Assimilation and egestion

Digested and undigested foods have different outcomes once they have passed through the alimentary canal (gut).


Assimilation is the movement of digested food molecules into the cells of the body where they are used. For example:

Glasses and bottles of wine
The liver is also where toxins, such as alcohol, are broken down

The liver is important in assimilation. For example, it converts glucose into glycogen (a complex carbohydrate used for storage) and amino acids into proteins.

The liver is involved in the process of deamination. This is the removal of the nitrogen-containing part of amino acids, to form urea, followed by the release of energy from the remainder of the amino acid.


The small intestine absorbs most of the water in the contents of the gut. By the time the contents reach the end of the small intestine, most of the digested food has also been absorbed.

The remaining material consists of:

  • water
  • bacteria (living and dead)
  • cells from the lining of the gut
  • indigestible substances - such as cellulose from plant cell walls

The colon is the first part of the large intestine. It absorbs most of the remaining water. This leaves semi-solid waste material called faeces. The faeces are stored in the rectum, the last part of the large intestine. Egestion happens when these faeces pass out of the body through the anus.

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