4.4 circulation

• structure of the heart

  as shown...

  
• structure of the heart chambers linked to functions:

  • atria - thin wall, elastic so can stretch when filled
  • ventricles - thick muscular wall, pumps blood under high pressure.
  • left ventricle thicker than right - has to transport blood around whole body
• arteries

  • carry blood from heart to tissue
  • thick walls - elastic to withstand high pressure
  • small lumen
  • no valves
  • blood at high pressure - oxygenated
• arterioles

  • carry blood from artery to capillary bed
  • thick wall - smooth muscle to control flow in capillary
  • small lumen
  • no valve
  • blood pressure falls - oxygenated
• capillaries

  • allow exchange of material
  • thin walls - one cell thick (short diffusion distance)
  • very small lumen
  • no valves
  • blood pressure falls more - changes to deoxygenated
• veins

  • carry blood from tissue to heart
  • thin wall - collagen
  • large lumen - reduce resistance to flow
  • valves - prevent back flow
  • blood at lowest pressure - deoxygenated
• the heart is a double circulatory system. why?

  • maintain blood pressure around whole body
  • when blood passes capillaries of lungs, pressure drops sharply so blood flow would not be strong enough. so is returned to the heart to get oxygenated again.
• steps of the cardiac cycle

  • diastole
  • atrial systole
  • ventricular systole
• diastole

  • heart is relaxed
  • blood flows into atria
  • pressure increases
  • causing AV valves to open
  • blood flows into ventricle
  • pressure is lower than in atria
  • SL valves stay closed
• atrial systole


  • atria contract
  • pressure increases
  • AV valves open
  • blood enters ventricle
• ventricular systole


  • ventricle contract
  • pressure increases
  • AV valves close
  • SL valves open
  • blood enters artery
• what does myogenic mean?

  • heart contraction initiated by muscles
  • not nerve impulses
• where are the 2 nodes located?

  • sino-atrial node - wall of right atria
  • atrio-ventricular node - between 2 atria

  
• function of the SAN

  • produces impulse
  • travels to AVN
  • causes muscles to contract
• control of the cardiac cycle - how does the heart contract?

  • SAN initiates impulse
  • wave of excitation spreads through atria
  • atria contracts
  • AVN receives and delays the wave
  • wave passes down bundle of his, septum and along purkyne fibres
  • ventricle contracts
• why does impulse need to be delayed?

  • wouldn't be enough time for atrial systole to occur
• advantage of slow conductivity?

  • longer delays
  • until after atria contracts
  • and atrial systole has occurred.
• difference in thickness in right atria and ventricle?

  • higher pressure required
  • right atria - thicker muscle
  • pumps blood to right ventricle
  • right ventricle pumps blood to lungs
• what is an ECG?

  graph showing electrical activity during the cardiac cycle
• what does ECG show?

  p wave = atrial systole - caused by SAN

  QRS complex = ventricular systole

  T wave = ventricle repolarisation

  Q = purkyne fibre excitation, R = start of ventricular systole, S = ventricles fully contracted

  
• what effect do nerve connections from the brain to the AVN have on heart activity?

  • no change
  • heart is myogenic
• using the graph - determine when each valve opens and closes

  
• function of blood

  • transport
  • formation of tissue fluid
  • defence against infection
• components of blood

  • plasma
  • platelets
  • erythrocytes
  • leucocytes
• plasma

  • fluid
  • contains water, ions, proteins
• erythrocytes

  • red blood cells
  • biconcave, no nucleus (large SA)
  • lots of haemoglobin
  • transports oxygen (via oxyhaemoglobin)
• leucocytes

  • lymphocytes - release antibodies (B) or chemicals in the immune response (T)
  • phagocyte, monocyte, macrophage - ingest bacteria
  • eosinophil - contain enzymes that detoxify foreign proteins
• function of blood clotting?

  • prevent blood loss and entry of pathogens
• blood clotting cascade

  • platelets release thromboplastin in response to damage
  • which is an enzyme
  • catalyses prothrombin into thrombin (active form)
  • via calcium ions
  • thrombin catalyses (soluble) fibrinogen into (insoluble) fibrin
  • fibrin forms strong fibres
  • trapping blood cells into mesh
• what is atherosclerosis?

  • build up in the wall of artery
  • after endothelium damages and causing blood clots, substances harden and form plaque
  • made up of cholesterol and lipoproteins
• how does atherosclerosis cause a myocardial infarction?

  • builds up in artery
  • breaks lining of arteriole - surface is roughened
  • weakens artery wall
  • so blood pressure causes aneurism (swelling)
  • platelets accumulate on rough surface and begin blood clotting cascade
  • if blood clot becomes mobile, it can block vessels
  • causing a heart attack.
• why can blood clots cause a stroke?

  • less blood flow
  • less oxygen reaching brain
  • less aerobic respiration
  • lactic acid produced from anaerobic respiration
  • which inhibits enzyme activity
• risk factors for cardiovascular disease?

  • age - increases as you get older
  • genetics
  • smoking
  • alcohol - leads to higher concentration of cholesterol
  • lack of exercise
  • obesity
  • high cholesterol levels - blocks vessels