Can someone please explain these to me?

[superoxide]

In the endocrine disorders chapter in goljans rapid review (page 287 at the top), it says that in GH adenoma you have an increase in GH and IGF-1 and you will see hyperglycemia. GH is gluconeogenic, but doesnt the IGF caus HYPOGLYCEMIA because it is "insulin like" and so if you have a lot of it, it would cause hypoglycemia?

second thing: I dont get free, ionized calcium and bound calcium. On page 292 it says that when u have hypoalbuminemia you decrease total serum calcium. I dont get that. From what i understand, total serum calcium= bound calcium + free calcium. so if u have hypoalbuminemia you will have a decrease in BOUND calcium and an increase in free calcium (what was bound before is now free due to lack of albumin). So shouldnt the total serum calcium stay the same? just the ratio of free and bound calcium has changed. before the bound:free was (lets say) 60:40 but in the case of hypoalbuminemia it is now 30:70. so u still end up with a total serum of 100 in both cases


thanks

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[(nicedream)]

Could it be that the unbound calcium is peed out since it's not attached to albumin?

 

[daeojkim]

I don't know about the IGF Q but regarding the calcium Q, I think this is how it works.

free Ca and bound Ca are in state of equilibrium.

Free Ca <--> Bound Ca
Total Ca = free + bound

If bound Ca decreases then free Ca must also decrease to maintain the same free/bound ratio, since they are in equilibrium. So overall, total Ca should decrease with hypoalbuminemia.

 

[bananamd]

The "insulin like" in Insulin-like Growth Factor does not refer to its method of action, but instead that the receptor for IGF is a tyrosine kinase receptor just like insulin. Hence, the respective name.

In regards to the calcium, it a is a positive cation. It exists in several states, the two important ones being protein bound and free/ionized form. Now, albumin is a protein (which has a negative charge) -> hence the understandable inability to cross the GBM in the kidney (which also has a negative charge due to heparin sulfate). So, getting back to your question, when albumin increases (hyperalbuminemia), it binds more positively charged Ca and increases the amount of bound Ca resultin gin increased total Ca. BUT, when you have hypoalbuminemia, there is less protein bound calcium and hence, less total calcium. In both these cases, free Ca remains the same.

I hope that helped.

 

[superoxide]

Got it. Thank you everyone!