General circulatory

• Types of circulatory system:

  • Open circulatory system
  • Closed circulatory system
  • Single closed circulatory system
  • Double closed circulatory system
• Open circulatory system:

  • The blood is not always held within the blood vessels and can circulate through the blood cavity so that cells are immersed directly in the blood.
  • In insects the heart will pump blood towards the head by peristalsis; it re-enters the heart through pores called ostia.
  • There is little control over direction of circulation. Movement of muscles assist with the movement of blood back to the head region.
  • No respiratory pigment - insect blood doesn't carry oxygen
  • Blood pumped at low pressure into a fluid filled cavity - the haemocoel
  • Example: Insects
• Closed circulatory system:

  • Blood is enclosed within blood vessels
  • Tissues are not in direct contact with the blood, a separate fluid called tissue fluid exits the capillaries and bathes the cells.
  • This allows the heart to pump at a higher pressure

  Advantages

  1. Blood flow is more rapid and efficient
  2. Blood flow can be directed where it is needed by vasoconstriction and dilation e.g. more working muscles or to the body surface if hot
  3. More efficient delivery of oxygen and nutrients (glucose) and removal of waste products e.g. CO2
• Single closed circulatory system:

  Blood stays in vessels on a single pathway around the body. Blood only passes through the heart once before returning to the gills

  E.g. Fish

  Heart -> gills -> body -> heart
• Double closed circulatory system:

  Mammals are endothermic (produce their own heat) so have a high metabolic rate and high energy. Therefore their cells need a large amount of glucose and oxygen and the removal of waste products like CO2.

  Blood passes through the heart twice.

  Pulmonary: Heart -> lungs -> heart

  Systemic: Heart -> body -> heart
• Advantages of Double over single system:

  1. The heart increases the pressure after it has passed through the lungs so the blood flows more quickly to the blood tissues
  2. More efficient delivery of oxygen and nutrients to body tissues
  3. The oxygen supply to heart muscles is better
  4. The systemic circulation can carry blood at a higher pressure than the pulmonary circulation
• The mammalian heart is a 4 chambered pump for both pulmonary and circulatory systems. It is a double pump working synchronously keeping oxygenated and deoxygenated blood separate. It is made of cardiac muscle (myogenic) that beats from within the muscle itself therefore never gets tired.
• Septum

  • separates the 2 sides of the heart
  • stops oxygenated and deoxygenated blood from mixing and ensures oxygenated blood gets to the body and deoxygenated blood to the lungs
  • allows different pressures to be maintained on each side. If there is a hole in the heart there would be a drop in blood pressure
• Atria

  • have a thin muscle wall which exerts a small pressure to push blood into the ventricles
• Right ventricle

  • higher pressure than the atria to push blood to the lungs, therefore the muscle wall is thicker than the atria
• Left ventricle

  • has the highest pressure as it has to pump blood through the aorta to the rest of the body. This means that the muscle wall is up to 3 times thicker than the right ventricle
• The heart is a pump that creates pressure, the blood vessels maintain the pressure
• Right side of the heart:

  Body

  Vena Cava

  Right Atrium

  Tricuspid valve

  Right ventricle

  Pulmonary valve

  Pulmonary artery

  Lungs
• Left side of the heart:

  Lungs

  Pulmonary vein

  Left atrium

  Bicuspid valve

  Left ventricle

  Aortic valve

  Aorta

  Body