AQA AS Absorption of glucose in Small Intestine HELP!!!

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sechdent8
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#1
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#1
Hey guys,
i got a question about the sodium glucose co transport thing, i understand that the glucose and sodium move into the epithelial cells together but what i dont understand is that my textbook (AQA AS Nelson Thornes) says sodium is moved down its conc. gradient ( i get that) but then glucose is moved up its conc. gradient :s could someone please explain why there is a higher conc. of glucose in the epithelial cells before the co transport of glucose and sodium pleasee
Thanks
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BlueSheep32
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#2
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#2
(Original post by sechdent8)
Hey guys,
i got a question about the sodium glucose co transport thing, i understand that the glucose and sodium move into the epithelial cells together but what i dont understand is that my textbook (AQA AS Nelson Thornes) says sodium is moved down its conc. gradient ( i get that) but then glucose is moved up its conc. gradient :s could someone please explain why there is a higher conc. of glucose in the epithelial cells before the co transport of glucose and sodium pleasee
Thanks
I must admit I've never considered why that is and I'm doing a Biochemistry degree! I'd say it's because glucose has to diffuse from the epithelial cells into the bloodstream and does so by facilitated diffusion so the intracellular concentration of glucose in the epithelial cells has to be quite high to allow a large net movement of glucose from the cells to the blood. This means that glucose has to enter the epithelial cells from the gut lumen by active transport, which is made possible by co-transport with sodium.

Hope this helps!
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SnakehipsTTC
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#3
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#3
From what I've been taught, about the reabsorbtion of glucose in the kidney, it sounds exactly the same as what are talking about in the small intestine.

Basically, the sodium ion diffuses down it's concentration gradient through a co-transporter protein, and the gradient maintained is so high that the energy released by the rapid movement of sodium ions through the protein is enough to transport glucose up its concentration gradient. Obviously it's far more complicated than this, in fact the glucose is converted into 2 molecules of pyruvate within the protein, releasing two ATP, supplying the SOME energy needed for co-transpotation. If you want more information on this I can certainly give it to you if requested
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Qari
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#4
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#4
(Original post by sechdent8)
Hey guys,
i got a question about the sodium glucose co transport thing, i understand that the glucose and sodium move into the epithelial cells together but what i dont understand is that my textbook (AQA AS Nelson Thornes) says sodium is moved down its conc. gradient ( i get that) but then glucose is moved up its conc. gradient :s could someone please explain why there is a higher conc. of glucose in the epithelial cells before the co transport of glucose and sodium pleasee
Thanks
This is for Oral Rehydration Treatment
As the concentration of glucose and sodium increases the amount of water decreases so water from the lumen can come in via osmosis.

You have equal concentration of water so you have to get rid of water for concentration gradient.
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sechdent8
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#5
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#5
(Original post by Qari)
This is for Oral Rehydration Treatment
As the concentration of glucose and sodium increases the amount of water decreases so water from the lumen can come in via osmosis.

You have equal concentration of water so you have to get rid of water for concentration gradient.
Umm im not talking about ORS, im talking about absorption of glucose in the small intestine, co transport of it actually. it comes before ORS in the aqa nelson thornes textbook
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Qari
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#6
Co teransporter moves one against its concentration gradient whilst moving the other one down
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sechdent8
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#7
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@Qari, yes i understand that but why is there a high conc. of glucose inside the epithelial cells before co transport occurs?
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Birdybirdy
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#8
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#8
I agree. that book is not very clear at times...
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Mimir
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#9
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#9
(Original post by sechdent8)
Hey guys,
i got a question about the sodium glucose co transport thing, i understand that the glucose and sodium move into the epithelial cells together but what i dont understand is that my textbook (AQA AS Nelson Thornes) says sodium is moved down its conc. gradient ( i get that) but then glucose is moved up its conc. gradient :s could someone please explain why there is a higher conc. of glucose in the epithelial cells before the co transport of glucose and sodium pleasee
Thanks
The Sodium moving down its concentration gradient assists in the active process of Glucose being transported against its concentration gradient.

A high concentration of glucose is present in the cell as it needs to be higher than that of the blood, which it moves into by facilitated diffusion.

Sometimes it's easier at A-Level just to accept some facts, not delve into the 'why' because it's typical that those facts won't be in the exams or mark scheme!
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