The abdominal cavity is the upper portion of a continuous abdominopelvic cavity bounded above by the respiratory diaphragm and below by the pelvic diaphragm, which separates the pelvic cavity from the perineum (Fig. 1; Gr 2.22, 3.2; Ne 323).  The abdominopelvic cavity contains a serous sac, the peritoneum, and the tissues around it inside a musculoaponeurotic and skeletal abdominal wall.  The peritoneum has visceral and parietal layers enclosing a potential space, the peritoneal cavity, that normally contains only a small amount of serous fluid (Gr 2.22, 2.23B; Ne 323, 327).  This is the same basic arrangement that was seen in the pericardial and pleural cavities, with which the peritoneal cavity shares a developmental origin.  The accumulation of excess fluid within the peritoneal cavity (ascities) can result from a number of pathological conditions (e.g., cirrhosis, cancer, infection).  The peritoneal cavity may be punctured and some of the fluid aspirated for analysis or the excess fluid may be drained (paracentesis), e.g., to relieve respiratory distress. 

The visceral layer of peritoneum forms the outer layer (serosa) covering some abdominal organs.  The parietal layer of peritoneum lines the inside of the abdominal wall and the inferior surface of the respiratory diaphragm.  Immediately outside the parietal peritoneum is a layer of extraperitoneal connective tissue.  The largest amount of extraperitoneal connective tissue in the abdominal cavity is located posteriorly, the retroperitoneum, enclosing multiple organs (e.g., the kidneys, pancreas, aorta).

Parts of the peritoneum that connect two organs or connect organs to the abdominal wall are given special names.  A mesentery is a double layer of peritoneum that suspends an organ (e.g., small intestine, transverse colon) from the abdominal wall because the organ had invaginated the peritoneal sac from behind during embryonic development (Fig. 1).  Nerves and vessels that supply the suspended organ reach it through the mesentery.  The more obvious mesenteries are the mesentery (proper) for the jejunum and ileum of the small intestine, the transverse mesocolon for the transverse colon, and the sigmoid mesocolon for the sigmoid colon.

An omentum is a double layer of peritoneum that connects the stomach to adjacent organs.  The greater omentum (or more specifically its gastrocolic ligament component) is an apron-like peritoneal fold that usually hangs in front of the small intestine (Gr 2.19, 2.20A; Ne 261, 267).  Its anterior layer descends from the greater curvature of the stomach and its posterior layer ascends to fuse with visceral peritoneum on the transverse colon and with the transverse mesocolon (Fig. 1; Gr 2.22; Ne 323).  The lesser omentum passes from the lesser curvature of the stomach and the first part of the duodenum below to the liver above.  The lesser omentum is correspondingly subdivided into hepatogastric and hepatoduodenal ligaments (Ne 267).  

Organs that are suspended by a mesentery have a covering of visceral peritoneum and are classified as intraperitoneal organs.  Some intraperitoneal organs have no obvious mesentery but nevertheless are enclosed by visceral peritoneum.  These include the liver, gallbladder, and cecum. 

Organs that remain behind the peritoneal sac and lack a mesentery are classified as retroperitoneal organs.  They either are not covered at all with peritoneum, or are covered only on their anterior surface.  Retroperitoneal organs include most of the duodenum and pancreas, ascending and descending colons, kidneys and ureters, suprarenal glands, abdominal aorta, and inferior vena cava.  Of these, the first four mentioned—duodenum, pancreas, ascending colon, and descending colon—were originally intraperitoneal during embryonic development and later became retroperitoneal during rotation of the gut and fusion of various fasciae.  The originally intraperitoneal organs that later became retroperitoneal—duodenum, pancreas, ascending colon, and descending colon—are said to be secondarily retroperitoneal (Fig. 2).  The organs that were originally retroperitoneal and remained that way are said to be primarily retroperitoneal.

The peritoneal cavity is a closed sac in males. In females the open ends (ostia) of the uterine tubes connect the peritoneal cavity with the outside world via the uterine tubes, cavity of the uterus, and the vagina. This provides a potential pathway for an external infection to enter the peritoneal cavity, resulting in peritonitis. The patency of the uterine tubes can be examined by injection of a radiopaque dye into the uterine cavity, from where it normally flows through the uterine tubes into the peritoneal cavity (hysterosalpingography) (Gr 3.33B).

The peritoneal cavity is a closed sac in males.  In females the open ends (ostia) of the uterine tubes connect the peritoneal cavity with the outside world via the uterine tubes, cavity of the uterus, and the vagina.  This provides a potential pathway for an external infection to enter the peritoneal cavity, resulting in peritonitis.  The patency of the uterine tubes can be examined by injection of a radiopaque dye into the uterine cavity, from where it normally flows through the uterine tubes into the peritoneal cavity (hysterosalpingography) (Gr 3.33B [no image]).   

The peritoneal cavity is subdivided into the small lesser peritoneal sac (omental bursa) behind the stomach and lesser omentum and the large greater peritoneal sac, which occupies the rest of the peritoneal cavity (Fig. 1; Gr 2.22, 2.23B; Ne 323, 327).  The lesser and greater sacs communicate on the right side through the omental (epiploic) foramen, which is located posterior to the hepatoduodenal ligament above the first part of the duodenum (Gr 2.20, 2.22, 2.23A; Ne 267, 323, 327).

The internal (posterior) surface of the anterolateral abdominal wall is viewed during some laparoscopic surgeries (e.g, inguinal or femoral henia repair), and a physician needs to be familiar with its basic features.  There are five umbilical peritoneal folds and associated depressions, the peritoneal fossae, on the internal surface.  The umbilical peritoneal folds are the median, medial, and lateral umbilical folds.  The median umbilical fold is parietal peritoneum raised over a fibrous remnant of the embryonic allantois, the urachus.  The median fold extends upward from the apex of the urinary bladder to the umbilicus (Gr 2.18, 3.13B; Ne 247, 347).  A patent urachus (urachal fistula) in a newborn may result in urine leaking from the umbilicus. 

The medial umbilical fold on each side is parietal peritoneum raised over the medial umbilical ligament, which also ascends to the umbilicus.  The medial umbilical ligament is the obliterated distal portion of the umbilical artery.  Laterally on each side is the lateral umbilical fold.  It is parietal peritoneum raised over the inferior epigastric artery and vein, which ascend medially to enter the rectus sheath near the arcuate line.

The supravesical fossa lies above the bladder between the median and medial umbilical folds.  The medial inguinal fossa is bounded by the medial and lateral umbilical folds.  The lower part of the medial inguinal fossa, lateral to the rectus abdominis and above the iliopubic tract, is the inguinal (Hesselbach’s) triangle.  The iliopubic tract is a thickening of transversalis fascia that parallels the internal surface of the inguinal ligament.  The inguinal triangle is the site where a direct inguinal hernia leaves the abdominal cavity. 

The lateral inguinal fossa is lateral to the lateral umbilical fold.  Note the ductus deferens and testicular vessels or the round ligament of the uterus entering the deep inguinal ring in the lower part of the lateral inguinal fossa.  The deep inguinal ring is where an indirect inguinal hernia leaves the abdominal cavity. 

In a supine patient the hepatorenal recess is the lowest part of the peritoneal cavity.  Therefore, gravity may cause infectious fluids to drain into it from the subphrenic recesses or omental foramen.  The subphrenic recesses are frequent sites of abscess formation, which may result in referred pain to the shoulder from irritation of the diaphragmatic peritoneum.  For more on abdominal abscesses, see http://emedicine.medscape.com/article/189468-overview.

In Fig. 5, notice that the liver is suspended from the diaphragm by peritoneal reflections, the anterior and posterior layers of the coronary ligament.The liver is covered by visceral peritoneum except for a posterior bare area, which isin direct contact with the diaphragm.

The stomach is saclike dilatation of the digestive tract connecting the abdominal portion of the esophagus and the small intestine(Gr 2.19, 2.20, 2.27A; Ne 261, 267, 268, 269).  What was originally the left side of the embryo’s stomach faces anteriorly in the adult due to the stomach’s 90° clockwise rotation around a longitudinal axis () during development (Fig. 6).  The stomach also rotates 90° around an anteroposterior axis () during development.

The stomach has four parts (Gr 2.27, 2.31B, C, D; Ne 267, 268).  The cardia (cardiac part) surrounds the cardial orifice, the opening into the stomach at the gastroesophageal junction.  The fundus is the dilated superior part of the stomach to the left of the cardia.  It is related to the left dome of the diaphragm and often contains gas in x-rays.  The body forms the major part of the stomach.  The pyloric part is the funnel-shaped outflow region of the stomach.  It consists of the pyloric antrum leading into the narrow pyloric canal.  The angular incisure on the lesser curvature indicates the junction between the body and pyloric antrum.  The pylorus consists of the opening of the stomach into the first part of the duodenum, the pyloric orifice, surrounded by the thick, circular smooth muscle of the pyloric sphincter.  Relaxation of the pyloric sphincter under parasympathetic control of the vagus nerves (anterior vagal trunk) allows emptying of the stomach. 

The stomach has two curvatures.  The lesser curvature of the stomach faces superiorly and to the right.  The angular incisure indicates the junction of the body and pyloric part of the stomach.  The lesser curvature and the first part of the duodenum are attached to the liver by the hepatogastric and hepatoduodenal ligaments, respectively, which are parts of the lesser omentum. 

The greater curvature of the stomach faces inferiorly and to the left.  A double-layered fold of peritoneum laden with fat, the greater omentum, hangs down from the greater curvature of the stomach to cover the intestine (Gr 2.19, 2.22; Ne 261, 267, 323).  As shown in Fig. 6, the greater omentum is formed by a ballooning to the left () of the dorsal mesentery (dorsal mesogastrium) that accompanies rotation of the stomach. The greater omentum is a mobile structure and is important in part because it “walls off” areas of localized infection (e.g., during appendicitis) by forming adhesions around them.  This sometimes prevents the spread of infection throughout the peritoneal cavity with the development of a potentially fatal general peritonitis. Its mobility also means that the position of the greater omentum in the cadaver is somewhat variable. 

The spleen is the largest of the lymphatic organs.  It lies deep to ribs 9-11 on the left side with its long axis roughly parallel to the 10th rib.  Despite this seemingly protected position, the living spleen is relatively fragile and it is the most frequently injured abdominal organ.  It rests on the shelf of peritoneum (phrenicocolic ligament) that suspends the angled junction of the transverse and descending colons (splenic, or left colic, flexure) from the diaphragm.  The spleen is positioned between the stomach and left kidney by two other peritoneal ligaments, the gastrosplenic (gastrolienal) ligament and the splenorenal (lienorenal) ligament (Fig. 6H; Gr 2.23B; Ne 264, 327).  

Pay particular attention to the relationships of the spleen on the left side and of the liver on the right side (Gr 2.20A, 2.21, 2.63; Ne 242, 267, 278, 308).  Each organ lies deep to the lower ribs but is separated from them by the diaphragm and the costodiaphragmatic recess of its side.  The liver and spleen may be damaged by blunt abdominal trauma with or without fractures the lower ribs.  During biopsies of the spleen and liver, care must be taken not to damage a lung or its pleura.  During a liver biopsy, a trocar or needle inserted through the right 9th or 10th intercostal space in the midaxillary line would penetrate, in order, the skin and superficial fascia; intercostal muscles; endothoracic (extrapleural) fascia; costal pleura, costodiaphragmatic recess, and diaphragmatic pleura; diaphragm; diaphragmatic peritoneum, subphrenic recess, and visceral peritoneum; and the liver.  In patients with ascites or increased risk of bleeding a transjugular approach may be used to perform the liver biopsy:  internal jugular veinbrachiocephalic veinsuperior vena cavaright atriuminferior vena cavahepatic veinliver.  Thus, any resultant bleeding is back into the venous system.

The stomach opens into the small intestine, which is the primary site for the absorption of nutrients (Gr 2.26).  The small intestine consists of the duodenum, jejunum, and ileum.  All of the duodenum, except the first couple of centimeters, is retroperitoneal and will be studied later. The junction of the duodenum and jejunum, the duodenojejunal junction, is where the small intestine again becomes an intraperitoneal organ.  The jejunum and ileum are intraperitoneal. 

The small intestine opens into the large intestine at the ileocecal junction (Gr 2.26; Ne 273, 274).  The large intestine is a site for water absorption and the temporary storage of the resulting semisolid feces until its elimination.  The large intestine comprises the cecum and appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and upper part of the anal canal.  

The mesentery that suspends the jejunum and ileum from the posterior abdominal wall has a fan-shaped structure.  Its attachment on the abdominal wall, the root of the mesentery, extends from the duodenojejunal junction to the ileocecal junction, a length of about 15 cm (6 inches) (Gr 2.23A; Ne 266, 270).  The much longer intestinal side of the mesentery, attached to the jejunum and ileum, averages about 7 m (21 feet).  Therefore, the small intestine is highly coiled. 

Distinguishing the jejunum from the ileum may be difficult, especially if adhesions are present.  The jejunum forms the proximal two-fifths of their combined length and lies mainly in the left upper quadrant.  The ileum makes up the distal three-fifths and is mostly in the right lower quadrant. 

There is a gradual transition in structure between jejunum and ileum, but the proximal jejunum can be distinguished from the distal ileum by the amount of fat in the mesentery and the arrangement of its arterial supply (Gr 2.43; Ne 272).  The mesentery of the proximal jejunum usually contains little fat and may be translucent, while the mesentery of the distal ileum is laden with fat (Gr 2.43, insets).  The proximal jejunum also is characterized by only 1-2 arterial arcades (anastomotic loops) and long vasa recta (straight arteries) in its mesentery, while the distal ileum typically has 3-5 arterial arcades and short vasa recta.  The jejunum and ileum develop from the embryonic midgut and, therefore, the arterial supply is from the superior mesenteric artery (Gr 2.43, 2.44; Ne 287). 

The jejunum and ileum are framed by the cecum and ascending colon on the right side, the transverse colon above, and the descending colon on the left side (Gr 2.26, 2.39, 2.41; Ne 261, 263).  The large intestine is approximately 1.7 m (5 feet) in length and has features, aside from position, that usually make it easy to distinguish from the small intestine. 

The outer longitudinal layer of smooth muscle in the large intestine is incomplete and arranged in three narrow bands, the teniae coli (Gr 2.42, 2.43, 2.47; Ne 273, 276).  The appendix, rectum, and upper portion of the anal canal are exceptions and have a complete longitudinal layer of smooth muscle.  This fact may be used to find an elusive appendix by tracing the convergence of the three teniae coli toward its base. The teniae coli are slightly shorter than the rest of the colon, drawing its wall into a series of sacculations, the haustra. Also characteristic of the large intestine is the presence of fat-filled pouches of visceral peritoneum, the omental (epiploic) appendices, suspended from it. 

Study the cecum and appendix.  The cecum is a blind pouch located in the iliac fossa of the right lower quadrant.  It receives the ileum at the ileocecal junction, which is guarded by an ileocecal valve (Fig. 7; Gr 2.1A, 2.26, 2.41-2.43, 2.47; Ne 273, 274, 276).  The ileocecal valve prevents the reflux of chyme into the terminal ileum.  The valve may be obstructed by a gallstone (gallstone ileus) that has entered the lumen of the intestine (usually the superior part of the duodenum or the transverse colon) via a fistula with the gallbladder (cholecystenteric fistula).The cecum has no distinct mesentery but in most bodies it is enveloped by peritoneum and, therefore, is mobile.  It is classified as an intraperitoneal organ.

The appendix (vermiform appendix) is a diverticulum of the posteromedial wall of the cecum below the ileocecal junction (Gr 2.42; Ne 273-275).  Usually it is short, 6-10 cm, but occasionally it may be 20 cm or more in length.  The appendix has a short mesentery, the mesoappendix, derived from the mesentery of the terminal ileum.  Although the base of the appendix occupies a relatively constant position one-third of the distance along a line drawn from the right anterior superior iliac spine to the umbilicus (McBurney’s point), the orientation of the appendix is variable ().  The majority of the time (≈65%) the appendix extends superiorly behind the cecum toward the right colic flexure (retrocecal position).  The variability in anatomical position is important because it determines the signs and symptoms as an inflamed appendix (appendicitis) irritates contiguous structures.  Typically appendicitis presents with vague periumbilical pain that later shifts to become severe right lower quadrant pain.  The initial vague pain is due to visceral afferent (GVA) innervation, while the subsequent sharp, localized right lower quadrant pain results from irritation of the parietal peritoneum, which is innervated by somatic afferent (GSA) nerve fibers.  Flexing the right thigh without resistance may relieve the patient’s pain by relaxing the psoas major muscle, but flexing the thigh against resistance or extending it may increase pain due to the irritation resulting from  inflammation (positive psoas/iliopsoas sign).  Vomiting, when it occurs, characteristically follows the onset of appendicitis pain, whereas vomiting that precedes pain suggests another cause, such as intestinal obstruction. 

The ascending colon passes superiorly from the cecum along the right side of the abdominal cavity toward the right lobe of the liver (Gr 2.26, 2.39, 2.41, 2.47; Ne 261, 263).  There it has an angled junction with the transverse colon at the hepatic (right colic) flexure.  The ascending colon is secondarily retroperitoneal.  A deep vertical groove, the right paracolic gutter, lies between the lateral aspect of the ascending colon and the abdominal wall. 

The transverse colon is the longest part of the large intestine and crosses the abdominal cavity from right to left.  It has a mesentery, the transverse mesocolon, and hangs down a variable distance toward the pelvis (Gr 2.39, 2.41; Ne 261).  The attachment of the transverse mesocolon on the posterior abdominal wall crosses the descending (2nd) part of the duodenum and the inferior border of the pancreas (Gr 2.23A, 2.62A; Ne 266, 270). 

The transverse colon is continuous with the descending colon at the splenic (left colic) flexure, which is usually somewhat posterior and superior to the hepatic flexure (Gr 2.26, 2.39, 2.41; Ne 270, 276).   The descending colon descends along the left side of the abdominal cavity to become continuous with the sigmoid colon in the left iliac fossa.  Like the ascending colon, the descending colon is secondarily retroperitoneal.  The left paracolic gutter is located on its lateral aspect. 

Located lateral to the ascending and descending colons are vertical grooves lined with parietal peritoneum.  These right and left paracolic gutters, respectively, provide pathways for the movement of infectious fluid or cancer cells into the pelvic cavity in the upright patient.  In fact, patients with peritonitis may be propped in a seated position to facilitate the flow of infectious fluid into the pelvis, where the absorption of toxins is slower than it is nearer to the diaphragm.  Since the ascending and descending colons are secondarily retroperitoneal organs with a mesentery that fused to the posterior abdominal wall on their medial side during development, the paracolic gutters also provide an approach for surgical mobilization of the ascending and descending colons that doesn’t endanger their nerve and blood supplies.    

The sigmoid colon is an S-shaped segment of colon of variable length.  It is continuous above with the descending colon in the iliac fossa and below with the rectum in the pelvis in front of the third sacral vertebra (Sv3).  The sigmoid colon is suspended by the sigmoid mesocolon from its attachment on the posterior abdominal wall, the root of the sigmoid mesocolon (Gr 2.23A; Ne 263, 266).  The root is roughly in the form of an inverted V with the apex over the terminal division of the left common iliac artery.   The sigmoid colon is the most common site of volvulusresulting from twisting of the colon around its mesentery with intestinal obstruction and possible necrosis due to loss of the blood supply (e.g., see  http://www.learningradiology.com/notes/ginotes/sigmoidvolvpage.htm ) .  The sigmoid colon is also the most frequent location for the development of outpouchings of the intestinal mucosa (diverticulosis), which commonly occurs in middle-aged and elderly individuals, probably due to a lifetime of insufficient fiber in the diet.  Diverticula are prone to infection and inflammation (diverticulitis), hemorrhage, and perforation (producing peritonitis).  For example, see  http://digestive.niddk.nih.gov/ddiseases/pubs/diverticulosis/    The rectum will be studied with other pelvic organs. 

Once again review the organization of the peritoneal cavity.  It consists of a greater peritoneal sac and a lesser peritoneal sac, or omental bursa.  The omental bursa (lesser sac) communicates with the greater sac only at the omental (epiploic) foramen (Gr 2.20, 2.22, 2.23B, 2.24; Ne 265, 267, 323, 327). 

The omental foramen is bounded anteriorly by the hepatoduodenal ligament, which is the free right edge of the lesser omentum that contains the bile duct, proper hepatic artery, and portal vein (Gr 2.23, 2.35, 2.36; Ne 265, 266, 278, 283, 327).  The posterior boundary of the omental foramen is the inferior vena cava behind parietal peritoneum, the superior boundary is the caudate lobe of the liver, and the inferior boundary is the first(superior) part of the duodenum.  The omental foramen may be the site of an internal hernia if a loop of small intestine becomes entrapped there.  Fluid sometimes accumulates in the omental bursa (e.g., following a perforation through the posterior wall of the stomach).  Injury and inflammation of the pancreas (pancreatitis) can result in an encapsulated collection of pancreatic fluid, usually in the posterior wall of the omental bursa (pancreatic pseudocyst) (e.g., see http://www.emedicine.com/radio/topic576.htm ).   

The blood supply to the abdominal portion of the gastrointestinal system from three unpaired ventral branches of the aorta reflects its embryonic origin (Fig. 8).  Derivatives of the embryonic caudal foregut, which extends from the distal esophagus to the entrance of the (common) bile duct into the second, or descending, part of the duodenum, are supplied by branches of the celiac trunk (celiac artery).  Midgut derivatives extend from just distal to the bile duct entrance to near the splenic (left colic) flexure and are supplied by branches of the superior mesenteric artery.  The hindgut extends from just proximal to the splenic flexure to the middle of the anal canal and is supplied by branches of the inferior mesenteric artery.

Note that the abdominal aorta is a retroperitoneal structure, and so the celiac trunk, superior mesenteric artery, and inferior mesenteric artery arise in a retroperitoneal position.  Some of their branches, however, enter a mesentery to supply intraperitoneal organs.  The celiac trunk arises in front of vertebra Tv12, the superior mesenteric artery at the Lv1 level, and the inferior mesenteric artery at the Lv3 level.  Pay particular attention to the fact that the autonomic innervation of the gastrointestinal tract follows the blood vessels that supply it.  Since the general visceral afferent nerve fibers that accompany sympathetic fibers carry pain from visceral organs, knowledge of their arrangement provides a basis for understanding pain referred to the body wall (Gr 2.77, Table 2.7 [p. 169]).

The venous drainage of the abdominal portion of the gastrointestinal tract and spleen differs fundamentally from that of the rest of the body.  The abdominal digestive tract is drained by the portal system of veins, which carries the nutrient-rich blood to the liver rather than directly to the systemic circulation as represented by the inferior vena cava (Gr 2.60; Ne 292).  In the liver nutrients are extracted from the blood and stored, while toxins are extracted and broken down, and bile is produced for transport in the bile duct to the duodenum.  The secreted bile both neutralizes acid in the chyme leaving the stomach and emulsifies fat to facilitate its digestion.  Only the larger tributaries of the portal vein will be dissected.   

The celiac trunk (celiac artery) is the first branch of the abdominal aorta to be studied.  It has three branches—the left gastric, common hepatic, and splenic arteries (Fig. 9; Gr 2.28, 2.30, 2.34; Ne 283, 284).

The left gastric artery ascends briefly toward the esophageal hiatus of the diaphragm, giving off esophageal branches before descending to the right along the lesser curvature of the stomach.  It anastomoses with the right gastric artery. 

The common hepatic artery courses to the right from its origin to divide into proper hepatic and gastroduodenal arteries near the pylorus.  The proper hepatic artery usually gives origin to the right gastric artery, then ascends in the hepatoduodenal ligament.  It bifurcates into right and left hepatic arteries to their respective lobes of the liver.  The cystic artery to the gallbladder typically arises from the right hepatic artery, but variations are common (Fig. 10; Gr 2.57; Ne 283, 284).  The cystic artery crosses a triangle bounded on the left side by the common hepatic duct, on the right side by the cystic duct, and above by the liver (cystohepatic/hepatobiliary triangle).  This is an important relationship during the surgical removal of the gallbladder (cholecystectomy).  The triangle contains a lymph node (Calot’s node) that is enlarged during inflammation of the gallbladder (cholecystitis) or bile ducts  (cholangitis).

The gastroduodenal artery descends behind the first part of the duodenum to divide into the superior pancreaticoduodenal and right gastro-omental arteries (Fig. 9; Gr 2.28, 2.33, 2.34; Ne 283, 284).  In this position the gastroduodenal artery may hemorrhage due to a peptic ulcer that erodes through the posterior wall of the first part of the duodenum, the most common location for a peptic ulcer.  Alternatively, a duodenal ulcer may erode inferiorly into the pancreas, producing pancreatitis, or anteriorly into the peritoneal cavity, causing peritonitis, both potentially life-threatening conditions.

The superior pancreaticoduodenal artery divides into anterior and posterior branches that anastomose with corresponding branches of the inferior pancreaticoduodenal artery from the superior mesenteric.  As the name suggests, the pancreaticoduodenal arteries supply the head of the pancreas and adjacent duodenum. 

The right gastro-omental artery follows the greater curvature of the stomach within the greater omentum.  It anastomoses with the left gastro-omental branch of the splenic artery.

The splenic artery is the third branch of the celiac trunk.  It branches from the left side of the celiac trunk and passes posterior to the stomach along the superior border of the pancreas.  In this position it may be the cause of fatal hemorrhage following the rare erosion of a peptic ulcer through the posterior wall of the stomach.  Fatal hemorrhage also may result from the rupture of a splenic artery aneurysm, while an unruptured aneurysm may cause severe epigastric pain and vomiting (emesis) (e.g., see http://shortreports.rsmjournals.com/content/1/3/24.full)

Along with the tail of the pancreas, the splenic artery enters the splenorenal ligament to reach the hilum of the spleen (Fig. 9; G11 2.28, 2.32, 2.34; G12 2.29, 2.33, 2.34; N 281-284).  The splenic artery gives branches to the pancreas, short gastric arteries to the fundus of the stomach, and the left gastro-omental artery to the greater curvature.  Pancreatic branches regularly include a dorsal pancreatic artery given off near the origin of the splenic artery and a great pancreatic artery near the middle of the body of the pancreas (N 284, 286).

Occasionally the right hepatic artery arises from the superior mesenteric artery and/or the  left hepatic artery arises from the left gastric artery (labeled aberrant or accessory hepatic arteries depending on whether or not they are the sole blood supply or a supplemental blood supply, respectively, to that lobe of the liver) (Gr 2.55).  Be aware of these possible variations.

Study the organs supplied by the blood vessels just dissected.  The stomach consists of a cardial portion, fundus, body, and pyloric portion (Gr 2.27; Ne 267, 268).  The cardia surrounds the cardial orifice at the gastroesophageal junction.  A physiologic lower esophageal sphincter, formed in part by the diaphragmatic musculature of the esophageal hiatus, prevents regurgitation into the esophagus. Chronic reflux of gastric contents into the lower esophagus may cause metaplastic change of the mucosa, ulceration, and stricture formation.  This Barrett’s esophaguspredisposes to the development of esophageal adenocarcinoma. 

The fundus is the dilated upper portion of the stomach below the left dome of the diaphragm and often contains gas bubbles that are apparent on a radiograph.  The body forms the major portion of the stomach.  It is continuous at a notch on the lesser curvature (angular incisure) with the pyloric part.  The pyloric part consists of the wide pyloric antrum leading into the narrow pyloric canal.  The pyloric canal ends at the pyloric orifice connecting the stomach with the duodenum.  The pyloric orifice is guarded by a thickened circular layer of smooth muscle under parasympathetic control by the vagus nerves (anterior vagal trunk), the pyloric sphincter. 

The liver is the largest gland in the body.  It has diaphragmatic and visceral surfaces separated anteriorly by a sharp inferior border (Figs. 5, 11; Gr 2.22, 2.24, 2.49, 2.50A; Ne 267, 277, 278).

Posteriorly the diaphragmatic surface has a bare area where the liver isn’t covered by visceral peritoneum and is in direct contact with the diaphragm.  The inferior vena cava traverses the groove for the inferior vena cava in the bare area (Fig. 11).  The bare area is bordered by peritoneal reflections that suspend the liver from the diaphragm, the anterior and posterior layers of the coronary ligament.  These layers meet laterally to form the right and left triangular ligaments on their respective sides of the falciform ligament.

The liver is subdivided into functional right and left lobes by a sagittal line joining the fossa for the gallbladder and the groove for the inferior vena cava.  The functional right lobe of the liver is a single large lobe.  The functional left lobe includes the smaller caudate and quadrate lobes medially separated from the main portion of the left lobe by the fissure for the ligamentum teres hepatis (round ligament of the liver) and the fissure for the ligamentum venosum.  The caudate and quadrate lobes are separated from each other by a transverse fissure, the porta hepatis, where the portal vein, hepatic arteries, hepatic ducts, and associated lymphatic vessels and nerves enter or leave the leave (Gr 2.50, 2.55A; Ne 277, 283, 284).  The large portal vein carries 75% of the blood to the liver.

Some authors consider the caudate lobe to be a separate lobe functionally distinct from the right and left lobes.  The caudate lobe may have a papillary process projecting toward the porta hepatis.  A caudate process extends to the right between the inferior vena cava and the porta hepatis, connecting the caudate and right lobes (Gr 2.50A). 

The ligamentum teres hepatis (round ligament of the liver) is a fibrous remnant of the fetal left umbilical vein (usually just referred to as the “umbilical vein”) (Fig. 11; Gr 2.50; Ne 267, 277).  The left umbilical vein carried well oxygenated blood from the placenta to the fetus before birth.  The ligamentum venosum is a fibrous remnant of the fetal ductus venosus.  The ductus venosus shunted much of the oxygenated blood from the left umbilical vein to the inferior vena cava, bypassing the hepatic sinusoids of the liver. 

The liver is often divided for descriptive purposes into anatomical right and left lobes as well. The large anatomical right lobe is separated from the anatomical left lobe by the fissures for the ligamentum teres hepatis and ligamentum venosum. Thus, the caudate and quadrate lobes would be considered part of the anatomical right lobe of the liver. 

The gallbladder is an elongated thin-walled sac occupying the gallbladder fossa on the visceral surface of the liver.  The gallbladder stores and concentrates bile and is usually stained green in the cadaver.  Visceral peritoneum envelops the gallbladder and helps bind it to the liver.  The gallbladder consists of a fundus, body, and neck (Figs. 10, 11; Gr 2.37, 2.50, 2.58; Ne 277, 280).  The fundus is the wide end of the organ that projects slightly below the inferior border of the liver.  Its surface projection is near the junction of the tip of the right 9th costal cartilage and the linea semilunaris (i.e., about the midclavicular line).  A patient with an inflamed gallbladder (cholecystitis), which often results from gallstones, experiences pain at this site and abruptly stops inspiration with the pressure of palpation (Murphy’s sign).  Alternatively, the inflamed gallbladder may irritate diaphragmatic peritoneum, referring pain to the right shoulder.  An inflamed gallbladder may adhere to the superior part of the duodenum with development of a cholecystenteric fistula.  A gallstone entering the duodenum through such a fistula may pass distally and obstruct the ileocecal junction(gallstone ileus). Instead of the superior part of the duodenum, an inflamed gallbladder may adhere to the transverse colon and develop a cholecysteneric fistula with it. Would this result in gallstone ileus?

The body of the gallbladder occupies the gallbladder fossa of the liver.  The neck is the tapered S-shaped portion of the gallbladder that is connected by the cystic duct to the common hepatic duct.  The cystic duct is kept open by a spiral fold (spiral valve) of mucosa (Gr 2.37A; Ne 280), facilitating the passage of bile.  The cystic duct joins the common hepatic duct to form the bile duct.  A pouchlike dilatation of the neck of the gallbladder (Hartmann’s pouch) may develop as a pathological change and be a site of gallstone accumulation. 

The gallbladder and cystic duct are supplied by the cystic artery, which usually branches from the right hepatic artery, but variations occur (Gr 2.57; Ne 283, 284).  Small cystic veins directly enter the liver from the fundus and body of the gallbladder and sometimes from the neck and cystic duct.  A cystic vein from the neck of the gallbladder and cystic duct rarely is a direct extrahepatic tributary of the portal vein. 

The large superior mesenteric artery and vein emerge from behind the neck of the pancreas to cross anterior to the uncinate process of the pancreas and the inferior (3rd) part of the duodenum to enter the mesentery (Fig. 13; Gr 2.25, 2.33, 2.34, 2.43, 2.44; Ne 284, 288, 323).  In rare patients the superior mesenteric vessels may compress the duodenum, obstructing the passage of intestinal contents (superior mesenteric syndrome).  The superior mesenteric artery is also a common site for acute mesenteric ischemia produced by an thromboembolus dislodged from the heart or by sudden occlusion at a focus of long-standing atherosclerosis (e.g., seehttp://emedicine.medscape.com/article/758674-overview  )

The superior mesenteric artery gives off the inferior pancreaticoduodenal artery and jejunal and ileal branches to the small intestine (Figs. 12, 13).  It supplies the large intestine via middle colic, right colic, and ileocolic branches.  The ileocolic artery also contributes to the blood supply of the terminal ileum.

The middle colic artery arises from the right side of the superior mesenteric artery just distal to the pancreas and enters the transverse mesocolon.  Near the wall of the transverse colon it divides into right and left branches (Gr 2.43, 2.44A, 2.45; Ne 287, 288). 

The next branch of the superior mesenteric artery is the right colic artery, which has a variable origin.  It may arise from the superior mesenteric artery or from a common stem with the ileocolic artery.  The right colic artery passes to the right side in a retroperitoneal position and divides into ascending and descending branches to supply the ascending colon. 

The ileocolic artery descends toward the ileocecal junction (Gr 2.43, 2.44A; Ne 287, 288).  It has ascending colic, cecal, and ileal branches.  The appendicular artery also commonly branches directly from the ileocolic artery.  The appendicular artery is anend artery(i.e., it doesn’t have anastomoses).  Consequently, if acute infection and inflammation of the appendix (acute appendicitis) results in edema compressing the artery or in the artery’s thrombosis, then necrosis and perforation of the appendix may result.  A potentially fatal generalized peritonitis may be prevented if the greater omentum walls off the site of infection, producing a localized abscess.

The pancreas is a combination exocrine and endocrine gland.  Its exocrine secretions enter the duodenum through the main and accessory pancreatic ducts.  Its endocrine secretions enter the blood.  The pancreas is divided for descriptive purposes into a head, neck, body, and tail (Figs. 10, 13; Gr 2.32, 2.33; Ne 281). The head of the pancreas occupies the C-shaped curvature of the duodenum.  The uncinate process is a projection from the inferior part of the head that passes to the left posterior to the superior mesenteric vessels.  The neck of the pancreas lies anterior to the superior mesenteric artery.  The superior mesenteric vein joins the splenic vein behind the neck to form the portal vein.  The body of the pancreas continues to the left from the neck and ends in the tail.  The tail of the pancreas occupies the splenorenal ligament with the splenic vessels (Fig. 14) and is in danger during removal of the spleen (splenectomy).

Pancreatic cancer is the fourth leading cause of cancer deaths with a five-year survival rate of less than 5% (see http://emedicine.medscape.com/article/280605-overview ).  Adenocarcinoma of the head of the pancreas may cause extrahepatic obstruction of the bile duct.  Excess bile is absorbed into the blood, producing yellowing of mucous membranes, conjunctiva, and skin (obstructivejaundice).  Painless jaundice is often the first indication of cancer involving the head of the pancreas.  Pancreatic cancer involving the body and tail commonly causes severe abdominal pain that radiates to the back.  New-onset diabetes mellitus or hyperglycemia in individuals over the age of 50 without a family history may be the first indication of pancreatic cancer. 

The duodenum is the first part of the small intestine (Figs. 10, 13; Gr 2.32, 2.33, 2.37; Ne 270, 271, 281).  It begins at the pylorus and ends at the dudodenojejunal junction, where the duodenum is continuous with the jejunum.  The duodenum is divided into four parts.  The superior (first) part, which is approximately 5 cm long, has an initial short segment (2 cm) that is intraperitoneal.  This intraperitoneal part has the greater omentum attached to its lower margin and has its upper margin connected to the liver by the hepatoduodenal ligament.  This intraperitoneal part of the duodoenum has a distinct appearance on radiographs using contrast medium and is called the duodenal cap (ampulla) (Gr 2.31B-D).  The remainder of the duodenum is secondarily retroperitoneal. 

The descending (second) part of the duodenum near its midpoint receives the openings of the bile duct and main pancreatic duct at the major duodenal papilla (Gr 2.37; Ne 271).  Usually these ducts unite to form the hepatopancreatic ampulla.  The accessory pancreatic duct enters the duodenum a little higher at the minor duodenal papilla.  However, there is occasional variation in these ducts (Gr 2.38 D-G). 

The inferior (third or horizontal) part of the duodenum runs transversely toward the left over the inferior vena cava and aorta at the level of the 3rd lumbar vertebra.  The superior mesenteric artery and vein pass anterior to the third part of the duodenum (Fig. 13; Gr 2.83G, 2.85 B-C). 

The ascending (fourth) part of the duodenum passes superiorly and to the left to join the jejunum at the duodenojejunal junction (duodenojejunal flexure) (Gr 2.32, 2.47; Ne 262).  The duodenojejunal junction is supported by a fibromuscular slip of tissue, the suspensory muscle of the duodenum (ligament of Treitz), which is a surgical landmark.  The duodenojejunal junction is where the small intestine again becomes intraperitoneal.  It is also the demarcation between upper and lower GI bleeding, which have different clinical characteristics.

The inferior mesenteric artery sends a left colic branch to the descending colon and sigmoid branches to the sigmoid colon.  It terminates as the superior rectal artery to the rectum and upper half of the anal canal (Figs. 15, 16; Gr 2.45, 2.46; Ne 288).

The left colic artery passes to the left behind the peritoneum and divides into ascending and descending branches.The ascending branch anastomoses with the left branch of the middle colic artery from the superior mesenteric, helping to form a marginal arterythat extends from the ileocecal junction to the sigmoid colon.  This is important during the atherosclerotic occlusion or surgical ligation of the inferior mesenteric artery.

The descending branch of the left colic artery anastomoses with its sigmoid branches that enter the sigmoid mesocolon to supply the sigmoid colon (Fig. 15; Gr 2.45, 2.46; Ne 288, 378).  The direct continuation of the inferior mesenteric artery is the superior rectal artery.  It descends into the pelvis and anastomoses with the middle rectal arteries from the right and left internal iliac arteries.  These arteries will be studied during dissection of the pelvis.