298
UNIT 3
Organ Systems
Colon
Descending
colon
Sigmoid
colon
Rectum
Transverse colon
Ascending
colon
Cecum
Appendix
Appendix
Appendix
Teniae coli
Adipose tissue
Serosa/adventitia
Mucosa
Epithelium
Lamina
propria
Muscularis
mucosae
Teniae coli
Circular muscle
Longitudinal muscle
band (teniae coli)
Submucosa
Muscularis
externa
Vein
Artery
Nerve
Rectum
Rectum
Rectum
Figure 15-16.
Overview of the large intestine.
H&E (left),
3
14; (right)
3
36
The
large intestine
connects the small intestine to the anal canal. The large intestine is about 1.5 m long, much shorter than the
small intestine. It consists of the
cecum
,
appendix
,
colon
,
rectum
, and
anal canal
. (1) The
cecum
is a small blind pouch of the large
intestine, at the junction of the ileum and the ascending colon. The ileum and cecum are separated by the
ileocecal valve
, which
prevents feces from backing up into the small intestine. (2) The
appendix
is a very short, small-diameter blind end tube that attaches
to the posterior-medial wall of the cecum. It contains aggregates of lymphatic nodules in the lamina propria. (3) The
colon
is the
longest part of the large intestine and includes ascending, transverse, descending, and sigmoid colons. (4) The
rectum
connects the
sigmoid colon to the anal canal. (5) The
anal canal
is externally surrounded by a layer of skeletal muscle called the
exterior sphincter
.
The junction between the rectum and the anal canal is called the
anorectal junction
, also called the
dentate line
, which marks the
transitional epithelium change from simple columnar epithelium to stratiF ed squamous epithelium. The large intestine has the same
general structure of mucosa, submucosa, muscularis externa, and serosa/adventitia as the small intestine. However, the large intestine
has a large lumen (excepting the appendix) and a large number of goblet cells lining the surface of the mucosa. It has crypts (intestinal
glands) but no villi, and the outer longitudinal muscle layer of the muscularis externa has become three narrow bands called
teniae
coli
. ±unctions of the large intestine include the absorption of water and salts and the formation, storage, and elimination of feces.
Large Intestine
Large Intestine
I. Cecum
A. Mucosa (crypts/glands; no villi)
B. Submucosa
C. Muscularis externa (inner circular muscle; teniae coli)
D. Serosa
II. Appendix
A. Mucosa (aggregated lymphatic nodules)
B. Submucosa
C.
Muscularis externa (inner circular and outer longitudinal
muscles)
D. Serosa
III.
Colon:
ascending, transverse, descending, and sigmoid
portions
A. Mucosa (crypts/glands; no villi)
B. Submucosa
C. Muscularis externa (inner circular muscle; teniae)
D. Serosa/adventitia
IV. Rectum
A. Mucosa
B. Submucosa
C.
Muscularis externa (inner circular and outer longitudinal
muscles)
D. Adventitia
V. Anal Canal
A. Mucosa (stratiF
ed squamous)
B. Submucosa
C. Muscularis externa (internal and external sphincters)
D. Adventitia
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