Download The intestines

The intestines
Small Intestine
The small intestine is
the longest part of the
alimentary canal and
extends from the
pylorus of the stomach
to the ileocecal
junction. The greater
part of digestion and
food absorption takes
place in the small
intestine. It is divided
into three parts: the
duodenum, the
jejunum, and the
ileum.
General arrangement of abdominal viscera
Duodenum
Location and Description
The duodenum is a C-shaped tube,
about 10 in. (25 cm) long, which
joins the stomach to the jejunum.
It receives the openings of the bile
and pancreatic ducts. The
duodenum curves around the head
of the pancreas. The first inch (2.5
cm) of the duodenum resembles
the stomach in that it is covered on
its anterior and posterior surfaces
with peritoneum and has the lesser
omentum attached to its upper
border and the greater omentum
attached to its lower border; the
lesser sac lies behind this short
segment. The remainder of the
duodenum is retroperitoneal, being
only partially covered by
peritoneum.
Pancreas and anterior relations of the kidneys
Parts of the Duodenum
The duodenum is situated in
the epigastric and umbilical
regions and, for purposes of
description, is divided into
four parts.
First Part of the Duodenum
The first part of the
duodenum begins at the
pylorus and runs upward and
backward on the transpyloric
plane at the level of the first
lumbar vertebra.
Posterior relations of the duodenum and the
pancreas. The numbers represent the four
parts of the duodenum.
The relations of this
part are as follows:
Anteriorly: The
quadrate lobe of the
liver and the
gallbladder
Posteriorly: The
lesser sac (first inch
only), the
gastroduodenal artery,
the bile duct and portal
vein, and the inferior
vena cava
Attachment of the lesser omentum to the
stomach and the posterior surface of the liver
Superiorly: The
entrance into the
lesser sac (the
epiploic foramen)
Transverse section of the lesser sac showing the arrangement
of the peritoneum in the formation of the lesser omentum, the
gastrosplenic omentum, and the splenicorenal ligament. Arrow
indicates the position of the opening of the lesser sac.
Inferiorly:
The head of
the pancreas
Pancreas and anterior relations of the kidneys.
Second Part of the Duodenum
The second part of
the duodenum runs
vertically
downward in front
of the hilum of the
right kidney on the
right side of the
second and third
lumbar vertebrae.
Posterior relations of the duodenum and the
pancreas. The numbers represent the four
parts of the duodenum.
About halfway down its
medial border, the bile
duct and the main
pancreatic duct pierce
the duodenal wall. They
unite to form the
ampulla that opens on
the summit of the major
duodenal papilla.
The accessory pancreatic
duct, if present, opens
into the duodenum a
little higher up on the
minor duodenal papilla.
Entrance of the bile duct and the main and
accessory pancreatic ducts into the second part of
the duodenum. Note the smooth lining of the first
part of the duodenum, the plicae circulares of the
second part, and the major duodenal papilla.
The relations of this part
are as follows:
Anteriorly: The fundus of the
gallbladder and the right lobe of
the liver, the transverse colon,
and the coils of the small intestine
Posteriorly: The hilum of the
right kidney and the right ureter
Laterally: The ascending colon,
the right colic flexure, and the
right lobe of the liver
Medially: The head of the
pancreas, the bile duct, and the
main pancreatic duct
Note the relation of the gallbladder to the
transverse colon and the duodenum.
Third Part of the Duodenum
The third part of the duodenum runs
horizontally to the left on the
subcostal plane, passing in front of
the vertebral column and following
the lower margin of the head of the
pancreas.
The relations of this part are as
follows:
Anteriorly: The root of the
mesentery of the small intestine, the
superior mesenteric vessels contained
within it, and coils of jejunum
Posteriorly: The right ureter, the
right psoas muscle, the inferior vena
cava, and the aorta
Superiorly: The head of the pancreas
Inferiorly: Coils of jejunum
Pancreas and anterior relations of the
kidneys.
Fourth Part of the Duodenum
The fourth part of the
duodenum runs
upward and to the
left to the
duodenojejunal
flexure.
Posterior relations of the duodenum and the pancreas.
The numbers represent the four parts of the duodenum.
The flexure is held in
position by a
peritoneal fold, the
ligament of Treitz,
which is attached to
the right crus of the
diaphragm.
Peritoneal recesses, which may be present in the
region of the duodenojejunal junction. Note the
presence of the inferior mesenteric vein in the
peritoneal fold, forming the paraduodenal recess.
The relations of this part
are as follows:
Anteriorly: The
beginning of the root
of the mesentery and
coils of jejunum
Posteriorly: The left
margin of the aorta
and the medial border
of the left psoas
muscle
Attachment of the root of the mesentery of the
small intestine to the posterior abdominal wall.
Note that it extends from the duodenojejunal
flexure on left of the aorta, downward and to the
right to the ileocecal junction. The superior
mesenteric artery lies in the root of the mesentery.
Mucous Membrane and
Duodenal Papillae
The mucous membrane of the
duodenum is thick. In the first
part of the duodenum it is
smooth. In the remainder of the
duodenum it is thrown into
numerous circular folds called
the plicae circulares. At the
site where the bile duct and the
main pancreatic duct pierce the
medial wall of the second part is
a small, rounded elevation
called the major duodenal
papilla. The accessory
pancreatic duct, if present,
opens into the duodenum on a
smaller papilla about 0.75 in.
(1.9 cm) above the major
duodenal papilla.
Entrance of the bile duct and the main and
accessory pancreatic ducts into the second part of
the duodenum. Note the smooth lining of the first
part of the duodenum, the plicae circulares of the
second part, and the major duodenal papilla.
Blood Supply
Arteries
The upper half is supplied
by the superior
pancreaticoduodenal
artery, a branch of the
gastroduodenal artery.
The lower half is supplied
by the inferior
pancreaticoduodenal
artery, a branch of the
superior mesenteric artery.
Arteries that supply the stomach.
Note that all the arteries are derived
from branches of the celiac artery.
Veins
The superior pancreaticoduodenal vein
drains into the portal vein; the inferior
vein joins the superior mesenteric vein.
Lymph Drainage
The lymph vessels follow the arteries
and drain upward via
pancreaticoduodenal nodes to the
gastroduodenal nodes and then to the
celiac nodes and downward via
pancreaticoduodenal nodes to the
superior mesenteric nodes around the
origin of the superior mesenteric artery.
Nerve Supply
The nerves are derived from
sympathetic and parasympathetic
(vagus) nerves from the celiac and
superior mesenteric plexuses.
Tributaries of the portal vein
Clinical Notes
Trauma to the Duodenum
In severe crush injuries to the anterior abdominal wall, the third part of the duodenum may
be severely crushed or torn against the third lumbar vertebra.
Duodenal Ulcer
As the stomach empties its contents into the duodenum, the acid chyme is squirted against
the anterolateral wall of the first part of the duodenum. This is thought to be an important
factor in the production of a duodenal ulcer at this site. An ulcer of the anterior wall of the
first inch of the duodenum may perforate into the upper part of the greater sac, above the
transverse colon. The transverse colon directs the escaping fluid into the right lateral
paracolic gutter and thus down to the right iliac fossa.
An ulcer of the posterior wall of the first part of the duodenum may penetrate the wall and
erode the relatively large gastroduodenal artery, causing a severe hemorrhage.
Duodenal Recesses
The importance of the duodenal recesses and the occurrence of herniae of the intestine.
Important Duodenal Relations
The relation to the duodenum of the gallbladder, the transverse colon, and the right kidney
should be remembered. Cases have been reported in which a large gallstone ulcerated
through the gallbladder wall into the duodenum. Operations on the colon and right kidney
have resulted in damage to the duodenum.
Jejunum and Ileum
Location and Description
The jejunum and ileum
measure about 20 ft (6 m)
long; the upper two fifths of
this length make up the
jejunum. The jejunum
begins at the duodenojejunal
flexure, and the ileum ends
at the ileocecal junction.
The coils of jejunum and
ileum are freely mobile and
are attached to the posterior
abdominal wall by a fanshaped fold of peritoneum
known as the mesentery of
the small intestine.
Attachment of the root of the mesentery of
the small intestine to the posterior
abdominal wall. Note that it extends from
the duodenojejunal flexure on left of the
aorta, downward and to the right to the
ileocecal junction. The superior mesenteric
artery lies in the root of the mesentery.
The long free edge of the fold
encloses the mobile intestine.
The short root of the fold is
continuous with the parietal
peritoneum on the posterior
abdominal wall along a line
that extends downward and to
the right from the left side of
the second lumbar vertebra to
the region of the right
sacroiliac joint. The root of the
mesentery permits the entrance
and exit of the branches of the
superior mesenteric artery and
vein, lymph vessels, and nerves
into the space between the two
layers of peritoneum forming
the mesentery.
In the living,
The jejunum can be
distinguished from the
ileum by the following
features:
The jejunum lies
coiled in the upper part
of the peritoneal cavity
below the left side of
the transverse
mesocolon; the ileum
is in the lower part of
the cavity and in the
pelvis.
Abdominal contents after the greater
omentum has been reflected upward. Coils of
small intestine occupy the central part of the
abdominal cavity, whereas ascending,
transverse, and descending parts of the colon
are located at the periphery.
The jejunum is wider bored,
thicker walled, and redder than
the ileum. The jejunal wall feels
thicker because the permanent
infoldings of the mucous
membrane, the plicae circulares,
are larger, more numerous, and
closely set in the jejunum,
whereas in the upper part of the
ileum they are smaller and more
widely separated and in the
lower part they are absent.
The jejunal mesentery is
attached to the posterior
abdominal wall above and to the
left of the aorta, whereas the
ileal mesentery is attached
below and to the right of the
aorta.
Some external and internal differences
between the jejunum and the ileum.
The jejunal mesenteric vessels form
only one or two arcades, with long
and infrequent branches passing to the
intestinal wall. The ileum receives
numerous short terminal vessels that
arise from a series of three or four or
even more arcades.
At the jejunal end of the mesentery,
the fat is deposited near the root
and is scanty near the intestinal wall.
At the ileal end of the mesentery the
fat is deposited throughout so that it
extends from the root to the intestinal
wall.
Aggregations of lymphoid tissue
(Peyer's patches) are present in the
mucous membrane of the lower ileum
along the antimesenteric border. In the
living these may be visible through
the wall of the ileum from the outside.
Blood Supply
Arteries
The arterial supply is
from branches of the
superior mesenteric
artery. The intestinal
branches arise from the
left side of the artery and
run in the mesentery to
reach the gut. They
anastomose with one
another to form a series
of arcades. The lowest
part of the ileum is also
supplied by the ileocolic
artery.
Superior mesenteric artery and its branches. Note
that this artery supplies blood to the gut from
halfway down the second part of the duodenum
to the distal third of the transverse colon (arrow).
Veins
The veins correspond to the
branches of the superior
mesenteric artery and drain into
the superior mesenteric vein.
Lymph Drainage
The lymph vessels pass through
many intermediate mesenteric
nodes and finally reach the
superior mesenteric nodes, which
are situated around the origin of
the superior mesenteric artery.
Nerve Supply
The nerves are derived from the
sympathetic and parasympathetic
(vagus) nerves from the superior
mesenteric plexus.
Clinical Notes
Trauma to the Jejunum and Ileum
Because of its extent and position, the small intestine is commonly damaged
by trauma. Small, penetrating injuries may self-seal as a result of the
mucosa plugging up the hole and the contraction of the smooth muscle wall.
The presence of the vertebral column and the prominent anterior margin of
the first sacral vertebra may provide a firm background for intestinal
crushing in cases of midline crush injuries.
Recognition of the Jejunum and Ileum
A physician should be able to distinguish between the large and small
intestine. He or she may be called on to examine a case of postoperative
burst abdomen, where coils of gut are lying free in the bed.
Tumors and Cysts of the Mesentery of the Small Intestine
A tumor or cyst of the mesentery, when palpated through the anterior
abdominal wall, is more mobile in a direction at right angles to the line of
attachment than along the line of attachment.
Pain Fibers from the Jejunum and Ileum
Pain fibers traverse the superior mesenteric sympathetic plexus and pass to the spinal
cord via the splanchnic nerves. Referred pain from this segment of the gastrointestinal
tract is felt in the dermatomes supplied by the 9th, 10th, and 11th thoracic nerves.
Strangulation of a coil of small intestine in an inguinal hernia first gives rise to pain in
the region of the umbilicus.
Mesenteric Arterial Occlusion
The superior mesenteric artery, a branch of the abdominal aorta, supplies an extensive
territory of the gut, from halfway down the second part of the duodenum to the left colic
flexure. Occlusion of the artery or one of its branches results in death of all or part of
this segment of the gut. The occlusion may occur as the result of an embolus, a
thrombus, an aortic dissection, or an abdominal aneurysm.
Mesenteric Vein Thrombosis
The superior mesenteric vein, which drains the same area of the gut supplied by the
superior mesenteric artery, may undergo thrombosis after stasis of the venous bed.
Cirrhosis of the liver with portal hypertension may predispose to this condition.
Meckel's Diverticulum
Meckel's diverticulum, a congenital anomaly of the ileum.
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 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.
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 2.5 in. (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 cecum is often distended with gas.
The terminal part of the ileum enters the large
intestine at the junction of the cecum with the
ascending colon. The 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.
Cecum and appendix. Note that
the appendicular artery is a branch
of the posterior cecal artery.
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.
Posterior abdominal wall showing posterior
relations of the kidneys and the colon.
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.
Lymph Drainage
The lymph vessels pass through several mesenteric nodes and finally reach the superior
mesenteric nodes.
Nerve Supply
Branches from the sympathetic and parasympathetic (vagus) nerves form the superior
mesenteric plexus.
leocecal Valve
A rudimentary structure, 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. The smooth
muscle tone is reflexly increased when the cecum is distended; the hormone gastrin,
which is produced by the stomach, causes relaxation of the muscle tone.
Appendix
Location and Description
The appendix is a
narrow, muscular tube
containing a large
amount of lymphoid
tissue. It varies in
length from 3 to 5 in.
(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 mesoappendix
contains the appendicular
vessels and nerves.
The appendix lies in the right iliac fossa, and in relation to the
anterior abdominal wall its base is situated one third of the way
up the line joining the right anterior superior iliac spine to the
umbilicus (McBurney's point). Inside the abdomen, the base of
the appendix is easily found by identifying the teniae coli of
the cecum and tracing them to the base of the appendix, where
they converge to form a continuous longitudinal muscle coat.
Common Positions of the Tip of the Appendix
The tip of the appendix is subject to a considerable range of
movement and may be found in the following positions:
(a) hanging down into the pelvis against the right pelvic wall,
(b) coiled up behind the cecum,
(c) projecting upward along the lateral side of the cecum, and
(d) in front of or behind the terminal part of the ileum.
The first and second positions are the most common sites.
Blood Supply
Arteries
The appendicular artery is a branch of the
posterior cecal artery.
Veins
The appendicular vein drains into the
posterior cecal vein.
Lymph Drainage
The lymph vessels drain into one or two
nodes lying in the mesoappendix and then
eventually into the superior mesenteric nodes.
Nerve Supply
The appendix is supplied by the sympathetic
and parasympathetic (vagus) nerves from the
superior mesenteric plexus. Afferent nerve
fibers concerned with the conduction of
visceral pain from the appendix accompany
the sympathetic nerves and enter the spinal
cord at the level of the 10th thoracic segment.
Ascending Colon
Location and Description
The ascending colon is
about 5 in. (13 cm) long and
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.
Abdominal cavity showing the terminal part
of the ileum, the cecum, the appendix, the
ascending colon, the right colic flexure, the
left colic flexure, and the descending colon.
Note the teniae coli and the appendices
epiploicae.
Relations
Anteriorly: Coils of
small intestine, the
greater omentum,
and the anterior
abdominal wall
Abdominal contents after the greater
omentum has been reflected upward. Coils
of small intestine occupy the central part of
the abdominal cavity, whereas ascending,
transverse, and descending parts of the
colon are located at the periphery.
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.
Blood Supply
Arteries
The ileocolic and right colic branches of
the superior mesenteric artery supply
this area.
Veins
The veins correspond to the arteries and
drain into the superior mesenteric vein.
Lymph Drainage
The lymph vessels drain into lymph
nodes lying along the course of the colic
blood vessels and ultimately reach the
superior mesenteric nodes.
Nerve Supply
Sympathetic and parasympathetic
(vagus) nerves from the superior
mesenteric plexus supply this area of
the colon.
Transverse Colon
Location and Description
The transverse colon is
about 15 in. (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 right colic flexure, the left colic flexure, and
the descending colon. Note the teniae coli and
the appendices epiploicae.
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. Because of
the length of the transverse
mesocolon, the position of
the transverse colon is
extremely variable and may
sometimes reach down as
far as the pelvis.
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 ileum
Blood Supply
Arteries
The proximal two thirds are supplied by the
middle colic artery, a branch of the superior
mesenteric artery.
The distal third is supplied by the left colic
artery, a branch of the inferior mesenteric
artery.
Veins
The veins correspond to the arteries and drain
into the superior and inferior mesenteric veins.
Lymph Drainage
The proximal two thirds drain into the colic
nodes and then into the superior mesenteric
nodes; the distal third drains into the colic
nodes and then into the inferior mesenteric
nodes.
Nerve Supply
The proximal two thirds are innervated by
sympathetic and vagal nerves through the
superior mesenteric plexus; the distal third is
innervated by sympathetic and parasympathetic
pelvic splanchnic nerves through the inferior
mesenteric plexus.
Inferior mesenteric artery and its branches. Note
that this artery supplies the large bowel from the
distal third of the transverse colon to halfway
down the anal canal. It anastomoses with the
middle colic branch of the superior mesenteric
artery (arrow).
Descending Colon
Location and Description
The descending colon is
about 10 in. (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. The
peritoneum covers the
front and the sides and
binds it to the posterior
abdominal wall.
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.
Posterior abdominal wall showing posterior
relations of the kidneys and the colon
Blood Supply
Arteries
The left colic and the sigmoid branches
of the inferior mesenteric artery supply
this area.
Veins
The veins correspond to the arteries
and drain into the inferior mesenteric
vein.
Lymph Drainage
Lymph drains into the colic lymph
nodes and the inferior mesenteric nodes
around the origin of the inferior
mesenteric artery.
Nerve Supply
The nerve supply is the sympathetic
and parasympathetic pelvic splanchnic
nerves through the inferior mesenteric
plexus.
Clinical Notes
Colonoscopy
is now being extensively used for early
detection of malignant tumors. In this
procedure, the mucous membrane of the
colon can be directly visualized through an
elongated flexible tube, or endoscope. The
interior of the large bowel can be observed
from the anus to the cecum . Photographs
of suspicious areas, such as polyps, can be
taken and biopsy specimens can be
removed for pathologic examination.
Series of the interior of the large bowel taken during a colonoscopy procedure. A. The rectal mucosa shows a
small benign polyp (arrowhead). B. The sigmoid mucous membrane shows evidence of a mild diverticulosis.
Arrowheads indicate the entrances into the mucosal pouches. C. The splenic flexure is normal. Note the light
reflections from the drops of mucus on the mucous membrane. D. The transverse colon shows the
characteristic normal folds or ridges (arrowheads) between the sacculations of the wall of the colon. E. The
ileocecal valve shows the upper lip (arrowheads) of the valve, which has a normal appearance. F. Finally, the
mucous membrane lining the inferior wall or floor of the cecum looks normal.
Variability of Position of the Appendix
The inconstancy of the position of the appendix should be borne in mind
when attempting to diagnose an appendicitis. A retrocecal appendix, for
example, may lie behind a cecum distended with gas, and thus it may be
difficult to elicit tenderness on palpation in the right iliac region. Irritation
of the psoas muscle, conversely, may cause the patient to keep the right hip
joint flexed.
An appendix hanging down in the pelvis may result in absent abdominal
tenderness in the right lower quadrant, but deep tenderness may be
experienced just above the symphysis pubis. Rectal or vaginal examination
may reveal tenderness of the peritoneum in the pelvis on the right side.
Pain of Appendicitis
Visceral pain in the appendix is produced by distention of its lumen or
spasm of its muscle. The afferent pain fibers enter the spinal cord at the
level of the 10th thoracic segment, and a vague referred pain is felt in the
region of the umbilicus. Later, the pain shifts to where the inflamed
appendix irritates the parietal peritoneum. Here the pain is precise, severe,
and localized.
Trauma of the Cecum and Colon
Blunt or penetrating injuries to the colon occur. Blunt injuries
most commonly occur where mobile parts of the colon (transverse and
sigmoid) join the fixed parts (ascending and descending).
Penetrating injuries following stab wounds are common. The
multiple anatomic relationships of the different parts of the colon
explain why isolated colonic trauma is unusual.
Cancer of the Large Bowel
Cancer of the large bowel is relatively common in persons older
than 50 years. The growth is restricted to the bowel wall for a
considerable time before it spreads via the lymphatics. Bloodstream
spread via the portal circulation to the liver occurs late.
Diverticulosis
Diverticulosis of the
colon is a common
clinical condition. It
consists of a herniation
of the lining mucosa
through the circular
muscle between the
teniae coli and occurs
at points where the
circular muscle is
weakest that is, where
the blood vessels pierce
the muscle.
Blood supply to the colon (A) and formation of the
diverticulum (B). Note the passage of the mucosal
diverticulum through the muscle coat along the course
of the artery.
Cecostomy and Colostomy
Because of the anatomic mobility of the cecum, transverse colon, and
sigmoid colon, they may be brought to the surface through a small
opening in the anterior abdominal wall. These procedures are referred
to as cecostomy or colostomy, respectively, and are used to relieve
large-bowel obstructions.
Volvulus
Because of its extreme mobility, the sigmoid colon sometimes rotates
around its mesentery. This may correct itself spontaneously or the
rotation may continue until the blood supply of the gut is cut off
completely.
Intussusception
Intussusception is the telescoping of a proximal segment of the bowel
into the lumen of an adjoining distal segment. Needless to say, there is
a grave risk of cutting off the blood supply to the gut and developing
gangrene.