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Biology 2nd Baccalaureate

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3.2.3. Absorption

Nutrient absorption

The absorption allows passage of nutrients resulting from digestion, along with waterminerals and vitamins, which do not need digestion, from the intestine to the circulatory system, which will take them to the cells. All nutrients are absorbed in the small intestine, except for water, which is absorbed in the large intestine.

Small intestine

The walls of the intestine are lined by numerous folds called intestinal villi, which greatly increases the absorption surface. They have many blood capillaries that allow digested nutrients to be absorbed and passed into the bloodstream.

In addition, to further increase the surface area, the intestinal cells have numerous folds called intestinal microvilli, achieving an absorption surface of about 400 m2.

The nutrients (except fats) pass around blood vessels that lead to the liver, where they will be treated chemically and modified.

The fat, rather than pass the blood, pass through the vessels chyliferous to the lymphatic system to move then to the blood.

Answer in your notebook

3.13.- How are intestinal villi different from microvilli? What function do they have?

Answer in your notebook

3.14.- Why do you think the surface of our small intestine is as big as a tennis court?

Answer in your notebook

3.15.- What is the function of the lymphatic vessels of the intestinal villi?

Large intestine

The large intestine consists of several parts: cecum, colon ascendingtransverse coloncolon descending and rectum.

After the nutrients have been absorbed in the small intestine, what remains of the chyle passes, through the ileocecal valve, to the large intestine, where three processes take place:

  • Water and some mineral salts, such as sodium, are absorbed. In this way, the water used in the entire digestive process is recovered.
  • The intestinal flora is made up of bacteria that live in symbiosis with us in our intestines that carry out supplementary digestion, taking advantage of some cellulose (which we cannot digest), and providing us with vitamins K  and 12.
  • Stool is formed , which is how the remains of digestion that have not been absorbed are eliminated.

The feces move outwards through peristaltic movements that direct them towards the anus.

Do not have to confuse the stool, in which waste disposed of digestion, the urine, where the waste excreted of the metabolism to clean the blood that transports.

Intestino grueso

By OpenStax College [CC BY 3.0], via Wikimedia Commons

Activity: Review the parts of the large intestine.


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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.