The heart

• explain why atrioventricular valves need to close?

  when ventricles contract to force blood into the arteries, pressure increases and surpasses that in the atria

  so valves need to close to prevent backflow of blood from a high to low pressure
• During the cardiac cycle, the pressure changes in the left atrium and left ventricle are different.
• The atrium has smaller pressure changes than the ventricle because the ventricle has a thicker muscle wall which is needed to pump blood at a high enough pressure to travel around the body.
• Pressure increases in the atrium first to generate a pressure difference so blood fills in the ventricle.
• The AV valve opens when atrial pressure surpasses ventricle pressure and closes when ventricular pressure surpasses atrial to prevent back flow.
• Explain how the structure of an artery wall is adapted to both withstand and maintain high blood pressure?

  collagen provides strength to withstand pressure

  thick muscle withstands pressure and constrict to maintain blood pressure

  elastic fibres allow lumen to stretch and recoil to maintain blood pressure
• Explain how the artery walls on the left side differ to the artery walls on the right side of the heart?

  the left side experiences a higher pressure

  aorta have thicker walls

  collagen to withstand high pressure

  Thick muscle wall to withstand and maintain pressure by contracting

  thick elastic fibres to maintain pressure by stretching and recoiling
• Explain why humans need a heart?

  1 to pump blood to supply glucose and oxygen to body cells and remove waste

  2 by mass transport

  3 because a small surface area to volume ratio results in a high diffusion distance and rate is not sufficient
• Name layer C?

  endothelium

  
• Explain the importance of elastic fibers in the aorta wall?


  the aorta expands when the left ventricle contracts and forces very high pressure blood. When the heart relaxes (diastole) there is risk that blood will be sucked downwards, so when the ventricle relaxes, the elastic fibers recoil which forces the blood upwards and maintains the high blood pressure and smoothing any pressure surges
• How can muscle fibers in the arterioles reduce blood flow to some capillary beds?

  vasoconstriction due to muscle contraction
• How is the structure of artery related to function (5 marks)?

  Muscular wall is thick with collagen fibers to withstand Pressure

  elastic tissue can stretch and

  recoil

  to maintain blood pressure

  smooth muscle wall is thick to withstand pressure and contract to reduce lumen size
• Describe the differences between the structure of veins and capillaries?

  veins have more than one layer, capillaries are only one layer thick

  capillaries have no smooth muscle or collagen in wall

  capillaries have no valves, veins do

  capillaries have a much narrower lumen
• What generates a greater pressure in the aorta rather than the pulmonary artery?

  the left ventricle is thicker and so contracts more forcefully
• Explain why the mammalian heart is divided into two sides?

  it keeps deoxygenated and oxygenated blood separate

  meaning as much oxygen as possible is carried to cells
• Explain how pressure differences in the heart allow for the movement of blood into the arteries 


  1- ventricles contract during ventricular systole, causing pressure to increase

  2 pressure in the ventricles surpasses the pressure in the atria and arteries

  3 this causes the AV valves to close, preventing backflow

  4 and causes the SL valves to open, forcing blood to flow into the arteries
• Describe why a heart is needed

  1. Pumps blood at a high pressure to supply oxygen and glucose to body cells

  2. This occurs via mass transport in the blood, removal of waste

  3. This occurs in organisms with a low surface area to volume so diffusion alone is insufficient to meet metabolic demands