Small Intestines
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In
human beings, the membranous tubulararatus that extends from the stoappmach
to the anus.
The first part, or small
intestine, smaller only in diameter, being about twenty-three feet long
,while the large intestine is about five in length. The small intestine
occupies the greater portion of the a bdominal cavity.
The small intestine includes the duodenum, which is about eleven inches
long; the jejunum, comprising about two-fifths of the intestine; and the
ileum, which makes up the remaining three-fifths.
The intestines are lined with tissue which secrete digestive fluids in
some portions, and with other tissues which absorb the nutrients, water,
and fats at other points. The muscular wall of the intestine consists of
outer and inner layers of fibers. The inner surface of the small intestine
is covered by villi, which are tiny, finger like projections containing
the lacteals which convey fates to larger vessels of the system.
The process of digestion which begins in the mouth and continues through
the mouth, is completed chiefly in the upper part of the partly digested
food leaves about four hours for the food to pass through the small intestine.
The food passed along by muscular contractions, in waves, which are known
collectively as peristalsis. The food is also broken up by a series
of contractions within the wavelike motions, by segmentation.
Almost all ft digestion occurs
in the small intestine. I is greatly facilitated by presence of bile.
Although not an enzyme, bile aids the digestion of fat by emulsifying it
(reducing large masses of fat into small globules) and thus providing a
greater surface area to react with the lipases, or fat-splitting enzymes.
The lipases, which are contained in both pancreatic and intestinal juice,
split fats into molecules of fatty acids and glycerol.
Disorders of the intestinal tract
are numerous and discussed, at length in separate articles. Obstruction
of the action of the intestine may follow the passing of one portion of
intestine into another known as intussusception. It occurs most frequently
at the ileocecal valve, located at the opening from the small intestine
into large intestine. It may be due to a tumor, to the presence of
hardened and impacted indigestible material, or it may be caused by a rupture
into which a portion of the bowel is pushed.
Regional
ileitis, also known as enteritis, is an inflammatory disease of the ileum,
the lower portion of the small intestine, lying at a point close to the
appendix. Sometimes it extends the full length of the small intestine
and even into the large bowel. The cause is uncertain, but it is
believed that emotional stress and anxiety play a large part. Both
sexes are affected, generally between the age of 35 and 50. The course
of the disease is marked by periods of apparent cure, unfortunately followed
frequently by relapses. There is no way of preventing ileitis, but
if it is diagnosed soon enough the progress of the disease can be halted.
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