Porth's Essentials of Pathophysiology, 4e

679

Structure and Function of the Gastrointestinal System

C h a p t e r 2 8

Greater omentum

Transverse colon Transverse mesocolon

Lesser omentum

Liver

Pancreas

Jejunum

Stomach

Descending colon

Duodenum

Transverse colon

Blood vessels

Mesentery

Greater omentum

Mesentery

Sigmoid mesocolon

Small intestine Parietal peritoneum Visceral peritoneum

Double layer of peritoneum

Ileum

Sigmoid colon

A

Bladder

Rectum

C

Uterus

Arterial arcades in mesentery

Mesentery

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.

Ileum

B

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.

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)