CHAPTER 15
Digestive Tract
301
Serosa
Submucosa
Submucosa
Submucosa
Mucosa
Mucosa
Mucosa
Muscularis externa
Muscularis externa
Muscularis externa
Lymphatic
nodules
Lumen
A
Anal canal
Anal canal
Anal canal
Stratified
squamous
epithelium
Simple
columnar
epithelium
Rectum
Rectum
Rectum
Glands (crypts) of
Glands (crypts) of
Lieberkühn
Lieberkühn
Glands (crypts) of
Lieberkühn
Muscularis
Muscularis
mucosae
mucosae
Muscularis
mucosae
Large
Large
vein
vein
Large
vein
B
Figure 15-19A.
Appendix and cecum.
H&E,
3
17
The
appendix
is a f
ngerlike blind-ended tubular structure, about
10 cm in length, extending From the cecum distal to the ileocecal
valve. The
cecum
is the f
rst segment oF the large intestine, where it
connects with the ileum. The small and large intestines are separated
by the
ileocecal valve
. The appendix has a small, irregular lumen
and many lymphatic nodules in the mucosa. Although its role in
digestion is not clear, it may participate in immunological Func-
tion and help maintain normal bacteria fl
ora in the large intestine.
The epithelium oF the appendix is simple columnar epithelium, and
lymphatic nodules are located in the lamina propria oF the mucosa,
which may extend into the submucosa. The muscularis externa
contains inner circular and outer longitudinal smooth muscles.
Figure 15-19B.
Anorectal junction.
H&E,
3
34; insets (
left
)
3
131, (
right
)
3
87
The junction between the rectum and the anal canal is called the
anorectal junction
. The
rectum
connects the sigmoid colon to the anal
canal. The rectum is the distalmost portion oF the large intestine and
Functions mainly to store Feces until elimination. The mucosa oF the
rectum is similar to that oF the colon, but it has Fewer intestinal glands
oF Lieberkühn. The
anal canal
is a continuation oF the large intes-
tine and has longitudinal Folds (
anal columns
) in the gross view. The
mucosa oF the anal canal is covered by stratif ed squamous epithe-
lium. The lamina propria contains many large veins (venous plexus).
The muscularis mucosae is visible here. The muscularis externa con-
tains inner circular and outer longitudinal smooth muscle layers (
not
shown here
). The inner circular smooth muscle becomes thicker and
Forms the
internal anal sphincter
. The external anal sphincter sur-
rounds the anal canal. It is a thick layer oF skeletal muscle that vol-
untarily controls the elimination oF Feces. On the
left
in the photomi-
crograph is the distal end oF the rectum; on the
right
is the proximal
portion oF the anal canal. Sebaceous glands and apocrine glands may
be Found in the distal end oF the anal canal.
CLINICAL CORRELATION
Figure 15-19C.
Hemorrhoids.
H&E,
3
19
Hemorrhoids
are
swollen
,
infl amed veins
in the
anal region
deep
in the anal mucosa and are classif ed as
internal hemorrhoids
and
external hemorrhoids
, based on whether the hemorrhoids are
above (internal) or below (external) the
anorectal (line) junction
(dentate/pectinate line)
. Causes include repeated pregnancy, con-
stipation, and portal hypertension. Common symptoms include
bleeding, itching, and pain. Pathologically, hemorrhoids are thin-
walled varicose veins that extend into the
submucosal layer
. In time,
thrombosis
(clotting) may occur with resultant inFarct and f ssure
Formation. Treatments include surgical removal oF hemorrhoids,
coagulation therapy, and a procedure in which a rubber band is
used to tie oFF the hemorrhoids. This photomicrograph shows anal
squamous mucosa with underlying
dilated anorectal veins
.
Appendicitis
usually results From a bacterial inFection and may
develop slowly or acutely. A cardinal sign is pain in the lower
right abdominal quadrant or when pressure is applied to the
Mc Burney point
. The most common treatment is surgical exci-
sion oF the appendix.
Dilated
anorectal
vein
C
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