Atrial Contractions

bell asked:


What consequences does fibrillation have for cardiac muscle contraction and for the pumping efficiency of the heart? which is more serious–atrial or ventricular fibrillation?

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kab55 asked:


this may sound stupid but i just really want it to make sense in my head so pls help!

this is about S1, S2 compared to an ECG..

i understand that S1 is heard when the AV valves close caused by the contraction of the ventricles. S2 is heard when the semilunar valves close caused by the contraction of the atria.

i also understand that the P wave represents the atrial depolarization (which then equals to atrial contraction) and QRS to ventriclular depolarization (ventricle contraction).

thus, QRS basically is when you hear the S1 sound and P is when you hear the S2 sound.

now how come we hear it as “lub dub” (S1 and then S2) but when we look at the monitor, it looks like a “dub lub” (S2 or P wave first; then S1 or QRS)? why is P closer to QRS versus QRS closer to the next P so that it looks like a lub dub?

i understand that the first electrical impulse comes from the SA node and so the atria contracts first but why do we HEAR it to the order of S1 (QRS) to S2 (P) which would technically be lub (gap) dub (versus lub-dub)

i dont know. i guess i’m just confused about how in the monitor, there seems to be a longer gap between QRS to P (where T and U come in) versus P to QRS.

sorry if it’s confusing..

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thaiger306 asked:


The tricuspid valve is closed
A)during active filling of the ventricles.
B)when the mitral valve is open.
C)while the atria are contracting.
D)during systolic ejection.
E)during passive filling of the ventricles.

As soon as left ventricular pressure exceeds the pressure in the aorta, the
A)AV valves open.
B)aortic semilunar valve opens.
C)atria pump blood into the ventricles.
D)ventricles pump blood into the atria.
E)pulmonary semilunar valve closes.

During the isovolumic contraction period of the cardiac cycle,
A)AV and semilunar valves are closed.
B)the atria are contracted.
C)ventricular volume increases.
D)blood is pumped into the large arteries.
E)pressure in the ventricles decreases.

When ventricular pressure exceeds atrial pressure, the
A)ejection occurs.
B)atria pump blood into the ventricles.
C)ventricle is in diastole.
D)blood is pumped into the atrium.
E)the first heart sound (S1) is heard.

Which of the following is true?
A)Blood enters the right and left atria only during diastole.
B)Most ventricular filling occurs before the atria contract.
C)During ventricular systole, the AV valves open.
D)The semilunar valves remain closed throughout ventricular systole.
E)Most of end-diastolic volume comes from active filling.

Having some trouble with these questions on my homework and having some trouble finding the answers.
Thanks to all!

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Duhh_hh asked:


List the sequence of events that results in atrial and ventricular contraction.

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