CHAPTER 15
Digestive Tract
299
Submucosa
S
u
b
m
u
c
o
s
a
Submucosa
Mucosa
Mucosa
Mucosa
Mucosa
Mucosa
Mucosa
Submucosa
Submucosa
Circular muscle of
Circular muscle of
muscularis externa
muscularis externa
Circular muscle of
muscularis externa
A
Figure 15-17A.
Colon, large intestine.
H&E,
3
15
The
colon
is the longest part of the large intestine. It contains an
ascending colon
,
transverse colon
,
descending colon
, and
sigmoid
colon
. The colon receives digestive contents from the small intes-
tine and absorbs a large volume of water and electrolytes from the
contents. Bacteria in the colon make large quantities of vitamins
K and B12, but absorption is limited. The colon also forms and
stores
feces
, the waste matter leftover after the digestion process
has been completed. The movement of the contents in the large
intestine is slower than in the small intestine, taking 8 to 15 hours
to move the
chyme
(thick, semifl uid mass) from the cecum to the
rectum, where feces are stored. The
mucosa
of the colon has a
smooth surface (no villi) and contains glands of Lieberkühn. The
submucosa
contains blood vessels, lymphatic vessels, and nerve
F bers as well as submucosal plexuses, but no glands are present.
The
muscularis externa
includes the
circular muscle
(
shown here
).
The longitudinal muscle is aggregated into three bands called
teniae coli
(±ig. 15-16). The myenteric (Auerbach) plexuses are
located between these two muscle layers.
Glands of
Glands of
Lieberkuhn
Lieberkuhn
Glands of
Lieberkühn
Glands of
Glands of
Lieberkühn
Lieberkühn
Glands of
Lieberkühn
Submucosa
Submucosa
Blood
Blood
vessels
vessels
Blood
vessels
Normal colon
B
Figure 15-17B.
Colon, large intestine.
H&E
,
×
68
(
left
); mucous stain,
×
44
(
upper right
)
The
glands of Lieberkühn
are intestinal glands
that are straight tubular glands and are located
in the lamina propria of the mucosa. The glands
of Lieberkühn in the large intestine are similar to
those of the small intestine, but they contain no
Paneth cells. They are composed of great numbers
of goblet cells, columnar absorptive cells, and
some enteroendocrine cells. A thin layer of the
muscularis mucosae is found beneath the lamina
propria; it is part of the mucosa. The upper right
image shows the goblet cells, which appear red
because of the mucous stain.
Goblet
Goblet
cells
cells
Goblet
cells
Goblet
Goblet
cell
cell
Goblet
cell
Lumen of the
Lumen of the
gland of Lieberkühn
gland of Lieberkühn
Lumen of the
gland of
Lieberkühn
Columnar
Columnar
absorptive cell
absorptive cell
Columnar
absorptive cells
C
Figure 15-17C.
Mucosa of the colon, large intestine.
H&E,
3
272
Upper
: The superior part and surface of the
mucosa
of the
colon consists of
columnar absorptive cells
and
goblet cells
.
These absorptive cells play an important role in the absorp-
tion of water and electrolytes. Water enters the absorptive
cells entirely by diffusion. Most water absorption occurs in
the colon, especially in the proximal colon. Goblet cells pro-
duce
mucus
, which protects the wall of the large intestine,
glues fecal material together, and lubricates the passage.
The surface of the large intestine is much smoother than the
small intestine because there are
no villi
.
Lower
: The inferior part of the mucosa in the colon contains
straight tubular glands,
glands of Lieberkühn
, which are cut
in cross section here. Most cells in these glands are goblet cells
with basally positioned nuclei. The secretory (mucinogen)
granules located at the apical ends of the cells appear white
here. Enteroendocrine cells and stem cells also can be found.
The stem cells are located at the base of the glands (crypts) of
Lieberkühn and can be differentiated from other cell types of
epithelia. Paneth cells are not present in the large intestine.
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