Download Large Intestine

ANATOMY AND HISTOLOGY
OF THE GIT HOLLOW
ORGANS III
LARGE INTESTINE
DR. NABIL KHOURI, MD. PH.D
LARGE INTESTINE
• The large intestine extends from the ileum to the anus.
It is divided into the cecum, appendix, ascending
colon, transverse colon, descending colon, and
sigmoid colon.
• The rectum and anal canal are considered in the
sections on the pelvis and perineum.
• The primary function of the large intestine is the
absorption of water and electrolytes and the storage
of undigested material until it can be expelled from
the body as feces.
LARGE INTESTINE
Has three unique features: •
Teniae coli – three bands of longitudinal smooth muscle in •
its muscularis
Haustra – pocketlike sacs caused by the tone of the teniae •
coli
Epiploic appendages – fat-filled pouches of visceral •
peritoneum
Is subdivided into the cecum, appendix, colon, •
rectum, and anal canal
The saclike cecum: •
Lies below the ileocecal valve in the right iliac fossa •
Contains a wormlike vermiform appendix •
ASCENDING COLON
Location and Description
• The ascending colon lies in the right lower quadrant.
• It extends upward from the cecum to the inferior surface of the
right lobe of the liver, where it turns to the left, forming the right
colic flexure, and becomes continuous with the transverse colon.
The peritoneum covers the front and the sides of the ascending
colon, binding it to the posterior abdominal wall.
Relations
• ■■ Anteriorly: Coils of small intestine, the greater omentum, and the
anterior abdominal wall.
• ■■ Posteriorly: The iliacus, the iliac crest, the quadratus lumborum,
the origin of the transversus abdominis muscle, and the lower pole
of the right kidney. The iliohypogastric and the ilioinguinal nerves
cross behind it
CECUM
LOCATION AND DESCRIPTION
• The cecum is that part of the large intestine that lies below
the level of the junction of the ileum with the large
intestine.
• It is a blind-ended pouch that is situated in the right iliac
fossa. It is about 6 cm long and is completely covered
with peritoneum.
• It possesses a considerable amount of mobility, although it
does not have a mesentery.
• Attached to its posteromedial surface is the appendix.
• The presence of peritoneal folds in the vicinity of the
cecum creates the superior ileocecal, the inferior
ileocecal, and the retrocecal recesses .
• As in the colon, the longitudinal muscle is restricted to
three flat bands, the TENIAE COLI, which converge on
the base of the appendix and provide for it a
complete longitudinal muscle coat .
• The terminal part of the ileum enters the large intestine
at the junction of the cecum with the ascending colon.
• This opening is provided with two folds, or lips, which
form the so-called ILEOCECAL VALVE.
• The appendix communicates with the cavity of the
cecum through an opening located below and behind
the ileocecal opening.
RELATIONS
■■ Anteriorly: Coils of small intestine, sometimes part
of the greater omentum, and the anterior abdominal
wall in the right iliac region
■■ Posteriorly: The psoas and the iliacus muscles, the
femoral nerve, and the lateral cutaneous nerve of the
thigh. The appendix is commonly found behind the
cecum.
■■ Medially: The appendix arises from the cecum on
its medial side.
BLOOD SUPPLY
• Arteries Anterior and posterior cecal arteries
form the ileocolic artery, a branch of the
superior mesenteric artery
• Veins The veins correspond to the arteries and
drain into the superior mesenteric vein.
ILEO-CECAL VALVE
• The ileocecal valve consists of two horizontal folds of
mucous membrane that project around the orifice of
the ileum.
• The valve plays little or no part in the prevention of
reflux of cecal contents into the ileum.
• The circular muscle of the lower end of the ileum
(CALLED THE ILEOCECAL SPHINCTER BY
PHYSIOLOGISTS)
• serves as a sphincter and controls the flow of contents
from the ileum into the colon.
APPENDIX
Location and Description
• The appendix is a narrow, muscular tube containing a
large amount of lymphoid tissue.
• It varies in length from 8 to 13 cm.
• The base is attached to the posteromedial surface of
the cecum about 1 in. (2.5 cm) below the ileocecal
junction.
• The remainder of the appendix is free.
• It has a complete peritoneal covering, which is
attached to the mesentery of the small intestine by a
short mesentery of its own, the mesoappendix.
• The line joining the right anterior superior iliac spine to
the umbilicus (McBurney’s point).
The glands are lined with simple
columnar epithelium and a high
number of mucin producing goblet
cells.
The lamina propria typically contains
lymphocytes that partly obscure the
underlying muscularis
Mucosae.
The submucosa is almost fully
occupied by lymphoid tissue mainly
arranged in lymphatic nodules.
The center of the lymphoid nodules
stain lighter and are termed germinal
centers.
The germinal center contains the larger
dividing lymphoblasts, similar to the
arrangement in lymph nodes.
The outer portions of the submucosa
harbor larger vessels and have less
dense infiltrates of immune cells.
TRANSVERSE COLON
Location and Description
• The transverse colon is about 38 cm long and extends across the
abdomen, occupying the umbilical region.
• It begins at the right colic flexure below the right lobe of the liver
and hangs downward, suspended by the transverse mesocolon
from the pancreas . It then ascends to the left colic flexure below
the spleen.
• The left colic flexure is higher than the right colic flexure and is
suspended from the diaphragm by the phrenicocolic ligament.
• The transverse mesocolon, or mesentery of the transverse colon,
suspends the transverse colon from the anterior border of the
pancreas. The mesentery is attached to the superior border of the
transverse colon, and the posterior layers of the greater omentum
are attached to the inferior border
RELATIONS
• ■■ Anteriorly: The greater omentum and the
anterior abdominal wall (umbilical and hypogastric
regions)
• ■■ Posteriorly: The second part of the duodenum,
the head of the pancreas, and the coils of the
jejunum and the ileum
DESCENDING COLON
Location and Description
• The descending colon is about 25 cm long and lies in the
left upper and lower quadrants . It extends downward
from the left colic flexure, to the pelvic brim, where it
becomes continuous with the sigmoid colon..
Relations
• ■■ Anteriorly: Coils of small intestine, the greater
omentum, and the anterior abdominal wall .
• ■■ Posteriorly: The lateral border of the left kidney, the
origin of the transversus abdominis muscle, the quadratus
lumborum, the iliac crest, the iliacus, and the left psoas.
The iliohypogastric and the ilioinguinal nerves, the lateral
cutaneous nerve of the thigh, and the femoral nerve also
lie posteriorly.
SIGMOID COLON
Location and Description
• The sigmoid colon is 25 to 38 cm long and begins as a
continuation of the descending colon in front of the pelvic brim.
Below, it becomes continuous with the rectum in front of the 3rd
sacral vertebra.
• The sigmoid colon is mobile and hangs down into the pelvic
cavity in the form of a loop. The sigmoid colon is attached to
the posterior pelvic wall by the fan-shaped sigmoid mesocolon.
Relations
• ■■ Anteriorly: In the male, the urinary bladder; in the female,
the posterior surface of the uterus and the upper part of the
vagina
• ■■ Posteriorly: The rectum and the sacrum. The sigmoid colon is
also related to the lower coils of the terminal part of the ileum.
LOCATION AND DESCRIPTION
RECTUM
• The rectum is about 13 cm long and begins in front of the third sacral
vertebra as a continuation of the sigmoidcolon.
It passes downward, following the curve of the sacrum and coccyx, and ends
in front of the tip of the coccyx by piercing the pelvic diaphragm and
becoming continuous with the anal canal.
The lower part of the rectum is dilated to form the rectal ampulla. The rectum
deviates to the left, but it quickly returns to the median plane . On lateral
view, the rectum follows the anterior concavity of the sacrum before bending
downward and backward at its junction with the anal canal
The peritoneum covers the anterior and lateral surfaces of the first third of the
rectum and only the anterior surface of the middle third, leaving the lower
third devoid of peritoneum .
The muscular coat of the rectum is arranged in the usual outer longitudinal and
inner circular layers of smooth muscle.
The three teniae coli of the sigmoid colon, however, come together so that the
longitudinal fibers form a broad band on the anterior and posterior surfaces
of the rectum.
THE RECTUM
• The mucous membrane of the rectum, together with the circular
muscle layer, forms two or three semicircular permanent folds
called the transverse folds of the rectum they vary in position.
Relations
• ■■ Posteriorly: The rectum is in contact with the sacrum and
coccyx; the piriformis, coccygeus, and levatores ani muscles; the
sacral plexus; and the sympathetic trunks.
• ■■ Anteriorly: In the male, the upper two thirds of the rectum, which
is covered by peritoneum, is related to the sigmoid colon and coils
of ileum that occupy the rectovesical pouch. The lower third of the
rectum, which is devoid of peritoneum, is related to the posterior
surface of the bladder, to the termination of the vas deferens and
the seminal vesicles on each side, and to the prostate .In the
female, the upper two thirds of the rectum, which is covered by
peritoneum, is related to the sigmoid colon and coils of ileum that
occupy the rectouterine pouch (pouch of Douglas). The lower third
of the rectum, which is devoid of peritoneum, is related to the
posterior surface of the vagina .
ANO-RECTAL
JUNCTION
ANAL CANAL
Location and Description
• The anal canal is about 4 cm long and passes downward and
backward from the rectal ampulla to the anus . Except during
defecation, its lateral walls are kept in apposition by the
levatores ani muscles and the anal sphincters.
Relations
• ■■ Posteriorly: The anococcygeal body, which is a mass of
fibrous tissue lying between the anal canal and the coccyx.
• ■■ Laterally: The fat-filled ischiorectal fossae (Fig. 8.5).
• ■■ Anteriorly: In the male, the perineal body, the urogenital
diaphragm, the membranous part of the urethra, and the
bulb of the penis. In the female, the perineal body, the
urogenital diaphragm, and the lower part of the vagina.
STRUCTURE
• The mucous membrane of the upper half of the anal
canal
• is derived from hindgut entoderm. It has the following
important anatomic features:
• ■■ It is lined by columnar epithelium.
• ■■ It is thrown into vertical folds called anal columns,
which are joined together at their lower ends by small
semilunar folds called anal valves (remains of
proctodeal membrane).
• ■■ The arterial supply is that of the hindgut—namely, the
superior rectal artery, a branch of the inferior mesenteric
artery. The venous drainage is mainly
VALVES AND SPHINCTERS OF THE RECTUM
AND ANUS
Three valves of the rectum stop feces from being •
passed with gas
The anus has two sphincters: •
Internal anal sphincter composed of smooth muscle •
External anal sphincter composed of skeletal •
muscle
These sphincters are closed except during defecation •
HISTOLOGY
Colon mucosa is simple columnar epithelium •
except in the anal canal
Has numerous deep crypts lined with goblet cells •
Anal canal mucosa is stratified squamous •
epithelium
Anal sinuses exude mucus and compress feces •
Superficial venous plexuses are associated with the •
anal canal
Inflammation of these veins results in itchy •
varicosities called hemorrhoids
LARGE INTESTINE
Mucosa
folded
No plecae circulares
two types of cells
Goblet Mucus-secreting
Absorptive
Glands packed straight tubular
Crypts extend to the MM
LARGE INTESTINE
SMALL VS LARGE INTESTINE
Villi
Small intestine
Large intestine
1. Crypts shallow
2. Goblet cells less
1. Absence of
villi
2. Crypts
deeper, More
Goblet cells
Longitudinal 1. Uniformly thick
muscle coat
of muscularis
externa
1. Three bands
of Taenia coli