Overview of the Digestive Process
One simple way to describe the digestive process is in
terms of the following stages
(other sources may identify fewer or more "main stages" according to the level of detail of the description given):
- Absorption / Assimilation
- Elimination / Defecation
These can be summarised with a few sentences about each.
The Basic Stages of the Digestive Process
Ingestion is the process by which food is taken
into the alimentary canal.
It includes the processes that take place while the
food is in the mouth (mouth = "buccal cavity"),
such as chewing and grinding using the teeth,
the lubrication and chemical effects of saliva released
from the salivary glands, and swallowing of the food
- which sends it onwards down the digestive tract.
Digestion is the process by which ingested (food)
material is broken down in the earlier stages of the
alimentary canal into a form that can then be absorbed
and assimilated into the tissues of the body.
Digestion includes two types of processes -
- Mechanical (e.g. chewing, grinding,
churning, mixing), and
- Chemical (e.g. action of digestive
enzymes, bile, acids, etc.).
The mechanical processes
include the chewing and grinding of food by the teeth
and also the churning and mixing of the contents of
that contribute to digestion also begin in the mouth
with action of saliva on food. However, most of the
chemical digestive processes occur in the stomach
and small intestine
- where the partly-digested materials are subjected
to gastric juices, pancreatic juice, succus entericus
and so on.
is the uptake of fluids or other substances by the
tissues of the body.
Digested "food" (which is referred to
by other terms depending on its stage of passage through
the digestive system - see transit
through the alimentary canal) is absorbed
into the bodily fluids blood
and lymph from the alimentary canal. Most of the absorption
part of the digestive process occurs in the jejunum
and the ileum of the small
intestine, though alcohol is readily absorbed
through the stomach. The
small intestine is lined with minute finger-like processes
(called "villi", a single example being
a "villus"), that greatly increase its surface
area, and hence the rate at which absorption can take
is the process by which components/chemicals from
food (incl. liquid refreshments such as milk drinks,
fruit juices etc.) are taken into the cells of the
body - after the food/beverage has been digested and
Elimination is the final stage of this 4-stage
summary of digestion.
In physiology more generally the term "elimination"
can apply to the entire process of excretion
of metabolic waste products, incl. from the blood
via the kidneys
tract (as described in the section about the Renal
Summary of Overview:
Remember these four stages and be able to explain what
the terms mean and give examples of what happens at each
Ingestion ... (2) Digestion ...
(3) Absorption / Assimilation ... (4)
Elimination / Defecation
Note that description of the digestive process
in terms of these stages is a much simplified summary. While it is a useful start, this is an incomplete description that includes some over-lap, e.g. of Ingestion
(Stage 1) including use of teeth -
which may also be included as a form of Mechanical Digestion
(Stage 2). Next read about each stage in more detail. ...
The following page describes the digestive process
step-by-step, identifying the part played by each component
of the digestive system in the order in which ingested foodstuffs
pass through the alimentary tract.
Go to next page - about
passage through the alimentary tract.