Absorption in the Digestive Tract (Digestive System)

This follows the page about transit of foodstuffs through the alimentary tract.

Ingested foods pass through the:

1. buccal cavity (mouth)*
2. oesophagus (also known as the esophagus and as the 'windpipe')*
3. stomach
4. small intestine
5. large intestine (incl. the rectum*)
6. anus*

* Not a significant absorption site or no absorption takes place at all

Different types of substances (including e.g. nutrients such as vitamins and minerals) are absorbed into the bloodstream at different parts of the alimentary tract (which is also known as the alimentary canal, the gastrointestinal tract and simply the digestive tract).

The locations at which certain types of atoms, molecules or ions are absorbed are called absorption sites.

It is useful to know which nutrients are absorbed by which parts of the digestive system.

The main absorption sites are listed below together with notes about important substances absorbed by each. (Recall from the function of the small intestine that approx 90% of the digestion and absorption of food occurs in the small intestine, the remaining 10% taking place in the stomach and large intestine.)

Absorption Sites in the Digestive Tract:

1. Stomach Alcohol (20%) Aspirin (a common pharmaceutical drug) 2. Small Intestine (where approx. 90% absorption takes place) Alcohol (80%) Water ... see also 12 health benefits of drinking water Fats Amino Acids Glucose Water-soluble vitamins (incl. C and B group incl. vitamin B12 ) Fat-soluble vitamins (incl. A, D, E and K) Some minerals, incl. sodium (Na), potassium (K), calcium (Ca), magnesium (Mg) and iron (Fe) Bile (a thick alkaline fluid secreted by the liver and stored in the gallbladder; helps with chemical digestion) 3. Large Intestine Acids and bases Water Remainder of sodium (Na) and potassium (K) i.e. remaining because not already absorbed in the small intestine. 4.   Rectum and Anus The rectum and anus are not absorption sites but the route via which indigestible material that has not been broken-down and absorbed by the body leaves the gastrointestinal tract in the form of faeces. Faeces are formed and stored in the rectum then expelled via the anus during the process of defecation.

The absorption sites indicated below are listed only in terms of the organ. More detailed information about which parts of organs are involved in absorption processes and how specific substances are absorbed is expected for advanced courses covering this topic.

This information about absorption in the digestive tract is useful for answering questions such as:

• List the nutrients absorbed in the small intestine.
  (or "List 6 nutrients absorbed in the small intestine", "List 8 nutrients absorbed in the small intestine", etc.)
• State which parts of the digestive tract absorb which components of broken-down foodstuffs.
• Where in the digestive tract is / are ________ absorbed ?
• State the main absorption sites in the digestive tract and give examples of what is absorbed at each location.

See also related topics about food and digestion, such as: What is Metabolism ? and What is a Balanced Diet ?