Term
| Approximately how long is the refractory period for a pacemaker cell and when does this occur? |
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Definition
250msec.
As soon as the threshold potential has been reached until the membrane potential is back below threshold. |
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Term
| Why can't tetanus occur in contractile cardiac muscle? |
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Definition
| The contractile response begins almost immediately after the threshold potential has been reached and a single twitch terminates almost immediately after the membrane potential has fallen below threshold. Thusm due to the refractory period, it is not possible to get twitch summation. |
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Term
| How do the cardiac valves operate? |
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Definition
| They are one way valves that prevent backflow. What determines if they are opened or closed is the pressure gradient across them. For example, the AV will be open when the pressure is higher in the atrium than the ventricle and closed for the converse. |
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Term
| What causes the sounds that we can hear the heart making? |
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Definition
| They are the result of turbulance in blood flow through the heart when the valves close. First it is the AV valves, then the aortic and the pulmonary valves. |
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Term
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Definition
| The phase of the heartbeat when the atria or ventricles contract. The former is atrial systole and the latter ventricular systole. |
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Term
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Definition
| It is the volume of blood ejected by the left ventricle, into the aorta, in one cardiac cycle. |
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Term
| What is end-diastolic ventricular volume (EDV)? |
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Definition
| It is the volume of blood in the ventricle at the end of ventricular diastole. |
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Term
| What is end-systolic ventricular volume (ESV)? |
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Definition
| It is the volume of blood in the ventricle at the end of ventricular systole. |
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Term
| What is the ejection fraction and what is its normal range? |
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Definition
It is the ratio of stroke volume to end-diastolic ventricular volume:
EF = SV/EDV.
The normal range is between 50-70%. |
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Term
| How do peak pressures of the right ventricle and the pulmonary artery compare with the peak pressures of the left ventricle and the aorta? |
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Definition
| The peak pressure is higher in the left ventricle and the aorta as it has to supply the whole systemic system, whereas the right ventricle and the pulmonary artery only have to travel to the lungs. |
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Term
| What is the usual magnitude of arterial pressure? |
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Definition
| Very low, usually close to zero. It increases slightly after atrial contraction which occurs shortly after the beginning of the P wave. |
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Term
| When do the heart sounds occur in relation to the ECG recording? |
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Definition
The first sound, that of the AV valves, occurs slightly after the beginning of the QRS complex.
The second sound, that of the pulmonary/aortic valves, occurs almost immediately after the T wave. |
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Term
| Describe ventricular pressure during a typical heart beat. |
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Definition
| Pressure raises slightly with atrial systole. Then it increases serveral fold in a parabolic fashion, returning to about zero. this dramatic increase, and subsequent decrease occurs from the QRS complex to the end of the T wave. |
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Term
| When during the contractile response does the AP trigger the L-type Ca2+ channels? |
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Definition
| During the plateau phase. This is the phase when extracellular Ca2+ enters the cardiac contractile cell. |
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Term
| Detail the positive feedback response between L-type Ca2+ channels and Ryanodine receptors during cardiac mucle contraction. |
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Definition
| The ryanodine receptors in the membrane of the sarcoplasmic reticulum detect the increase in intracellular Ca2+ and releasef more Ca2+ from the cytosol into the cardiac contractile cell. |
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Term
| What is the relationship between calcium ion sparks and calcium ion signals? |
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Definition
| Calcium ion sparks occur as a result of increases in intracellular calcium ions as a consequence of APs. These sparks summate to form calcium ion signals which bind to and shift the troponin C from the tropomyosin. |
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Term
| What are the two ways calcium ions are removed from the cardiac contractile cell? |
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Definition
1. Pumped back into the sarcoplasmic reticulum by Ca2+ APTase pumps.
2. Exchanged with extracellular sodium ions by the NCX antiporter. |
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Term
| How is the sodium ion gradient maintained when the NCX antiporter is active? |
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Definition
| As extracellular sodium is being exchanged for intracellular calcium, Na+-K+ ATPase pump is exchanging 3 sodiums ions for 2 potassium ions. |
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Term
| What contribution does the sarcoplasmic reticular release of calcium ions make on intracellular calcium as compared to the calcium ions from the extracellular fluid? |
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Definition
| The calcium released from the sarcoplasmic reticulum makes up 90% of the calcium needed for contraction. The other 10% comes from extracellular sources. |
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Term
| Describe the electrochemical gradients of the types of ions associated with the NCX antiporter. |
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Definition
1. Calcium is pumped out of the cell against its electrochemical gradient.
2. Sodium is pumped into the cell along its electrochemical gradient. |
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Term
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Definition
| The phase of the heartbeat when the atria or ventricles relax from a contracted state. The former is atrial diastole, and the latter ventricular diastole. |
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Term
| What is the formula for calculating stroke volume? |
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Definition
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Term
| Describe the state of the atrioventricular valves and the pulmonary/aortic valve during a cardiac cycle. |
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Definition
1. ventricular filling:
AV - open
P/A valves - closed
2. Ventricular systole:
AV - closed
P/A valves - open
3. Early diastole:
AV - open
P/A - closed |
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Term
| What valves are open at R? |
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Definition
| No valves. The AV valves and the pulmonary and the aortic valves are closed. |
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Term
| What is an isovolumetric contraction and when and why does it occur? |
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Definition
| Occuring during the QRS complex, when all the valves are closed, the ventricle contracts. As the blood is trapped in the ventricle, the volume remains the same during the contraction. |
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Term
| During the period of ejection, when is the ejection most rapid? |
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Definition
| At the beginning when the pressure is the greatest. As blood leaves the ventricles, pressure decreases. |
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Term
| How full is the ventricle as atrial systole initiates? |
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Definition
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Term
| What two factors does the work of the heart depend on? |
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Definition
1. Volume work - the stroke volume
2. Pressure work - the pressure against which the left ventricle pumps. |
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Term
| How does the work of the heart change during exercise? |
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Definition
| The work of the heart increases, as stroke volume increases. |
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Term
| How is the work of the heart in a normal person in comparsion to a person with high blood pressure? |
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Definition
| The work of the heart is greater in the person with high blood pressure because of increaed arterial pressure. |
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Term
| What is responsible for the transformation of the blood flow pattern from pulsatile in the arteries to non-pulsatile in the capillaries? |
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Definition
| The arterioles provide a bottle neck. The arteries bulge during systole and contract during diastole. |
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Term
| How is blood pressure represented? |
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Definition
systolic pressure
diastolic pressure
(normally 120/80) |
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Term
| What causes the dicrotic notch? |
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Definition
| As the aortic vavle closes it causes a blip in the aortic pressure. |
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