Abdomen Drake

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4 Abdomen Conceptual overview 218 Regional anatomy 240 Surface anatomy 342 Clinical cases 351 217-360_Ch04_Drake 4/14/04 3:28 PM Page 217

Transcript of Abdomen Drake

Page 1: Abdomen Drake

4Abdomen

Conceptual overview 218

Regional anatomy 240

Surface anatomy 342

Clinical cases 351

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pelvic wall at the pelvic inlet. Superficially, the inferiorlimit of the abdominal wall is the superior margin of thelower limb.

The chamber enclosed by the abdominal wall contains asingle large peritoneal cavity, which freely communi-cates with the pelvic cavity.

Conceptual overviewGENERAL DESCRIPTION

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The abdomen is a roughly cylindrical chamber extendingfrom the inferior margin of the thorax to the superior mar-gin of the pelvis and the lower limb (Fig. 4.1A).

The inferior thoracic aperture forms the superioropening to the abdomen, and is closed by the diaphragm.Inferiorly, the deep abdominal wall is continuous with the

Diaphragm

A

Inferior thoracic aperture

Iliac crest Pelvic inlet

Abdominal wall

Inguinal ligament

Lower limb

Fig. 4.1 Abdomen. A. Boundaries.

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Conceptual overview • Functions

Abdominal viscera are either suspended in the peri-toneal cavity by mesenteries or are positioned between thecavity and the musculoskeletal wall (Fig. 4.1B).

Abdominal viscera include:

� major elements of the gastrointestinal system—thecaudal end of the esophagus, stomach, small and largeintestines, liver, pancreas, and gallbladder;

� the spleen; � components of the urinary system—kidneys and

ureters; � the suprarenal glands; � major neurovascular structures.

FUNCTIONS

Houses and protects major visceraThe abdomen houses major elements of the gastrointesti-nal system (Fig. 4.2), as well as the spleen and parts of theurinary system.

Much of the liver, gallbladder, stomach, and spleen, andparts of the colon are under the domes of the diaphragm,which project superiorly above the costal margin of thethoracic wall, and as a result these abdominal viscera areprotected by the thoracic wall. The superior poles of thekidneys are deep to the lower ribs.

Viscera not under the domes of the diaphragm are sup-ported and protected predominantly by the muscular wallsof the abdomen.

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Costal margin

MesenteryAorta

Left kidney

Right kidney

Muscles

Inferior vena cava

Peritoneal cavity

B

Fig. 4.1, cont’d. Abdomen. B. Arrangement of abdominalcontents. Inferior view.

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Abdomen

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Rib cage

Stomach

Spleen

Small intestine

Liver

Costal margin

Colon

Fig. 4.2 The abdomen contains and protects the abdominal viscera.

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Conceptual overview • Functions

BreathingOne of the most important roles of the abdominal wall is toassist in breathing:

� it relaxes during inspiration to accommodate expan-sion of the thoracic cavity and the inferior displace-ment of abdominal viscera during contraction of thediaphragm (Fig. 4.3);

� during expiration, it contracts to assist in elevating thedomes of the diaphragm thus reducing thoracic vol-ume.

Material can be expelled from the airway by forced expi-ration using the abdominal muscles, as in coughing orsneezing.

Changes in intra-abdominalpressureContraction of abdominal wall muscles can dramaticallyincrease intra-abdominal pressure when the diaphragm is

in a fixed position (Fig. 4.4). Air is retained in the lungs byclosing valves in the larynx of the neck. Increased intra-abdominal pressure assists in voiding the contents of thebladder and rectum and in giving birth.

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Inspiration Expiration

Diaphragm

Relaxation of diaphragm

Contraction ofdiaphragm

Contraction of abdominal muscles

Relaxation ofabdominal

muscles

Fig. 4.3 The abdomen assists in breathing.

Laryngeal cavity closed

Air retained in thorax

Fixed diaphragm

Contraction of abdominal wall

Increase in intra–abdominal pressure

MicturitionChild birth Defecation

Fig. 4.4 Increasing intra-abdominal pressure to assist inmicturition, defecation, and child birth.

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� lateral to the vertebral column, the quadratus lumbo-rum, psoas major, and iliacus muscles reinforce theposterior aspect of the wall—the distal ends of thepsoas and iliacus muscles pass into the thigh and aremajor flexors of the hip joint;

� lateral parts of the abdominal wall are predominantlyformed by three layers of muscles, which are similar inorientation to the intercostal muscles of the thorax—transversus abdominis, internal oblique, and externaloblique;

� anteriorly, a segmented muscle (the rectus abdominis)on each side spans the distance between the inferiorthoracic wall and the pelvis.

Structural continuity between posterior, lateral, andanterior parts of the abdominal wall is provided by thick

COMPONENT PARTS

WallThe abdominal wall consists partly of bone but mainly ofmuscle (Fig. 4.5). The skeletal elements of the wall (Fig.4.5A) are:

� the five lumbar vertebrae and their intervening inter-vertebral discs;

� the superior expanded parts of the pelvic bones; � bony components of the inferior thoracic wall includ-

ing the costal margin, rib XII, the end of rib XI and thexiphoid process

Muscles make up the rest of the abdominal wall (Fig. 4.5B):

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External oblique

Internal oblique

Transversusabdominis

Psoas major

Rectus abdominis

Gap between inguinalligament and pelvic bone

Quadratuslumborum

Iliacus

Costal marginRib XII

Iliolumbarligament

Pelvic inlet

Inguinal ligament

A B

Fig. 4.5 Abdominal wall. A. Skeletal elements. B. Muscles.

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Conceptual overview • Component parts

fascia posteriorly and by flat tendinous sheets (aponeu-roses) derived from muscles of the lateral wall. A fasciallayer of varying thickness separates the abdominal wallfrom the peritoneum, which lines the abdominal cavity.

Abdominal cavityThe general organization of the abdominal cavity is one inwhich a central gut tube (gastrointestinal system) is sus-pended from the posterior abdominal wall and partly fromthe anterior abdominal wall by thin sheets of tissue(mesenteries; Fig. 4.6):

� a ventral (anterior) mesentery for proximal regions ofthe gut tube;

� a dorsal (posterior) mesentery along the entire lengthof the system.

Different parts of these two mesenteries are named according to the organs they suspend or with which theyare associated.

Major viscera, such as the kidneys, that are not sus-pended in the abdominal cavity by mesenteries are associ-ated with the abdominal wall.

The abdominal cavity is lined by peritoneum, whichconsists of an epithelial-like single layer of cells, (themesothelium) together with a supportive layer of con-nective tissue. Peritoneum is similar to the pleura andserous pericardium in the thorax.

The peritoneum reflects off the abdominal wall to become a component of the mesenteries that suspend theviscera:

� parietal peritoneum lines the abdominal wall; � visceral peritoneum covers suspended organs.

Normally, elements of the gastrointestinal tract and itsderivatives completely fill the abdominal cavity, making theperitoneal cavity a potential space, and visceral peri-toneum on organs and parietal peritoneum on the adja-cent abdominal wall slide freely against one another.

Abdominal viscera are either intraperitoneal orretroperitoneal:

� intraperitoneal structures, such as elements of thegastrointestinal system, are suspended from theabdominal wall by mesenteries;

� structures that are not suspended in the abdominalcavity by a mesentery and that lie between the parietalperitoneum and abdominal wall are retroperitonealin position.

Retroperitoneal structures include the kidneys andureters, 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 thesmall and large intestines, are suspended initially in the abdominal cavity by a mesentery, and later becomeretroperitoneal secondarily by fusing with the abdominalwall (Fig. 4.7).

Large vessels, nerves, and lymphatics are associatedwith the posterior abdominal wall along the median axis ofthe body in the region where, during development, theperitoneum reflects off the wall as the dorsal mesentery,which supports the developing gut tube. As a consequence,branches of the neurovascular structures that pass toparts of the gastrointestinal system are unpaired, originatefrom the anterior aspects of their parent structures, andtravel in mesenteries or pass retroperitoneally in areaswhere the mesenteries secondarily fuse to the wall.

Generally, vessels, nerves, and lymphatics to the abdom-inal wall and to organs that originate as retroperitonealstructures branch laterally from the central neurovascularstructures and are usually paired, one on each side.

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Branch of aorta Aorta

Dorsal mesentery

Ventral mesenteryKidney–posterior to

peritoneum

Visceral peritoneum

Parietal peritoneum

Fig. 4.6 The gut tube is suspended by mesenteries.

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Mesentery

Visceral peritoneum

Parietal peritoneum

Artery to gastrointestinal tract

Retroperitoneal structures

Mesentery before fusion with wall

Intraperitoneal part of tract

Secondary retroperitoneal part of tract

A

B

C

Fig. 4.7 A series showing the progression (A to C) from an intraperitoneal organ to a secondarily retroperitoneal organ.

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Conceptual overview • Component parts

Inferior thoracic apertureThe superior aperture of the abdomen is the inferior tho-racic aperture, which is closed by the diaphragm (see p.000). The margin of the inferior thoracic aperture consistsof vertebra TXII, rib XII, the distal end of rib XI, the costalmargin, and the xiphoid process of the sternum.

DiaphragmThe musculotendinous diaphragm separates the abdomenfrom the thorax.

The diaphragm attaches to the margin of the inferiorthoracic aperture, but the attachment is complex posteri-orly and extends into the lumbar area of the vertebral col-umn (Fig. 4.8). On each side, a muscular extension (crus)firmly anchors the diaphragm to the anterolateral surfaceof the vertebral column as far down as vertebra LIII on theright and vertebra LII on the left.

Because the costal margin is not complete posteriorly,the diaphragm is anchored to arch-shaped (arcuate) liga-ments, which span the distance between available bonypoints and the intervening soft tissues;

� medial and lateral arcuate ligaments cross musclesof the posterior abdominal wall and attach to verte-brae, the transverse processes of vertebra LI and ribXII, respectively;

� a median arcuate ligament crosses the aorta and iscontinuous with the crus on each side.

The posterior attachment of the diaphragm extendsmuch further inferiorly than the anterior attachment.Consequently, the diaphragm is an important componentof the posterior abdominal wall, to which a number of vis-cera are related.

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Esophageal opening

Costal margin

Median arcuate ligament

Medial arcuate ligament

Lateral arcuateligament

Left crus

Right crus Quadratus lumborum

Psoas major

Fig. 4.8 Inferior thoracic aperture and the diaphragm.

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Pelvic inletThe abdominal wall is continuous with the pelvic wall atthe pelvic inlet, and the abdominal cavity is continuouswith the pelvic cavity.

The circular margin of the pelvic inlet is formed entirelyby bone:

� posteriorly by the sacrum; � anteriorly by the pubic symphysis; � laterally, on each side, by a distinct bony rim on the

pelvic bone (Fig. 4.9).

Because of the way in which the sacrum and attachedpelvic bones are angled posteriorly on the vertebral col-umn, the pelvic cavity is not oriented in the same verticalplane as the abdominal cavity. Instead, the pelvic cavityprojects posteriorly, and the inlet opens anteriorly andsomewhat superiorly (Fig. 4.10).

RELATIONSHIP TO OTHERREGIONS

ThoraxThe abdomen is separated from the thorax by the dia-phragm. Structures pass between the two regions throughor posterior to the diaphragm (see Fig. 4.8).

PelvisThe pelvic inlet opens directly into the abdomen and struc-tures pass between the abdomen and pelvis through it.

The peritoneum lining the abdominal cavity is continu-ous with the peritoneum in the pelvis. Consequently, theabdominal cavity is entirely continuous with the pelviccavity (Fig. 4.11). Infections in one region can thereforefreely spread into the other.

The bladder expands superiorly from the pelvic cavity intothe abdominal cavity and, during pregnancy, the uterus expands freely superiorly out of the pelvic cavity into the abdominal cavity.

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Ala of sacrum

S I

L V

Pelvic inlet

Inguinal ligament

False pelvis

Fig. 4.9 Pelvic inlet.

Thoracic wall

Axis of abdominal cavity

Abdominal cavity

Pelvic cavity

Pelvic inlet Axis of pelvic cavity

Fig. 4.10 Orientation of abdominal and pelvic cavities.

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Conceptual overview • Relationship to other regions

Lower limbThe abdomen communicates directly with the thighthrough an aperture formed anteriorly between the infe-rior margin of the abdominal wall (marked by the inguinalligament) and the pelvic bone (Fig. 4.12). Structures thatpass through this aperture are:

� the major artery and vein of the lower limb;

� the femoral nerve, which innervates the quadricepsfemoris muscle, which extends the knee;

� lymphatics;� the distal ends of psoas major and iliacus muscles,

which flex the thigh at the hip joint.

As vessels pass inferior to the inguinal ligament, theirnames change—the external iliac artery and vein of theabdomen become the femoral artery and vein of the thigh.

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Rectum

Peritoneum

Pelvic inlet

Shadow of internal iliac vessels

BladderUterus

Shadow of ureter

Fig. 4.11 The abdominal cavity is continuous with the pelvic cavity.

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KEY FEATURES

Arrangement of abdominal viscerain the adultA basic knowledge of the development of the gastrointesti-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 smallerventral mesentery.

Superiorly, the dorsal and ventral mesenteries are anch-ored to the diaphragm.

The primitive gut tube consists of the foregut, themidgut, and the hindgut. Massive longitudinal growth ofthe 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 adultarrangement of abdominal organs.

Development of the foregutIn abdominal regions, the foregut gives rise to the distalend of the esophagus, the stomach, and the proximal partof the duodenum. The foregut is the only part of the guttube suspended from the wall both by the ventral and dor-sal mesenteries.

A diverticulum from the anterior aspect of the foregutgrows into the ventral mesentery, giving rise to the liverand gallbladder, and ultimately, to the ventral part of thepancreas.

The dorsal part of the pancreas develops from an out-growth of the foregut into the dorsal mesentery. The spleendevelops in the dorsal mesentery in the region between thebody wall and presumptive stomach.

In the foregut, the developing stomach rotates clock-wise and the associated dorsal mesentery, containing thespleen, moves to the left and greatly expands. During thisprocess, part of the mesentery becomes associated with,and secondarily fuses with, the left side of the body wall.

At the same time, the duodenum, together with its dor-sal mesentery and an appreciable part of the pancreas,swings to the right and fuses to the body wall.

Secondary fusion of the duodenum to the body wall, mas-sive growth of the liver in the ventral mesentery, and fusionof the superior surface of the liver to the diaphragm restricts

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LV vertebra

Inguinal ligament

Psoas major muscle

Iliacus muscle

LIV vertebra

Aorta

Inferior vena cava

Fig. 4.12 Structures passing between the abdomen and thigh.

the opening to the space enclosed by the ballooned dorsalmesentery associated with the stomach. This restricted open-ing is the omental foramen (epiploic foramen).

The part of the abdominal cavity enclosed by the expanded dorsal mesentery, and posterior to the stomach,is the omental bursa (lesser sac). Access, through the omental foramen to this space from the rest of the peritoneal cavity (greater sac) is inferior to the free edgeof the ventral mesentery.

Part of the dorsal mesentery that initially forms part ofthe lesser sac greatly enlarges in an inferior direction, andthe two opposing surfaces of the mesentery fuse to form anapron-like structure (the greater omentum). The greateromentum is suspended from the greater curvature of thestomach, lies over other viscera in the abdominal cavity,and is the first structure observed when the abdominalcavity is opened anteriorly.

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Conceptual overview • Key features 4

229

A

Superiormesenteric artery

Superiormesentericartery

Dorsal mesentery

Colon

StomachSpleenLiver

Cecum

Ventral pancreatic bud

Dorsal pancreatic bud

B

Fig. 4.13 A series (A to H) showing the development of the gut and mesenteries.

Greater omentum

C D

LiverLiver

StomachStomach

Cecum

Superior mesenteric artery

Continued

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Stomach

Spleen

Developing greater omentum

Greater omentum

Omental bursaLiver

Cecum

Cecum

E F

Greater omentum

Omental bursaLesser omentum

G H

LiverLiver

Stomach

SpleenSpleen

Cecum

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

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T6

T7

T8

T9

T10

T11

T12

L1

Fig. 4.14 Innervation of the anterior abdominal wall.

Development of the midgutThe midgut develops into the distal part of the duode-num, the jejunum, ileum, ascending colon, and proximaltwo-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 aloop of the midgut herniating out of the abdominal cavityand into the umbilical cord. As the body grows in size andthe connection with the yolk sac is lost, the midgut returnsto the abdominal cavity. While this process is occurring,the two limbs of the midgut loop rotate counterclockwisearound their combined central axis, and the part of theloop that becomes the cecum descends into the inferiorright aspect of the cavity.

The cecum remains intraperitoneal, the ascendingcolon fuses with the body wall becoming secondarilyretroperitoneal, and the transverse colon remains sus-pended by its dorsal mesentery (transverse mesocolon).The greater omentum hangs over the transverse colonand the mesocolon and usually fuses with these struc-tures.

HindgutThe distal one-third of the transverse colon, descendingcolon, sigmoid colon, and the superior part of rectum develop from the hindgut.

Proximal parts of the hindgut swing to the right and 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.The sigmoid colon passes through the pelvic inlet and iscontinuous with the rectum at the level of vertebra SIII.

Skin and muscles of the anteriorand lateral abdominal wall andthoracic intercostal nervesThe anterior rami of thoracic spinal nerves T7 to T12 followthe inferior slope of the lateral parts of the ribs and crossthe costal margin to enter the abdominal wall (Fig. 4.14).Intercostal nerves T7 to T11 supply skin and muscle of theabdominal wall, as does the subcostal nerve T12. In addi-

tion, T5 and T6 supply upper parts of the external obliquemuscle of the abdominal wall; T6 also supplies cutaneousinnervation to skin over the xiphoid.

Skin and muscle in the inguinal and suprapubic regionsof the abdominal wall are innervated by L1 and not by tho-racic nerves.

Dermatomes of the anterior abdominal wall are indi-cated in Figure 4.14. In the midline, skin over the infra-sternal angle is T6 and that around the umbilicus is T10.L1 innervates skin in the inguinal and suprapubic regions.

Muscles of the abdominal wall are innervated segmen-tally in patterns that generally reflect the patterns of theoverlying dermatomes.

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the gubernaculum, between the processus vaginalis andthe accompanying coverings derived from the abdominalwall.

The inguinal canal is the passage through the anteriorabdominal wall created by the processus vaginalis. Thespermatic cord is the tubular extension of the layers ofthe abdominal wall into the scrotum that contains allstructures passing between the testis and the abdomen.

The distal sac-like terminal end of the spermatic cord oneach side contains the testis, associated structures, and thenow isolated part of the peritoneal cavity (the cavity of thetunica vaginalis).

In women, the gonads descend to a position just insidethe pelvic cavity and never pass through the anterior abdominal wall. As a result, the only major structure pass-ing through the inguinal canal is a derivative of the guber-naculum (the round ligament of uterus).

In both men and women, the groin (inguinal region) isa weak area in the abdominal wall (Fig. 4.15).

The groin is a weak area in theanterior abdominal wallDuring development, the gonads in both sexes descendfrom their sites of origin on the posterior abdominal wallinto the pelvic cavity in women and the developing scro-tum in men (Fig. 4.15).

Before descent, a cord of tissue (the gubernaculum)passes through the anterior abdominal wall and connectsthe inferior pole of each gonad with primordia of the scro-tum in men and the labia majora in women (labioscrotalswellings).

A tubular extension (the processus vaginalis) of theperitoneal cavity and the accompanying muscular layersof the anterior abdominal wall project along the guber-naculum on each side into the labioscrotal swellings.

In men, the testis, together with its neurovascularstructures and its efferent duct (the ductus deferens) descends into the scrotum along a path, initially defined by

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Gubernaculum

Muscle wall

Processus vaginalis

Genital tubercle

A

Urogenital membraneLabioscrotal swelling

Gonad

Fig. 4.15 Inguinal region. A. Development.

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233

Inferior vena cava

Right testicular artery

Left testicular arteryRight testicular vein

Left testicular vein

Aorta

Pelvic brim

Left ductus deferens

Ductus deferens

Inguinal canalSuperficial

inguinal ring

Deep inguinal ring

Spermatic cord

Remnant ofgubernaculum

Epididymis

Testis

Tunica vaginalis

Testicularartery and vein

B

Inferior vena cava

Aorta

Left renal artery

Left ovarian artery

Left renal vein

Left ovarian vein

Pelvic inlet

Uterine tube

Round ligament of uterus (remnantsof gubernaculum)

Uterus

Superficialinguinal ring

C

Fig. 4.15, cont’d Inguinal region. B. In men. C. In women.

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Vertebral level LIThe transpyloric plane is a horizontal plane that transectsthe body through the lower aspect of vertebra LI (Fig.4.16). It:

� is about midway between the jugular notch and thepubic symphysis, and crosses the costal margin oneach side at roughly the ninth costal cartilage;

� crosses through the opening of the stomach into theduodenum (the pyloric orifice), which is just to theright of the body of LI—the duodenum then makes acharacteristic 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 loopof the duodenum, and the body of the pancreas extends across the midline to the left;

� crosses through the body of the pancreas;� approximates the position of the hila of the kidneys,

though because the left kidney is slightly higher thanthe right, the transpyloric plane crosses through theinferior aspect of the left hilum and the superior part ofthe right hilum.

The gastrointestinal system and itsderivatives are supplied by threemajor arteriesThree large unpaired arteries branch from the anteriorsurface of the abdominal aorta to supply the abdominalpart of the gastrointestinal tract and all of the structures(liver, pancreas, and gallbladder) to which this part of thegut gives rise to during development (Fig. 4.17). These ar-teries pass through derivatives of the dorsal and ventralmesenteries to reach the target viscera. These vesselstherefore also supply structures such as the spleen andlymph nodes that develop in the mesenteries. These threearteries are:

� the celiac artery, which branches from the abdominalaorta at the upper border of vertebra LI and suppliesthe foregut;

� the superior mesenteric artery, which arises from theabdominal aorta at the lower border of vertebra LI andsupplies the midgut;

� the inferior mesenteric artery, which branches fromthe abdominal aorta at approximately vertebral levelLIII and supplies the hindgut.

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Jugular notch

Rightkidney

LI (transpyloric)plane

Pubic symphysis

Costal margin

Pyloric orifice betweenstomach and duodenum

Position of umbilicus

Fig. 4.16 Vertebral level LI.

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Celiac trunk

Superior mesenteric artery

Inferior mesenteric artery

Inferior vena cava

Aorta

Celiac trunk

Superior mesenteric artery

Inferior mesenteric artery

Foregut

A B

Midgut

Hindgut

Fig. 4.17 Blood supply of the gut. A. Relationship of vessels to the gut and mesenteries. B. Anterior view.

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of large vessels cross the midline to deliver blood from theleft side of the body to the inferior vena cava:

� one of the most significant is the left renal vein, whichdrains the kidney, suprarenal gland, and gonad on thesame side;

� another is the left common iliac vein, which crossesthe midline at approximately vertebral level LV to joinwith its partner on the right to form the inferior venacava—these veins drain the lower limbs, the pelvis, theperineum, and parts of the abdominal wall.

Venous shunts from left to right All blood returning to the heart from regions of the bodyother than the lungs flows into the right atrium of theheart. The inferior vena cava is the major systemic vein inthe abdomen and drains this region together with thepelvis, perineum, and both lower limbs (Fig. 4.18).

The inferior vena cava lies to the right of the vertebralcolumn and penetrates the central tendon of the dia-phragm at approximately vertebral level TVIII. A number

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Superior vena cava

HeartRight atrium

Diaphragm

Right suprarenal veinLeft renal vein

Right gonadal vein

Left gonadal vein

Left suprarenal vein

Left lumbar vein

Left common iliac vein

Pelvic inlet

Fig. 4.18 Left to right venous shunts.

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Conceptual overview • Key features

� other vessels crossing the midline include the left lum-bar veins, which drain the back and posterior abdomi-nal wall on the left side.

All venous drainage from thegastrointestinal system passesthrough the liver Blood from abdominal parts of the gastrointestinal systemand the spleen passes through a second vascular bed, in theliver, before ultimately returning to the heart (Fig. 4.19).

Venous blood from the digestive tract, pancreas, gall-bladder, and spleen enters the inferior surface of the liver

through the large hepatic portal vein. This vein thenramifies like an artery to distribute blood to small endothe-lial-lined hepatic sinusoids, which form the vascular ex-change network of the liver.

After passing through the sinusoids, the blood collectsin a number of short hepatic veins, which drain into theinferior vena cava just before the inferior vena cava pene-trates the diaphragm and enters the right atrium of theheart.

Normally, vascular beds drained by the hepatic portalsystem interconnect, through small veins, with bedsdrained by systemic vessels, which ultimately connect di-rectly with either the superior or inferior vena cava.

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Hepatic veins

Hepatic portal vein

Umbilicus

Rectum

Esophagus

Fig. 4.19 Hepatic portal system.

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that interconnect the portal and caval systems can becomegreatly enlarged and tortuous, allowing blood in tribu-taries of the portal system to bypass the liver, enter thecaval system, and thereby return to the heart. Portal hypertension can result in esophageal varices and hemor-rhoids at the esophageal and rectal ends of the gastrointesti-nal system, respectively, and in ‘caput Medusae’ in whichsystemic vessels that radiate from para-umbilical veins en-large and become visible on the abdominal wall.

Abdominal viscera are supplied by a large prevertebral plexusInnervation of the abdominal viscera is derived from alarge prevertebral plexus associated mainly with the ant-erior and lateral surfaces of the aorta (Fig 4.20). Branchesare distributed to target tissues along vessels that originatefrom the abdominal aorta.

The prevertebral plexus contains sympathetic, para-sympathetic, and visceral sensory components:

� sympathetic components originate from spinal cordlevels T5 to L2;

� parasympathetic components are from the vagus nerve[X] and spinal cord levels S2 to S4;

� visceral sensory fibers generally parallel the motorpathways.

Portacaval anastomoses Among the clinically most important regions of overlapbetween the portal and caval systems are those at each endof the abdominal part of the gastrointestinal system:

� around the inferior end of the esophagus; � around the inferior part of the rectum.

Small veins that accompany the degenerate umbilicalvein (round ligament of the liver) establish another im-portant portal–caval anastomosis.

The round ligament of the liver connects the umbilicusof the anterior abdominal wall with the left branch of theportal vein as it enters the liver. The small veins that accompany this ligament form a connection between theportal system and para-umbilical regions of the abdominalwall, which drain into systemic veins.

Other regions where portal and caval systems intercon-nect include:

� where the liver is in direct contact with the diaphragm(the bare area of the liver);

� where the wall of the gastrointestinal tract is in directcontact with the posterior abdominal wall (retroperi-toneal areas of the large and small intestine);

� the posterior surface of the pancreas (much of thepancreas is secondarily retroperitoneal).

Blockage of the hepatic portal veinor vascular channels in the liverBlockage of the hepatic portal vein or of vascular channelsin 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

239

Sympathetic input Parasympathetic input

Prevertebral plexus

Lumbar splanchnicnerves ( L1,L2)

Pelvic splanchnic nerves (S2 to S4)

Anterior and posterior vagus trunks (cranial)

Greater, lesser and least splanchnic nerves

(T5 to T12)

Fig. 4.20 Prevertebral plexus.

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� a four-quadrant pattern;� a nine-region organizational description.

Four-quadrant pattern For the simple four-quadrant topographical pattern a hor-izontal transumbilical plane passes through the umbilicusand the intervertebral disc between vertebrae LIII and LIVand intersects with the vertical median plane to form fourquadrants—the right upper, left upper, right lower, and leftlower quadrants (Fig. 4.22).

Regional anatomy

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240

The abdomen is the part of the trunk inferior to the thorax(Fig. 4.21). Its musculomembranous walls surround a largecavity (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 asthe fourth intercostal space, and is continuous inferiorlywith the pelvic cavity. It contains the peritoneal cavityand the abdominal viscera.

SURFACE TOPOGRAPHYTopographical divisions of the abdomen are used to describe the location of abdominal organs and the pain associated with abdominal problems. The two schemesmost often used are:

Diaphragm

Sternum

Abdominal cavity

Pelvic cavity

Pubic symphysis

Pelvic inlet

Fi 4 21

Fig. 4.21 Boundaries of the abdominal cavity.

Transumbilical plane Median plane

Right upperquadrant

Left upperquadrant

Right lowerquadrant

Left lowerquadrant

Fig. 4.22 Four-quadrant topographical pattern.

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Regional anatomy • Surface topography

Nine-region organizational patternThe nine-region organizational description is based on twohorizontal and two vertical planes (Fig. 4.23):

� the superior horizontal plane (the subcostal plane) isimmediately inferior to the costal margins, whichplaces it at the lower border of the costal cartilage ofrib X and passes posteriorly through the body of verte-bra LIII (note, however, that sometimes the trans-pyloric plane halfway between the suprasternal(jugular) notch and the symphysis pubis or halfway be-tween the umbilicus and the inferior end of the body ofthe sternum, passing posteriorly through the lowerborder of vertebrae LI and intersecting with the costalmargin at the ends of the ninth costal cartilages isused instead);

� the inferior horizontal plane (the intertubercularplane) connects the tubercles of the iliac crests, whichare palpable structures 5 cm posterior to the anterior

superior iliac spines, and passes through the upperpart of the body of vertebra LV;

� the vertical planes pass from the midpoint of the clavi-cles inferiorly to a point midway between the anteriorsuperior iliac spine and pubic symphysis.

These four planes establish the topographical divisionsin the nine-region organization. The following designa-tions are used for each region: superiorly the righthypochondrium, the epigastric region, and the left hypo-chondrium; inferiorly the right groin (inguinal region), pubic region, and left groin (inguinal region); and in themiddle the right flank (lateral region), the umbilical region,and the left flank (lateral region) (Fig. 4.23).

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Subcostal plane

Transtubercular plane

Midclavicular planes

Righthypochondrium

Right flank

Right groin

Lefthypochondrium

Left flank

Left groin

Epigastric region

Umbilical region

Pubic region

Fig. 4.23 Nine-region organizational pattern.

In the clinic

Surgical incisionsAccess to the abdomen and its contents is usually

obtained through incisions in the anterior abdominal

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).

Other approaches use much smaller incisions. With

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

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

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.

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However, in the lower region of the anterior part of the abdominal wall, below the umbilicus, it forms two layers: asuperficial fatty layer and a deeper membranous layer.

Superficial layerThe superficial fatty layer of superficial fascia (Camper’sfascia) contains fat and varies in thickness (Figs. 4.25 and4.26). It is continuous over the inguinal ligament with thesuperficial fascia of the thigh and with a similar layer inthe perineum.

In men, this superficial layer continues over the penisand, after losing its fat and fusing with the deeper layer ofsuperficial fascia, continues into the scrotum where itforms a specialized fascial layer containing smooth musclefibers (the dartos fascia). In women, this superficial layerretains some fat and is a component of the labia majora.

ABDOMINAL WALLThe abdominal wall covers a large area. It is bounded superiorly by the xiphoid process and costal margins, posteriorly by the vertebral column, and inferiorly by theupper parts of the pelvic bones. Its layers consist of skin,superficial fascia (subcutaneous tissue), muscles and theirassociated deep fascias, extraperitoneal fascia, and parietalperitoneum (Fig. 4.24).

Superficial fascia The superficial fascia of the abdominal wall (subcutaneoustissue of abdomen) is a layer of fatty connective tissue. It isusually a single layer similar to, and continuous with, thesuperficial fascia throughout other regions of the body.

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242

Skin

Superficial fascia–fatty layer

(Camper's fascia)

Superficial fascia–membranous layer

(Scarpa's fascia)

External oblique muscle

Parietal peritoneum Extraperitoneal fascia

Internal oblique muscle

Transversus abdominis muscle

Transversalis fascia

Fig. 4.24 Layers of the abdominal wall.

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Regional anatomy • Abdominal wall

Deeper layer The deeper membranous layer of superficial fascia(Scarpa’s fascia) is thin and membranous, and containslittle or no fat (Fig. 4.25). Inferiorly, it continues into thethigh, but just below the inguinal ligament, it fuses withthe deep fascia of the thigh (the fascia lata; Fig. 4.26). In

the midline, it is firmly attached to the linea alba and thesymphysis pubis. It continues into the anterior part of theperineum where it is firmly attached to the ischiopubicrami and to the posterior margin of the perineal mem-brane. Here, it is referred to as the superficial perinealfascia (Colles’ fascia).

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Superficial fascia

Fatty layer(Camper's fascia)

Membranous layer(Scarpa's fascia)

Skin

Pubic symphysis

Penis

Dartos fasciaScrotum

Inguinal ligament

Aponeurosis of external oblique

Fascia lata of thigh

Fig. 4.25 Superficial fascia.

Continuity with superficialpenile fascia

Continuity withdartos fascia

External oblique muscleand aponeurosis

Membranous layer ofsuperficial fascia (Scarpa's fascia)

Attachment to fascia lata

Superficial perinealfascia (Colles' fascia)

Attachment toischiopubic rami

Fig. 4.26 Continuity of membranous layer of superficial fascia into other areas.

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many normal physiologic functions. By their positioning,they form a firm, but flexible, wall that keeps the abdomi-nal viscera within the abdominal cavity, protects the vis-cera from injury, and helps maintain the position of theviscera in the erect posture against the action of gravity.

In addition, contraction of these muscles assists in bothquiet and forced expiration by pushing the viscera upward(which helps push the relaxed diaphragm further into thethoracic cavity) and in coughing and vomiting.

All these muscles are also involved in any action that increases intra-abdominal pressure, including partur-ition (childbirth), micturition (urination), and defecation(expulsion of feces from the rectum).

Flat muscles

External obliqueThe most superficial of the three flat muscles in the anterolateral group of abdominal wall muscles is the ex-ternal oblique, which is immediately deep to the superfi-cial fascia (Fig. 4.27). Its laterally placed muscle fibers passin an inferomedial direction, while its large aponeuroticcomponent covers the anterior part of the abdominal wallto the midline. Approaching the midline, the aponeurosesare entwined, forming the linea alba, which extends fromthe xiphoid process to the pubic symphysis.

In men, the deeper membranous layer of superficial fas-cia blends with the superficial layer as they both pass overthe penis, forming the superficial fascia of the penis, beforethey continue into the scrotum where they form the dartosfascia (Fig. 4.25). Also in men, extensions of the deepermembranous layer of superficial fascia attached to the pu-bic symphysis pass inferiorly onto the dorsum and sides ofthe penis to form the fundiform ligament of penis. Inwomen, the membranous layer of the superficial fasciacontinues into the labia majora and the anterior part ofthe perineum.

Anterolateral musclesThere are five muscles in the anterolateral group ofabdominal wall muscles:

� three flat muscles whose fibers begin posterolaterally,pass anteriorly, and are replaced by an aponeurosis asthe muscle continues towards the midline—the exter-nal oblique, internal oblique, and transversus abdom-inis muscles;

� two vertical muscles, near the midline, which are enclosed within a tendinous sheath formed by theaponeuroses of the flat muscles.

Each of these five muscles has specific actions, but to-gether the muscles are critical for the maintenance of

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244

Linea alba

Latissimus dorsi muscle

External oblique muscle

Abdominal part ofpectoralis major muscle

Aponeurosis of external oblique

Inguinal ligament

Anterior superior iliac spine

Fig. 4.27 External oblique muscle and its aponeurosis.

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Regional anatomy • Abdominal wall

Associated ligaments The lower border of the external oblique aponeurosisforms the inguinal ligament on each side (Fig. 4.27).This thickened reinforced free edge of the external obliqueaponeurosis passes between the anterior superior iliacspine laterally and the pubic tubercle medially (Fig. 4.28).It folds under itself forming a trough, which plays an im-portant role in the formation of the inguinal canal.

Several other ligaments are also formed from extensionsof the fibers at the medial end of the inguinal ligament:

� the lacunar ligament is a crescent-shaped extensionof fibers at the medial end of the inguinal ligamentthat pass backward to attach to the pecten pubis onthe superior ramus of the pubic bone (Figs. 4.28 and4.29);

� additional fibers extend from the lacunar ligamentalong the pecten pubis of the pelvic brim to form thepectineal (Cooper’s) ligament.

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External oblique

Aponeurosis ofexternal oblique

Femoral artery and vein

Inguinal ligament Lacunar ligament

Pubic tubercle

Anterior superioriliac spine

Fig. 4.28 Ligaments formed from the external obliqueaponeurosis.

Inguinal ligament

Anterior superior iliac spine

Pectineal line

Pectineal ligament

Lacunar ligamentPubic symphysis

Pubic tubercle

Fig. 4.29 Ligaments of the inguinal region.

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Internal obliqueDeep to the external oblique muscle is the internaloblique muscle, which is the second of the three flat mus-cles (Fig. 4.30). This muscle is smaller and thinner thanthe external oblique, with most of its muscle fibers passingin a superomedial direction. Its lateral muscular compo-nents end anteriorly as an aponeurosis that blends into thelinea alba at the midline.

Transversus abdominis Deep to the internal oblique muscle is the transversus abdominis muscle (Fig. 4.31), so-named because of thedirection of most of its muscle fibers. It ends in an anterioraponeurosis, which blends with the linea alba at the midline.

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246

External oblique muscle

Rib X

Internal oblique muscleand aponeurosis

Linea alba

External oblique muscle

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

Transversalis fasciaEach of the three flat muscles is covered on its anterior andposterior surfaces by a layer of investing abdominal fascia.In general, these layers are unremarkable except for thelayer deep to the transversus abdominis muscle (the trans-versalis fascia), which is better developed.

The transversalis fascia is a continuous layer of fasciathat lines the abdominal cavity and continues into thepelvic cavity. It crosses the midline anteriorly, associatingwith the transversalis fascia of the opposite side, and iscontinuous with the fascia on the inferior surface of the di-aphragm. It is continuous posteriorly with the deep fascia

covering the muscles of the posterior abdominal wall andattaches to the thoracolumbar fascia.

After attaching to the crest of the ilium, the transvers-alis fascia blends with the fascia covering the muscles asso-ciated with the upper regions of the pelvic bones and withsimilar fascia covering the muscles of the pelvic cavity. At this point, it is referred to as the parietal pelvic (or endopelvic) fascia.

There is therefore a continuous layer of fascia sur-rounding the abdominal cavity that is thick in some areas,thin in others, attached or free, and participates in the for-mation of specialized structures.

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External oblique muscle

Rib X

Transversus abdominismuscle and aponeurosis

Linea alba

External oblique muscle

Aponeurosis of internal oblique

Aponeurosis of external oblique

Anterior superior iliac spine

Fig. 4.31 Transversus abdominis muscle and its aponeurosis.

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Rectus abdominis The rectus abdominis is a long, flat muscle and extendsthe length of the anterior abdominal wall. It is a pairedmuscle, separated in the midline by the linea alba, and it

Vertical musclesThe two vertical muscles in the anterolateral group ofabdominal wall muscles (Table 4.1) are the large rectusabdominis and the small pyramidalis (Fig. 4.32).

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248

External oblique muscle

Posterior wall of rectus sheathRectus abdominis muscle

Tendinous intersection Internal oblique muscle

Arcuate line

Transversalis fascia

Linea albaPyramidalis muscle

Fig. 4.32 Rectus abdominis and pyramidalis muscles.

Table 4.1 Abdominal wall muscles

Muscle Origin Insertion Innervation Function

External oblique

Internal oblique

Transversus abdominis

Rectus abdominis

Pyramidalis

Muscular slips from theouter surfaces of the lowereight ribs (ribs V to XII)

Thoracolumbar fascia; iliaccrest between origins ofexternal and transversus;lateral two-thirds of in-guinal ligament

Thoracolumbar fascia; me-dial lip of iliac crest; lateralone-third of inguinal liga-ment; costal cartilageslower six ribs (ribs VII to XII)

Pubic crest, pubic tubercle,and pubic symphysis

Front of pubis and pubicsymphysis

Lateral lip of iliac crest;aponeurosis ending inmidline raphe (lineaalba)

Inferior border of thelower three or four ribs;aponeurosis ending inlinea alba; pubic crestand pectineal line

Aponeurosis ending inlinea alba; pubic crestand pectineal line

Costal cartilages of ribsV to VII; xiphoid process

Into linea alba

Anterior rami of lowersix thoracic spinal nerves(T7 to T12)

Anterior rami of lowersix thoracic spinal nerves(T7 to T12) and L1

Anterior rami of lowersix thoracic spinal nerves(T7 to T12) and L1

Anterior rami of lowerseven thoracic spinalnerves (T7 to T12)

Anterior ramus of T12

Compress abdominal contents;both muscles flex trunk; eachmuscle bends trunk to sameside, turning anterior part ofabdomen to opposite side

Compress abdominal contents;both muscles flex trunk; eachmuscle bends trunk and turnsanterior part of abdomen tosame side

Compress abdominal contents

Compress abdominal contents;flex vertebral column; tenseabdominal wall

Tenses the linea alba

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Regional anatomy • Abdominal wall

widens and thins as it ascends from the pubic symphysis tothe costal margin. Along its course, it is intersected bythree or four transverse fibrous bands or tendinous intersections (Fig. 4.32). These are easily visible on indi-viduals with a well-developed rectus abdominis.

Pyramidalis The second vertical muscle is the pyramidalis. This small,triangular-shaped muscle, which may be absent, is ant-erior to the rectus abdominis, has its base on the pubis, andits apex is attached superiorly and medially to the lineaalba (Fig. 4.32).

Rectus sheathThe rectus abdominis and pyramidalis muscles are en-closed in an aponeurotic tendinous sheath (the rectussheath) formed by a unique layering of the aponeuroses ofthe external and internal oblique, and transversus abdom-inis muscles (Fig. 4.33).

The rectus sheath completely encloses the upper three-quarters of the rectus abdominis and covers the anteriorsurface of the lower one-quarter of the muscle. As nosheath covers the posterior surface of the lower quarter ofthe rectus abdominis muscle, the muscle at this point is indirect contact with the transversalis fascia.

The formation of the rectus sheath surrounding the upper three-quarters of the rectus abdominis muscle hasthe following pattern:

� the anterior wall consists of the aponeurosis of the external oblique and half of the aponeurosis of the in-ternal oblique, which splits at the lateral margin of therectus abdominis;

� the posterior wall of the rectus sheath consists of theother half of the aponeurosis of the internal obliqueand the aponeurosis of the transversus abdominis.

At a point midway between the umbilicus and the pubicsymphysis, corresponding to the beginning of the lowerone-quarter of the rectus abdominis muscle, all of theaponeuroses move anterior to the rectus muscle. There isno posterior wall of the rectus sheath and the anterior wallof the sheath consists of the aponeuroses of the externaloblique, the internal oblique, and the transversus abdo-minis muscles. From this point inferiorly, the rectus abdominis muscle is in direct contact with the transver-salis fascia. Marking this point of transition is an arch offibers (the arcuate line; see Fig. 4.32).

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External obliqueA

BExternal oblique

Internal oblique

Transversus abdominis

Linea alba Rectus abdominis

Linea alba Rectus abdominis

Parietal peritoneum

Transversalis fascia

Parietal peritoneum

Transversalis fasciaInternal oblique

Transversus abdominis

Fig. 4.33 Organization of the rectus sheath. A. Transverse section through the upper three-quarters of the rectus sheath. B. Transversesection through the lower one-quarter of the rectus sheath.

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these terms would be the continuity of fat in the inguinalcanal with the preperitoneal fat and a transabdominalpreperitoneal laparoscopic repair of an inguinal hernia.

PeritoneumDeep to the extraperitoneal fascia is the peritoneum (seeFigs 4.6 and 4.7 on pp. 4-7–4-8). This thin serous mem-brane lines the walls of the abdominal cavity and, at vari-ous points, reflects onto the abdominal viscera, providingeither a complete or a partial covering. The peritoneum lin-ing the walls is the parietal peritoneum; the peritoneumcovering the viscera is the visceral peritoneum.

The continuous lining of the abdominal walls by theparietal peritoneum forms a sac. This sac is closed in men,but has two openings in women where the uterine tubesprovide a passage to the outside. The closed sac in men andthe semi-closed sac in women is called the peritoneal cavity.

Extraperitoneal fasciaDeep to the transversalis fascia is a layer of connective tis-sue, the extraperitoneal fascia, which separates thetransversalis fascia from the peritoneum (Fig. 4.34).Containing varying amounts of fat, this layer not onlylines the abdominal cavity, but is also continuous with asimilar layer lining the pelvic cavity. It is abundant on theposterior abdominal wall, especially around the kidneys,continues over organs covered by peritoneal reflections,and, as the vasculature is located in this layer, extends intomesenteries with the blood vessels. Viscera in the extra-peritoneal fascia are referred to as retroperitoneal.

In the description of specific surgical procedures, the termi-nology used to describe the extraperitoneal fascia is furthermodified. The fascia towards the anterior side of the body isdescribed as preperitoneal (or, less commonly, properitoneal)and the fascia towards the posterior side of the body has beendescribed as retroperitoneal (Fig. 4.35). Examples of the use of

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250

Transversalis fascia

Extraperitoneal fascia

Visceral peritoneum

Parietal peritoneum

Transversus abdominis muscle

Internal oblique muscle

External oblique muscle

Aponeuroses

Superficial fascia

Fatty layer(Camper's)

Membranous layer(Scarpa's)

Skin

Fig. 4.34 Transverse section showing the layers of the abdominal wall.

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