Page 295 - Biology_F5

Biology for Advanced Level Secondary Schools

Caecum: This is a sac-like structure reabsorbed, it could lead to dehydration of
of about 6 cm suspended anterior to the body. Thus, re-absorption of water in
the ileocecal valve. Undigested food the large intestine is necessary to prevent
materials from the ileum are first received water loss.
by this region of the large intestine, where
absorption of water and salts is continued. Rectum: After food residues have passed
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In this region a winding tube called through the sigmoid colon, the remaining
appendix is attached and its function is intestinal content is stored as faeces in the
not clearly known, hence it is considered rectum, which measures about 20 cm long.
as a vestigial organ. However, appendix is
reported to have immunological function Rectum is located interior to the pelvis
because it contains a group of white blood and it produces some mucus materials,
cells. Recent studies have also shown which are added to the faeces in order
appendix to have bacteria reservoir, which to lubricate it for ease of passage to the
are important in repopulating the enteric outside by the process called defecation.
bacteria in the early stages of individuals The desire for defecation is caused by the
suffering diarrheal illness. As the faeces presence of a large quantity of faeces in
pass along the large intestine, some water the rectum. The walls of the rectum have
is absorbed into the blood stream. curved contours and lateral bends, which
create internal transverse folds called
Colon: This region of the intestine rectal valves. The function of these valves
borders with caecum and it is made up of is to separate faeces from gas in order to
four sub regions, namely the ascending prevent simultaneous passage of faeces
region, transverse region, descending and gas.
region and sigmoid region. Food residues
from caecum enter the ascending region
of the colon first which is on the right Anus: This region is also called anal canal
side of abdomen and travel up through the and constitutes the final part of the large
first bend of the colon to the transverse intestine. The length of the anal canal is
region of the colon. The residue continues between 3.8 to 5 cm and it opens to the
through the second bend to the descending exterior of the body at the anus. It has
region which is on the left side of the two types of muscles; the internal anal
posterior abdominal wall and enters the sphincter and external anal sphincter. The
sigmoid colon. former is made up of smooth muscles, and
its contractions are involuntary, while the
Generally, colon is very important in the latter is made up of skeletal muscles and
water balance of the body. Every day, they are under voluntary control. Under
about seven litres of water from drinks normal conditions, these two types of
and watery secretions produced internally, muscles make the sphincter remain closed
enter the gut. If most of these were not except when defaecating.

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