Kaplan glucagon/insulin question

[bxadook]

A 10 year old boy goes to a physician complaining of polyuria. A blood test reveals elevated blood glucose. What would further tests reveal?

A. Low insulin

B. Low glucagon

My answer was glucagon. Kaplan says insulin, anyone willing to explain?
The basis behind my answer is this, why would the body tell itself to secrete more glucose into the blood when there is an abundance of it? I dont really trust their explanation.

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[fizzgig]

not sure, but this is the situation you'd encounter in typeI diabetes right? pancreatic cells die, insulin isn't made, and blood sugar gets high, producing symptoms?

 

[bxadook]

Right, but the only definitive answer is low glucagon! You can say with absolute certainty that the ratio of glucagon to insulin is low. You cannot know whether the kid has type 2 or type 1 diabetes based on the information given in the question.

 

[fizzgig]

i guess if you had a pancreatic alpha cell tumor it could produce loads and loads of glucagon, making blood sugar high as well...

now i'm confused too.. dunno how you know if high blood sugar is the result of too much glucagon or not enough insulin, because in theory it could be either?

 

[QUOTiDIAN]

A 10 year old boy goes to a physician complaining of polyuria. A blood test reveals elevated blood glucose. What would further tests reveal?

A. Low insulin

B. Low glucagon

My answer was glucagon. Kaplan says insulin, anyone willing to explain?
The basis behind my answer is this, why would the body tell itself to secrete more glucose into the blood when there is an abundance of it? I dont really trust their explanation.

How I understand insulin is, non-orthodox, insulin allows blood glucose to get INto the cells. so if insulin is low, blood glucose wont be getting into the cells but remain in the blood. this will result in elevated blood glucose.

Insulin antagonizes glucagon. the function of glucagon is to increase blood glucose, so if glucagon level is low, blood glucose level would be low, because glucagon activity of converting glycogen to glucose will be limited due to the low glucagon doing the job

I hope this helps,

 

[Charles_Carmichael]

If blood glucose is high, there wouldn't be any need for glucagon to be in the blood. The purpose of glucagon is to raise blood sugar. And when blood glucose is already high, glucagon will not be secreted. The physiological response to high blood glucose is to increase insulin secretion.

The reason blood glucose is high is because there is a lack of insulin. You can't automatically assume the kid has diabetes. Don't overthink this. Think basic endocrine physiology. Insulin facilitates glucose uptake by cells. Without this facilitation (ie. lack of insulin), glucose will remain in the bloodstream. If insulin was functioning normally, there will be tight control of blood glucose. With normal insulin functioning, you will not see glucose in the urine due to high blood glucose.

Hope this helps.

 

[Charles_Carmichael]

Right, but the only definitive answer is low glucagon! You can say with absolute certainty that the ratio of glucagon to insulin is low. You cannot know whether the kid has type 2 or type 1 diabetes based on the information given in the question.

You can't say that with certainty. In your sentence following the bolded one is the reason why you can't say that with certainty.

 

[bxadook]

Ahh you are correct, I did contradict myself. But as I recall from biochem, you don't completely stop producing insulin or glucagon. The pancreas is producing both at all times, just one predominates over the other during certain periods. So if you analyze the situation without knowing if the kid has diabetes or not, if he has high blood sugar he must have low glucagon. I know the function of both. I know test taking strategy tells me to pick the most correct answer, this just seems more correct in this situation.

 

[Charles_Carmichael]

Ahh you are correct, I did contradict myself. But as I recall from biochem, you don't completely stop producing insulin or glucagon. The pancreas is producing both at all times, just one predominates over the other during certain periods. So if you analyze the situation without knowing if the kid has diabetes or not, if he has high blood sugar he must have low glucagon. I know the function of both. I know test taking strategy tells me to pick the most correct answer, this just seems more correct in this situation.

I understand what you're saying. I really do. But it doesn't matter what you or I think is the correct answer. Whatever the test writer says is the correct answer is the correct answer.

For me, this would've been a question I wouldn't spend more than a few seconds on due to how many times I've seen this sort of question asked. Asking about polyuria and elevated blood glucose in a kid? Type I diabetes just jumps out at me yelling "pick me, pick me!" Because it's a kid, Type I is more likely and the polyuria is most likely due to the elevated blood glucose...the kidneys cannot fully reabsorb the filtered glucose due to saturation of transporters. Everything about this question, to me, screams diabetes (in particular, Type I due to the reasons I mentioned earlier). I personally don't remember ever coming across a question during practice passages, practice AAMCs, and the actual MCAT that asked a question like this and the answer didn't involve insulin.

Like I said, I understand what you're saying. I guess, based on experience, insulin immediately jumps out as the correct answer to me. Or maybe it's because my physio background is telling me that the signs seem to point to Type I diabetes.

 

[bxadook]

Right Kaushik and thanks, I appreciate the help... the more I think about it insulin would be more correct, because glucagon resistance or dependence isn't as widely talked about as insulin.

 

[fizzgig]

so if you have high blood sugar, there's no prediction for glucagon?

just checking... the answer insulin jumped out at me too, but if i stopped and overthought for just ONE second i'd go down that road too... well if glucose is high, no need for glucagon, so if glucagon is fxning normally then it should be low. insulin i can't be as sure about since type I and II would imply opposite insulin levels...

maybe they're insisting on 'what got us here' versus 'what is the reaction to this situation'...

what got us here is low insulin or high glucagon. what the reaction SHOULD at least be would be higher insulin or lower glucagon...

 

[orthomyxo]

A 10 year old boy goes to a physician complaining of polyuria. A blood test reveals elevated blood glucose. What would further tests reveal?

A. Low insulin

B. Low glucagon

My answer was glucagon. Kaplan says insulin, anyone willing to explain?
The basis behind my answer is this, why would the body tell itself to secrete more glucose into the blood when there is an abundance of it? I dont really trust their explanation.

First, you must know the functions of both hormones.

Insulin is released when the blood glucose level rises above a set point, and causes the liver/muscle cells/fat cells to store it as glycogen, eventually lowering glucose levels back to the set point.

Glucagon is released when the blood glucose level falls below the set point, and causes the liver/fat cells/muscle cells to release their stored glycogen (in that order, if I remember correctly) causing glucose levels to rise back to normal.

That being said, it makes much more sense that a child with elevated blood glucose would have an excess of insulin in the blood. The body will try to correct the problem and will continue to release it in an attempt to cause an uptake of glucose. Unless there was something wrong with the kid's hypothalamus or something, the body wouldn't continue to release glucagon if the normal blood glucose set point was already reached.

Edit: I thought the choices were "high insulin" and "high glucagon." Now I'm confused lol

I still can rationalize the "low insulin" choice. Assuming the child's problem is pre-diabetes/diabetes, and not something much more complicated, there wouldn't be a need for glucagon in the bloodstream at all. So we can say that low insulin levels are preventing his cells from absorbing the glucose as glycogen, causing his blood glucose level to remain high.

 

[Rayhaan]

If he has high glucose in his urine it means there was more plasma concentration of glucose, more so than he was able to reabsorb from the kidneys. Insulin let's glucose into cells by upregulating its transport. If insulin is low the glucose doesn't get into the cells, so it builds up in high concentrations. Glucagon low doesn't make sense to me.

 

[dw88]

The question is confusing because:

elevated plasma glucose is a result of low insulin (glucose isn't getting pulled into cells enough) however the bodies response to this would be to produce excess insulin to correct it.

This would suggest that its caused by low insulin but by the time you tested it, you may find high insulin.

Similarly with glucagon, this could be caused by excess glucagon causing excess blood sugar, but this would negatively feedback to reduce glucagon synthesis.

Bottom line - this situation would be caused by low insulin, high glucagon, or insulin that is failing to do its job.

In any case the bodies natural response would be to shut down glucagon production and make much more insulin which is the style of answer the original poster was going for. Unfortunately I think the question was asking which of these situations could be causing high blood sugar, not what would high blood sugar cause.

low insulin --> low glucose uptake --> high plasma glucose levels. done.
Although I agree the answer isn't that satisfying, I would like to see something like "mutated insulin which isn't able to satisfy its functional role"