Organ Systems
Figure 15-11B
Villi of the Small Intestine
Figure 15-12A
Columnar Absorptive and Goblet Cells of the Small Intestine
Figure 15-12B
Goblet, Columnar Absorptive Cells, and Microvilli
Figure 15-13A
Paneth Cells, Small Intestine
Figure 15-13B
Enteroendocrine Cells, Small Intestine
Figure 15-14A
Submucosal/Meissner Plexus, Small Intestine
Figure 15-14B
Muscularis Externa, Small Intestine
Figure 15-14C
Myenteric/Auerbach Plexus, Muscularis Externa of the Small Intestine
Figure 15-15A
Jejunum, Small Intestine
Figure 15-15B
Ileum with Peyer Patches, Small Intestine
Figure 15-15C
Mucosa of the Ileum, Small Intestine
Large Intestine
Figure 15-16
Overview of the Large Intestine
Figure 15-17A,B
Colon, Large Intestine
Figure 15-17C
Mucosa of the Colon, Large Intestine
Figure 15-18A
Clinical Correlation: Colon Polyps
Figure 15-18B
Clinical Correlation: Colorectal Cancer
Figure 15-18C
Clinical Correlation: Meckel Diverticulum
Figure 15-19A
Appendix and Cecum
Figure 15-19B
Anorectal Junction
Figure 15-19C
Clinical Correlation: Hemorrhoids
Figure 15-20A
Clinical Correlation: Ulcerative Colitis
Figure 15-20B
Clinical Correlation: Crohn Disease
Synopsis 15-1
Pathological and Clinical Terms for the Digestive Tract
Table 15-1
Digestive Tract
Introduction and Key Concepts
for the Digestive Tract
digestive system
is composed of the
oral cavity
, and
digestive glands
with associated organs. The “Oral
Cavity” is discussed in Chapter 14; the “Digestive Glands and
Associated Organs” are discussed in Chapter 16. The diges-
tive tract is discussed in this chapter. It includes the
small intestine
, and
large intestine
. The digestive
tract is a continuation of the oral cavity, and its main functions
are to ingest food and to digest the food as it passes along the
tract. In this process, nutrients and water are absorbed, and
waste materials are prepared for elimination from the body.
Each section of the digestive tract has its unique histological
features, which are closely associated with the function of that
part of the tract, although there are some common character-
istics: (1) Organs of the digestive tract are all hollow; (2) they
are composed of four general tunic layers: mucosa, submu-
cosa, muscularis externa, and adventitia or serosa; (3) they
are innervated by the enteric portion of the autonomic ner-
vous system, also known as the
enteric nervous system
(or the
“second brain”); (4) they include epithelium, connective tissue,
muscle, blood and lymphatic vessels, lymphatic nodules, and
nerve F
bers; and (5) they contain glands in the lamina propria
or submucosa.
General Structure of the
Digestive Tract
Based on its histological organization, the wall of the digestive
tract can be divided into four tunics (±ig. 15-3).
is the innermost layer of the digestive wall. It
lamina propria
, and
muscularis muco-
. The
consists of simple columnar epithelium
lining most of the tract and stratiF
ed squamous epithelium
lining the two ends, the esophagus and anal canal. The
lamina propria
is a loose connective tissue that contains
abundant ground substance, many F
bers, and numerous
connective tissue cells such as F
broblasts, macrophages,
mast cells, plasma cells, and leukocytes (see
Chapter 4,
“Connective Tissue”). Various types of glands are found in
the lamina propria depending on the region of the digestive
tract. The
muscularis mucosae
is a very thin layer of smooth
muscle, which is the boundary between the mucosa and the
submucosa. It is usually arranged in an inner circular and
outer longitudinal layer. However, the muscularis mucosae
varies in different regions, and it is often difF
cult to distin-
guish between the muscle layers.
is a thick layer of dense irregular connective
tissue. This layer contains blood vessels, lymphatic vessels,
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