03 The Mammalian Heart

1. The Mammalian HeartThe Mammalian Heart
External and Internal StructureExternal and Internal Structure
Mass = 300 gMass = 300 g
Muscle = Cardiac muscleMuscle = Cardiac muscle
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Cardiac muscleCardiac muscle

3. A mammalian heart seen from the A mammalian heart seen from the
front (External)front (External)
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Coronary arteriesCoronary arteries

5. Vertical section through a Vertical section through a
mammalian heart (Internal) mammalian heart (Internal)
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6. Vertical section through a Vertical section through a
mammalian heart (Internal)mammalian heart (Internal)
• septum
• papillary
muscle
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(mitral)

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Atrio-ventricular valvesAtrio-ventricular valves

8. Difference in thickness of the Difference in thickness of the
walls of different chambers and walls of different chambers and
their functions?their functions?
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9. Closed double
circulation
Mammalian circulatory systemMammalian circulatory system
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10. Cardiac cycleCardiac cycle
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* Sequence of events which makes up one heart beat

11. Heart action controlHeart action control
MyogenicMyogenic – naturally contracts and relaxes, not – naturally contracts and relaxes, not
needing to receive impulses from a nerve to make it needing to receive impulses from a nerve to make it
contractcontract
Important components:Important components:
i) sinoatrial node (SAN/pacemaker) – sets the rhythm of i) sinoatrial node (SAN/pacemaker) – sets the rhythm of
contraction for all other cardiac muscle cellscontraction for all other cardiac muscle cells
ii) atrio-ventricular node (AVN) – picks up the excitation ii) atrio-ventricular node (AVN) – picks up the excitation
wave as it spreads across the atria and passes it on to wave as it spreads across the atria and passes it on to
Purkyne tissuePurkyne tissue
iii) Purkyne tissue – conducting fibres that transmits iii) Purkyne tissue – conducting fibres that transmits
excitation wave through ventrical wallsexcitation wave through ventrical walls
Fibrillation Fibrillation – heart wall flutters rather than contracting – heart wall flutters rather than contracting
as a whole and then relaxing as a whole (started by as a whole and then relaxing as a whole (started by
electric shock or by damage to large areas of muscle in electric shock or by damage to large areas of muscle in
the walls of the heart)the walls of the heart)
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FibrillationFibrillation

13. Heart action controlHeart action control
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Purkyne tissue

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Electrocardiogram (ECG)Electrocardiogram (ECG)
Electrodes placed over opposite sides of Electrodes placed over opposite sides of
the heart and the electrical potentials the heart and the electrical potentials
generated recorded with timegenerated recorded with time
ECG – graph of voltage against timeECG – graph of voltage against time

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