Sympathetic - Ep/NEp

[reising1]

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Here's a question from 1001 EK Bio

671. While deriving his 3rd law, Starling needed to increase cardiac heart rate and may have used which of the following mechanisms to do so?
I. acetycholine
II. norepinephrine
III. epinephrine

A. I only
B. II only
C. II and III only
D. I, II, and III

Answer: C

I picked D because I was under the impression that sympathetic first uses ACh in preganglionic, and then uses NEp/Ep in postganglionic, so any of the three seem to be able to work. Why is this wrong?

 

[RyanRt]

It seems like they are asking about which directly act on the receptor and ACH isn't correct because it acts indirectly.

 

[reising1]

It seems like they are asking about which directly act on the receptor and ACH isn't correct because it acts indirectly.

Hm, I'm not sure how you can see that they are asking about what directly affects it. I don't care too much about this particular question, but I just wanted to make sure that my interpretation is correct and that ACh can be considered to also have an effect?

 

[Patassa]

Hm, I'm not sure how you can see that they are asking about what directly affects it. I don't care too much about this particular question, but I just wanted to make sure that my interpretation is correct and that ACh can be considered to also have an effect?

I would guess that they are basically trying to test to make sure you know the difference between S and PS, "all of the above" answer does not demonstrate that. I would have picked C for the same reason as the other poster. In fact on my last MCAT FL #10, I missed a question because it asked which one of the choices "directly" affected something. When in doubt, pick the more specific answer because that shows a more indepth knowledge of the material.

 

[RyanRt]

Hm, I'm not sure how you can see that they are asking about what directly affects it. I don't care too much about this particular question, but I just wanted to make sure that my interpretation is correct and that ACh can be considered to also have an effect?

If you pump a bunch of ACH into a patient (simplification) then it will work on directly on the heart to slow it down regardless of what secondary effects it has.

 

[reising1]

If you pump a bunch of ACH into a patient (simplification) then it will work on directly on the heart to slow it down regardless of what secondary effects it has.

Really? Why is that?

 

[rayovac]

Postganglionic for parasympathetic is ach as well. So both pre/post ganglion is ach for para which would slow the heart, i believe.

Sym- ach/epi or norepi
Para - ach/ach

 

[krogers21]

My thought process for a question like this is:

Introducing acetylcholine only will result in either parasympathetic or sympathetic response since both use it preganglionically (I'm not sure if this is a word) where parasympathetic uses it postganglionically(again, not a word?). Giving Ep or NEp is specific only to sympathetic response, which is needed for increased HR. I'd refrain from D because ACh may or may not aid in the increased HR because it would probably aid in DECREASING the HR of the patient.

 

[reising1]

My thought process for a question like this is:

Introducing acetylcholine only will result in either parasympathetic or sympathetic response since both use it preganglionically (I'm not sure if this is a word) where parasympathetic uses it postganglionically(again, not a word?). Giving Ep or NEp is specific only to sympathetic response, which is needed for increased HR. I'd refrain from D because ACh may or may not aid in the increased HR because it would probably aid in DECREASING the HR of the patient.

Ah, okay, that makes sense. Yeah, now I see why ACh is a bad choice. It's ambiguous. Thanks!

 

[RyanRt]

My thought process for a question like th.roducing acetylcholine only will result in either parasympathetic or sympathetic response since both use it preganglionically (I'm not sure if this is a word) where parasympathetic uses it postganglionically(again, not a word?). Giving Ep or NEp is specific only to sympathetic response, which is needed for increased HR. I'd refrain from D because ACh may or may not aid in the increased HR because it would probably aid in DECREASING the HR of the patient.

That's what I was trying to say, only your explanation is better 🙂

And thats what's so difficult in my opinion about the mcat is the ambiguous questions. "Well.......that could be right in certain situations. " etc