circulatory system

• Red Blood Cells

  • Specialised to carry OXYGEN
  • They are really small so can fit through small capillaries.
  • NO NUCLEUS to increase space to carry OXYGEN.
  • BICONCAVE DISC shape, increasing SURFACE AREA to carry more oxygen.
  • Contain HAEMOGLOBIN, a protein that binds to oxygen in the lungs and releases it in body tissues.
• White Blood Cells

  • Fight INFECTION and are a key part of the IMMUNE SYSTEM. 
  • Phagocytes engulf and digest pathogens through phagocytosis.
  • Lymphocytes identify pathogens and produce antibodies that bind to the antigens on pathogens and cause them to clump together. Makes them easier to be engulfed by phagocytes. Some lymphocytes also release antitoxins that neutralise toxic substances produced by pathogens.
• Platelets

  • Cell fragments important for BLOOD CLOTTING and SCABS.
  • They activate at injury sites to form clots, preventing excessive bleeding and STOP pathogens getting into body.
  • A lack of platelets can lead to EXCESSIVE BLEEDING, BRUISING AND INFECTION.
• Plasma

  • LIQUID in blood, carrying all the substances.
  • It transports red blood cells, white blood cells, platelets, nutrients, hormones, proteins, carbon dioxide and urea
• The Heart

  • The heart is the central PUMP of the circulatory system, maintaining the flow of blood throughout the body.
  • It supplies OXYGENATED blood to tissues and organs and returns DEOXYGENATED blood to the lungs for re-oxygenation.
  • The walls of the heart are mostly made up of MUSCLE TISSUE which contract to pump the blood.
  • The heart contains VALVES which prevent the BACKFLOW of blood.
• How does the heart pump blood:

  • Blood enters the atria from the VENA CAVA and PULMONARY VEIN.
  • The atria contract, pushing blood into the ventricles, which then contract to send blood out of the heart via the PULMONARY ARTERY and AORTA. 
  • The LEFT side of the heart has THICKER WALLS than the right side. This because the left side needs to pump the blood to the REST OF THE BODY, therefore it needs to be pumped out at a much HIGHER PRESSURE.
• Double circulatory system

  Humans have a double circulatory system consisting of two separate circuits that work together, with the heart at the centre pumping blood
• Double circulatory system


  1. One circuit pumps blood to the lungs

  2. The other circuit pumps blood to the rest of the body

  3. through heart twice, round body once
• Heart


  • Pumps blood in the double circulatory system
• Blood flow in double circulatory system

  1. Right ventricle pumps deoxygenated blood to the lungs for gas exchange

  2. Oxygenated blood returns from the lungs to the left ventricle, which then pumps it to the rest of the body

  3. After delivering oxygen and collecting waste, blood returns to the heart, completing the cycle
• Hearts oxygen supply:

  The heart receives oxygenated blood through its own network of CORONARY ARTERIES, ensuring it has the oxygen it needs to function effectively. This is what causes the heart muscles to contract.
• The Heart's Natural Pacemaker

  • A group of cells in the RIGHT ATRIUM act as a natural PACEMAKER.
  • It regulates the HEARTBEAT by generating ELECTRICAL IMPULSES that cause the heart muscles to contract.
  • Some people may have a natural pacemaker that does NOT work properly. They can use an ARTIFICIAL pacemaker, which is a small device that is placed under the skin with a wire that connects it to the heart. The device produces an ELECTRICAL CURRENT that keeps the heart beating.

   
• Arteries:

  • Arteries transport blood AWAY from the heart under HIGH PRESSURE.
  • Their walls are THICK and muscular, with elastic fibres to withstand and maintain this pressure.
  • The LUMEN is SMALL
• Veins:

  • Veins carry deoxygenated blood back TOWARDS the heart.
  • They have a LARGER LUMEN than arteries with THINNER WALLS.
  • They carry blood at a LOWER PRESSURE.
  • They have VALVES to prevent backflow of blood.
• Capillaries:

  • Capillaries are tiny blood vessels where the actual EXCHANGE of gases and nutrients occurs.
  • They are extremely small, with walls only ONE CELL THICK, short diffusion distance.
  • Oxygen and nutrients pass from capillaries to body cells, while carbon dioxide and other wastes are collected for removal.
• Lungs:

  The lungs are an important part of the circulatory system, which are involved in the OXYGENATING of the blood
• Structure of the Lungs

  • The LUNGS are located in the THORAX.
  • Air enters the lungs through the TRACHEA, which divides into two BRONCHI, one for each lung.
  • The BRONCHI branch into smaller tubes called BRONCHIOLES, ending in tiny air sacs known as ALVEOLI where gas exchange occurs.
• Gas Exchange Process

  • ALVEOLI are the sites of gas exchange, and are surrounded by a CAPILLARY NETWORK.
  • Oxygen diffuses from the alveoli into the blood, while carbon dioxide moves from the blood into the alveoli to be exhaled.
  • This exchange ensures oxygenation of blood and removal of carbon dioxide, a by-product of respiration.
• Coronary heart disease:

  1. Build up of fatty materials in coronary arteryn narrowing lumen
  2. Cutting off the blood supply to part of the heart muscle. That part of the heart cannot continue to contract
  3. Limits the amount of oxygen reaching the cells and could cause a heart attack.
• Stents:


  • Surgery to insert a small balloon into a blood vessel which is then inflated to remove a blockage. Mesh plate hold the arteries open, allowing blood to flow through and access respiring muscle cells.
• Stents:


  • Surgery to insert a small balloon into a blood vessel which is then inflated to remove a blockage. Mesh plate holds the arteries open, allowing blood to flow through and access respiring muscle cells.

  ADVANTAGE:

  • Improved blood flow in coronary vessels preventing heart attackproved blood flow in coronary vessels preventing heart attack

  DISADVANTAGE:

  • Sometimes only a temporary measure
  • Blood clots called thrombosis near the stent.
• Statins:

  A daily medication to control blood cholesterol levels

  ADVANTAGE:

  • Cheap
  • Reduce the risk of strokes, coronary heart disease and heart attacks 
  • Do not require surgery.
  • They contribute to increasing 'good' cholesterol, which helps remove bad cholesterol from the body.

  DISADVANTAGES:

  • May have side effects, and the patient has to remember to take them.
• Artificial hearts


  Devices utilised when a patient's heart has failed and a heart transplant isn't immediately available or suitable
• Artificial hearts:


  • They are typically a temporary solution but can sometimes be permanent
  • reduced risk of rejection by the body's immune system because they are made from man-made materials, unlike donor hearts which could be seen as foreign
  • There are risks of bleeding and infection
  • Mechanical parts can wear out, and the electrical motor could fail
  • increased chance of blood clots leading to strokes in an artificial heart as the blood doesn’t flow as easily. To aid the flow, patients must take blood thinning drugs but can cause serious problems if accidentally hurt.
• Faulty valves:

  Valve is leaky and blood flows where it shouldn’t or the valve is stiff and amount of blood that gets pumped is reduced. 

  • BIOLOGICAL valves are derived from other mammals, like cows or pigs.
  • MECHANICAL valves are man-made and durable.
  • Valve replacement is safer surgery than heart transplantation but still risk of blood clots.