transport in animals

• Circulatory system


  The main transport system of all mammals, including humans, is the blood system
• Circulatory system


  • It is a network of tubes, called blood vessels
  • A pump, the heart, keeps blood flowing through the vessels
  • Valves in the heart and blood vessels make sure the blood flows in the correct direction
• Figure 9.2 shows the general layout of the human blood system
• Blood flow in the circulatory system

  1. Blood flows from the lungs into the left-hand side of the heart

  2. Blood flows out to the rest of the body

  3. Blood flows back to the right-hand side of the heart

  4. Blood flows to the lungs again
• Oxygenated blood


  Blood that contains oxygen, which was picked up in the capillaries surrounding the alveoli
• Deoxygenated blood


  Blood that has had some of its oxygen taken up by the body cells
• Double circulatory system


  Blood passes through the heart twice on one complete circuit of the body
• Pulmonary system


  Blood vessels that take the blood to the lungs and back
• Systemic system


  Blood vessels that take the blood to the rest of the body and back
• Single circulatory system


  Blood passes through the heart only once on a complete circuit
• Advantages of double circulatory systems over single circulatory systems

  • Low-pressure blood is delivered back to the heart, which raises its pressure again before sending it off to the rest of the body
  • Blood travels much more slowly to a fish's body organs than it does in a mammal
• The function of the heart is to pump blood around the body
• Heart


  • It is made of a special type of muscle that contracts and relaxes regularly, throughout life
  • It is divided into four spaces, called chambers
  • The two upper chambers are called atria
  • The two lower chambers are ventricles
  • The chambers on the left-hand side are completely separated from the ones on the right-hand side by a septum
• Blood flow through the heart

  1. Blood flows into the heart at the top, into the atria

  2. The left atrium receives blood from the pulmonary veins, which come from the lungs

  3. The right atrium receives blood from the rest of the body, arriving through the venae cavae

  4. From the atria, the blood flows into the ventricles

  5. The muscles in the walls of the ventricles contract, pumping the blood out of the heart

  6. The left ventricle pumps blood into the aorta

  7. The right ventricle pumps blood into the pulmonary artery
• Atrioventricular valves


  Valves between the atria and the ventricles that allow blood to flow from the atria into the ventricles but prevent it from going in the opposite direction
• Semilunar valves


  Valves in the entrances to the aorta and the pulmonary artery that allow blood to flow from the ventricles into the arteries, but stop it going the other way
• Differences in muscle wall thickness

  • The ventricles have much thicker, more muscular walls than the atria
  • The left ventricle has an especially thick wall of muscle to enable it to pump blood to the rest of the body
• The blood flowing to the lungs in the pulmonary artery has a much lower pressure than the blood in the aorta
• Coronary arteries supply blood to the heart muscles
• Coronary heart disease (CHD)


  Blockage of the coronary arteries, caused by cholesterol deposits building up inside the artery walls
• If the coronary artery is blocked, the cardiac muscle does not get any oxygen and the heart stops beating
• CHD is one of the commonest causes of death in many countries
• Ways to prevent CHD

  • Don't smoke cigarettes
  • Eat a diet low in saturated fats
  • Exercise regularly
• Most people's hearts beat about 60 to 75 times a minute when at rest
• Meat is higher in saturated fats than plant-based foods, so one simple way to reduce the risk of CHD is to substitute animal fats with plant oils when you are cooking
• Fast foods are often high in animal fat, so these should be eaten in moderation
• Regular exercise


  • Has a very beneficial effect on many parts of the body, including the heart
  • Helps to keep you fit
  • Prevents excessive weight gain
  • Decreases blood pressure
  • Has a 'feel-good' effect, by helping to clear your mind of things that may be worrying you and causing the release of chemicals in the brain that increase feelings of well-being
• Regular exercise can decrease the risk of developing CHD
• Heartbeat


  The expansion and relaxation of an artery, caused by the heart pushing blood through it
• Most people's hearts beat about 60 to 75 times a minute when they are resting
• Each complete 'lub-dub' represents one heartbeat
• Pulse


  The expansion and relaxation of an artery, caused by the heart pushing blood through it
• Your pulse rate is the same as your heart rate
• An ECG records the electrical activity in the heart
• How the heart beats

  1. Muscles in the heart walls contract

  2. Heart becomes smaller, squeezing blood out

  3. Muscles relax

  4. Heart becomes larger, allowing blood to flow into the atria and ventricles
• Atrioventricular valves


  • Bicuspid valve (mitral valve) between left atrium and left ventricle
  • Tricuspid valve between right atrium and right ventricle
• How blood flows through the heart

  1. Contraction of atria increases blood pressure, pushing blood through open atrioventricular valves into ventricles

  2. Contraction of ventricles closes atrioventricular valves
• Types of blood vessels

  • Arteries
  • Capillaries
  • Veins
• Arteries


  • Carry blood away from the heart
  • Have thick, strong walls with muscle and elastic tissue to withstand high pressure and pulsing blood flow
• Capillaries


  • Very small, penetrate to every part of the body
  • Walls are only one cell thick to allow easy exchange of substances