Really need help!

[amygardner]

this question is actually in regard to a question in my university assessment, but the subject is human biosciences. This is the question:

Correctly sequence the casual links that explain the occurence of the first heart sound in the cardiac cycle (4 steps)

- Atrio-ventricular valves open
- Atrio-ventricular valves close
- Blood flows from the atria to the ventricles
- contraction of the ventricular heart muscles
- ventricular pressure exceeds pressure in the aorta
- depolarization of ventricular heart muscles

My answer so far is:
- depolarization
- blood flows from atria into ventricles
- contraction of the ventricles
- av valves open

sorry this is nothing to do with vce and that the question is soo long, just thought it would be a good place to ask. 

[Edmund]

The Atrio-ventricular valves are the ones between the atrium and ventricles

I think:

depolarisation
Atrio-ventricular valves open
Blood flows from the atria to the ventricles
Atrio-ventricular valves close
depolarization of ventricular heart muscles
contraction of the ventricular heart muscles
ventricular pressure exceeds pressure in the aorta

Then the aortic valve/pulmonary valve opens depending on left/right ventricle.

[shinny]

The first heart sound is generated by the closure of the AV valves, so naturally, the last of the four steps being asked for would be that. It's a bit of a silly question given that it's a cycle and you can't really define a starting point per se, so I guess the answer just involves working backwards 3 more steps. That gives us...

1. Atrio-ventricular valves open
2. Blood flows from the atria to the ventricles
3. Depolarisation of the atria (this was an option right? you included it in your answer but it's not in the list of answers you gave)
4. Atrio-ventricular valves close

The reason for 2 being before 3 is because the blood passively fills from the atria to the ventricles due to the pressure difference between them, even prior to the atria contracting. IIRC, two-thirds of the blood which flows from the atria to the ventricles occurs passively, with only a third flowing through due to that last atrial contraction push.

[Russ]

You can add repolarization of the atria as overlapping with the depolarization of the ventricles I guess, but shinny and Edmund have most of it