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Lo.Lee.Ta. Lo.Lee.Ta.
wrote...
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9 years ago
I am trying to understand about glucose metabolism! I have been researching this stuff forever! X(
Would you see if my explanations are right, and if not, tell my why? Thank you SO much!
That would be a HUGE help!

1. Is it true that uptake and release of gas/nutrients only occur in the capillaries? (There is no gas or nutrient exchange going on in the veins or arteries, right?)
Capillary uptake and release of gas/nutrients is only powered by diffusion, right?

2. Do capillaries only use facilitated diffusion to take up or release glucose and simple diffusion for gas exchange?

3. If facilitated diffusion is used, will there always be a lower concentration of glucose in the capillaries than in the interstitial fluid of villi?
(That seems like the only way glucose could actually enter capillaries and not stay in the interstitial fluid...)

4. From the villi capillaries, is glucose then transported by arteries until it ends up in a different capillary, where the interstitial fluid has a lower glucose concentration?

5. If this is the case, does facilitated diffusion occur so that now the capillary and the interstitial fluid now have equal glucose concentration?

6. Glucose in the interstitial fluid enters a nearby cell by facilitated diffusion?

7. Will glucose always enter cells (except for intestinal cells) by facilitated diffusion because as soon as it does enter, glycolysis takes place to convert it to Acetyl-CoA- meaning there is never a build-up of glucose in the cell?
(If ATP is needed, Acetyl-CoA undergoes TCA and the electron transport chain. If ATP is not needed (sedentary), excess Acetyl-CoA can be converted into adipose tissue.)
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wrote...
Staff Member
9 years ago
1. Is it true that uptake and release of gas/nutrients only occur in the capillaries? (There is no gas or nutrient exchange going on in the veins or arteries, right?)
Capillary uptake and release of gas/nutrients is only powered by diffusion, right?

Yes, correct.


2. Do capillaries only use facilitated diffusion to take up or release glucose and simple diffusion for gas exchange?

Diffusion to and from capillaries is caused by the main law of diffusion, namely that a substance will travel from where it has a high concentration to where it has a low concentration.

In this case, glucose and oxygen travel from where their concentration is high (the capillary) to where their concentration is lower (the respiring cell). This is aided by the structure of the capillary and the cell, as the capillary is only one cell thick, and so it is easy for the glucose and oxygen to leave it. Likewise, the cell membrane is very thin, making entry easy.
Ask another question, I may be able to help!
Lo.Lee.Ta. Author
wrote...
9 years ago
Thanks, habiba, for helping me! Slight Smile Okay, so now I know that capillaries only use diffusion, but now I'm confused about is how the villi transfer the glucose they absorbed to the capillaries.
I have researched this everywhere it seems, but I don't see any answer as to what type of transport makes this happen.
First of all, the villi cell is able to absorb glucose from the lumen of the small intestines by secondary active transport (Na+/glucose cotransport).
Glucose can leave the villi cell on the other side, where there is the GLUT-2 transport protein.
Does GLUT-2 just carry out facilitated diffusion?
Glucose is now in the interstitial fluid. Now, if diffusion did take place here (as capillaries always do, right?), how could glucose diffuse into the capillary if blood sugar is high?
I could see that during a low blood sugar, the glucose could be taken in just fine, but how could it be taken in against the concentration gradient during a high blood sugar?
Glucose wouldn't just stay in the interstitial fluid until blood sugar went back down, would it?
Because in that case, it seems like an untreated Type 1 diabetic would have super sugary interstitial fluid...
Is the transport not diffusion here, or what...?

Ugh, confused about how high blood sugar affects things...
Please help!
Thank you SO much! Slight Smile
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