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4
Abdomen
Conceptual overview 218
Regional anatomy 240
Surface anatomy 342
Clinical cases 351

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Abdomen
Conceptual overview
GENERAL DESCRIPTION
The abdomen is a roughly cylindrical chamber extending pelvic wall at the pelvic inlet. Superficially, the inferior
from the inferior margin of the thorax to the superior mar- limit of the abdominal wall is the superior margin of the
gin of the pelvis and the lower limb (Fig. 4.1A). lower limb.
The inferior thoracic aperture forms the superior The chamber enclosed by the abdominal wall contains a
opening to the abdomen, and is closed by the diaphragm. single large peritoneal cavity, which freely communi-
Inferiorly, the deep abdominal wall is continuous with the cates with the pelvic cavity.
A
Diaphragm
Inferior thoracic aperture
Abdominal wall
Iliac crest Pelvic inlet
Lower limb
Inguinal ligament
Fig. 4.1 Abdomen. A. Boundaries.
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Conceptual overview • Functions 4
B Costal margin Abdominal viscera are either suspended in the peri-
toneal cavity by mesenteries or are positioned between the
Left kidney
Peritoneal cavity cavity and the musculoskeletal wall (Fig. 4.1B).
Abdominal viscera include:
I major elements of the gastrointestinal system—the
caudal end of the esophagus, stomach, small and large
intestines, liver, pancreas, and gallbladder;
I the spleen;
I components of the urinary system—kidneys and
ureters;
I the suprarenal glands;
I major neurovascular structures.
FUNCTIONS
Houses and protects major viscera
The abdomen houses major elements of the gastrointesti-
nal system (Fig. 4.2), as well as the spleen and parts of the
urinary system.
Much of the liver, gallbladder, stomach, and spleen, and
Muscles parts of the colon are under the domes of the diaphragm,
which project superiorly above the costal margin of the
Aorta thoracic wall, and as a result these abdominal viscera are
Mesentery protected by the thoracic wall. The superior poles of the
Inferior vena cava
Right kidney kidneys are deep to the lower ribs.
Viscera not under the domes of the diaphragm are sup-
Fig. 4.1, cont’d. Abdomen. B. Arrangement of abdominal ported and protected predominantly by the muscular walls
contents. Inferior view. of the abdomen.
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Abdomen
Rib cage
Costal margin
Spleen
Liver
Stomach
Colon
Small intestine
Fig. 4.2 The abdomen contains and protects the abdominal viscera.
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Conceptual overview • Functions 4
Diaphragm
Contraction of
diaphragm Relaxation of
diaphragm
Relaxation of
abdominal
muscles
Contraction of
abdominal
muscles
Inspiration Expiration
Fig. 4.3 The abdomen assists in breathing.
Laryngeal
Breathing cavity closed
One of the most important roles of the abdominal wall is to
Air retained
assist in breathing:
in thorax
I it relaxes during inspiration to accommodate expan- Fixed diaphragm
sion of the thoracic cavity and the inferior displace-
Contraction of
ment of abdominal viscera during contraction of the abdominal wall
diaphragm (Fig. 4.3);
I
Increase in
during expiration, it contracts to assist in elevating the intra–abdominal pressure
domes of the diaphragm thus reducing thoracic vol-
ume.
Micturition
Material can be expelled from the airway by forced expi- Child birth
Defecation
ration using the abdominal muscles, as in coughing or
sneezing. Fig. 4.4 Increasing intra-abdominal pressure to assist in
micturition, defecation, and child birth.
Changes in intra-abdominal
in a fixed position (Fig. 4.4). Air is retained in the lungs by
pressure closing valves in the larynx of the neck. Increased intra-
Contraction of abdominal wall muscles can dramatically abdominal pressure assists in voiding the contents of the
increase intra-abdominal pressure when the diaphragm is bladder and rectum and in giving birth. 221

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Abdomen
I lateral to the vertebral column, the quadratus lumbo-
COMPONENT PARTS rum, psoas major, and iliacus muscles reinforce the
posterior aspect of the wall—the distal ends of the
Wall psoas and iliacus muscles pass into the thigh and are
The abdominal wall consists partly of bone but mainly of major flexors of the hip joint;
muscle (Fig. 4.5). The skeletal elements of the wall (Fig. I lateral parts of the abdominal wall are predominantly
4.5A) are: formed by three layers of muscles, which are similar in
I the five lumbar vertebrae and their intervening inter- orientation to the intercostal muscles of the thorax—
vertebral discs; transversus abdominis, internal oblique, and external
I the superior expanded parts of the pelvic bones; oblique;
I anteriorly, a segmented muscle (the rectus abdominis)
I bony components of the inferior thoracic wall includ-
ing the costal margin, rib XII, the end of rib XI and the on each side spans the distance between the inferior
xiphoid process thoracic wall and the pelvis.
Muscles make up the rest of the abdominal wall Structural continuity between posterior, lateral, and
(Fig. 4.5B): anterior parts of the abdominal wall is provided by thick
A B
Quadratus
External oblique lumborum
Rib XII
Costal margin
Rectus
Iliolumbar abdominis
ligament Internal oblique
Transversus
abdominis
Pelvic inlet
Inguinal ligament Gap between inguinal Iliacus
ligament and pelvic bone
Psoas major
Fig. 4.5 Abdominal wall. A. Skeletal elements. B. Muscles.
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Conceptual overview • Component parts 4
fascia posteriorly and by flat tendinous sheets (aponeu- Major viscera, such as the kidneys, that are not sus-
roses) derived from muscles of the lateral wall. A fascial pended in the abdominal cavity by mesenteries are associ-
layer of varying thickness separates the abdominal wall ated with the abdominal wall.
from the peritoneum, which lines the abdominal cavity. The abdominal cavity is lined by peritoneum, which
consists of an epithelial-like single layer of cells, (the
mesothelium) together with a supportive layer of con-
Abdominal cavity nective tissue. Peritoneum is similar to the pleura and
The general organization of the abdominal cavity is one in serous pericardium in the thorax.
which a central gut tube (gastrointestinal system) is sus- The peritoneum reflects off the abdominal wall to
pended from the posterior abdominal wall and partly from become a component of the mesenteries that suspend the
the anterior abdominal wall by thin sheets of tissue viscera:
(mesenteries; Fig. 4.6):
I parietal peritoneum lines the abdominal wall;
I a ventral (anterior) mesentery for proximal regions of I visceral peritoneum covers suspended organs.
the gut tube;
I a dorsal (posterior) mesentery along the entire length Normally, elements of the gastrointestinal tract and its
of the system. derivatives completely fill the abdominal cavity, making the
peritoneal cavity a potential space, and visceral peri-
Different parts of these two mesenteries are named toneum on organs and parietal peritoneum on the adja-
according to the organs they suspend or with which they cent abdominal wall slide freely against one another.
are associated. Abdominal viscera are either intraperitoneal or
retroperitoneal:
Branch of aorta Aorta
I intraperitoneal structures, such as elements of the
Kidney–posterior to
Ventral mesentery peritoneum gastrointestinal system, are suspended from the
abdominal wall by mesenteries;
I structures that are not suspended in the abdominal
cavity by a mesentery and that lie between the parietal
peritoneum and abdominal wall are retroperitoneal
in position.
Retroperitoneal structures include the kidneys and
ureters, which develop in the region between the peri-
toneum and the abdominal wall and remain in this posi-
tion in the adult.
During development, some organs, such as parts of the
small and large intestines, are suspended initially in the
abdominal cavity by a mesentery, and later become
retroperitoneal secondarily by fusing with the abdominal
wall (Fig. 4.7).
Large vessels, nerves, and lymphatics are associated
with the posterior abdominal wall along the median axis of
the body in the region where, during development, the
peritoneum reflects off the wall as the dorsal mesentery,
which supports the developing gut tube. As a consequence,
branches of the neurovascular structures that pass to
parts of the gastrointestinal system are unpaired, originate
from the anterior aspects of their parent structures, and
travel in mesenteries or pass retroperitoneally in areas
Dorsal mesentery
where the mesenteries secondarily fuse to the wall.
Parietal peritoneum
Generally, vessels, nerves, and lymphatics to the abdom-
Visceral peritoneum inal wall and to organs that originate as retroperitoneal
structures branch laterally from the central neurovascular
Fig. 4.6 The gut tube is suspended by mesenteries.
structures and are usually paired, one on each side. 223

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Abdomen
A Visceral peritoneum
Artery to gastrointestinal tract
B
Mesentery Retroperitoneal structures
Parietal peritoneum
Intraperitoneal part of tract
C
Mesentery before fusion with wall
Secondary retroperitoneal part of tract
Fig. 4.7 A series showing the progression (A to C) from an intraperitoneal organ to a secondarily retroperitoneal organ.
224

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Conceptual overview • Component parts 4
Inferior thoracic aperture Because the costal margin is not complete posteriorly,
the diaphragm is anchored to arch-shaped (arcuate) liga-
The superior aperture of the abdomen is the inferior tho- ments, which span the distance between available bony
racic aperture, which is closed by the diaphragm (see p. points and the intervening soft tissues;
000). The margin of the inferior thoracic aperture consists
I medial and lateral arcuate ligaments cross muscles
of vertebra TXII, rib XII, the distal end of rib XI, the costal
margin, and the xiphoid process of the sternum. of the posterior abdominal wall and attach to verte-
brae, the transverse processes of vertebra LI and rib
XII, respectively;
Diaphragm I a median arcuate ligament crosses the aorta and is
The musculotendinous diaphragm separates the abdomen continuous with the crus on each side.
from the thorax.
The posterior attachment of the diaphragm extends
The diaphragm attaches to the margin of the inferior
much further inferiorly than the anterior attachment.
thoracic aperture, but the attachment is complex posteri-
Consequently, the diaphragm is an important component
orly and extends into the lumbar area of the vertebral col-
of the posterior abdominal wall, to which a number of vis-
umn (Fig. 4.8). On each side, a muscular extension (crus)
cera are related.
firmly anchors the diaphragm to the anterolateral surface
of the vertebral column as far down as vertebra LIII on the
right and vertebra LII on the left.
Esophageal opening
Costal margin
Median arcuate ligament
Lateral arcuate
ligament
Medial arcuate ligament
Left crus
Right crus Quadratus lumborum
Psoas major
Fig. 4.8 Inferior thoracic aperture and the diaphragm.
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Abdomen
Pelvic inlet Pelvis
The abdominal wall is continuous with the pelvic wall at The pelvic inlet opens directly into the abdomen and struc-
the pelvic inlet, and the abdominal cavity is continuous tures pass between the abdomen and pelvis through it.
with the pelvic cavity. The peritoneum lining the abdominal cavity is continu-
The circular margin of the pelvic inlet is formed entirely ous with the peritoneum in the pelvis. Consequently, the
by bone: abdominal cavity is entirely continuous with the pelvic
I
cavity (Fig. 4.11). Infections in one region can therefore
posteriorly by the sacrum;
I
freely spread into the other.
anteriorly by the pubic symphysis;
I
The bladder expands superiorly from the pelvic cavity into
laterally, on each side, by a distinct bony rim on the
the abdominal cavity and, during pregnancy, the uterus
pelvic bone (Fig. 4.9).
expands freely superiorly out of the pelvic cavity into the
Because of the way in which the sacrum and attached abdominal cavity.
pelvic bones are angled posteriorly on the vertebral col-
umn, the pelvic cavity is not oriented in the same vertical
plane as the abdominal cavity. Instead, the pelvic cavity
projects posteriorly, and the inlet opens anteriorly and
somewhat superiorly (Fig. 4.10).
RELATIONSHIP TO OTHER
REGIONS
Thorax
The abdomen is separated from the thorax by the dia-
phragm. Structures pass between the two regions through
or posterior to the diaphragm (see Fig. 4.8).
Thoracic wall
False pelvis Ala of sacrum
Abdominal
Axis of abdominal
cavity
LV cavity
SI
Pelvic cavity
Pelvic inlet Axis of pelvic
cavity
Pelvic inlet
Inguinal ligament
Fig. 4.9 Pelvic inlet. Fig. 4.10 Orientation of abdominal and pelvic cavities.
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Conceptual overview • Relationship to other regions 4
I the femoral nerve, which innervates the quadriceps
Lower limb
femoris muscle, which extends the knee;
The abdomen communicates directly with the thigh I lymphatics;
through an aperture formed anteriorly between the infe- I the distal ends of psoas major and iliacus muscles,
rior margin of the abdominal wall (marked by the inguinal which flex the thigh at the hip joint.
ligament) and the pelvic bone (Fig. 4.12). Structures that
pass through this aperture are: As vessels pass inferior to the inguinal ligament, their
names change—the external iliac artery and vein of the
I the major artery and vein of the lower limb; abdomen become the femoral artery and vein of the thigh.
Pelvic inlet
Shadow
of ureter
Peritoneum
Rectum
Shadow of internal
iliac vessels
Bladder
Uterus
Fig. 4.11 The abdominal cavity is continuous with the pelvic cavity.
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Abdomen
KEY FEATURES Inferior vena cava
Arrangement of abdominal viscera Aorta
Psoas major
in the adult muscle
LIV vertebra
A basic knowledge of the development of the gastrointesti- Iliacus muscle LV vertebra
nal tract is needed to understand the arrangement of vis-
cera and mesenteries in the abdomen (Fig. 4.13).
The early gastrointestinal tract is oriented longitudi-
nally in the body cavity and is suspended from surround-
ing walls by a large dorsal mesentery and a much smaller
ventral mesentery.
Superiorly, the dorsal and ventral mesenteries are anch-
ored to the diaphragm.
The primitive gut tube consists of the foregut, the
midgut, and the hindgut. Massive longitudinal growth of
the gut tube, rotation of selected parts of the tube, and sec-
ondary fusion of some viscera and their associated mesen-
teries to the body wall participate in generating the adult
arrangement of abdominal organs.
Development of the foregut Inguinal ligament
In abdominal regions, the foregut gives rise to the distal
end of the esophagus, the stomach, and the proximal part
of the duodenum. The foregut is the only part of the gut
tube suspended from the wall both by the ventral and dor-
sal mesenteries. Fig. 4.12 Structures passing between the abdomen and thigh.
A diverticulum from the anterior aspect of the foregut
grows into the ventral mesentery, giving rise to the liver
and gallbladder, and ultimately, to the ventral part of the the opening to the space enclosed by the ballooned dorsal
pancreas. mesentery associated with the stomach. This restricted open-
The dorsal part of the pancreas develops from an out- ing is the omental foramen (epiploic foramen).
growth of the foregut into the dorsal mesentery. The spleen The part of the abdominal cavity enclosed by the
develops in the dorsal mesentery in the region between the expanded dorsal mesentery, and posterior to the stomach,
body wall and presumptive stomach. is the omental bursa (lesser sac). Access, through
In the foregut, the developing stomach rotates clock- the omental foramen to this space from the rest of the
wise and the associated dorsal mesentery, containing the peritoneal cavity (greater sac) is inferior to the free edge
spleen, moves to the left and greatly expands. During this of the ventral mesentery.
process, part of the mesentery becomes associated with, Part of the dorsal mesentery that initially forms part of
and secondarily fuses with, the left side of the body wall. the lesser sac greatly enlarges in an inferior direction, and
At the same time, the duodenum, together with its dor- the two opposing surfaces of the mesentery fuse to form an
sal mesentery and an appreciable part of the pancreas, apron-like structure (the greater omentum). The greater
swings to the right and fuses to the body wall. omentum is suspended from the greater curvature of the
Secondary fusion of the duodenum to the body wall, mas- stomach, lies over other viscera in the abdominal cavity,
sive growth of the liver in the ventral mesentery, and fusion and is the first structure observed when the abdominal
of the superior surface of the liver to the diaphragm restricts cavity is opened anteriorly.
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Conceptual overview • Key features 4
Stomach
Liver Dorsal pancreatic bud Spleen
A B
Ventral pancreatic bud
Dorsal
mesentery
Superior
mesenteric
artery
Superior
mesenteric artery Cecum
Colon
Liver
Liver
Stomach
Stomach
C D
Superior
mesenteric
artery
Greater
omentum
Cecum
Fig. 4.13 A series (A to H) showing the development of the gut and mesenteries.
Continued
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Abdomen
Liver Omental bursa
E F
Spleen
Cecum Stomach
Greater
omentum
Cecum
Developing greater omentum
Liver
Liver Lesser omentum
Omental bursa
Stomach
Spleen
Spleen
G H
Cecum
Greater omentum
Fig. 4.13, cont’d A series (A to H) showing the development of the gut and mesenteries.
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Conceptual overview • Key features 4
Development of the midgut
The midgut develops into the distal part of the duode-
num, the jejunum, ileum, ascending colon, and proximal
two-thirds of the transverse colon. A small yolk sac pro-
jects anteriorly from the developing midgut into the um-
bilicus.
Rapid growth of the gastrointestinal system results in a
loop of the midgut herniating out of the abdominal cavity
and into the umbilical cord. As the body grows in size and T6
the connection with the yolk sac is lost, the midgut returns
T7
to the abdominal cavity. While this process is occurring,
the two limbs of the midgut loop rotate counterclockwise T8
around their combined central axis, and the part of the
loop that becomes the cecum descends into the inferior T9
right aspect of the cavity.
The cecum remains intraperitoneal, the ascending T10
colon fuses with the body wall becoming secondarily
T11
retroperitoneal, and the transverse colon remains sus-
pended by its dorsal mesentery (transverse mesocolon). T12
The greater omentum hangs over the transverse colon
L1
and the mesocolon and usually fuses with these struc-
tures.
Hindgut
The distal one-third of the transverse colon, descending
colon, sigmoid colon, and the superior part of rectum
develop from the hindgut.
Proximal parts of the hindgut swing to the right and Fig. 4.14 Innervation of the anterior abdominal wall.
become the descending colon and sigmoid colon. The
descending colon and its dorsal mesentery fuse to the
body wall, while the sigmoid colon remains intraperitoneal.
tion, T5 and T6 supply upper parts of the external oblique
The sigmoid colon passes through the pelvic inlet and is
muscle of the abdominal wall; T6 also supplies cutaneous
continuous with the rectum at the level of vertebra SIII.
innervation to skin over the xiphoid.
Skin and muscle in the inguinal and suprapubic regions
Skin and muscles of the anterior of the abdominal wall are innervated by L1 and not by tho-
and lateral abdominal wall and racic nerves.
Dermatomes of the anterior abdominal wall are indi-
thoracic intercostal nerves cated in Figure 4.14. In the midline, skin over the infra-
The anterior rami of thoracic spinal nerves T7 to T12 follow sternal angle is T6 and that around the umbilicus is T10.
the inferior slope of the lateral parts of the ribs and cross L1 innervates skin in the inguinal and suprapubic regions.
the costal margin to enter the abdominal wall (Fig. 4.14). Muscles of the abdominal wall are innervated segmen-
Intercostal nerves T7 to T11 supply skin and muscle of the tally in patterns that generally reflect the patterns of the
abdominal wall, as does the subcostal nerve T12. In addi- overlying dermatomes.
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Abdomen
The groin is a weak area in the the gubernaculum, between the processus vaginalis and
the accompanying coverings derived from the abdominal
anterior abdominal wall wall.
During development, the gonads in both sexes descend The inguinal canal is the passage through the anterior
from their sites of origin on the posterior abdominal wall abdominal wall created by the processus vaginalis. The
into the pelvic cavity in women and the developing scro- spermatic cord is the tubular extension of the layers of
tum in men (Fig. 4.15). the abdominal wall into the scrotum that contains all
Before descent, a cord of tissue (the gubernaculum) structures passing between the testis and the abdomen.
passes through the anterior abdominal wall and connects The distal sac-like terminal end of the spermatic cord on
the inferior pole of each gonad with primordia of the scro- each side contains the testis, associated structures, and the
tum in men and the labia majora in women (labioscrotal now isolated part of the peritoneal cavity (the cavity of the
swellings). tunica vaginalis).
A tubular extension (the processus vaginalis) of the In women, the gonads descend to a position just inside
peritoneal cavity and the accompanying muscular layers the pelvic cavity and never pass through the anterior
of the anterior abdominal wall project along the guber- abdominal wall. As a result, the only major structure pass-
naculum on each side into the labioscrotal swellings. ing through the inguinal canal is a derivative of the guber-
In men, the testis, together with its neurovascular naculum (the round ligament of uterus).
structures and its efferent duct (the ductus deferens) In both men and women, the groin (inguinal region) is
descends into the scrotum along a path, initially defined by a weak area in the abdominal wall (Fig. 4.15).
A
Gonad
Muscle wall
Gubernaculum
Genital tubercle
Processus vaginalis
Urogenital membrane
Labioscrotal swelling
Fig. 4.15 Inguinal region. A. Development.
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Conceptual overview • Key features 4
*
Inferior vena cava
Aorta
Left testicular vein
Right testicular artery
Right testicular vein Left testicular artery
Pelvic brim
Left ductus deferens
Deep inguinal ring
Inguinal canal
Superficial
inguinal ring
Spermatic cord Ductus deferens
Testicular
artery and vein
Epididymis
Testis
Remnant of
gubernaculum
Tunica vaginalis
C
Left renal artery
Inferior vena cava Left renal vein
Left ovarian vein
Aorta
Left ovarian artery
Pelvic inlet
Uterine tube
Uterus
Round ligament
of uterus (remnants
Superficial of gubernaculum)
inguinal ring
Fig. 4.15, cont’d Inguinal region. B. In men. C. In women.
233

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Abdomen
Vertebral level LI Pyloric orifice between
stomach and duodenum
The transpyloric plane is a horizontal plane that transects Costal margin Jugular notch
the body through the lower aspect of vertebra LI (Fig.
4.16). It:
I is about midway between the jugular notch and the
pubic symphysis, and crosses the costal margin on
each side at roughly the ninth costal cartilage;
I crosses through the opening of the stomach into the
duodenum (the pyloric orifice), which is just to the
right of the body of LI—the duodenum then makes a
characteristic C-shaped loop on the posterior abdomi-
nal wall and crosses the midline to open into the
jejunum just to the left of the body of vertebra LII,
while the head of the pancreas is enclosed by the loop
of the duodenum, and the body of the pancreas
LI (transpyloric)
extends across the midline to the left; Right plane
I crosses through the body of the pancreas; kidney
I approximates the position of the hila of the kidneys,
though because the left kidney is slightly higher than
the right, the transpyloric plane crosses through the
inferior aspect of the left hilum and the superior part of
the right hilum.
The gastrointestinal system and its
derivatives are supplied by three
major arteries Position of umbilicus Pubic symphysis
Three large unpaired arteries branch from the anterior
Fig. 4.16 Vertebral level LI.
surface of the abdominal aorta to supply the abdominal
part of the gastrointestinal tract and all of the structures
(liver, pancreas, and gallbladder) to which this part of the
gut gives rise to during development (Fig. 4.17). These ar-
teries pass through derivatives of the dorsal and ventral
mesenteries to reach the target viscera. These vessels
therefore also supply structures such as the spleen and
lymph nodes that develop in the mesenteries. These three
arteries are:
I the celiac artery, which branches from the abdominal
aorta at the upper border of vertebra LI and supplies
the foregut;
I the superior mesenteric artery, which arises from the
abdominal aorta at the lower border of vertebra LI and
supplies the midgut;
I the inferior mesenteric artery, which branches from
the abdominal aorta at approximately vertebral level
LIII and supplies the hindgut.
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Conceptual overview • Key features 4
A Celiac trunk B Celiac trunk
Inferior vena cava Superior mesenteric artery
Foregut
Midgut
Hindgut Aorta
Inferior mesenteric
artery
Superior mesenteric artery
Inferior mesenteric artery
Fig. 4.17 Blood supply of the gut. A. Relationship of vessels to the gut and mesenteries. B. Anterior view.
235

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Abdomen
Venous shunts from left to right of large vessels cross the midline to deliver blood from the
left side of the body to the inferior vena cava:
All blood returning to the heart from regions of the body
I one of the most significant is the left renal vein, which
other than the lungs flows into the right atrium of the
heart. The inferior vena cava is the major systemic vein in drains the kidney, suprarenal gland, and gonad on the
the abdomen and drains this region together with the same side;
I another is the left common iliac vein, which crosses
pelvis, perineum, and both lower limbs (Fig. 4.18).
The inferior vena cava lies to the right of the vertebral the midline at approximately vertebral level LV to join
column and penetrates the central tendon of the dia- with its partner on the right to form the inferior vena
phragm at approximately vertebral level TVIII. A number cava—these veins drain the lower limbs, the pelvis, the
perineum, and parts of the abdominal wall.
Superior vena cava
Heart
Right atrium
Diaphragm
Left suprarenal vein
Right suprarenal vein
Left renal vein
Left gonadal vein
Left lumbar vein
Right gonadal vein
Left common iliac vein
Pelvic inlet
Fig. 4.18 Left to right venous shunts.
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Conceptual overview • Key features 4
I other vessels crossing the midline include the left lum- through the large hepatic portal vein. This vein then
bar veins, which drain the back and posterior abdomi- ramifies like an artery to distribute blood to small endothe-
nal wall on the left side. lial-lined hepatic sinusoids, which form the vascular ex-
change network of the liver.
After passing through the sinusoids, the blood collects
All venous drainage from the in a number of short hepatic veins, which drain into the
gastrointestinal system passes inferior vena cava just before the inferior vena cava pene-
through the liver trates the diaphragm and enters the right atrium of the
heart.
Blood from abdominal parts of the gastrointestinal system
Normally, vascular beds drained by the hepatic portal
and the spleen passes through a second vascular bed, in the
system interconnect, through small veins, with beds
liver, before ultimately returning to the heart (Fig. 4.19).
drained by systemic vessels, which ultimately connect di-
Venous blood from the digestive tract, pancreas, gall-
rectly with either the superior or inferior vena cava.
bladder, and spleen enters the inferior surface of the liver
Hepatic veins
Esophagus
Hepatic portal vein
Umbilicus
Rectum
Fig. 4.19 Hepatic portal system.
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Abdomen
Portacaval anastomoses that interconnect the portal and caval systems can become
greatly enlarged and tortuous, allowing blood in tribu-
Among the clinically most important regions of overlap
taries of the portal system to bypass the liver, enter the
between the portal and caval systems are those at each end
caval system, and thereby return to the heart. Portal
of the abdominal part of the gastrointestinal system:
hypertension can result in esophageal varices and hemor-
I around the inferior end of the esophagus; rhoids at the esophageal and rectal ends of the gastrointesti-
I around the inferior part of the rectum. nal system, respectively, and in ‘caput Medusae’ in which
systemic vessels that radiate from para-umbilical veins en-
Small veins that accompany the degenerate umbilical
large and become visible on the abdominal wall.
vein (round ligament of the liver) establish another im-
portant portal–caval anastomosis.
The round ligament of the liver connects the umbilicus Abdominal viscera are supplied
of the anterior abdominal wall with the left branch of the by a large prevertebral plexus
portal vein as it enters the liver. The small veins that
Innervation of the abdominal viscera is derived from a
accompany this ligament form a connection between the
large prevertebral plexus associated mainly with the ant-
portal system and para-umbilical regions of the abdominal
erior and lateral surfaces of the aorta (Fig 4.20). Branches
wall, which drain into systemic veins.
are distributed to target tissues along vessels that originate
Other regions where portal and caval systems intercon-
from the abdominal aorta.
nect include:
The prevertebral plexus contains sympathetic, para-
I where the liver is in direct contact with the diaphragm sympathetic, and visceral sensory components:
(the bare area of the liver);
I sympathetic components originate from spinal cord
I where the wall of the gastrointestinal tract is in direct
levels T5 to L2;
contact with the posterior abdominal wall (retroperi-
I parasympathetic components are from the vagus nerve
toneal areas of the large and small intestine);
I
[X] and spinal cord levels S2 to S4;
the posterior surface of the pancreas (much of the
I visceral sensory fibers generally parallel the motor
pancreas is secondarily retroperitoneal).
pathways.
Blockage of the hepatic portal vein
or vascular channels in the liver
Blockage of the hepatic portal vein or of vascular channels
in the liver can affect the pattern of venous return from
abdominal parts of the gastrointestinal system. Vessels
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Conceptual overview • Key features 4
Sympathetic input Parasympathetic input
Anterior and posterior
vagus trunks (cranial)
Greater, lesser and least
splanchnic nerves
(T5 to T12)
Lumbar splanchnic
nerves ( L1,L2)
Prevertebral plexus
Pelvic splanchnic
nerves (S2 to S4)
Fig. 4.20 Prevertebral plexus.
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Abdomen
Regional anatomy
The abdomen is the part of the trunk inferior to the thorax I a four-quadrant pattern;
(Fig. 4.21). Its musculomembranous walls surround a large I a nine-region organizational description.
cavity (the abdominal cavity), which is bounded superi-
orly by the diaphragm and inferiorly by the pelvic inlet.
The abdominal cavity may extend superiorly as high as
Four-quadrant pattern
the fourth intercostal space, and is continuous inferiorly For the simple four-quadrant topographical pattern a hor-
with the pelvic cavity. It contains the peritoneal cavity izontal transumbilical plane passes through the umbilicus
and the abdominal viscera. and the intervertebral disc between vertebrae LIII and LIV
and intersects with the vertical median plane to form four
quadrants—the right upper, left upper, right lower, and left
SURFACE TOPOGRAPHY lower quadrants (Fig. 4.22).
Topographical divisions of the abdomen are used to
describe the location of abdominal organs and the pain
associated with abdominal problems. The two schemes
most often used are:
Sternum
Diaphragm
Right upper Left upper
quadrant quadrant
Abdominal cavity
Right lower Left lower
quadrant quadrant
Pelvic inlet
Pelvic cavity
Pubic symphysis
Transumbilical plane Median plane
Fig. 4.21 Boundaries of the abdominal cavity. Fig. 4.22 Four-quadrant topographical pattern.
240 Fi 4 21

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Regional anatomy • Surface topography 4
Nine-region organizational pattern superior iliac spines, and passes through the upper
part of the body of vertebra LV;
The nine-region organizational description is based on two I the vertical planes pass from the midpoint of the clavi-
horizontal and two vertical planes (Fig. 4.23): cles inferiorly to a point midway between the anterior
I the superior horizontal plane (the subcostal plane) is superior iliac spine and pubic symphysis.
immediately inferior to the costal margins, which These four planes establish the topographical divisions
places it at the lower border of the costal cartilage of in the nine-region organization. The following designa-
rib X and passes posteriorly through the body of verte- tions are used for each region: superiorly the right
bra LIII (note, however, that sometimes the trans- hypochondrium, the epigastric region, and the left hypo-
pyloric plane halfway between the suprasternal chondrium; inferiorly the right groin (inguinal region),
(jugular) notch and the symphysis pubis or halfway be- pubic region, and left groin (inguinal region); and in the
tween the umbilicus and the inferior end of the body of middle the right flank (lateral region), the umbilical region,
the sternum, passing posteriorly through the lower and the left flank (lateral region) (Fig. 4.23).
border of vertebrae LI and intersecting with the costal
margin at the ends of the ninth costal cartilages is
used instead);
I the inferior horizontal plane (the intertubercular In the clinic
plane) connects the tubercles of the iliac crests, which
are palpable structures 5 cm posterior to the anterior Surgical incisions
Access to the abdomen and its contents is usually
obtained through incisions in the anterior abdominal
Subcostal plane Midclavicular planes
wall. Traditionally, incisions have been placed at and
around the region of surgical interest. The size of these
incisions was usually large to allow good access and
optimal visualization of the abdominal cavity. As anes-
thesia has developed and muscle-relaxing drugs have
become widely used, the abdominal incisions have
become smaller.
Currently, the most commonly used large abdominal
incision is a central craniocaudad incision from the
xiphoid process to the symphysis pubis, which provides
wide access to the whole of the abdominal contents and
allows an exploratory procedure to be performed
(laparotomy).
Right Epigastric region Left
Other approaches use much smaller incisions. With
hypochondrium hypochondrium the advent of small cameras and the development of
minimal access surgery, tiny incisions can be made in
the anterior abdominal wall and cameras inserted. The
Right flank Umbilical region Left flank peritoneal cavity is ‘inflated’ with carbon dioxide to
increase the space in which the procedure is performed.
Further instruments may be inserted through small port-
holes and procedures such as cholecystectomy (removal
Right groin Pubic region Left groin
of the gallbladder) and appendectomy (removal of the
appendix) can be carried out, allowing the patient to
return home sooner than a large abdominal incision
would allow.
Transtubercular plane
Fig. 4.23 Nine-region organizational pattern.
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Abdomen
However, in the lower region of the anterior part of the
ABDOMINAL WALL abdominal wall, below the umbilicus, it forms two layers: a
The abdominal wall covers a large area. It is bounded superficial fatty layer and a deeper membranous layer.
superiorly by the xiphoid process and costal margins,
posteriorly by the vertebral column, and inferiorly by the
upper parts of the pelvic bones. Its layers consist of skin,
Superficial layer
superficial fascia (subcutaneous tissue), muscles and their The superficial fatty layer of superficial fascia (Camper’s
associated deep fascias, extraperitoneal fascia, and parietal fascia) contains fat and varies in thickness (Figs. 4.25 and
peritoneum (Fig. 4.24). 4.26). It is continuous over the inguinal ligament with the
superficial fascia of the thigh and with a similar layer in
the perineum.
Superficial fascia In men, this superficial layer continues over the penis
The superficial fascia of the abdominal wall (subcutaneous and, after losing its fat and fusing with the deeper layer of
tissue of abdomen) is a layer of fatty connective tissue. It is superficial fascia, continues into the scrotum where it
usually a single layer similar to, and continuous with, the forms a specialized fascial layer containing smooth muscle
superficial fascia throughout other regions of the body. fibers (the dartos fascia). In women, this superficial layer
retains some fat and is a component of the labia majora.
Skin
External oblique muscle
Superficial fascia–
fatty layer
(Camper's fascia) Internal oblique muscle
Superficial fascia–
membranous layer Transversus abdominis muscle
(Scarpa's fascia)
Transversalis fascia
Parietal peritoneum Extraperitoneal fascia
Fig. 4.24 Layers of the abdominal wall.
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Regional anatomy • Abdominal wall 4
Deeper layer the midline, it is firmly attached to the linea alba and the
symphysis pubis. It continues into the anterior part of the
The deeper membranous layer of superficial fascia
perineum where it is firmly attached to the ischiopubic
(Scarpa’s fascia) is thin and membranous, and contains
rami and to the posterior margin of the perineal mem-
little or no fat (Fig. 4.25). Inferiorly, it continues into the
brane. Here, it is referred to as the superficial perineal
thigh, but just below the inguinal ligament, it fuses with
fascia (Colles’ fascia).
the deep fascia of the thigh (the fascia lata; Fig. 4.26). In
Superficial fascia
Aponeurosis of
external oblique
Fatty layer
(Camper's fascia)
Membranous layer
(Scarpa's fascia)
Skin Inguinal ligament
Penis
Fascia lata of thigh
Pubic symphysis
Scrotum Dartos fascia
Fig. 4.25 Superficial fascia.
Membranous layer of
superficial fascia
External oblique muscle (Scarpa's fascia)
and aponeurosis
Continuity with superficial Attachment to fascia lata
penile fascia
Attachment to Superficial perineal
ischiopubic rami fascia (Colles' fascia)
Continuity with
dartos fascia
Fig. 4.26 Continuity of membranous layer of superficial fascia into other areas.
243

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Abdomen
In men, the deeper membranous layer of superficial fas- many normal physiologic functions. By their positioning,
cia blends with the superficial layer as they both pass over they form a firm, but flexible, wall that keeps the abdomi-
the penis, forming the superficial fascia of the penis, before nal viscera within the abdominal cavity, protects the vis-
they continue into the scrotum where they form the dartos cera from injury, and helps maintain the position of the
fascia (Fig. 4.25). Also in men, extensions of the deeper viscera in the erect posture against the action of gravity.
membranous layer of superficial fascia attached to the pu- In addition, contraction of these muscles assists in both
bic symphysis pass inferiorly onto the dorsum and sides of quiet and forced expiration by pushing the viscera upward
the penis to form the fundiform ligament of penis. In (which helps push the relaxed diaphragm further into the
women, the membranous layer of the superficial fascia thoracic cavity) and in coughing and vomiting.
continues into the labia majora and the anterior part of All these muscles are also involved in any action that
the perineum. increases intra-abdominal pressure, including partur-
ition (childbirth), micturition (urination), and defecation
(expulsion of feces from the rectum).
Anterolateral muscles
There are five muscles in the anterolateral group of
abdominal wall muscles: Flat muscles
I three flat muscles whose fibers begin posterolaterally, External oblique
pass anteriorly, and are replaced by an aponeurosis as The most superficial of the three flat muscles in the
the muscle continues towards the midline—the exter- anterolateral group of abdominal wall muscles is the ex-
nal oblique, internal oblique, and transversus abdom- ternal oblique, which is immediately deep to the superfi-
inis muscles; cial fascia (Fig. 4.27). Its laterally placed muscle fibers pass
I two vertical muscles, near the midline, which are in an inferomedial direction, while its large aponeurotic
enclosed within a tendinous sheath formed by the component covers the anterior part of the abdominal wall
aponeuroses of the flat muscles. to the midline. Approaching the midline, the aponeuroses
Each of these five muscles has specific actions, but to- are entwined, forming the linea alba, which extends from
gether the muscles are critical for the maintenance of the xiphoid process to the pubic symphysis.
Latissimus dorsi muscle
Abdominal part of
pectoralis major muscle
Linea alba External oblique muscle
Aponeurosis of external oblique
Anterior superior iliac spine
Inguinal ligament
Fig. 4.27 External oblique muscle and its aponeurosis.
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Regional anatomy • Abdominal wall 4
Associated ligaments Anterior superior iliac spine
The lower border of the external oblique aponeurosis
forms the inguinal ligament on each side (Fig. 4.27).
This thickened reinforced free edge of the external oblique Pectineal ligament
aponeurosis passes between the anterior superior iliac
spine laterally and the pubic tubercle medially (Fig. 4.28). Inguinal ligament
It folds under itself forming a trough, which plays an im-
portant role in the formation of the inguinal canal. Pectineal line
Several other ligaments are also formed from extensions
of the fibers at the medial end of the inguinal ligament:
I the lacunar ligament is a crescent-shaped extension
of fibers at the medial end of the inguinal ligament
that pass backward to attach to the pecten pubis on
the superior ramus of the pubic bone (Figs. 4.28 and
4.29);
I additional fibers extend from the lacunar ligament
along the pecten pubis of the pelvic brim to form the
pectineal (Cooper’s) ligament.
External oblique
Anterior superior Aponeurosis of
Pubic tubercle
iliac spine external oblique
Pubic symphysis Lacunar ligament
Fig. 4.29 Ligaments of the inguinal region.
Inguinal ligament Lacunar ligament
Pubic tubercle
Femoral artery and vein
Fig. 4.28 Ligaments formed from the external oblique
aponeurosis.
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Abdomen
Internal oblique Transversus abdominis
Deep to the external oblique muscle is the internal Deep to the internal oblique muscle is the transversus
oblique muscle, which is the second of the three flat mus- abdominis muscle (Fig. 4.31), so-named because of the
cles (Fig. 4.30). This muscle is smaller and thinner than direction of most of its muscle fibers. It ends in an anterior
the external oblique, with most of its muscle fibers passing aponeurosis, which blends with the linea alba at the
in a superomedial direction. Its lateral muscular compo- midline.
nents end anteriorly as an aponeurosis that blends into the
linea alba at the midline.
External oblique muscle External oblique muscle
Rib X
Linea alba
Internal oblique muscle
and aponeurosis
Aponeurosis of external oblique
Anterior superior iliac spine
Fig. 4.30 Internal oblique muscle and its aponeurosis.
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Regional anatomy • Abdominal wall 4
Transversalis fascia covering the muscles of the posterior abdominal wall and
attaches to the thoracolumbar fascia.
Each of the three flat muscles is covered on its anterior and
After attaching to the crest of the ilium, the transvers-
posterior surfaces by a layer of investing abdominal fascia.
alis fascia blends with the fascia covering the muscles asso-
In general, these layers are unremarkable except for the
ciated with the upper regions of the pelvic bones and with
layer deep to the transversus abdominis muscle (the trans-
similar fascia covering the muscles of the pelvic cavity.
versalis fascia), which is better developed.
At this point, it is referred to as the parietal pelvic (or
The transversalis fascia is a continuous layer of fascia
endopelvic) fascia.
that lines the abdominal cavity and continues into the
There is therefore a continuous layer of fascia sur-
pelvic cavity. It crosses the midline anteriorly, associating
rounding the abdominal cavity that is thick in some areas,
with the transversalis fascia of the opposite side, and is
thin in others, attached or free, and participates in the for-
continuous with the fascia on the inferior surface of the di-
mation of specialized structures.
aphragm. It is continuous posteriorly with the deep fascia
External oblique muscle External oblique muscle
Rib X
Aponeurosis of external oblique
Transversus abdominis
muscle and aponeurosis
Aponeurosis of internal oblique
Anterior superior iliac spine
Linea alba
Fig. 4.31 Transversus abdominis muscle and its aponeurosis.
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Abdomen
Vertical muscles Rectus abdominis
The two vertical muscles in the anterolateral group of The rectus abdominis is a long, flat muscle and extends
abdominal wall muscles (Table 4.1) are the large rectus the length of the anterior abdominal wall. It is a paired
abdominis and the small pyramidalis (Fig. 4.32). muscle, separated in the midline by the linea alba, and it
Table 4.1 Abdominal wall muscles
Muscle Origin Insertion Innervation Function
External oblique Muscular slips from the Lateral lip of iliac crest; Anterior rami of lower Compress abdominal contents;
outer surfaces of the lower aponeurosis ending in six thoracic spinal nerves both muscles flex trunk; each
eight ribs (ribs V to XII) midline raphe (linea (T7 to T12) muscle bends trunk to same
alba) side, turning anterior part of
abdomen to opposite side
Internal oblique Thoracolumbar fascia; iliac Inferior border of the Anterior rami of lower Compress abdominal contents;
crest between origins of lower three or four ribs; six thoracic spinal nerves both muscles flex trunk; each
external and transversus; aponeurosis ending in (T7 to T12) and L1 muscle bends trunk and turns
lateral two-thirds of in- linea alba; pubic crest anterior part of abdomen to
guinal ligament and pectineal line same side
Transversus Thoracolumbar fascia; me- Aponeurosis ending in Anterior rami of lower Compress abdominal contents
abdominis dial lip of iliac crest; lateral linea alba; pubic crest six thoracic spinal nerves
one-third of inguinal liga- and pectineal line (T7 to T12) and L1
ment; costal cartilages
lower six ribs (ribs VII to XII)
Rectus Pubic crest, pubic tubercle, Costal cartilages of ribs Anterior rami of lower Compress abdominal contents;
abdominis and pubic symphysis V to VII; xiphoid process seven thoracic spinal flex vertebral column; tense
nerves (T7 to T12) abdominal wall
Pyramidalis Front of pubis and pubic Into linea alba Anterior ramus of T12 Tenses the linea alba
symphysis
External oblique muscle
Rectus abdominis muscle Posterior wall of rectus sheath
Tendinous intersection Internal oblique muscle
Arcuate line
Transversalis fascia
Linea alba
Pyramidalis muscle
Fig. 4.32 Rectus abdominis and pyramidalis muscles.
248