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Transcript
Learning Modules - Medical Gross Anatomy
Abdominal Viscera Basics - Page 1 of 10
Topographically,
the abdomen can be
divided into right and
left upper and right
and left lower
quadrants by vertical
and horizontal lines
through the
umbilicus.
The abdomen may also be
divided into nine regions by two
longitudinal lines (right and left
midclavicular lines) and two
transverse planes (subcostal
and intertubercular planes). The
regions are: right and left
hypochondriac, right and left
lumbar, right and left inguinal (or
iliac), epigastric, umbilical and
hypogastric.
Copyright© 2002 The University of Michigan. Unauthorized use prohibited.
Learning Modules - Medical Gross Anatomy
Abdominal Viscera Basics - Page 2 of 10
The abdominal cavity
is bounded above by the
thoraco-abdominal
diaphragm (the
respiratory diaphragm or
"THE" diaphragm) and
below by the pelvic inlet.
It is continuous through
the pelvic inlet with the
pelvic cavity, and the
combined space is the
abdominopelvic cavity.
The abdominal cavity
contains the peritoneal
cavity, the abdominal
organs, and the
retroperitoneal space.
The peritoneal
cavity is a potential
space between the
parietal peritoneum lining
the body wall and visceral
peritoneum covering the
abdominal organs. The
peritoneal cavity is a
serous sac, similar to the
pleural and pericardial
cavities. The
retroperitoneal space is
behind the peritoneum of
the posterior abdominal
wall.
Copyright© 2002 The University of Michigan. Unauthorized use prohibited.
Learning Modules - Medical Gross Anatomy
Abdominal Viscera Basics - Page 3 of 10
The peritoneal cavity
is a potential space
between the parietal and
visceral layers of the
peritoneum and there are
no structures within it.
The layer lining the
abdominal wall, the pelvic
wall and pelvic viscera,
and the inferior surface of
the diaphragm is
the parietal peritoneum
and the layer lining the
surface of the organs is
called the visceral
peritoneum. Just as in
the pleural and pericardial
cavities, the peritoneal
cavity contains a film of
serous fluid that
lubricates the peritoneal
surfaces and allows free
movement of the viscera.
As with the pleural
and pericardial cavities,
the peritoneal cavity
surrounds, but does not
contain, most of the
abdominal organs. Most,
but not all, of the organs
associated with the GI
tract are suspended
"within" the peritoneal
cavity by connections to
the posterior abdominal
wall called mesenteries.
Copyright© 2002 The University of Michigan. Unauthorized use prohibited.
Learning Modules - Medical Gross Anatomy
Abdominal Viscera Basics - Page 4 of 10
Before looking at the development of the gut, let's consider the basic terminology of the
abdominal viscera.
The digestive tract begins at the oral cavity, which opens posteriorly into the pharynx,
the common food/air tube leading to both larynx and esophagus.
The esophagus passes through the lower neck, through the chest, and then pierces the
diaphragm at the esophageal hiatus to empty into the stomach.
The stomach empties into the first part of the small intestine, called the duodenum. The
head of the pancreas lies in the G-shape of the duodenum and it drains its digestive juices
into the duodenum.
The liver lies above and to the right of the stomach. The bile duct, which drains the liver,
also drains into the duodenum. The gallbladder is a resevoir in the biliary tract.
Copyright© 2002 The University of Michigan. Unauthorized use prohibited.
Learning Modules - Medical Gross Anatomy
Abdominal Viscera Basics - Page 5 of 10
The spleen is not an organ of the digestive tract, but it is an
abdominal organ. It lies beneath the diaphragm to the left of the
pancreas, and mostly posterior to the stomach.
Copyright© 2002 The University of Michigan. Unauthorized use prohibited.
Learning Modules - Medical Gross Anatomy
Abdominal Viscera Basics - Page 6 of 10
The small intestine comprises the duodenum,
jejunum, and ileum. The duodenum, the first and
shortest part, empties into the jejunum at the
duodenojejunal junction. The jejunum coils for
approximately 8 feet before becoming (by gradual
transition) the ileum. The ileum then coils for
another 12 feet, approximately, before emptying
into the large intestine.
Copyright© 2002 The University of Michigan. Unauthorized use prohibited.
Learning Modules - Medical Gross Anatomy
Abdominal Viscera Basics - Page 7 of 10
The large intestine or large bowel comprises in order the
cecum, ascending colon, transverse colon, descending colon,
and sigmoid colon. The cecum receives the contents of the
ileum at the ileocecal junction, and the vermiform appendix is
attached to the cecum posteroinferiorly. The ascending colon
bends to the left at the hepatic or right colic flexure to become
the transverse colon. The transverse colon bends down at the
left colic or splenic flexure to become the descending colon.
The descending colon becomes the S-shaped sigmoid colon to
pass over the pelvic brim into the pelvis. The sigmoid colon
straightens out as the rectum (which means straight), and
rectum ends as the anal canal.
Copyright© 2002 The University of Michigan. Unauthorized use prohibited.
Learning Modules - Medical Gross Anatomy
Abdominal Viscera Basics - Page 8 of 10
Mesenteries are doublelayer sheets of peritoneum that
suspend most of the gut and
associated structures from the
posterior body wall and provide
pathways for blood vessels and
nerves to the viscera, which
travel between the two layers.
The mesenteries are named
according to their associated
organ. For instance, the
transverse mesocolon suspends
the transverse colon from the
posterior abdominal wall, the
sigmoid mesocolon suspends
the sigmoid colon, and "THE
MESENTERY" suspends the
small intestine. Organs that
have a
mesentery are called
intraperitoneal. Organs without
a mesentery are
called retroperitoneal.
Copyright© 2002 The University of Michigan. Unauthorized use prohibited.
Learning Modules - Medical Gross Anatomy
Abdominal Viscera Basics - Page 9 of 10
Intraperitoneal organs are peritoneal organs that have an
associated mesentery, such as the stomach, small intestine (jejunum
and ileum), transverse and sigmoid colon, liver, and gallbladder.
Retroperitoneal organs do not have a mesentery and are
associated with the posterior body wall. Retroperitoneal organs are
subdivided into two categories: primarily retroperitoneal
and secondarily retroperitoneal. Primarily retroperitoneal organs
were present posterior to the peritoneal cavity in the embryo, such
as the aorta, inferior vena cava, ureters, kidneys, and suprarenal
glands. Secondarily retroperitoneal organs become fused to the
posterior abdominal wall during development.
Copyright© 2002 The University of Michigan. Unauthorized use prohibited.
Learning Modules - Medical Gross Anatomy
Abdominal Viscera Basics - Page 10 of 10
Secondarily
retroperitoneal
organs once had a
mesentery and lost it
during development.
This happens to
certain gut structures
during the return of
the intestines into the
abdominal cavity
(discussed later).
These organs include
the pancreas,
duodenum,
ascending and
descending colons,
which are associated
with fusion fascia
adhering them to the
posterior abdominal
wall.
In the
accompanying movie
of a cross-section of
an embryo, the
kidneys (dark purple)
are primarily
retroperitoneal in the
retroperitoneal space
(yellow area). The
ascending and
descending colon
develop, suspended
within the peritoneal
cavity (white area) by
a mesentery, and
become secondarily
retroperitoneal during
development. As the
colon fuses to the
posterior abdominal
wall, the peritoneum
is lost, and all that
remains is an
avascular plane, the
"fusion fascia"
(purple dotted lines)
shown at the end of
the movie.
Copyright© 2002 The University of Michigan. Unauthorized use prohibited.