CHAPTER 4: The cardiovascular system
Question - text book page 52
Why does the human body need a double circulatory system?
Answer:
• There are two circulatory systems with quite distinct functions.
• The pulmonary system provides deoxidised blood to the lungs.
• Where carbon dioxide (carried by the blood) is expelled into the lungs.
• And oxygen from the air in the lungs is transferred into the blood
• So that blood arriving at the heart from the lungs has very little CO2, but is full of O2.
• The systemic system then takes this oxygenated blood and carries it out to the rest of the body.
• Including muscle, liver, kidneys, stomach, brain.
• Where the O2 in the blood is transferred to the tissue.
• And CO2 produced by the energy creating process in the tissue is picked up and transferred back into the blood.
• Which is then carried in the blood back to the heart ready to be taken to the lungs - and so on.
Exam style questions - text book page 63 - 64
1) Figure 4.23 shows a diagrammatic picture of the cardiac impulse. Using the information in this diagram, describe the flow
of blood during the specific stages of the cardiac cycle in relation to the cardiac impulse. In your answer explain how the
heart valves help control the direction of blood flow. 8 marks
Answer:
Atrial and ventricular diastole:
• During atrial and ventricular diastole there is no electrical impulse from the SA node.
• And so relaxed heart muscle chambers (atria and ventricles) fill with blood.
• From the venae cavae (on the right hand side of the heart).
• And the pulmonary veins (on the left hand side of the heart).
• As the cuspid valves open and the semi-lunar valves close.
Diastole is followed by systole consisting of two distinct phases:
Atrial systole:
• The SA node creates an electrical impulse.
• This causes a wave-like contraction over the atria myocardium.
• Forcing the remaining blood from the atrial chambers.
• Past the cuspid valves.
• Into the ventricles.
Ventricular systole:
• The impulse reaches the AV node.
• The cuspid valves close during ventricular systole.
• The impulse travels down the bundle of His to the Purkinje fibres.
• Across ventricular myocardium.
• Which then contracts as the semi-lunar valves open.
• Blood is forced out of the ventricles.
• Into the aorta (left hand side).
• And the pulmonary arteries (right hand side).
• Myocardial contractions, during systole, are said to be myogenic or under involuntary nervous control.
SAnode
AV node
bundle
of His
myogenic
Purkinje
fibres
figure 4.23 – the cardiac impulse
QUESTIONS AND ANSWERS
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