents are used to keep the arteries open by inserting the collapsed stent on a balloon catheter into the artery and expanding the catheter so that the stent reaches its proper size before removing the catheter; the stent may be a smart alloy that keeps its shape or release a drug that prevents fibrosis
  1. The pacemaker tissue is called the sinoatrial node ↩
  2. The four main valves in the heart are: the two atrioventricular valves between the atria and the ventricles, mitral or bicuspid valve in the left and the tricuspid valve in the right, and the two semilunar valves in the arteries, the aortic valve & pulmonary valve ↩
  3. There are, in fact, 35 blood group systems ↩
  4. This is called atheroslerosis ↩