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Activity 4 Intestinal absorption

The small intestine is the place where the main part of digestion occurs; it is as well the place of
absorption. It is at this level where the nutrients cross by diffusion the wall of the digestive tract

towards the blood or the lymph.
How does the structure of the small intestine facilitate the absorption ?

1 Absorption of nutrients

A- The nutrients

Every day, approximately 10
Nutrients Origin
liters of ingested food, liquids
and gastro-intestinal Water Drinks and food
secretions pass through the
Mineral salts Nearly all the ingested food
digestive tract. All the
ingested food (except the Simple sugars Digestion of the disaccharides and
fibers) are decomposed and mainly glucose polysaccharides
transformed to a liquid, rich
Amino acids Digestion of proteins and polypeptides
in water and nutrients.
The nutrients are absorbed
Fatty acids Digestion of lipids
and distributed by the blood
and the lymph. These Doc 1- Origin of nutrients.
nutrients serve as the substances that the cells use to produce energy and synthesize their
constituents.

B- Structure and properties of the small intestine

The small intestine is a long (6 to 8 meters)
and highly vascularized tube.

The small intestine contains 800 to 900 folds
2
or ridges that increase the surface to 200 m .
Each ridge is formed from 10 000 to 12 000
villi that are microscopic folds.
Each villus is made up 4 000 to 7 000 intestinal

cells and is crossed by a lymphatic and blood
network.
Doc 2- The small intestine is a highly
vascularized organ.

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