There are different types of enzymes, which break down different molecules.
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Different molecules are absorbed and digested in different
Carbohydrates are initially digested in the mouth as salivary
glands release enzymes; it is continued in the stomach and
the small intestine and finally absorbed in the small intestine.
Proteins are digested in the stomach by the stomach acid and
are absorbed in the small intestine.
The stomach initially digests lipids, and then bile is released
into the small intestine, which helps to digest the lipids even
further. The fatty acids and glycerol are then absorbed in the
Humans do not possess the enzymes to break down dietary
fibre so therefore it cannot be absorbed.
The small intestine
The small intestines have many adaptations to ensure that
absorption occurs as efficiently as possible.
The main adaptations are: