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Cardiac Physiology
Lecture 2
33
Physiology
Undergraduate 2
06/09/2011

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Term
Approximately how long is the refractory period for a pacemaker cell and when does this occur?
Definition

250msec.

As soon as the threshold potential has been reached until the membrane potential is back below threshold.

Term
Why can't tetanus occur in contractile cardiac muscle?
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.
Term
How do the cardiac valves operate?
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.
Term
What causes the sounds that we can hear the heart making?
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.
Term
What is systole?
Definition
The phase of the heartbeat when the atria or ventricles contract. The former is atrial systole and the latter ventricular systole.
Term
What is stroke volume?
Definition
It is the volume of blood ejected by the left ventricle, into the aorta, in one cardiac cycle.
Term
What is end-diastolic ventricular volume (EDV)?
Definition
It is the volume of blood in the ventricle at the end of ventricular diastole.
Term
What is end-systolic ventricular volume (ESV)?
Definition
It is the volume of blood in the ventricle at the end of ventricular systole.
Term
What is the ejection fraction and what is its normal range?
Definition

It is the ratio of stroke volume to end-diastolic ventricular volume:

EF = SV/EDV.

The normal range is between 50-70%.

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?
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.
Term
What is the usual magnitude of arterial pressure?
Definition
Very low, usually close to zero. It increases slightly after atrial contraction which occurs shortly after the beginning of the P wave.
Term
When do the heart sounds occur in relation to the ECG recording?
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.

Term
Describe ventricular pressure during a typical heart beat.
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.
Term
When during the contractile response does the AP trigger the L-type Ca2+ channels?
Definition
During the plateau phase. This is the phase when extracellular Ca2+ enters the cardiac contractile cell.
Term
Detail the positive feedback response between L-type Ca2+ channels and Ryanodine receptors during cardiac mucle contraction.
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.
Term
What is the relationship between calcium ion sparks and calcium ion signals?
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.
Term
What are the two ways calcium ions are removed from the cardiac contractile cell?
Definition

1. Pumped back into the sarcoplasmic reticulum by Ca2+ APTase pumps.

2. Exchanged with extracellular sodium ions by the NCX antiporter.

Term
How is the sodium ion gradient maintained when the NCX antiporter is active?
Definition
As extracellular sodium is being exchanged for intracellular calcium, Na+-K+ ATPase pump is exchanging 3 sodiums ions for 2 potassium ions.
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?
Definition
The calcium released from the sarcoplasmic reticulum makes up 90% of the calcium needed for contraction. The other 10% comes from extracellular sources.
Term
Describe the electrochemical gradients of the types of ions associated with the NCX antiporter.
Definition

1. Calcium is pumped out of the cell against its electrochemical gradient.

2. Sodium is pumped into the cell along its electrochemical gradient.

Term
What is diastole?
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.
Term
What is the formula for calculating stroke volume?
Definition
SV=EDV-ESV
Term
Describe the state of the atrioventricular valves and the pulmonary/aortic valve during a cardiac cycle.
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

Term
What valves are open at R?
Definition
No valves. The AV valves and the pulmonary and the aortic valves are closed.
Term
What is an isovolumetric contraction and when and why does it occur?
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. 
Term
During the period of ejection, when is the ejection most rapid?
Definition
At the beginning when the pressure is the greatest. As blood leaves the ventricles, pressure decreases.
Term
How full is the ventricle as atrial systole initiates?
Definition
Greater than 80%
Term
What two factors does the work of the heart depend on?
Definition

1. Volume work - the stroke volume

2. Pressure work - the pressure against which the left ventricle pumps.

Term
How does the work of the heart change during exercise?
Definition
The work of the heart increases, as stroke volume increases.
Term
How is the work of the heart in a normal person in comparsion to a person with high blood pressure?
Definition
The work of the heart is greater in the person with high blood pressure because of increaed arterial pressure.
Term
What is responsible for the transformation of the blood flow pattern from pulsatile in the arteries to non-pulsatile in the capillaries?
Definition
The arterioles provide a bottle neck. The arteries bulge during systole and contract during diastole.
Term
How is blood pressure represented?
Definition

systolic pressure

diastolic pressure

 

(normally 120/80)

Term
What causes the dicrotic notch?
Definition
As the aortic vavle closes it causes a blip in the aortic pressure.
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