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How Are Nutrients Absorbed In The Small Intestines?

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Anonymous answered
They are absorbed through the walls of the small intestine. It depends on the type of nutrients as well. Different nutrients need different enzymes to work with them, to get them ready and help them to move through the intestinal wall.
Kath Senior Profile
Kath Senior answered
Nutrients from food are absorbed through the wall of the small intestine by a mixture of passive and active transport processes.

When we eat food, it passes into the stomach first, where the process of digestion begins. This carries on in the small intestine and, when individual food molecules are available, they start to diffuse through the intestine wall into the blood. The intestine is surrounded by a rich network of blood vessels, ready to receive the absorbed food molecules.

However, diffusion is only good when there are loads of nutrient molecules in the intestine and there is a good concentration gradient between in inside of the intestine and the blood. We still need to absorb food molecules at low concentrations, which is why intestine cells have special proteins that act as transporters. They actively catch specific food molecules - some catch proteins, some sugars - and pull them inside the intestinal wall cell. The food molecules are transported out into the blood at the other end by a similar transporter. This process is active - the cell has to use energy to do it.

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