mammalian heart

• What does myogenic mean?

  the heart's contraction is initiated from within the muscle itself, rather than by nerve impulses
• What is an electrocardiodiagram (ECG)?

  a graph showing the amount of electrical activity in the heart during the cardiac cycle
• What are types of abnormal activity that may be seen on an ECG?

  tachycardia: fast heartbeat (over 100bpm)

  bradycardia: slow heartbeat (under 60bpm)

  fibrillation: irregular, fast heartbeat

  ectopic: early or extra heartbeats
• What is the role of haemoglobin?

  present in red blood cells

  oxygen molecules bind to the haem groups and are carried around the body, then released where they are needed in respiring tissues
• How does partial pressure of oxygen affect oxygen-haemoglobin binding?

  as partial pressure of oxygen increases, the affinity of haemoglobin for oxygen also increases, so oxygen binds tightly to haemoglobin

  when partial pressure is low, oxygen is released from haemoglobin
• What do oxyhaemoglobin dissociation curves show?

  saturation of haemoglobin with oxygen in %, plotted against partial pressure of of oxygen in kPa

  curves further to the left show that the haemoglobin has a higher affinity for oxygen
• What is the Bohr effect?

  as partial pressure of carbon dioxide increases, the conditions become acidic causing haemoglobin to change shape

  the affinity of haemoglobin for oxygen thus decreases, so oxygen is released from haemoglobin
• What is the role of carbonic anhydrase in the Bohr effect?


  carbonic anhydrase is present in red blood cells

  it converts carbon dioxide to carbonic acid, which dissociates to produce H+ ions

  the H+ ions combine with the haemoglobin to form haemoglobinic acid

  encourages oxygen to dissociate from haemoglobin
• What is the role of bicarbonate ions (HCO3-) ions in gas exchange?

  produced alongside carbonic acid

  70% of carbon dioxide is carried in this form

  in the lungs, bicarbonate ions are converted back into carbon dioxide which we breathe out
• What is chloride shift?

  the intake of chloride ions across a red blood cell membrane

  this repolarises the cell after bicarbonate ions have diffused out
• What is the heart?

  the organ responsible for pumping the blood around the blood vessels

  it's made of cardiac muscle
• What is special about cardiac muscle?

  it's mygoenic meaning it automatically contracts and relaxes and never fatigues - a key difference from skeletal muscles
• What is the role of the coronary arteries?

  to supply the heart muscle with oxygenated blood for aerobic respiration

  this provies ATP so that the cardiac muscle can continually contract and relax
• What is the heart surrounded by?

  pericardial membranes- these are inelastic membranes which prevent the heart from filling and swelling with blood
• Why does the left ventricle have a thicker muscular wall than the right ventricle?

  so that it can contract with more force and pump the blood at a higher pressure

  this is needed so that the blood will flow all the way round the body
• Why does the right ventricle have a thinner muscular wall than the left ventricle?

  as it only pumps blood to the lungs, which is much closer and requires blood to flow slowly to allow time for gas exchange

  thus blood doesn't need to be pumped at as high a pressure, thus thin walls
• How thick/thin are the atria muscular walls?

  both atria have very thin muscular walls as the blood only needs to be pumped from the atria into the ventricles, thus minimal pressure and force is required