the heart

• why can't large organisms simply use diffusion?


  their SA to volume ratio isn't large enough for diffusion alone to supply substances, eg: oxygen and glucose, to cells where they are needed.
• what are the 4 features of a circulatory system?


  1. suitable medium. In mammals the transport medium is blood, water based so substances can easily dissolve into it.
  2. means of moving the medium. Animals have a pump, the heart, it maintains pressure differences around the body.
  3. mechanism to control flow around the body. valves are used in veins to prevent back flow.
  4. close system of vessels. circulatory system is closed and is branched to deliver substances to all parts of the body.
• how can you describe the mammalian circulatory system?

  a closed double circulatory system.
• how many pumps does the heart have?


  two pumps.
• what does the pumps do?


  one pumps blood to the lungs to be oxygenated.

  one pumps the oxygenated blood around the body to supply vital organs and tissues. This one is larger and stronger.
• what is the atrium like?


  thin walled and elastic. The atrium can stretch when filled with blood.
• what is the ventricles like?


  thick muscular wall to pump blood around the body or to the lungs.
• why does the heart need 2 pumps?

  in order to maintain blood pressure around the whole body. One wouldn't be able to do this as the slow down of the blood as it passes the lungs would cause it to lose all pressure.
• what valves are between the atria and ventricles?

  the left atrioventricular valve and the right atrioventricular valve.
• what is the other word for the left atrioventricular valve?


  bicuspid valce.
• what is the other word for the right atrioventricular valve?


  tricuspid valve.
• what are the 4 main vessels connecting the heart?

  1. aorta
  2. pulmonary artery
  3. pulmonary vein
  4. vena cava
• what is the aorta like?


  connected to the left ventricle, carried oxygenated blood to all parts of the body except the lungs.
• what is the pulmonary artery like?


  connected to the right ventricle, carried deoxygenated blood to the lungs where it is oxygenated and the carbon dioxide is removed.
• what is the pulmonary vein like?


  connected to the left atrium, brings oxygenated blood back from the lungs.
• what is the vena cava like?


  connected to the right atrium, brings deoxygenated blood back from the tissues except the lungs.
• why is the heart called myogenic?


  because the heart has the ability to imitiaye its own contraction.
• what is the pacemaker of the heart? 


  the pacemaker is a region of specialised fibres called the sinoatrial node. It initiates a wave of electrical stimulation which causes the atria to contract at roughly the same time.
• where is the hearts pacemaker?


  the right atrium.