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Biology: Topic 7 > The Cardiac Cycle > Flashcards

The Cardiac Cycle Flashcards

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1
Q

what is the cardiac cycle?

A
  • the heart undergoes a sequence of events about every 70 times each minuet
  • contraction occurs separately in the ventricles and the atria
  • relaxation takes place simultaneously in all chambers
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2
Q

what are the phases of each heart beat?

A
  • contraction (systole)

- relaxation (diastole)

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3
Q

what is diastole?

A
  • blood returns to the atria of the heart through the pulmonary vein and the vena cava
  • as the atria fill the pressure in them rises
  • when the pressure exceeds that in the ventricles so the atrioventricular valves open to allow the blood to pass into the ventricles
  • the passage of blood is aided by gravity so the muscular wall of both the atria and ventricles are relaxed at this stage
  • the relaxation of the ventricle walls causes them to recoil and reduces the pressure within the ventricle causing the pressure to be lower than that in the aorta and the pulmonary artery so the semi lunar valves in the aorta and the pulmonary artery closes
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4
Q

what is atrial systole?

A
  • the contraction of the atrial walls and the recoil of the relaxed ventricle walls forces the remaining blood into the ventricles from the atria
  • throughout this stage the muscle of the ventricle walls remains relaxed
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5
Q

what is the ventricular systole?

A
  • after a short delay to allow the ventricles to fill with blood so their walls contract simultaneously
  • this increases the blood pressure within them to force shut the atrioventricular valves to prevent the backflow of blood into the atria creating the lub sound
  • as the atrioventricular valves close the pressure in the ventricles rises further so it exceeds that of the aorta and the pulmonary artery so blood is forced from the ventricles into these vessels
  • the ventricles have thick muscular walls which mean they contract forcefully which creates the high pressure necessary to pump blood around the body
  • the thick wall of the left ventricle has to pump blood to the extremities of the body while the relatively thinner wall of the right ventricle has to pump blood to the lungs
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6
Q

how do valves control blood flow?

A
  • blood is kept flowing one direction through the heart and around the body by the pressure created by the heart muscle
  • blood will always move from a region of higher pressure to one of lower pressure
  • in some situations within the circulatory system the pressure differences would result in blood flowing in opposite direction from that which is desirable so the valves are used to prevent any unwanted backflow of bloodstream
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7
Q

what do valves in the cardiovascular system do?

A
  • they are designed to open whenever the differences in the blood pressure either side of them favours the movement of blood in the required direction
  • when pressure differences are reversed blood tends to flow in the opposite direction to what is desirable so the valves are designed to close
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8
Q

what are the atrioventricular valves?

A
  • they are found between the left atrium and ventricle and the right atrium and ventricle
  • they prevent the backflow of blood when contraction of the ventricles means that ventricular pressure exceeds articular pressure
  • closing these valves ensures that when the ventricles contract blood within them moves to the aorta and pulmonary artery rather than back into the atria
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9
Q

what are the semi lunar valves?

A
  • they are found in the aorta and pulmonary artery
  • they prevent backflow of blood into the ventricles when the pressure in these vessels exceeds that of the ventricles
  • this is needed when the elastic walls of the vessels recoil increasing the pressure within them and when the ventricle walls relax reducing the pressure within the ventricles
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10
Q

what is the structure of the valves in the cardiovascular system?

A
  • they are made up from a number of flaps of tough but flexible fibrous tissues which are cup shaped
  • when pressure is greater on the convex side of these cups they move apart to let blood pass between the cusps
  • when the pressure is greater on the concave side blood collects within the cusps which pushes them together to form a tight fit that prevents the passage of blood
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11
Q

how does pressure and volume change in the heart?

A

-mammals have a closed circulatory system so the blood is confined to vessels allowing the pressure within them to be maintained and regulated

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12
Q

what is cardiac output?

A
  • the volume of blood pumped by one ventricle of the heart in one minute
  • measures in dm^3min^-1
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13
Q

which factors affect cardiac output?

A
  • the heart rate

- the stroke volume

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14
Q

what is the stroke volume?

A

-the volume of blood pumped out at each beat?

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15
Q

what is the ventricular pressure in the left side of the heart?

A
  • its slow at first but gradually increases as the ventricles fill with blood as the atria contract
  • the left atrioventricular valves closes and the pressure rises dramatically as the thick muscular walls contract
  • as pressure rises above that of the aorta past the semilunar valves pressure falls as the ventricles empty and the walls relax
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16
Q

what is the aortic pressure in the left side of the heart?

A
  • the pressure rises as the ventricles contract so blood is forced into the aorta so it gradually falls but never below around 12kPa because of the elasticity of its wall which creates a recoil action which is essential for the blood to be constantly delivered to he tissuess
  • the recoil produces a temporary rise in pressure at the start of the relaxation phase
17
Q

what is the atrial pressure in the left side of the heart?

A
  • its always low because the thin walls of the atrium cannot create much force
  • it is the highest when they are contracting but drops when the left atrioventricular valve closes and its walls relax
  • the atria then fill with blood which leads to the gradual build up of pressure until a slight drop when the left atrioventricular valve opens and some blood moves into the ventricle
18
Q

what is the ventricular volume in the left side of the heart?

A
  • pressure raises as the atria contract and the ventricles fill with blood and then drops suddenly as blood is forced out into the aorta when the semi lunar valves open
  • the volume increases as the ventricles fill with blood

Biology: Topic 7 (9 decks)

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