5. Heart

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5. Heart

• Location
• Inside thorax, between lungs
• Function
• Pump the blood to the various parts of the body

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• Structure

• Enclosed by pericardium
• Made of cardiac muscle
• It is excitable, contractible, conductive and
  rhythmically self-regulated.
• Blood supplied by coronary arteries

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• Divided into 4 chambers left atrium, right
  atrium, left ventricle and right ventricles
• Valves
• Tricuspid valve lying between the right atrium
  and right ventricle
• Biscuspid valve lying between the left atrium
  and right ventricle
• Semi-lunar valve lying at the entrances of aorta
  and the pulmonary artery

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• Cardiac cycle
• Consists of a contraction and a relaxation of
  atria and ventricle
• Divided into systole and diastole periods

impulse reaching atria
impulse reaching atria
impulse reaching ventricles
impulse reaching ventricles
0
0.1
0.2
0.3
0.4
0.5
0.6
0.8
0.7
1.1
1.0
0.9
Time / sec
5

• Direction of blood flow
• atria contract ventricles relax ? bicuspid and
  tricuspid valves open ? blood flows into
  ventricles ? ventricles contract atria relax
  ?semi-lunar valves open, bicuspid and tricuspid
  valves close ? blood flows into pulmonary artery
  and aorta ? ventricles relax ? deoxygenated blood
  flows into right atrium, oxygenated blood flows
  into left atrium

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• The heart contracts about 70 times per minute.
• The network controlling heartbeat consists of
  Sino-atrial node (SA node), atrio-ventricular
  node (AV node), ventricular muscle, bundle of
  His containing Purkyne tissue.
• SA node is regarded as the pacemaker which
  initiates impulse control the heartbeat
  automatically and rhythmically.