CHAPTER 15
Digestive Tract
283
Esophagus
Small intestine
Small
Small
intestine
intestine
Small
intestine
Stomach
Large intestine
Rectum
Rectum
Rectum
Sigmoid
Ascending
colon
colon
colon
Descending
colon
Transverse
colon
Cecum
Appendix
Figure 15-1.
Overview of the digestive tract
. H&E,
3
5 to
3
6
The
digestive tract
, also called the
alimentary canal
, includes the
esophagus
,
stomach
,
small intestine
, and
large intestine
. (1) The
esophagus
transports food to the stomach. Its luminal surface is lined by stratiF
ed squamous nonkeratinized epithelium and contains
mucous glands in the
lamina propria
. It has both skeletal and smooth muscles in the
muscularis externa
. (2) The
stomach
temporarily
stores and digests food. Its luminal surface is lined by simple columnar epithelium and contains gastric glands in the lamina propria.
It has three layers of smooth muscle in the muscularis externa. (3) The
small intestine
digests and absorbs carbohydrates, proteins,
and lipids. The small intestine includes the
duodenum
,
jejunum
, and
ileum
. The luminal surface is lined by simple columnar epithe-
lium and contains the glands (crypts) of Lieberkühn in the lamina propria. There are two layers of smooth muscles (inner circular
and outer longitudinal muscles) in the muscularis externa. (4) The
large intestine
includes the
cecum
,
appendix
,
colon
,
rectum
, and
anal canal
. The main functions of the large intestine are the absorption both of a large volume of the water that enters it (90%)
and of electrolytes (e.g., Na
+
and Cl
) and the formation of the feces. Most parts of the large intestine are lined by simple columnar
epithelium, but stratiF ed squamous epithelium lines the anal canal. The glands of Lieberkühn are located in the lamina propria. The
muscularis externa contains an inner layer of circular smooth muscle and an outer layer of longitudinal smooth muscle, which forms
three
teniae coli
(see ±ig. 15-16). In general, the submucosa of the digestive tract is a thick layer of connective tissue containing blood
vessels, lymphatic vessels, and
submucosal (Meissner) plexuses
consisting of nerve F bers and neuron cell bodies in the
enteric nervous
system
. The
myenteric (Auerbach) plexuses
located in the muscularis externa are also components of the enteric nervous system.
Digestive Tract
I. Esophagus
A. Upper esophagus (skeletal muscle)
B. Middle esophagus (mixed skeletal and smooth muscles)
C. Lower esophagus (smooth muscle)
II. Stomach
A. Cardia
B. ±undus
C. Body
D. Pylorus
III. Small Intestine
A. Duodenum
B. Jejunum
C. Ileum
IV. Large Intestine
A. Cecum
B. Appendix
C. Colon (ascending, transverse, descending, and sigmoid)
D. Rectum
E. Anal canal
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