then why is it bad for blood sugar to rise in diabetics ?

Because diabetics don't produce insulin or enough insulin for the glucose in the blood to be used up by the cells. I do see why you're confused, because I think you have the impression that glucose is bad if it is in the blood and not used up. This, however, is not the case because a high glucose concentration in the blood isn't harmful; what is harmful is when this concentration is not regulated. If glucose levels keep increasing in blood plasma, then you know the person has a problem. In general, a glucose concentration spike after a mean isn't harmful; the physiological effects associate with a lack of glucose regulation is .

so it is not bad to have a high glucose level in blood.. it just indicates the presence of a problem in regulating glucose concentration .... so it is not harmful for a diabetic to eat something with a lot of sugar as long as this doesn't occur constantly.... so glucose concentrations aren't the direct cause of physiological problems, it's just the long term effects due to fat storage and insulin insufficiency that would cause such problems.. im just stating what i understood.. is it right ?

You're almost there in your understanding. Glucose is not poisonous, nor does it cause an immune response in diabetics causing an allergic reaction. In normal people, when glucose spikes up in blood concentration, it triggers a physiological effect involving the pancreas to secret insulin. In diabetics, insulin is produced insufficiently, so glucose stays in the blood for a longer period of time. If you read back what I wrote and what other members noted, you'll see what a high concentration of glucose could cause. For instance, if there is excess glucose in the blood, this also goes to the kidneys. The kidneys can RE-ABSORB and recycle normal amounts of glucose, as the body does not want to lose it in the urine. However, when the glucose is too high, it can exceed the kidneys' ability to re-absorb it. The excess glucose then goes out in the urine, literally dragging water with it. This means that more urine is produced, and you have to urinate more often. Recall how glucose enters and exists cells, either via active transport or facilitated transport, the latter involving a concentration gradient. All in all, glucose needs to be regulated in the blood, if its not, you will have physiological problems.

Unfortunately, the most common symptom of high blood sugars is to have no symptoms at all! This is why there are so many people walking around with diabetes without knowing it - they have no symptoms, but are slowly suffering internally.

thx, this whole article has been helpful.. i was just curious because i heard this question in biochemistry class and the professor's answer was very unconvincing with bad understanding of basic cell physiology.. and i couldn't think of an answer myself, so i had to ask this here, and it was a bit more complicated than i thought it would be.. i thought the answer would be something like that glucose would react with things inside the blood causing the problems, but apparently it's much more than that.. and it was good to know...

i didn't know you're also a math teacher ? have you also studied math in college ?

Hey Karim, no... glucose does not react with other components of the blood, but it's an excellent observation. Moreover, yes, I am a certified math teacher - I've studied several calculus, algebra, and statistic courses in university. I also teach math at a high school level. I'm not an expert, but I enjoy teaching it more than bio