Competition - post a photo you've taken of nature >>

Cardiac cycle wjec / eduqas

Hi, when you are asked to describe a cardiac cycle, do you describe the three stages or do you just describe SAN and AV. Is SAN and av the ones that initiate the cardiac cycle and this leads to systoles and diastoles? In this question which came up in the wjec past paper it asks 'describe how the sequence of event that takes place during cardiac cyle is initiated and controlled' but I wrote about the three stages instead which are wrong. But surely, this is what u get as the heart starts beating? I don't get why in the mark scheme, you will only get marks if you talk about the electrical stimulation. I knowbthat in this type of 10 marker wuestion, since its talking abiut the cardiac cycle, you could talk about a range of things, so why is it all about SAN only?? Thanks

(edited 8 years ago)

Reply 1

hknobody

the cycle is "initiated and controlled" by SAN and AVN

you describe the cycle when the question ask you to describe the events occurred during the cardiac cycle.

Reply 2

zabveniye

That is quite painfully specific for a longer question -- but really, to get the marks you have to just learn to play their game and give them exactly what they want in answers. If they're asking for how the cycle is initiated and controlled, they don't want you to write about what the cycle IS -- they're assuming that you know that well, and testing you instead just on the initiation and control of it. You don't need to describe the stages of the cardiac cycle, just explain why they happen. So yes, the sinoatrial node (SAN) and the atrioventricular node (AVN) -- if you have learnt these already, also chemoreceptors, baroreceptors and the medulla oblongata, but ignore these if they don't appear until a later unit in your specification. Focus on what the SAN and AVN are, what exactly they do, what causes them to do that, and how they affect the cardiac cycle -- what might happen if they weren't functioning properly, and couldn't initiate, or couldn't control it?

Reply 3

coconut64

Original post by zabveniye

So whenever a question asks me about how the cardiac cycle is initiated and controlled, I will only need to mention SAN and AVN? So what would the question be like if I have to describe the three stages? When do I talk about the styole,diastole, when do I talk about the flow of blood through the left atrium and into the lungs and when do I talk about the opening and closing of valves? I don't just know which is part this a question will ask because they are all to do with the cardiac cycle. Thanks .

(edited 8 years ago)

Reply 4

coconut64

Original post by hknobody

the cycle is "initiated and controlled" by SAN and AVN

you describe the cycle when the question ask you to describe the events occurred during the cardiac cycle.

But the flow of blood from the left side of heart is also part of the cardiac cycle. Also the opening and closing of valves. So how do I know that I need to talk about one specifically? Thank you.

Reply 5

wackojacko98

a good trick for them questions is overstating the lot if your not sure, i find when descibing each stage its easier to break it into 5 steps
1.Stage
2.Muscle
3.Pressure
4.Valves
5.Blood
In using this you will hit all the marks needed when taking about the 3 stages. Then all you have to do is get your head around the electical waves throught SAN etc

Reply 6

zabveniye

Original post by coconut64

It is hard to know -- again, I agree that the question was vague for the particular answer that they wanted, but sadly that often seems to be the case in exams. Of course they'll word them differently every year and you just have to really take in every word of the question and try to answer it as exactly as possible. I've been caught out by the same kind of thing plenty of times too.

One idea when you're not completely sure is to answer with the point-on answers first (it is initiated and controlled by the SAN and AVN) and then if you have some time later go back to write down more about the stages just in case.

Usually though, when they talk about co-ordination, initiation or control, they want you to specifically write about nerve impulses e.g. the wave of electrical excitation from the SAN. Aside from initiation, this is "control" because the body can detect changes in heart rate and change the frequency of electrical impulses to and from the SAN -- systole and diastole are more just consequences of this.

I found an example of a question which asks you to focus on the heart muscle and valves and not the SAN or AVN, and this one is more clearly worded:

“Explain how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta.” (5 marks)