Glucagon and Insulin TBR

[Meredith92]

Chapter 5 Passage 7
41. During times of stress the importance of having adequate levels of glucose, for utilization as energy, is dependent on hormonal secretions from the pancreas.
Which choice below will BEST ready the body for stressful situations?

A Increased levels of glucagon and insulin
B increased levels of glucagon and decreased levels of insulin
C decreased levels of glucagon and decreased levels of insulin
D decreased levels of glucagon and increased levels of insulin

B is correct
Increased levels of glucagon and decreased levels of insulin. it is important to remember that glucose is needed by the body as an energy source. thus, in times of stress when the body eneds energy to deal with the stressor, glucose plasma levels must increase. sympathetic stimulation of glucagon secretion will increase glycogen breakdown and increase glucose plasma levels. this will make glucose more available for tissue to utilize as an energy source. the sympathetic system will inhibit insulin secretion



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So here is an issue I've never really understood. I understand that the body, in times of stress, needs glucose for the tissues to use so blood glucose levels increase... BUT HOW DOES THE GLUCOSE GET INSIDE THE TISSUE? Doesnt it ALSO need insulin?

I feel like this is something EK may have left out.. but do some tissues, like muscle tissues not need insulin to take up glucose? I always get confused with these questions because yes, glucose blood levels must increase, but for the body to actually use the glucose to get energy, the glucose has to go inside cells, and that also needs insulin! (which decreases glucagon!)

Thanks for your help!

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[MedPR]

Chapter 5 Passage 7
41. During times of stress the importance of having adequate levels of glucose, for utilization as energy, is dependent on hormonal secretions from the pancreas.
Which choice below will BEST ready the body for stressful situations?

A Increased levels of glucagon and insulin
B increased levels of glucagon and decreased levels of insulin
C decreased levels of glucagon and decreased levels of insulin
D decreased levels of glucagon and increased levels of insulin

B is correct
Increased levels of glucagon and decreased levels of insulin. it is important to remember that glucose is needed by the body as an energy source. thus, in times of stress when the body eneds energy to deal with the stressor, glucose plasma levels must increase. sympathetic stimulation of glucagon secretion will increase glycogen breakdown and increase glucose plasma levels. this will make glucose more available for tissue to utilize as an energy source. the sympathetic system will inhibit insulin secretion



----


So here is an issue I've never really understood. I understand that the body, in times of stress, needs glucose for the tissues to use so blood glucose levels increase... BUT HOW DOES THE GLUCOSE GET INSIDE THE TISSUE? Doesnt it ALSO need insulin?

I feel like this is something EK may have left out.. but do some tissues, like muscle tissues not need insulin to take up glucose? I always get confused with these questions because yes, glucose blood levels must increase, but for the body to actually use the glucose to get energy, the glucose has to go inside cells, and that also needs insulin! (which decreases glucagon!)

Thanks for your help!

Glucose is mainly stored in certain tissues (liver) and the only way for it to move throughout your body to other tissues is via blood.

Sent from my SGH-T999 using SDN Mobile

 

[Meredith92]

But it can't be taken up by the actual cells to be used for energy (cellular respiration) without insulin... Just moving it close to the tissue wouldnt give the tissue energy it needs to be taken up by the cells

 

[MedPR]

But it can't be taken up by the actual cells to be used for energy (cellular respiration) without insulin... Just moving it close to the tissue wouldnt give the tissue energy it needs to be taken up by the cells

I see.. So you understand that glucose is primarily stored as glycogen in the liver, right? You also understand that in order for glucose to get to other tissues, glycogen must be converted to glucose, and then glucose must leave the liver and travel via blood, right? You know that glucagon causes glucose synthesis from glycogen right? You also know that insulin prevents glucagon release right? How do you intend to glycogen->glucose via glucagon if you have high levels of insulin?

 

[Postictal Raiden]

Norepinephrine is a stress hormone that has an inhibiting effects on the beta cells of the pancreas that release insulin. On the other hand, NE stimulates the alpha cells to release of glucagon into the blood stream. All this is triggered by the sympathetic autonomic nervous system.

I realize that this doesn't answer your question of how can glucose uptake from the blood stream occur if insulin is not secreted. However, you need first to understand that the brain doesn't require insulin to uptake glucose from the blood. Also, you need to remember that the the sympathetic and the parasympathetic branches of the nervous systems have an antagonistic relationship. This means, when one of them is activated, the other is inhibited. This type of relationship is reflected in insulin and glucagon.

 

[BB8730]

BUT HOW DOES THE GLUCOSE GET INSIDE THE TISSUE? Doesnt it ALSO need insulin?

I feel like this is something EK may have left out.. but do some tissues, like muscle tissues not need insulin to take up glucose? I always get confused with these questions because yes, glucose blood levels must increase, but for the body to actually use the glucose to get energy, the glucose has to go inside cells, and that also needs insulin! (which decreases glucagon!)

Thanks for your help!

You are right in that insulin is used to increase glucose uptake in skeletal muscle cells and other types of cells, but insulin is not absolutely required for glucose uptake. There are an upwards of 12 types of glucose transporters on cell membranes and only ONE of them is insulin dependent (GLUT 4). GLUT 1, for example, is found on most cell types and is not insulin dependent.

Try to think of insulin as an anabolic hormone - it helps the body "build up" and store things. Aside from glucose uptake, insulin also promotes fatty and amino acid uptake, glucose storage, and protein and fat synthesis. As you can see, it's not really something you're going to need in a stressful scenario.

Hope that helps!

 

[Meredith92]

Ok that helps a lot! So in general you want more glucose in the blood for stressful situations, which of course requires glucagon, and we assume that it gets taken up by some mechanism ( that can occur without insulin) for ATP production. Whereas when you want to store glucose it gets taken up by the cells in the presence of insulin- and here the cells aren't using it directly for energy like in the other case, but are instead packaging it away.

Great- thanks for clarifying this!! I had always just thought insulin was required for glucose uptake which didn't make sense if it needs to be taken up by cells in stressful times when no insulin is present.

 

[Meredith92]

Sorry one more follow up question!!

when insulin is present glucagon is inhibited and when glucagon is present insulin is inhibited? This doesn't agree with tbr question 44 in chap 5 bio which says after a meal heavy in protein both insulin and glucagon will be increased it says " increases in plasma amino acid concentrations will stimulate insulin secretion to promote protein production in cells. Furthermore glucagon secretion from the pancreas is also increased . Glucagon secretion is needed to prevent hypoglycemia after a heavy protein meal since amino acids also stimulate insulin secretion.


So does the whole inhibition system only happen in cases of stress with NE? Does it not happen with food scenarios/ non sympathetic responses?

Thanks again!!!

 

[slz1900]

I had this same question, and insulin does inhibit glucagon, but the effects of glucagon on insulin aren't as clear. There are some papers that say it inhibits insulin and others that say it stimulates insulin. I would guess that after a big meal whatever paracrine effects they have on each other are minimal compared to the response of the alpha and beta cells due to high blood glucose levels.

 

[MedPR]

Ok that helps a lot! So in general you want more glucose in the blood for stressful situations, which of course requires glucagon, and we assume that it gets taken up by some mechanism ( that can occur without insulin) for ATP production. Whereas when you want to store glucose it gets taken up by the cells in the presence of insulin- and here the cells aren't using it directly for energy like in the other case, but are instead packaging it away.

Great- thanks for clarifying this!! I had always just thought insulin was required for glucose uptake which didn't make sense if it needs to be taken up by cells in stressful times when no insulin is present.

You don't need to assume that. The question stem says "which will best ready the body...".

If you think of this as happening in two steps, the first step (high glucagon, low insulin) makes the body ready, the second step completes the process and pushes serum glucose into tissues (low glucagon, high insulin).

 

[MedPR]

Sorry one more follow up question!!

when insulin is present glucagon is inhibited and when glucagon is present insulin is inhibited? This doesn't agree with tbr question 44 in chap 5 bio which says after a meal heavy in protein both insulin and glucagon will be increased it says " increases in plasma amino acid concentrations will stimulate insulin secretion to promote protein production in cells. Furthermore glucagon secretion from the pancreas is also increased . Glucagon secretion is needed to prevent hypoglycemia after a heavy protein meal since amino acids also stimulate insulin secretion.


So does the whole inhibition system only happen in cases of stress with NE? Does it not happen with food scenarios/ non sympathetic responses?

Thanks again!!!

Glucagon regulates insulin. Insulin does not regulate glucagon.

 

[slz1900]

Glucagon regulates insulin. Insulin does not regulate glucagon.

You have it backwards. Insulin does inhibit glucagon. Glucagon sometimes inhibits and sometimes stimulates insulin.

http://www.ncbi.nlm.nih.gov/pubmed/7758872

http://www.ncbi.nlm.nih.gov/pubmed/2201531

http://www.ncbi.nlm.nih.gov/pubmed/10414926

 

[Meredith92]

MedPR --Yeah I realized that as well- but this same confusion has happened with me a few times on questions that did not necessarily say " ready itself" ... I've been trying to research it and it seems like some muscles do not require insulin, instead they can be stimulated to take in glucose just from a high blood glucose level

Thanks again for all the help- very appreciated

 

[Meredith92]

Slz1990--But then does tbr's answer make sense? They say insulin is secreted first and then glucagon... How can that be if insulin inhibits it?

 

[slz1900]

I'm not sure. I think the order tbr mentioned is probably unimportant and that we should just know that they work together via feedback and can work simultaneously to lower blood glucose levels. The best explanation here is just 'because that's how it is' 😛

 

[Meredith92]

Okay thanks again!!

 

[MedPR]

You have it backwards. Insulin does inhibit glucagon. Glucagon sometimes inhibits and sometimes stimulates insulin.

http://www.ncbi.nlm.nih.gov/pubmed/7758872

http://www.ncbi.nlm.nih.gov/pubmed/2201531

http://www.ncbi.nlm.nih.gov/pubmed/10414926

Right, my fault.

 

[BB8730]

Sorry one more follow up question!!

when insulin is present glucagon is inhibited and when glucagon is present insulin is inhibited? This doesn't agree with tbr question 44 in chap 5 bio which says after a meal heavy in protein both insulin and glucagon will be increased it says " increases in plasma amino acid concentrations will stimulate insulin secretion to promote protein production in cells. Furthermore glucagon secretion from the pancreas is also increased . Glucagon secretion is needed to prevent hypoglycemia after a heavy protein meal since amino acids also stimulate insulin secretion.

Just keep it simple and think of it this way - insulin is used to promote storage and synthesis. Glucagon is used to keep blood sugar levels up. In a heavy protein meal, your body will want insulin to promote amino acid uptake and protein synthesis, but insulin release will also cause a drop in blood sugar levels because insulin will increase the glucose uptake. Therefore, glucagon is also released to maintain euglycemia.

 

[Meredith92]

So if the mcat were to ask is the blood glucose level high or low following a protein meal you would say low? I just get confused about when they are referring to immediately after eating or after insulin has been released.


Brakk026- Then it seems like whenever insulin is released Glucagon will also have to be released to make sure the blood levels don't get too low?


Sorry I get so confused about all this!

 

[gettheleadout]

I had this question too. Good thread. 👍

 

[BB8730]

So if the mcat were to ask is the blood glucose level high or low following a protein meal you would say low?

If the meal was pure/mostly protein, then yes, your blood sugar would drop after the meal due to the insulin release.

Brakk026- Then it seems like whenever insulin is released Glucagon will also have to be released to make sure the blood levels don't get too low?

Not always. Insulin is secreted during a "fed state" (after a meal), and if your meal has a decent amount of sugar in it, you won't need glucagon to keep your blood sugar levels up. Glucagon is like an "oh crap" hormone that is secreted whenever blood sugar levels fall. Your brain needs glucose to function, and as you can imagine your brain is pretty high on the priority list of organs that you want to keep functioning. Whenever your blood sugar levels fall - for any reason - glucagon is secreted. Insulin, on the other hand, serves many functions and is secreted in many anabolic conditions when your body wants to utilize, build, and recover. If insulin causes blood sugar to drop, then yes, glucagon is also secreted. But most of the time our diet contains enough sugar so that we don't need glucagon after we eat a meal.

 

[Meredith92]

Ooo okay so specifically In a protein meal when there isn't a high level of glucose in the blood, that's when you also need glucagon!

Again another clarifying question.. Brakk026, You said insulin is released when the body needs to "utilize glucose" but it seems more that when the body needs to actually use glucose like during exercise/ fasting that's when glucagon and not insulin is released.

Gettheleadout- glad you had the same question!! This has always bothered me because I think a lot of mcat books over simplify this topic and I've seen so many practice questions on it!

 

[BB8730]

Again another clarifying question.. Brakk026, You said insulin is released when the body needs to "utilize glucose" but it seems more that when the body needs to actually use glucose like during exercise/ fasting that's when glucagon and not insulin is released.

Yep, you're absolutely right. Glucagon is secreted when your body really needs glucose, like during fasting and possibly during exercising. Insulin is secreted whenever your blood sugar levels are high (among other reasons) so that your body uptakes and stores the glucose.

We're probably going beyond the scope of the MCAT with our discussion here, but the major points to remember are:
*After a meal or when your blood sugar is elevated, insulin is released. Insulin also promotes fatty acid and amino acid storage/synthesis. If your meal contains very low sugar, insulin may cause your blood sugar levels to drop.
*Glucagon is your body's defense mechanism against low blood sugar levels. Your brain needs glucose to function, so glucagon is important for maintaining good blood sugar levels so that your brain can function. Whenever your blood sugar drops, your body will secrete glucagon.

 

[Meredith92]

AH I think TBR contradicted what we just concluded!

Answer to question 88 in chap 5 " we know from the passage that GIP mimics certain insulin responses. therefore we should look for an insulin response. choice D indicates a stimulation of pyruvate dehydrogenase, the enzyme converting pyruvate into acetyl CoA. this would indicate an aceeleration of glycolysis and the krebs cycle. this is certainly one of the effects of insulin, as the hormone promotes the use of glucose as a source of fuel."

I thought we had said insulin wants to STORE glucose.. not break it down and use it for energy...
i thought glucagon was the one that was used when the body needed energy quickly...

Why are they saying insulin is used for breaking down glucose, when it really should be storing glucose?

 

[Endure]

I realize I'm a bit late here, but I felt the same way when I encountered this question. Often times taking a step back and thinking about the intentions of the author helps simplify things. Right now way too much is going on to be helpful.

While insulin is obviously necessary for glucose entry into cells, you first need glucose. Readying the body for stress implies that the author is asking for the pancreatic hormone responsible for releasing glucose into the blood stream. Once glucose is available, then insulin will do it's job. Hormonal feedback mechanisms are well beyond the scope of this question.

I would also disagree that glucagon is only released when the body "really needs glucose". The insulin-glucagon byplay is continually in effect. You eat, BGL's increase, insulin's dispatched to permit glucose into cells. Glucagon is then released to restore homeostatic levels of serum glucose.

 

[BB8730]

AH I think TBR contradicted what we just concluded!

Answer to question 88 in chap 5 " we know from the passage that GIP mimics certain insulin responses. therefore we should look for an insulin response. choice D indicates a stimulation of pyruvate dehydrogenase, the enzyme converting pyruvate into acetyl CoA. this would indicate an aceeleration of glycolysis and the krebs cycle. this is certainly one of the effects of insulin, as the hormone promotes the use of glucose as a source of fuel."

I thought we had said insulin wants to STORE glucose.. not break it down and use it for energy...
i thought glucagon was the one that was used when the body needed energy quickly...

Why are they saying insulin is used for breaking down glucose, when it really should be storing glucose?

My last post is a little misleading - I didn't mean for it to sound like uptake and storage is insulin's only function. Insulin has tons of functions (http://en.wikipedia.org/wiki/Insulin#Physiological_effects). As I mentioned earlier, insulin also promotes utilization of glucose, which includes breaking it down and using it for energy.

 

[Meredith92]

Sorry to keep this going but i still can't seem to simplify it... Why would JUST glucagon be needed in times of stress like fasting or exercise? Don't you also always need insulin for the body to breakdown the glucose within the cell to be used for energy? I always get these questions wrong because I think the whole process through, when I usually the mcat is just looking for the immediate response ( glucagon release).

 

[BB8730]

Don't you also always need insulin for the body to breakdown the glucose within the cell to be used for energy?

Elevated levels of insulin promote those activities, but you don't absolutely need increased levels of insulin for those processes to still function.

Remember too that a lot of people (including me) think TBR is harder/trickier than the actual MCAT and a question like that will probably be more straightforward on the MCAT. I too was confused when I first read it because the question mentions utilizing glucose for energy, which would commonly involve insulin. If you ignore that part, though, the question is essentially asking which scenario will help maintain adequate levels of glucose (assumed to be blood glucose). The only answer that would maximize blood glucose is B.

 

[Endure]

Sorry to keep this going but i still can't seem to simplify it... Why would JUST glucagon be needed in times of stress like fasting or exercise? Don't you also always need insulin for the body to breakdown the glucose within the cell to be used for energy? I always get these questions wrong because I think the whole process through, when I usually the mcat is just looking for the immediate response ( glucagon release).

Unless I'm wrong (and please, correct me if I am), I don't see any mechanism by which insulin facilitates glucose breakdown. Without delving too deeply into the technicality, insulin promotes absorption of glucose by signaling its transporter to embed itself into the plasma membrane. The reason insulin actually opposes glucose breakdown is because it stimulates enzymes that confine glucose to the cytoplasm and ready it for glycogen storage. It also inhibits gluconeogenesis, meaning it prevents the cell from converting other macromolecules into glucose for energy.

Glucagon is the correct answer because you first need to liberate glucose from its polymerized form before you can permit its entry into cells.

 

[image187]

A basal level of insulin allows cells to maintain uptake of glucose from the blood stream for cellular metabolism. A relatively higher glucagon to insulin ratio as in the question favors increased amount of glucose sent to the bloodstream, and a relatively lower ratio favors storage in the liver as glycogen. it's all about relative levels of each hormone. If someone had glucagon and catecholamines to increase their serum glucose but NOT ENOUGH background insulin action for cells to make use of the energy, their tissue would starve and they would start breaking down other things for energy, which is exactly what happens in diabetic ketoacidosis

 

[Meredith92]

This is perfect! Thank you- completely answers it!