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Questions and Answers
What is the primary role of the atrioventricular valves?
What is the primary role of the atrioventricular valves?
Which phase of the cardiac cycle corresponds to the contraction of the heart?
Which phase of the cardiac cycle corresponds to the contraction of the heart?
How does the action potential propagate through the heart muscle?
How does the action potential propagate through the heart muscle?
Which statement best describes the sinoatrial (SA) node's function?
Which statement best describes the sinoatrial (SA) node's function?
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What occurs after the action potential spreads across the atria?
What occurs after the action potential spreads across the atria?
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Why is there a delay at the atrioventricular node?
Why is there a delay at the atrioventricular node?
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During which phase does the left ventricle fill with blood?
During which phase does the left ventricle fill with blood?
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What triggers contraction of the heart muscle?
What triggers contraction of the heart muscle?
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How long does a single contraction (systole) last?
How long does a single contraction (systole) last?
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What is the effect of the outflow valves during ventricular systole?
What is the effect of the outflow valves during ventricular systole?
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What happens to the aortic valve when intra-ventricular pressure exceeds aortic pressure?
What happens to the aortic valve when intra-ventricular pressure exceeds aortic pressure?
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During which phase is intra-ventricular pressure at its highest?
During which phase is intra-ventricular pressure at its highest?
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What is the consequence of a/v valve opening in relation to intra-ventricular pressure?
What is the consequence of a/v valve opening in relation to intra-ventricular pressure?
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What occurs during the isovolumetric relaxation phase?
What occurs during the isovolumetric relaxation phase?
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What characterizes the rapid filling phase of the ventricles?
What characterizes the rapid filling phase of the ventricles?
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How does intra-ventricular pressure change during ventricular relaxation?
How does intra-ventricular pressure change during ventricular relaxation?
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What happens when atrial pressure becomes greater than intra-ventricular pressure?
What happens when atrial pressure becomes greater than intra-ventricular pressure?
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What occurs during the diastolic phase as it continues beyond rapid filling?
What occurs during the diastolic phase as it continues beyond rapid filling?
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What causes the brief backflow that occurs when the ventricles begin to relax?
What causes the brief backflow that occurs when the ventricles begin to relax?
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Which event signifies the start of the ventricular systole phase?
Which event signifies the start of the ventricular systole phase?
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What happens during atrial systole?
What happens during atrial systole?
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What occurs during ventricular systole as intraventricular pressure rises?
What occurs during ventricular systole as intraventricular pressure rises?
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What characterizes isovolumetric contraction?
What characterizes isovolumetric contraction?
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What happens after the intraventricular pressure exceeds arterial pressure during systole?
What happens after the intraventricular pressure exceeds arterial pressure during systole?
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During the rapid ejection phase, what happens to arterial pressure?
During the rapid ejection phase, what happens to arterial pressure?
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What occurs towards the end of systole regarding artery and intraventricular pressures?
What occurs towards the end of systole regarding artery and intraventricular pressures?
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How is blood volume treated during isovolumetric contraction?
How is blood volume treated during isovolumetric contraction?
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What causes the closure of the atrioventricular (A/V) valves?
What causes the closure of the atrioventricular (A/V) valves?
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What role does the aorta play during the cardiac cycle?
What role does the aorta play during the cardiac cycle?
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During which phase is blood ejected rapidly into the arteries?
During which phase is blood ejected rapidly into the arteries?
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Study Notes
The Heart
- Two pumps in series; Each side has:
- Thin-walled atrium
- Muscular ventricle
- Flow into and out of ventricle controlled by valves:
- Atrioventricular valves (mitral & tricuspid)
- Outflow valves (aortic and pulmonary)
Heart Muscle
- Specialised tissue with discrete cells connected electrically; syncytium
- Cells contract when the action potential in the membrane reaches threshold
Heart Muscle
- Action potential causes a rise in intracellular calcium.
- Action potential is long, lasting 280 ms, called systole.
- Action potentials are triggered by spread of excitation from one cell to the next.
Pacemakers
- An action potential generated in a small group of cells will spread over the entire heart, producing a coordinated contraction.
- Pacemakers generate one action potential at regular intervals
Phases of the Cardiac Cycle
- Each action potential creates a heart beat with:
- Systole
- Diastole
Spread of excitation
- The pacemaker is in the sino-atrial node (SAN), located in the right atrium.
- Activity first spreads over the atria to cause atrial systole.
- It reaches the atrio-ventricular node (AVN), where it is paused for approximately 120 ms.
Spread of excitation - 2
- From the AVN, the excitation spreads down the septum between the ventricles.
- It then spreads through the ventricular myocardium from the inner (endocardial) to the outer (epicardial) surface.
- The ventricle contracts from the apex up, forcing blood towards the outflow valves.
The Cardiac Cycle
- At rest, the SA node generates an action potential about once a second.
- This produces a short atrial systole, followed by a longer ventricular systole.
- Ventricular systole lasts about 280 ms and is followed by a relaxation lasting about 700 ms before the next systole.
Ventricular Pumping
- The combination of regular alternating systole and diastole with inflow and outflow valves allows the heart to work as a reciprocating pump.
- The ventricles fill from the veins in diastole and pump blood into arteries in systole.
The Left Ventricle
- Inflow valve - the mitral valve:
- Allows blood from the atrium to the ventricle, but not vice-versa.
- Opens when atrial pressure exceeds intraventricular pressure.
- Closes when ventricular pressure exceeds atrial pressure.
The Left Ventricle
- Outflow valve - the aortic valve
- Allows blood from the ventricle to the aorta, but not vice-versa.
- Opens when intraventricular pressure exceeds aortic pressure.
- Closes when aortic pressure exceeds ventricular pressure.
The Cardiac Cycle
- Starts towards the end of ventricular systole:
- Ventricles are contracted.
- Intraventricular pressure is high.
- Outflow valves are open.
- Blood is flowing into the arteries.
- Ventricular pressure is greater than atrial pressure, so the AV valves close.
- Ventricles begin to relax.
- Intraventricular pressure falls.
- The intraventricular pressure becomes less than the arterial pressure.
- A brief back-flow closes the outflow valves.
- All valves are now closed, and isovolumetric relaxation occurs.
- During systole, blood has continued to return to the atria.
- Atrial pressure is relatively high.
- Intraventricular pressure falls.
- Atrial pressure eventually becomes greater than the intraventricular pressure.
- AV valves open.
The Cardiac Cycle - 4
- With the AV valves open, the ventricles:
- Fill rapidly - this is called the rapid filling phase.
- Lasts for about 200-300 ms.
- Most ventricular filling occurs during this phase
The Cardiac Cycle - 5
- As diastole continues, the ventricles fill more slowly.
- Intraventricular pressure rises as the ventricular walls stretch.
- Eventually, intraventricular pressure matches atrial pressure, and filling stops.
The Cardiac Cycle - 6
- Atrial systole:
- Forces a small amount of extra blood into the ventricles.
- The heart pumps perfectly well without atrial systole.
The Cardiac Cycle - 7
- Ventricular systole:
- Intraventricular pressure rises very rapidly.
- Quickly exceeds atrial pressure.
- After a brief backflow, the AV valves close.
- All valves are closed, and isovolumetric contraction occurs.
The Cardiac Cycle - 8
- Intraventricular pressure rises rapidly.
- It becomes greater than the arterial pressure, which has been decreasing during diastole.
- Outflow valves then open.
The Cardiac Cycle - 9
- As outflow valves open:
- Blood is ejected rapidly into the arteries, called the rapid ejection phase.
- Arterial pressure rises rapidly.
The Cardiac Cycle - 10
- As arterial pressure rises, the rate of ejection of blood falls:
- Arterial and intraventricular pressures peak towards the end of systole.
- Outflow eventually ceases with blood still in the ventricle.
The Cardiac Cycle - 11
- The cycle begins again.
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Description
Explore the anatomy and physiology of the heart in this quiz. Understand how the heart's structure, including atria and ventricles, contributes to its function. Test your knowledge on pacemakers, action potentials, and the phases of the cardiac cycle.
