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Absorption in the Small Intestine
Glucose is absorbed through the walls of the small intestine.

These are folded and possess finger-like projections called villi.

They have thin walls, lined with epithelial cells, on the other side of which is a blood rich
network of blood capillaries.

The villi considerably increase…

Page 2

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The Role of Diffusion in Absorption
Diffusion is the net movement of molecules or ions from a region where they are highly
concentrated to a region where their concentration is lower.

As carbohydrates are being digested continuously, there is normally a greater concentration
of glucose within the small intestine than…

Page 3

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The Role of Active Transport in Absorption
Diffusion only results in the concentrations either side of the intestinal epithelium
becoming equal.

This means that not all the available glucose can be absorbed in this way and some may pass
out of the body.

The reason why this does not happen…

Page 4

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1. Sodium ions are actively transported out of the epithelial cells, by the sodium-
potassium pump, into the blood.

This takes place in one type of protein-carrier molecule found in the cell surface
membrane of the epithelial cells.

2. There is now a much higher concentration of sodium ions in…


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