DrSal

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Seriously, i had to decide that today.... i think that Q was BS...you can make a case for either...

oh well....mcat's over... .... ..... YEAAAAAAAAAAAAAA!!!!!!!!!!!!!!!!!!
 

medic170

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I believe epi is a hormone and its neurotransmitter form (and precursor) is norepinephrine
 
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DrSal

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yea...i know it's a hormone, but i also know that it exerts its affects quickly, and...in a previous class there was really no distinction made. Seriously...i was like well, it's made int he adrenal glands...but...then i just said neurotransmitter b/c it seemed to fit in better with the passage. MAn, that could've been my 1 q away form the next point up :(

but i'm cool tho...it's all good. I'm just glad i finished :D
 

dollarbincommon

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I think epinephrine functions as both hormone and nt.
 

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I am damn sure that epinephrine is a hormone and a neurotransmitter
 

babinski bob

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epi is a hormone and not a neurotransmitter. neurotransmitters act locally and do NOT get dumped into the bloodstream. Hormones get dumped in the blood stream where they get dispersed and act at distant sites (epi gets dumped in the blood from the adrenals and acts on the heart, lungs, eye, etc). it is a tricky question and during the heat of the moment, it can certainly cause some serious head scratching.. :)
 

liverotcod

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OK, well what about acetylcholine?
 

bella_dottoressa

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That's tough. A chemical can be both a hormone and a neurotransmitter though and I think epi is such an example. Epi is secreted by the adrenal medulla as a hormone and by sympathetic neurons as a neurotransmitter- both have same effect, but circulation of hormone takes longer than conduction of nerve impulse; so epinephrine from a sympathetic neuron will cause more of an immediate effect, but circulating epinephrine from adrenal medulla will have a longer-lasting effect.

i know Ach is a really common neurotransmitter...not sure though if it has a role as a hormone..?
 

UCLAstudent

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I put that it's a hormone because it's produced and secreted by the adrenal medulla.
 

babinski bob

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ACh is definitely not a hormone at all. It would get hydrolyzed immediately in the plasma by plasmacholinesterase and various other cholinesterases.
 

rjhtamu

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What the above posters said, Epi is definitely a hormome, ACh is definitely a neurotransmitter.

There are many that are easily both, such as norepinephrine, however the two above are primarily in those categories.
 
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DrSal

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ok, well, i looked it up in my book.

The adrenal cortex is a true endocrine gland. However, the adrenal MEDULLA is modified sympathetic ganglion which lack axons, and their cell bodies, called chromafin, are what produce and secrete epi into the blood.

that Q was JUST NOT COOL!!!!
 

rjhtamu

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Very true, however there are also definitive guidelines on what exactly is a neurotransmitter.

Per the latest information:

1)Substance must be present or synthesized in the presynaptic neuron

2)Substance must be released in response to depolarization in a Ca2+ dependent manner.

3)Specific receptors for the substance must be present on the post synaptic cell

4)A mechanism must exist for the substance to be removed from the synaptic cleft.
 

DrSal

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rjhtamu said:
Very true, however there are also definitive guidelines on what exactly is a neurotransmitter.

Per the latest information:

1)Substance must be present or synthesized in the presynaptic neuron

2)Substance must be released in response to depolarization in a Ca2+ dependent manner.

3)Specific receptors for the substance must be present on the post synaptic cell

4)A mechanism must exist for the substance to be removed from the synaptic cleft.
Really? wow.... oh well...but it was a tough Q...no? Maybe we can say it was just experimental...so i can get some sleep at night? :laugh: Thanks for the input!!
 

phospho

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I know this thread is like 3 years old, but does someone have any new information in regards to this? Specifically, what's bothering me is trying to know the difference in the actions of epinephrine and norepinephrine. I know they both act as hormones, stimulating the sympathetic nervous system. I also know that in their sysnthesis pathway, we get dopamine, then we get norepi and then we get epi. But I still don't know what makes them different from each other in the kind of effects they have on the nervous system.:confused:

Also, if we get a question on the MCAT asking us if epi (or even norepi) is a hormone OR a neurotransmitter, then what the heck do we put?

thanks in advance:)
 

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NE is definately a neurotransmitter...this is what differentiates SNS and PNS postganglionic nurotransmitters. Both SNS and PNS use Ach in their preganglionic transmitters, however SNS has "adrenergic" neurons which release norepinephrine (noradrenaline) and the SNS still uses Ach to their cholinergic receptors. I am almost positive in the MCAT epinephrine will be considered a hormone b/c it is not used in this case and given some of the posters explainations above. I just got done with this in A&P so I hope this helps you.
 

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If being held at gunpoint by Tony Soprano, I'm calling epi a hormone because of how it behaves the majority of the time. However, I believe that it can act as both depending on where in the body you are referring. The molecule doesn't know how it got to its receptor when it arrives, so the discussion is odd from a physiological standpoint. If it arrives via blood, I call it a hormone. If it jumps a synapse, I call it an NT.

As far as effects go, both E and NE can stimulate adrenergic receptors, though NE is usually the one that acts locally as an NT while for undergrad purposes I might offer that epi arrives by blood from the adrenal medulla. Let me know if you want me to give you an example of epi acting as an NT.
 

phospho

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Thank you both for your replies. So, does that mean that one of the above posters is right in saying:

"epi is a hormone and its neurotransmitter form (and precursor) is norepinephrine?"

From this thread, does that mean that if I get a question on the MCAT asking me if epi or nor epi are hormones OR neurotransmitters, I should enter in hormones? The EK bio book specifically states that they are both hormones, that's why it got confusing.

Also, Critical Mass, would you mind giving me an example of epi acting as a neurotransmitter?

Thanks again:)
 

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Very true, however there are also definitive guidelines on what exactly is a neurotransmitter.

Per the latest information:

1)Substance must be present or synthesized in the presynaptic neuron

2)Substance must be released in response to depolarization in a Ca2+ dependent manner.

3)Specific receptors for the substance must be present on the post synaptic cell

4)A mechanism must exist for the substance to be removed from the synaptic cleft.
True, however there are putative neurotransmitters, epinephrine being one of them, which meet the above criteria except for #4 as no system exists for reuptake. So, the answer would be that yes, epi is both a hormone and a putative neurotransmitter (had to memorize this one last semester for Physiology)
 

Critical Mass

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"epi is a hormone and its neurotransmitter form (and precursor) is norepinephrine?"
I can see some justification for that statement. NE is the workhorse as an NT. Gimme a sec on the epi as an NT. Gotta look through my neuro notes really fast.
 

Critical Mass

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OK sweetie, this is straight from my MS 1 neuro course guide under the title "Epinephrine." Sorry that it took so long. Had to get some food.

"C1 and C2 cell groups are located in the medulla in the areas close to the A1 and A2 NE cell groups. The C1 cell group sends projections to the IML nucleus in the spinal cord. The C2 cell group sends projections to the hypothalamus. Little is known about the function of epinephrine (as an NT). The C1 cell group is thought to be involved in regulation of cardiovascular and respiratory function. The C2 cell group regulates the secretion of oxytocin and antidiuretic hormone."

So apparently its function as an NT is felt in the CNS but lives a hormone's lifestyle in the peripheral nervous system. I think that for the purposes of the MCAT you are good thinking of it like a hormone.

FWIW, the adrenal medulla contains specialized chromaffin cells that are innervated from preganglionic sympathetics. When stimulated, they spew mostly epi (but the epi is then released in an endocrine fashion via the bloodstream making it a hormone).

Also from my course guide:

"NE activates all alpha and beta-1 receptors. NE is less potent in activating beta-2 and beta-3 receptors. Epi activates all adrenergic receptors, but it has a greater potency for activating beta receptors compared to alpha receptors." Again, keep in mind that in this sense, the epi is also acting in an endocrine fashion, not necessarily as an NT.
 

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I think everyone on this board (and the board creating the MCAT) knows that these are both hormones that also act as neurotransmitters; thus, I would bet that this question must have been preceded by a passage providing the context of some specific situation/function.

phospho, you seem to be really exhaustively reviewing. out of curiosity - what kind of score are you shooting for?
 

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Okay, technically speaking, epinephrine is the hormone, and norepi is the nuerotransmitter.

Structurally, although they are very similar, nor epi has an protonated amine and methylene group, where as epi is simply a secondary amine with a methyl group. This is just for proper conjugation with the proper adrenergic receptor (in the case of norepi).

As for formation, well norepi is formed first from dopamine, and epi can be reformed from norepi.

Good Luck
 

phospho

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OK sweetie, this is straight from my MS 1 neuro course guide under the title "Epinephrine." Sorry that it took so long. Had to get some food.

"C1 and C2 cell groups are located in the medulla in the areas close to the A1 and A2 NE cell groups. The C1 cell group sends projections to the IML nucleus in the spinal cord. The C2 cell group sends projections to the hypothalamus. Little is known about the function of epinephrine (as an NT). The C1 cell group is thought to be involved in regulation of cardiovascular and respiratory function. The C2 cell group regulates the secretion of oxytocin and antidiuretic hormone."

So apparently its function as an NT is felt in the CNS but lives a hormone's lifestyle in the peripheral nervous system. I think that for the purposes of the MCAT you are good thinking of it like a hormone.

FWIW, the adrenal medulla contains specialized chromaffin cells that are innervated from preganglionic sympathetics. When stimulated, they spew mostly epi (but the epi is then released in an endocrine fashion via the bloodstream making it a hormone).

Also from my course guide:

"NE activates all alpha and beta-1 receptors. NE is less potent in activating beta-2 and beta-3 receptors. Epi activates all adrenergic receptors, but it has a greater potency for activating beta receptors compared to alpha receptors." Again, keep in mind that in this sense, the epi is also acting in an endocrine fashion, not necessarily as an NT.
thank you so much, I just wrote that down in my notes:D

:luck:
 

phospho

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phospho, you seem to be really exhaustively reviewing. out of curiosity - what kind of score are you shooting for?
Ideally, 35+, realistically, 30+... Physics is kicking my ass, so I really have to know my chemistries and bio... it's just that I come across these weird questions sometimes, and they make me think that there might be something I haven't focused on, etc... Let's hope for the best:oops:

:luck:
 
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