C h a p t e r 2 8
Structure and Function of the Gastrointestinal System
679
attach to the dorsal abdominal wall along a short line
of insertion, giving a fan-shaped appearance, with the
intestines at the edge.
An
omentum
is a double-layered extension or fold of
peritoneum that passes from the stomach or proximal
part of the duodenum to adjacent organs in the abdomi-
nal cavity or abdominal wall. The
greater omentum
extends from the stomach to cover the transverse colon
and the folds of the intestine, whereas the
lesser omen-
tum
extends between the transverse fissure of the liver
and the lesser curvature of the stomach (see Fig. 28-4C).
The greater omentum always contains some fat, which in
obese persons can be a considerable amount. It has con-
siderable mobility and moves around in the peritoneal
cavity with the peristaltic movements of the intestines,
and it cushions the abdominal organs against injury and
provides insulation against the loss of body heat. It often
forms adhesions (i.e., bands of fibrous scar tissue) adja-
cent to inflamed organs such as the appendix, walling off
the infection and thereby preventing its spread.
Liver
Stomach
Transverse
colon
Transverse
colon
Descending
colon
Sigmoid
colon
Sigmoid
mesocolon
Greater
omentum
Lesser
omentum
Small
intestine
Parietal
peritoneum
Visceral
peritoneum
Bladder
Pancreas
Duodenum
Mesentery
Mesentery
Uterus
Rectum
Blood
vessels
Greater
omentum
Transverse
mesocolon
Ileum
Jejunum
Ileum
Mesentery
Arterial arcades
in mesentery
Double layer
of peritoneum
A
B
C
FIGURE 28-4.
Mesenteries of the abdominal cavity.
(A)
The
greater omentum has been reflected superiorly to reveal the
mesentery attachments to the small and large intestines.
(B)
The attachment of the mesentery to the small bowel.The
mesentery contains the blood vessels, nerves, and lymphatic
vessels that supply the intestinal wall.
(C)
Sagittal section of the
abdominopelvic cavity in a woman, showing the relationships of
the peritoneal attachments and the greater and lesser omentums.
SUMMARY CONCEPTS
■■
The gastrointestinal (GI) tract is a long, hollow
tube that is in contact with the external
environment; food and fluids that enter the
GI tract do not become part of the internal
environment until they have been broken down
and absorbed into the blood or lymph.
■■
The digestive and absorptive functions of the
GI tract are distributed among structures of
the upper, middle, and lower parts of the tract.
The upper part—the mouth, esophagus, and
stomach—acts as an intake source and receptacle
through which food passes and in which initial
digestive processes take place.The middle
portion—the duodenum, jejunum, and ileum
(continued)
