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             Conceptual overview
             GENE...
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                A         Visceral peritoneum




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             Pelvic inlet                           ...
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             KEY FEATURES                           ...
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                                           Liver   ...
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             The groin is a weak area in the        ...
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             Venous shunts from left to right       ...
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             Portacaval anastomoses                 ...
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                                              Conceptual overview • Key fe...
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             Regional anatomy
             The abd...
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                In men, the deeper membranous layer ...
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             Internal oblique                       ...
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Abdomen Drake
Abdomen Drake
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Abdomen Drake

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Abdomen Drake

  1. 1. 217-360_Ch04_Drake 4/14/04 3:28 PM Page 217 4 Abdomen Conceptual overview 218 Regional anatomy 240 Surface anatomy 342 Clinical cases 351
  2. 2. 217-360_Ch04_Drake 4/14/04 3:28 PM Page 218 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. 218
  3. 3. 217-360_Ch04_Drake 4/14/04 3:29 PM Page 219 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. 219
  4. 4. 217-360_Ch04_Drake 4/14/04 3:29 PM Page 220 Abdomen Rib cage Costal margin Spleen Liver Stomach Colon Small intestine Fig. 4.2 The abdomen contains and protects the abdominal viscera. 220
  5. 5. 217-360_Ch04_Drake 4/14/04 3:29 PM Page 221 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
  6. 6. 217-360_Ch04_Drake 4/14/04 3:30 PM Page 222 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. 222
  7. 7. 217-360_Ch04_Drake 4/14/04 3:30 PM Page 223 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
  8. 8. 217-360_Ch04_Drake 4/14/04 3:31 PM Page 224 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
  9. 9. 217-360_Ch04_Drake 4/14/04 3:33 PM Page 225 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. 225
  10. 10. 217-360_Ch04_Drake 4/14/04 3:34 PM Page 226 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. 226
  11. 11. 217-360_Ch04_Drake 4/14/04 3:35 PM Page 227 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. 227
  12. 12. 217-360_Ch04_Drake 4/14/04 3:35 PM Page 228 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. 228
  13. 13. 217-360_Ch04_Drake 4/14/04 3:37 PM Page 229 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 229
  14. 14. 217-360_Ch04_Drake 4/14/04 3:40 PM Page 230 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. 230
  15. 15. 217-360_Ch04_Drake 4/14/04 3:40 PM Page 231 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. 231
  16. 16. 217-360_Ch04_Drake 4/14/04 3:41 PM Page 232 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. 232
  17. 17. 217-360_Ch04_Drake 4/14/04 3:41 PM Page 233 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
  18. 18. 217-360_Ch04_Drake 4/14/04 3:41 PM Page 234 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. 234
  19. 19. 217-360_Ch04_Drake 4/14/04 3:42 PM Page 235 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
  20. 20. 217-360_Ch04_Drake 4/14/04 3:42 PM Page 236 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. 236
  21. 21. 217-360_Ch04_Drake 4/14/04 3:42 PM Page 237 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. 237
  22. 22. 217-360_Ch04_Drake 4/14/04 3:42 PM Page 238 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 238
  23. 23. 217-360_Ch04_Drake 4/14/04 3:43 PM Page 239 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. 239
  24. 24. 217-360_Ch04_Drake 4/14/04 3:43 PM Page 240 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
  25. 25. 217-360_Ch04_Drake 4/14/04 3:43 PM Page 241 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. 241
  26. 26. 217-360_Ch04_Drake 4/14/04 3:43 PM Page 242 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. 242
  27. 27. 217-360_Ch04_Drake 4/14/04 3:44 PM Page 243 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
  28. 28. 217-360_Ch04_Drake 4/14/04 3:44 PM Page 244 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. 244
  29. 29. 217-360_Ch04_Drake 4/14/04 3:44 PM Page 245 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. 245
  30. 30. 217-360_Ch04_Drake 4/14/04 3:45 PM Page 246 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. 246
  31. 31. 217-360_Ch04_Drake 4/14/04 3:45 PM Page 247 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. 247
  32. 32. 217-360_Ch04_Drake 4/14/04 3:45 PM Page 248 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

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