Decrease Muscle [Glucose ]

[SaintJude]

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Say a passage said: "In McArdle's disease, there is a deficiency of enzyme phosphorylase in muscles, leading to a decrease in availability of glucose in muscle tissues. "

Will this affect blood glucose concentration?

 

[theseeker4]

Say a passage said: "In McArdle's disease, there is a deficiency of enzyme phosphorylase in muscles, leading to a decrease in availability of glucose in muscle tissues. "

Will this affect blood glucose concentration?

It could affect blood glucose concentration, as less glucose being trapped in muscle cells would result in more glucose in the blood. However, the effect may be minor, since feedback from the rise in blood glucose levels could decrease the amount of glucose that is dumped into the blood and increase the trapping and storage of glucose elsewhere.

 

[SaintJude]

You, see, that's what I incorrectly thought. And what annoys me is that it came up as a practice MCAT question but I don't remember studying this

A decrease in glucose concentration in muscles cells does NOT affect blood glucose concentrations! Muscle cells lack the enzyme glucose-6-phosphatase which is necessary for glucose to pass into blood.

I just wanted to see if this would trip someone else up (sorry, theseeker4)--but maybe, that's why this is a perfect MCAT question...😛

 

[theseeker4]

You, see, that's what I incorrectly thought. And what annoys me is that it came up as a practice MCAT question but I don't remember studying this

A decrease in glucose concentration in muscles cells does NOT affect blood glucose concentrations! Muscle cells lack the enzyme glucose-6-phosphatase which is necessary for glucose to pass into blood.

I just wanted to see if this would trip someone else up (sorry, theseeker4)--but maybe, that's why this is a perfect MCAT question...😛

What is the explanation for it not having any effect? Curious about this.

 

[MT Headed]

Say a passage said: "In McArdle's disease, there is a deficiency of enzyme phosphorylase in muscles, leading to a decrease in availability of glucose in muscle tissues. "

Will this affect blood glucose concentration?

A deficiency of phosphorylase would decrease the concentration of G6P, the first step of glycolysis. It shouldn't affect the "availability of glucose in muscle tissues" at all, though I suppose it would affect the ability of the muscle cell to use that glucose.

Would the blood glucose concentration be affected? I'm with theseeker4. The effect would be local, minor, and homeostatis would quickly put that glucose to another use somewhere else, perhaps storage as glycogen.

 

[MT Headed]

A decrease in glucose concentration in muscles cells does NOT affect blood glucose concentrations! Muscle cells lack the enzyme glucose-6-phosphatase which is necessary for glucose to pass into blood.

I'm not following this logic at all. Are we talking about glucose or G6P?.

A decrease in glucose concentration in a muscle cell would cause a favorable shift of the glucose/sodium symport and cause more glucose to be imported against its glucose concentration gradient (or if the concentration was low enough, with its gradient).

I'm really confused here. 😕

 

[SaintJude]

It's important to recognize that blood glucose concentration comes from three sources:
--ingested glucose
--glucogenesis in the liver
--glycogenolysis in the liver

I'm not going go into further detail, because frankly, it's not necessary for the MCAT.
This is important because for the MCAT, you have to understand that glucose concentration in muscle cells does not affect blood glucose concentration.

More info:
http://en.wikipedia.org/wiki/Glycogen#In_muscle_and_other_cells

 

[theseeker4]

It's important to recognize that blood glucose concentration comes from three sources:
--ingested glucose
--glucogenesis in the liver
--glycogenolysis in the liver

I'm not going go into further detail, because frankly, it's not necessary for the MCAT.
This is important because for the MCAT, you have to understand that glucose concentration in muscle cells does not affect blood glucose concentration.

More info:
http://en.wikipedia.org/wiki/Glycogen#In_muscle_and_other_cells

That is where glucose comes from, yes. However, the glucose goes somewhere, so the absorption of glucose and ability to lock the glucose into cells (via glucose --> G6P for example) should absolutely have an effect on the blood glucose levels, until that influence is counteracted by feedback mechanisms. Obviously, understanding where the glucose comes from is only part of the picture, and alterations to its consumption are definitely important to understanding what is going on. What was the explanation of the passage you referred to? I have already been accepted, so I am simply curious about the explanation, not worried about what will be on the MCAT.