organisation of the human body

• The heart is part of a double circulatory system
• Circulatory system is a system of blood vessels with a pump (the heart) and valves that maintain a one-way flow around the body
• the heart has four chambers separated into two halds
• The right side of the heart pumps blood into the lungs for gas exchange (this is the pulmonary circuit)
• The left side of the heart pumps blood under high pressure to the body (this is systematic circulation)
• Benefits of a double circulatory system:

  • Blood travelling through the small capillaries in the lungs loses a lot of pressure -> reduces the speed at which it can flow
  • By returning oxygenated blood to the heart from the lungs, the pressure can be raised before sending it to the body -> cells can be supplied with oxygenated blood more quickly
• heart structure: 4 chambers, 2 atria, 2 ventricles, 2 atrioventricular valves
• Layout of the heart:

  
• Blood is pumped towards the heart in veins and away from the heart in arteries
• Chambers at the top of the heart -> atria

  Chambers at the bottom of the heart -> ventricles
• pulmonary artery is the only artery of the body to carry deoxygenated blood; the pulmonary veins is the only vein to carry oxygenated blood in the body
• pacemaker sends out an electrical impulse which spreads to the surrounding muscle cells, causing them to contract
• pacemakers - located in the wall of the right atrium
• arteries: transport blood away from the heart at high pressure

  veins: transport blood to the heart

  capillaries: have thin walls
• the heart has four chambers: two atria and two ventricles
• blood vessels are made up of three layers: endothelium (inner layer), middle layer (smooth muscle) and outer layer (connective tissue)
• vena cava - carries deoxygenated blood from the body back to the heart
• pulmonary artery - carries deoxygenated blood from the heart to the lungs
• pulmonary vein - carries oxygenated blood from the lungs to the heart
• aorta - carries deoxygenated blood from the heart around the body
• heptic artery - carries deoxygenated blood to the liver
• • at the lungs:
• at the lungs:

  • oxygen diffuses into the blood from the alveoli - the blood becomes oxygenated
  • carbon dioxide diffuses from the blood into the lungs
• the systemic circulation transports:

  • oxygen and nutrients to the body
  • carbon dioxide and other wastes away from cells
• the systemic circulation is under high pressure - it has to deliver blood to the extremities of the body
• the pulmonary circulation is under lower pressure because:

  • blood is delivered to the lungs only -> very close to the heart
  • in a healthy person, this lower pressure is optimum for the diffusion of gases
• blood must flow only one way through the circulatory system. valves in the heart, aorta and veins ensure one-way flow
• closure of a valve prevents back flow
• heart valves may become faulty. a valve may not:

  • open as wide as it should, restricting blood flow through the heart - this means less blood passes through the body
  • close properly and allow blood to leak back into the atrium
• faulty heart valves can be replaced:

  • with a biological valve from a human donor or made with animal tissue from a cow or pig
  • with a mechanical valve made from strong, durable material
• specialised cells in the right atrium generate electrical signals which make the heart contract independently of the nervous system. these specialised cells act as a natural pacemaker
• artificial pace maker - a small, battery operated device implanted in a persons chest that sends out regular, adjustable electrical impulses to produce normal contractions of the heart.
• arteries - always carry blood away from the heart
• veins - always carry blood to the heart
• arteries have thick muscular and elastic walls to pump and accomodate blood
• veins have thin walls - less muscular tissue than arteries
• capillaries connect the smallest branches of arteries and veins
• exchange of molecules:

  • oxygen diffuses through the capillary wall, into the tissue fluid and the cells
  • carbon dioxide diffuses from the cells and into the tissue fluid, then across the capillary walls and into the blood plasma
  • glucose diffuses from the blood plasma, across the capillary walls to the tissue fluid and then to the cells
  • the waste product urea diffuses from the cells of the liver to the tissue fluid and then across the capillary walls into the blood plasma
• plasma - transports carbon dioxide, digested food molecules, urea and hormones; distributes heat
• red blood cells - transport oxygen