After the food has been digested in
the small intestine peristaltic contractions move the digested food
the large intestine, which is made up of the caecum, colon
and rectum. No further digestion occurs here, its role is to
remove most of the water and any remaining nutrients from the
chyme.
The undigested material from the small intestine is
vegetable roughage (cellulose), meat connective tissue, some
digested but unabsorbed nutrients and large amounts of water.
The large intestine has large colonies of bacteria
which act on the undigested waste and convert it into gases, acids
and vitamins. The water is reabsorbed through the intestinal wall
along with some mineral salts.
The bacteria and absorption of water turn the liquid
into a semisolid of pure waste called faeces. Faeces are
composed of bacteria, waste products brought by blood, products of
the action of bacteria in the intestines, salts, mucus, and the
indigestible components of food, such as cellulose which are called
fibre. The presence of fibre stimulates the lining of the
intestine to start peristalsis and the sphincter opens. This
allows the faeces to be removed from the body in a process called
.
A small part of the large intestine is the
appendix, which is a small piece of tissue coming off the
main tube of the intestine. It may have once been useful by our
ancestors in digesting cellulose, but today it is not used. It can
cause serious health problems if it becomes infected, when it may
rupture and break open causing a potentially deadly infection. This
can be prevented by removing the appendix in a simple
operation.
