Stomach

Development of Stomach and Greater Omentum

The foregut begins as a simple, midline, tubular structure lined by epithelium derived from endoderm. While the endoderm creates the lining of the stomach, the visceral mesoderm that surrounds it will form the muscles, connective tissues, and mesenteries that are associated with the organ. The portion of the foregut that will become the stomach first starts to expand in the sagittal plane, ballooning outward on its anterior and posterior surfaces. However, the expansion of the posterior surface quickly outpaces the other side and the stomach begins to bend. The enlarged expansion of the posterior side will become the stomach's greater curvature, and the anterior side will become the lesser curvature. As this is happening, the presumptive stomach rotates so that the posterior side shifts toward the left of the body and the right side shifts to the right. The rotation and expansion of the posterior side are what give the stomach its characteristic shape, with the esophagus entering just to the right of the fundus and greater curvature, whereas the outlet of the stomach, the pyloric region, shifts to the right and slightly superior to the greater curvature. This moves the stomach from a superior/inferior axis to more of a right/left axis within the abdomen. The inner, circular layer of muscle at the terminus of the stomach enlarges significantly to form the pyloric sphincter.

The rotation and expansion of the stomach do not occur in isolation. The foregut is attached to the posterior body wall by a dorsal (posterior) mesentery, in which the spleen and part of the pancreas will develop. The section of this mesentery between the developing spleen and the stomach will become the greater omentum. Anteriorly the stomach is connected to the liver, and thereafter, to the anterior body wall by a ventral (anterior) mesentery. The section of the ventral mesentery that attaches the liver to the anterior body wall will become the falciform ligament, and the section between the liver, stomach, and duodenum will form the lesser omentum. As the stomach's posterior surface expands and rotates to the left, the attached mesentery follows, so that the spleen lies along the left side of the abdominal cavity. The dorsal mesentery between the stomach and spleen expands, folding onto itself and creating a large pocket (omental bursa) between the two folds. Continued rotation and expansion of the greater curvature bring this double-layered “apron” to extend inferiorly from the stomach, falling anterior to the transverse colon and small intestines. The space between the two folds is termed the inferior recess of the omental bursa; however, this space typically disappears as development proceeds and the two folds adhere and create a single greater omentum. As the liver grows, the stomach shifts to the left side of the abdomen and the liver shifts to the right side. This brings the omental bursa to lie anterior to the pancreas, inferior to the inferior surface of the liver, and posterior to the stomach and lesser omentum, which can be subdivided into the hepatogastric and hepatoduodenal ligaments. Occasionally, the omental bursa can extend superiorly and posteriorly to the liver as the superior recess of the omental bursa. In its mature form, the omental bursa is isolated from the rest of the abdominal cavity except for a small opening called the omental foramen, located immediately posterior to the right edge of the hepatoduodenal ligament.

Anatomy, Normal Variations, and Relations of Stomach

The stomach is an enlarged reservoir of the proximal digestive tract, in which ingested food is soaked in gastric juice containing enzymes and hydrochloric acid and then released spasmodically into the duodenum by gastric peristalsis. The form and size of the stomach vary considerably, depending on the position of the body and the degree of filling.

The stomach has anterior and posterior walls that practically touch when the organ is empty and flattened. It is distended inferiorly and to the left, creating a convex greater curvature and a concave lesser curvature along its superior border. The superiormost region of the greater curvature includes the fundus of the stomach, a domed section on the superior left side of the abdomen, which is closely related to the diaphragm and spleen. The greater and lesser curvatures meet at the cardiac region of the stomach, where the esophagus enters. On the right the esophagus continues smoothly into the lesser curvature, but on the left there is a definite indentation, the cardial notch (incisure), which becomes most obvious when the fundus is full and bulges superiorly. The largest region of the stomach is the body ( corpus ) of the stomach, located inferior to the cardiac region and fundus. The massiveness of the greater curvature causes the stomach's lumen to shift to the right side of the abdomen, where it will empty into the duodenum. Prior to its terminus, the body of the stomach blends imperceptibly into the pyloric part, except along the lesser curvature, where the angular incisure (notch ) marks the boundary between the body and the pyloric part. The latter contains the pyloric antrum, which narrows into the pyloric canal, terminating at the pyloric valve.

The surface of the stomach is entirely covered and suspended by peritoneum. A double layer of peritoneum, deriving from the embryonic ventral mesentery, extends from the lesser curvature and first part of the duodenum toward the liver. This is the lesser omentum, and it may be subdivided into a larger, thinner, hepatogastric ligament and a smaller, thicker, distal hepatoduodenal ligament, which attaches to the pyloric region and to the upper horizontal portion of the duodenum. The portal vein, proper hepatic artery, and common bile duct are found within the hepatoduodenal ligament. The free edge of the hepatoduodenal ligament, located on the right end of the lesser omentum, forms the anterior border of the omental (epiploic) foramen (of Winslow), which gives access to the omental bursa (lesser sac) located posterior to the stomach. The greater omentum, a derivative of the embryonic dorsal mesentery, passes inferiorly from the greater curvature and contains, between its two frontal and two dorsal sheets, the inferior recess of the omental bursa. Typically this space is negligible and the entire greater omentum can be moved like a single apronlike object hanging from the greater curvature.

The anterior surface of the stomach contacts the peritoneum lining the anterior abdominal wall, the inferior surface of the left lobe of the liver, and, to some extent in the pyloric region, the quadrate lobe of the liver and the gallbladder. Its posterior surface is in apposition with retroperitoneal structures (pancreas, splenic vessels, left kidney, and adrenal gland) from which, however, it is separated by the omental bursa. The fundus of the stomach bulges against the left diaphragmatic dome. On the left, adjacent to the fundus, is the spleen, which is connected to the stomach by the gastrosplenic ligament, also derived from the embryonic dorsal mesentery.

Anatomy and Relations of Duodenum

The duodenum, the first part of the small intestine, has a total length of about 25 to 30 cm (approximately the width of 12 fingers; hence its name) and is shaped like a horseshoe with the open end facing to the left.

The superior (first) part, lying at the level of the first lumbar vertebra, extends horizontally from the pylorus of the stomach to the superior duodenal flexure. As a result of being attached to the hepatoduodenal ligament, this first duodenal portion has limited mobility and can adapt its course according to the filling condition of the stomach. The anterior and superior surfaces of the first half of this duodenal segment are in close relation to the inferior surface of the quadrate lobe of the liver and the gallbladder. The radiographic designation “duodenal bulb” refers to the most proximal end of the superior part of the duodenum, which is slightly dilated when the organ is filled and then more sharply separated from the stomach because of the pyloric contraction. The two layers of peritoneum that cover the anterosuperior and posteroinferior surfaces of the duodenum fuse superiorly to form the hepatoduodenal ligament, which contains the portal triad. This triad contains the portal vein, proper hepatic artery, and common bile duct. The head of the pancreas is positioned posterior to the first portion of the duodenum, with the two organs being separated by a peritoneal fold of the omental bursa.

The descending (second) part of the duodenum extends vertically from the superior to the inferior duodenal flexure, which lies approximately at the level of the third lumbar vertebra. The superior portion of the descending duodenum rests laterally upon the hilus of the right kidney, while medially its whole length is attached by connective tissue to the duodenal margin of the pancreatic head. About halfway, the descending portion is crossed anteriorly by the line of attachment of the transverse mesocolon. The portal triad is located posterior to the superior part of the duodenum and continues its course between the descending portion and the head of the pancreas to its opening at the major duodenal papilla (of Vater). This topographic relationship explains the danger of an obstruction of the duct in the presence of a tumor of the pancreatic head.

The inferior (third, or horizontal) part of the duodenum begins at the inferior duodenal flexure. It runs horizontally or sometimes in a slightly ascending direction until it reaches the region of the left border of the aorta, where, curving cranially, it changes direction to pass into the terminal, ascending (fourth) portion of the duodenum. Whereas the inferior part of the second portion and the inferior flexure lie over the psoas major of the right side of the body, the inferior duodenum, with its horizontal segment, passes over the vena cava and the abdominal aorta. The superior mesenteric vessels, before entering the root of the mesentery, cross over the inferior part of the duodenum near its transition to the ascending part. The third portion is retroperitoneal, but it becomes increasingly covered by the peritoneum, and the ascending duodenum gains a small mesentery, becoming intraperitoneal as it approaches the duodenojejunal flexure. The duodenojejunal flexure is located inferior to the transverse mesocolon at the level of the second lumbar vertebra or of the disc between L1 and L2.

Mucous Membrane of Stomach

The reddish-gray mucous membrane of the stomach, composed of a surface layer of epithelial cells, the lamina propria, and the muscularis mucosae, commences at the cardia along an irregular or zigzag line (referred to as the Z line). Deep to the mucosa is the submucosa and three external muscle layers of the stomach. When the stomach is empty, the mucosa appears to be formed of folds (rugae), which flatten considerably when the stomach is distended. In the region of the lesser curvature, where the mucosa is more strongly fixed to the underlying muscular layer, the folds take a longitudinal course. The rugae are generally smaller in the fundus and become larger as they approach the pyloric portion of the stomach, where they show a tendency to run diagonally across the stomach toward the greater curvature. Besides these broad folds, the gastric mucosa is further characterized by numerous shallow invaginations, which divide the mucosal surface into a mosaic of elevated areas varying in shape. When viewed under magnification, several delicate ledges, or mammillated areas, and depressions, known as gastric pits, can be seen. Gastric glands empty into the stomach lumen through the gastric pits.

The gastric epithelium consists of a single layer of simple columnar cells, and it is sharply demarcated from the stratified squamous epithelium of the esophagus at the gastroesophageal junction in the cardiac area of the stomach. The columnar epithelial cells are of the mucoid type and contain mucigen granules in their outer portions and a single ovoid nucleus at their base. These cells line the tubular cardiac glands along with mucoid neck, chief, parietal, and enteroendocrine cells that allow the stomach to carry out its functions.

• 1.

  The cardiac glands are confined to a narrow zone, 0.5 to 4 cm in width, around the cardiac orifice. They are coiled and are lined almost entirely by mucus-producing epithelial cells.

• 2.

  The gastric, or fundic, glands are located in the fundus and over the greater part of the body of the stomach. They are fairly straight, simply branched tubules, with a narrow lumen reaching down almost to the muscularis mucosae. They are lined by four types of cells: (1) The mucoid neck cells are the same as seen in the cardiac region but differ from the cells of the surface epithelium in that their mucigen granules have slightly different staining qualities and their nuclei tend to be flattened or concave at the base of the cells. (2) The chief cells are found primarily in the lower half of the glands. They have a spherical nucleus and contain light-refracting granules and a Golgi apparatus, the size and form of which vary with the state of secretory activity. They produce pepsinogen, the precursor of pepsin, a digestive enzyme. (3) Parietal cells are larger and usually clustered away from the gland's lumen, to which they connect by small gaps stemming from intracellular canaliculi. Their intraplasmatic granules are strongly eosinophilic; they refract light less than chief cells do. Parietal cells produce the hydrochloric acid that lowers the pH in the stomach. They also produce intrinsic factor, a glycoprotein that allows vitamin B ₁₂ to be absorbed further along in the ileum of the gastrointestinal tract. (4) Enteroendocrine cells are isolated glandular cells that release hormones into the lamina propria to modulate activity of the stomach and other digestive organs. Each enteroendocrine cell in the stomach may secrete gastrin (C cells), ghrelin, bombesin, enkephalins, vasoactive intestinal pep­tide, or somatostatin (D cells). Enterochromaffin-like cells secrete histamine, and enterochromaffin cells secrete serotonin. Different hormones are released by enteroendocrine cells elsewhere in the gastrointestinal tract.

• 3.

  The pyloric glands are located in the pyloric region but also spread into a transitional zone, in which both gastric and pyloric glands are found and which extends diagonally and distally from the lesser to the greater curvature. The tubes of the pyloric glands are shorter, more tortuous, and less densely packed, and their ends are more branched than the fundic glands. Pyloric gland pits are markedly deeper than those in other regions and are lined primarily by mucous cells (as in the cardiac region); occasional parietal or enteroendocrine cells may also be seen.

Musculature of Stomach

The musculature of the gastric wall consists solely of smooth muscle fibers, which, in contrast to the dual-layered arrangement elsewhere in the digestive tract, exist in three distinct layers. Only the middle circular layer covers the wall completely; the other two layers, the superficial longitudinal and deepest oblique layers, are present as incomplete coats. The longitudinal and circular layers are interconnected by continuous fibers, as are the circular layer and the deepest oblique muscular coats.

The longitudinal layer of the stomach is continuous with the longitudinal muscle layer of the esophagus, which divides at the cardia into two stripes. The stronger of these muscle bands follows the lesser curvature across the superior border of the stomach. The other set of fibers is somewhat broader but thinner as it migrates along the fundus, across the greater curvature toward the pylorus. Thus, the middle areas of the anterior and posterior surfaces of the stomach remain mostly free of longitudinal muscle fibers. The marginal muscle fibers of the upper longitudinal muscle stripe radiate obliquely toward the anterior and posterior surfaces of the fundus and corpus to unite with fibers of the circular layer. In the pyloric area, the two bands of longitudinal muscle fibers converge again to form a uniform layer, which, to a great extent is continuous with the external, longitudinal muscular layer of the duodenum. It is the increased thickness of the longitudinal muscle layer in the anterior and posterior parts of the pylorus that is responsible for the so-called pyloric ligaments (anterior and posterior pyloric ligaments, respectively).

The circular layer of smooth muscle is not only the most continuous but the strongest of the stomach's three layers. It also begins at the cardia as the continuation of the superficial fibers of the circular esophageal muscle. The circular layer becomes markedly more pronounced as it approaches the pylorus, forming the pyloric sphincter.

The innermost layer is formed by oblique fibers of the smooth muscle layer; it is most strongly developed in the region of the fundus and becomes progressively weaker as it approaches the pylorus. In the cardiac region, its fibers connect with the deeper circular layers of the esophageal muscle. No oblique fibers exist in the vicinity of the lesser curvature, but the fibers closest to it arise from a point to the left of the cardia and run parallel to the lesser curvature. There are longitudinal furrows in the lesser curvature caused by the absence of this innermost oblique layer. The oblique fiber bundles, following these first more or less longitudinal fibers, bend farther and farther to the left and, finally, become practically circular in the region of the fundus, where their continuity with the fibers of the circular layer is clearly evident. Because the oblique fibers of the anterior and posterior walls merge into one another in the region of the fundus, the oblique layer as a whole is made of U-shaped loops. The oblique fibers never reach the greater curvature in the region of the corpus but fan out and gradually disappear in the walls of the stomach. To the left of the esophagus the oblique fibers form sling fibers that project from the anterior wall of the stomach to the posterior wall, making a tight bend around the cardial notch. On the opposite side of the cardiac region, the circular layer has substantial clasp fibers that pinch and narrow the cardiac region. Acting together, the sling and clasp fibers help prevent gastric reflux and form a functional, but not anatomic, lower esophageal sphincter.

Duodenal Bulb and Mucosal Surface of Duodenum

The mucosa of the widened first portion of the duodenum, known also as the duodenal ampulla (cap, bulb), is relatively flat and smooth except for a few small longitudinal folds. Except for the smooth duodenal ampulla, the mucosal surface of the duodenum, which in living subjects is reddish in color, is lined with villi, giving the small intestines their velvety appearance. The mucosa of the distal duodenum is nearly identical to the small intestine with circular folds (of Kerckring) projecting into the lumen. These folds, which considerably increase the surface area of the intestine, begin in the region of the superior duodenal flexure, increasing in number and elevation in the more distal parts of the duodenum. They do not always form complete circles along the entire intestinal wall, because some are semicircular or crescent shaped, whereas others branch out to connect with adjacent folds. Very often they deviate from their circular pattern and pursue a more spiral course. The circular folds are large macroscopic structures and include mucosa and submucosa in their core. The more superficial layers of the duodenum, the muscularis externa and adventitia, are not included in the circular folds.

Approximately halfway down the posteromedial aspect of the descending part of the duodenum, a distance of approximately 8.5 to 10 cm from the pylorus, is located the major duodenal papilla, also known as the papilla (of Vater). This is where the common bile duct and the major pancreatic duct (of Wirsung) open into the duodenum. The common bile duct approaches the duodenum within the enfolding hepatoduodenal ligament of the lesser omentum and continues inferiorly in the groove between the descending portion of the duodenum and the pancreas. The terminal part of the common bile duct produces a slight but perceptible longitudinal impression in the posteromedial duodenal wall known as the longitudinal fold of the duodenum. This fold usually ends at the papilla but may occasionally continue for a short distance beyond the papilla in the form of the so-called frenulum. Small hoodlike folds at the top of the papilla protect the mouth of the combined bile duct and pancreatic duct. A small, wartlike, and generally less distinct second papilla, the minor duodenal papilla, is situated about 2.5 cm above and slightly medial to the major papilla. It serves as an opening for the minor pancreatic duct (of Santorini).

The duodenal ampulla, varying in form, size, position, and orientation, appears in an anteroposterior radiograph as a triangle, with its base at the pylorus and its tip pointing toward the superior flexure of the duodenum. The duodenum's longitudinal folds, as well as the circular folds in the lower parts of the duodenum, can be visualized radiographically if a barium meal of appropriate quantity and consistency is given. In such a relief picture of the mucosa, the region of the major duodenal papilla occasionally appears as a small, roundish filling defect. When the papilla is enlarged in the form of a small diverticulum, the contrast medium may sometimes enter the terminal portions of the bile and pancreatic ducts, with the result that on the x-ray, this area looks like the shape of a molar tooth with two roots.

Structures of Duodenum

The duodenum is part of the gastrointestinal tract and as such it is composed of a mucosa, submucosa, muscularis externa, and adventitia / serosa. The duodenum has a serosal covering wherever it is covered by peritoneum and an adventitia elsewhere. It is part of the small intestine, but it is embryonically, morphologically, and functionally distinct from the jejunum and ileum. Aside from the duodenal ampulla, the duodenum displays the macroscopically visible circular folds (of Kerckring), which project into the lumen and increase the available surface area. These circular folds contain cores of mucosa and submucosa. At the microscopic level, the surface area of the mucosa is extensively increased by the presence of villi, small fingerlike projections of the mucosa into the lumen. In between villi are the intestinal glands (crypts of Lieberkühn ), which project toward the submucosa. The villi of the duodenum are very dense, large, and, in some areas, leaflike. At the core of each villus is a clear area called a central lacteal that transports lymphatic fluid and fat-soluble substances from the small intestines.

The mucosa can be subdivided into a surface epithelium, lamina propria, and muscularis mucosae. The epithelium of the duodenal mucosa consists of a single layer of high columnar cells, enterocytes, with a marked cuticular border. Between enterocytes are a significant number of mucus-releasing goblet cells. In the depths of the crypts, there are cells filled with eosinophilic Paneth cells as well as some enteroendocrine cells. The lamina propria consists of loose connective tissue located deep to the epithelial lining. Many cells, such as plasma cells and lymphocytes, migrate in and out of the lamina propria in response to immune signals. Deep to the lamina propria is the muscularis mucosae, a double layer of smooth muscle cells, the fibers of which enter the lamina propria and continue to the tips of the villi, enabling the latter to pump fluid from their central lacteals.

The submucosa, lying between the mucosa and the muscularis externa, makes it possible for these two layers to shift in relation to each other. It is made up of dense irregular connective tissue, the fibers of which are arranged in a mesh. In this network are embedded the duodenal glands (of Brunner), characteristic of the duodenum. These are tortuous acinotubular glands with multiple branches at their ends; breaking through the muscularis mucosae, they open into the intestinal crypts. Cells of the duodenal glands release zymogen granules, mucus, bicarbonate, and alkaline glycoproteins. This fluid helps raise the pH of the gastric contents that enter the duodenum after digestion in the acidic environment of the stomach. This explains why the duodenal glands are larger and more numerous in the proximal duodenum and diminish in size and density as the duodenojejunal junction is approached. The number of glands is said to be much smaller in older than in younger individuals.

The two-layered muscularis externa of the duodenum is the same as in the jejunum and ileum. An inner circular layer is covered by a thinner outer longitudinal layer. As elsewhere in the small intestine, the submucosal (Meissner) plexus of nerves is found in the submucosa near its boundary with the muscularis externa. The myenteric (Auerbach) plexus can be located between the circular and longitudinal layers of the muscularis externa. The subserosa and the adventitia are composed of fine collagenous fibrils, which form a delicate lattice. The peritoneum of the duodenum consists, as do all serous membranes of the body, of a layer of flattened mesothelial cells.

Duodenal Fossae and Ligament of Treitz

The duodenojejunal flexure lies left of the midline at the level of the first and second lumbar vertebrae. The suspensory muscle of the duodenum (ligament of Treitz, suspensory ligament of the duodenum) is a flat, fibromuscular ligament arising from the right crus of the diaphragm near the aortic hiatus. It passes, with individual variations, inferior to the left of the celiac trunk and superior mesenteric artery, posterior to the pancreas, to reach the duodenojejunal flexure. The smooth muscle cells of the ligament are largely continuous with the musculature of the celiac and superior mesenteric arteries; at the intestinal attachment they are connected with the longitudinal muscular layer of the gut, some extending as far as the mesentery of the small intestine. The attachment of the ligament to the duodenum may be quite narrow or it may extend over a considerable portion of the third part of the duodenum. If the suspensory ligament of the duodenum is short, the duodenojejunal flexure is high; if it is long, the flexure may lie so low that the terminal duodenal segment does not take the usual ascending course.

Several peritoneal recesses exist to the left of the ascending portion of the duodenum. These result from secondary fixation of the mesentery of the descending colon to the posterior abdominal wall; they vary greatly in depth and size between individuals. The most important are those arising from the superior duodenal fold and the inferior duodenal fold. These originate from the point of attachment of the descending mesocolon and run archlike from left to right, the superior to reach the duodenojejunal flexure and the inferior to the ascending portion of the duodenum. The superior fold is inferiorly concave and forms the aperture of the superior duodenal fossa, whereas the inferior fold is superiorly concave and forms the aperture of the inferior duodenal fossa. These fossae may be clinically significant as sites of intraperitoneal herniation. They are bounded anteriorly by the superior and inferior duodenal folds, respectively, and on the left by the ascending portion of the duodenum or the duodenojejunal flexure. Both fossae are bounded on the right by the parietal peritoneum and extend behind the posterior duodenal wall, which is covered by visceral peritoneum. Near the insertion of the superior duodenal fold is the inferior mesenteric vein, ascending to reach the splenic vein. At the corresponding position in the inferior fold is the ascending branch of the left colic artery. The left ureter can be found immediately posterior to the inferior duodenal fossa.

Several rarer types of fossae may also be found in this region, such as the paraduodenal recess bounded by the inferior mesenteric vein and the ascending branch of the left colic artery. In this case, a somewhat longitudinal peritoneal fold, the paraduodenal fold, slightly concave to the right, occasionally gives rise to a so-called left duodenal hernia (of Moynihan). This fossa can sometimes be separated into two partial folds; the more ventral and superficial fold rises above the ascending branch of the left colic artery, whereas the deeper or more posterior fold is bordered by the inferior mesenteric vein.

On very rare occasions a duodenojejunal fossa (not illustrated) extends cranially from the duodenojejunal flexure under the root of the transverse mesocolon, or a retroduodenal recess runs superiorly between the aorta and the ascending portion of the duodenum. The mesentericoparietal fossa, invariably present in the fetus, occasionally forms the enclosing sac for a right paraduodenal hernia. It is bounded anteriorly by the superior mesenteric vessels as they enter the mesentery of the small intestine, and posteriorly by the parietal peritoneum over the right side of the aorta.

Blood Supply of Stomach and Duodenum

The conventional textbook description of the blood supply to the gastrointestinal organs and the spleen has established the misleading concept that the vascular patterns of these organs are uniform. In fact, they are unpredictable and vary in every instance. In the following account, we will first present the “typical” version of the vascular tree before examining the blood supply to each organ and then some of the common vascular variations that may be encountered in surgical resections.

Typically, the entire blood supply of the foregut organs (liver, gallbladder, stomach, duodenum, pancreas, and spleen) is derived from the celiac arterial trunk, a supplementary small portion being supplied by the superior mesenteric artery via its inferior pancreaticoduodenal branch. The caliber of the celiac arterial trunk varies from 8 to 40 mm in width. Most typically, it gives off three branches, the left gastric, common hepatic, and splenic arteries, which frequently have the appearance of a tripod (25%).

After branching from the celiac trunk, the left gastric artery travels superiorly and to the left. It reflects onto the cardiac region of the stomach and travels along the lesser curvature of the stomach, travelling from left to right. It also gives off an esophageal branch that ascends from the cardiac region of the stomach toward the distal esophagus.

The common hepatic artery leaves the celiac trunk and progresses to the right. In the vicinity of the portal vein it divides, sending the proper hepatic artery superiorly. The right gastric artery is also typically seen leaving this vessel and traveling to the lesser curvature of the stomach, where it will anastomose with the left gastric artery. As it travels superiorly, the proper hepatic artery divides into right and left hepatic arteries, which travel into the liver. Before entering the liver, the right hepatic artery most typically gives off the cystic artery to the gallbladder. The other branch of the common hepatic artery is the gastroduodenal artery. The small supraduodenal artery, which travels to the superior duodenal flexure, most frequently branches from the gastroduodenal artery. This vessel gives off the posterior superior pancreaticoduodenal artery, anterior superior pancreaticoduodenal artery, and, finally, right gastroomental (gastroepiploic) artery, which travels along the right side of the greater curvature of the stomach.

The splenic artery, the celiac trunk's third branch, is a large, coiled artery that travels to the left of the abdomen superior to, or within, the pancreas. It generally gives off a large dorsal pancreatic artery to supply the head and body of the pancreas, along with the greater pancreatic artery a bit further down its length. The artery to the tail of the pancreas can be seen as a small branch of the distal splenic artery connecting with the greater and dorsal pancreatic arteries by means of the inferior pancreatic artery within the pancreas. Near its terminus, the splenic artery gives off several branches that pierce the hilus of the spleen to supply the organ. As this is happening, the short gastric arteries leave the superiormost aspect of the splenic artery to supply the fundus of the stomach. Inferiorly, the left gastroomental (gastroepiploic) artery leaves the splenic artery to supply the left side of the stomach's greater curvature and anastomose with the right gastroomental artery.

The blood supply of the stomach and abdominal esophagus is accomplished by six primary and five secondary arteries. The primary arteries are the (1) right gastric and (2) left gastric, coursing along the lesser curvature; (3) right gastroomental and (4) left gastroomental, coursing along the greater curvature (each of these four vessels giving off branches to the anterior and posterior surfaces of the stomach, where they anastomose); (5) splenic, which gives off in its distal third a variable number (2 to 10) of short gastric branches, and from its superior or inferior terminal division the left gastroomental; and (6) gastroduodenal, by direct small branches (1 to 3) and, frequently, by a large pyloric branch.

The secondary arteries are the (7) anterior superior pancreaticoduodenal (end branch of the gastroduodenal) by short twigs and, frequently, by a large pyloric branch; (8) supraduodenal artery of varied origin (gastroduodenal, posterior superior pancreaticoduodenal, hepatic, right gastric) which, in addition to supplying the first inch of the duodenum, often sends one or more branches to the pylorus; (9) posterior superior pancreaticoduodenal, predominantly the first collateral of the gastroduodenal, which, in its tortuous descent along the left side of the common bile duct to reach the back of the pancreas and duodenum, frequently gives off one or more pyloric branches, the latter, in some instances, uniting with the supraduodenal and right gastric; (10) dorsal pancreatic artery of varied origin (splenic, hepatic, celiac, superior mesenteric), the right branch of which anastomoses with the superior pancreaticoduodenal, gastroduodenal, and right gastroomental and, in so doing, sends small branches to the pylorus; (11) left inferior phrenic, which, after passing inferior to the esophagus in its course to the diaphragm, in most instances gives off a large recurrent branch to the cardioesophageal end of the stomach posteriorly, where its terminals anastomose with other cardioesophageal branches derived from the left gastric, splenic terminals, aberrant left hepatic from the left gastric, and descending thoracic esophageal branches.

This conventional form of the celiac with its three branches occurs in only 55% of the population, for the celiac often lacks one or more of its typical branches. Whether in a complete or incomplete form, the celiac trunk forms a hepatosplenogastric trunk in about 90% of the population. The celiac may omit the left gastric, so that a hepatosplenic trunk is present (3.5%); omit one or more of the hepatic arteries, so that a splenogastric trunk is present (5.5%); or omit the splenic, so that a hepatogastric trunk is present (1.5%). Additional branches may originate from the celiac trunk: the dorsal pancreatic (22%), inferior phrenic (74%), and, occasionally, even the middle colic or an accessory middle colic artery. In many instances the common hepatic artery is absent, being replaced from the superior mesenteric, aorta, or left gastric.

Typically, the left gastric artery arises from the celiac (90%), most commonly as its first branch. In remaining cases it arises from the aorta, the splenic or hepatic artery, or a replaced hepatic trunk. Varying in width from 2 to 8 mm it is considerably larger than the right gastric, with which it anastomoses along the lesser curvature. Before its division into anterior and posterior gastric branches, the left gastric supplies the cardioesophageal end of the stomach, either by a single ramus that subdivides or by two to four rami given off in seriation by the main trunk. Accessory left gastric arteries occur frequently. They are (1) a large left gastric from the left hepatic; (2) a large ascending posterior gastroesophageal ramus from the splenic trunk or from the superior splenic polar; or (3) a slender, threadlike cardioesophageal branch from the celiac artery, aorta, first part of the splenic artery, or inferior phrenic artery.

The terminal branches of the left gastric anastomose with (1) branches of the right gastric; (2) short gastric arteries from the splenic terminals or splenic superior polar or left gastroomental; (3) cardioesophageal branches from the left inferior phrenic (via its recurrent branch), an aberrant left hepatic artery from the left gastric (A), or an accessory left gastric from the left hepatic (B) and from descending rami of thoracic esophageal branches. The degree of anastomosis about the cardioesophageal end of the stomach is variable; it may be very extensive or very sparse.

In about one fourth of the population, the left gastric artery gives off a large left hepatic artery (2 to 5 mm wide, 5 cm long) to the left lobe of the liver. Such a left hepatic may be either replaced or accessory. In the replaced type (12%), no celiac left hepatic is present, the entire blood supply to the lateral segment of the left lobe being derived from the left gastric artery. The accessory left hepatic is an additive vessel that supplies a region of the left lobe of the liver (either the superior or inferior area of the lateral segment) not supplied by the incomplete celiac left hepatic. From the functional point of view, none of the hepatic arteries is ever “accessory” because every hepatic artery supplies a definite region of the liver. In view of prevalent anatomic variations, every gastric resection should be preceded by an exploratory examination to determine what type of left gastric artery is present, for severance of a left hepatic derived from the left gastric results in ischemia and fatal necrosis (7th to 16th day) of the left lobe of the liver, as repeatedly evidenced in postmortem examinations. Quite frequently, the left gastric gives off an accessory left inferior phrenic and, in some instances, the left inferior phrenic itself.

The celiac trunk may be incomplete when the right or left hepatic arteries arise from some other source. The common hepatic artery may arise in its entirety from the superior mesenteric artery (C); the superior mesenteric artery may provide the right hepatic artery in its entirety, also supplying blood to the gallbladder (D); and the superior mesenteric artery may supply an accessory right hepatic artery, which may or may not supply the gallbladder (E). The common hepatic artery may also branch very proximally, giving off an early right and left hepatic arteries while the right hepatic and gastroduodenal arteries branch from each other further to the right (F). The left lobe of the liver may also receive an accessory left hepatic artery from the right hepatic artery (G), or the right hepatic artery may cross anterior to the hepatic duct before entering the substance of the liver (H).

Invariably, the right gastric artery is much smaller (2 mm) than the left gastric (4 to 5 mm), with which it anastomoses. On occasion (8%) it gives off the supraduodenal or a spray of twigs to the first part of the duodenum. Predominantly, the gastroduodenal artery arises from the common hepatic (75%), but, in some instances, especially with a split celiac trunk, it may arise from the left hepatic (10%), right hepatic (7%), replaced hepatic trunk from the superior mesenteric or aorta (3.5%), or even directly from the celiac or superior mesenteric artery (2.5%). These atypical origins are correlated with the mode of branching of the celiac artery, for the common hepatic may divide only into the gastroduodenal and right hepatic (leaving the left hepatic to be replaced from the left gastric) or into the gastroduodenal and left hepatic with replacement of the right hepatic from the superior mesenteric. Typical branches of the gastroduodenal are (1) the posterior superior pancreaticoduodenal (90%); (2) the anterior superior pancreaticoduodenal; and (3) the right gastroomental. Inconstant branches are (1) the right gastric (8%); (2) the supraduodenal (25%); (3) the transverse pancreatic (10%); (4) a cystic artery, either the superficial branch or the entire cystic (3%); (5) an accessory right hepatic; and (6) the middle colic or an accessory middle colic (rarely).

The relatively large posterior superior pancreaticoduodenal artery (1 to 3 mm in width) forms an arcade on the back of the head of the pancreas, with branches to the duodenum. In many instances (10%), the artery arises from a source other than the gastroduodenal and, when it arises from the latter, it does so as its uppermost collateral branch and not as an end branch. The right gastroomental artery is considerably larger than the left gastroomental and, in its course, extends far beyond the midline of the greater curvature of the stomach, where it anastomoses with the left gastroomental artery. Of great surgical import is the fact that, in many instances (10%), this anastomosis is not grossly visible, it being absent or reduced to small arterial twigs that dwindle to nothing before the two meet. The infragastric omental arc, formed by the right and left gastroomental arteries, gives off a large pyloric branch and then a variable number of ascending gastric and descending omental or anterior omental branches. The omental branches descend between the two anterior layers of the great omentum. The short ones anastomose with neighboring vessels, and the long ones proceed to the distal free edge of the great omentum, where they turn upward to become the posterior omental arteries. Many of these join the large omental arc situated in the posterior layer of the great omentum below the transverse colon. The arc is usually formed by the right omental (first branch of the right gastroomental) and left omental, a branch of the left gastroomental. Slender arteries ascend from the arc and anastomose with similar branches (posterior omentals) given off from the middle colic or left colic and from the transverse pancreatic coursing along the inferior surface of the pancreas. The ultimate and penultimate branches of the posterior omental arteries anastomose with the vasa recta of the middle colic but, apparently, are not of sufficient caliber to take over the blood supply if the middle colic has been rendered functionless. Aberrations of the right gastroomental are (1) an origin from the superior mesenteric (1.5%) or with the middle colic and superior pancreaticoduodenal (1%); (2) anastomoses with the middle colic, via a large vessel (1%); and (3) an origin from a gastroduodenal derived from the superior mesenteric.

Usually, the left gastroomental arises from the distal end of the splenic artery (75%) or from one of its splenic branches (25%) near its terminus. It may be replaced by two to three vessels, the main artery coming from the splenic trunk and the others from an inferior splenic polar artery. Branches of the left gastroomental are (1) short fundic branches (two to four); (2) a variable number of ascending short gastric arteries; (3) several short and long descending omental branches, some of which communicate with similar branches from the right gastroomental artery; (4) pancreatic rami to the tail of the pancreas, one of which, when large, is termed the artery to the tail of the pancreas; (5) an inferior splenic polar artery; and (6) the left omental artery, which descends in the great omentum to form the left limb of the omental arc, the right limb being formed by the right omental artery from the right gastroomental or transverse pancreatic artery.

The blood supply of the duodenum and head of the pancreas is one of the most variant in the body and, surgically considered, one of the most difficult to manipulate. The first inch of the duodenum is a critical transition zone. Paucity or insufficiency of its blood supply has repeatedly been correlated causatively with the tendency of ulcers to perforate the superior part of the duodenum just beyond the pylorus. Typically, the superior, anterior, and posterior surfaces of the first inch of the duodenum are supplied by the supraduodenal artery, which may be derived from either of two nearby arteries, the posterior superior pancreaticoduodenal artery or gastroduodenal and, in the remaining cases, from the right gastric, hepatic, or right hepatic. The supraduodenal artery frequently communicates with branches of the right gastric, gastroduodenal, and anterior and posterior superior pancreaticoduodenal arteries. The remaining portions of the duodenum are supplied by branches from two pancreaticoduodenal arcades, one anterior and the other posterior to the head of the pancreas. It is by virtue of these two arcades that the duodenum is the only section of the gut that has a double blood supply, one to its anterior surface and one to its posterior surface.

The anterior pancreaticoduodenal arcade is formed by the anterior superior pancreaticoduodenal artery, the smaller of the two end branches of the gastroduodenal artery. After making a loop of a half circle or less on the anterior surface of the pancreas, medial to the groove between the pancreas and duodenum, it sinks into the pancreas, turns to the left, and ascends, and upon reaching the posterior surface of the head of the pancreas, joins the anterior inferior pancreaticoduodenal artery, a branch from the superior mesenteric artery. The arcade gives off 8 to 10 relatively large branches to the anterior surface of all three portions of the duodenum and, in many instances, 1 to 3 branches to the first part of the jejunum; they reach the jejunum by passing deep to the superior mesenteric artery. The arc also supplies numerous pancreatic branches, some of which are arranged in arcade fashion and anastomose with branches given off by the dorsal pancreatic artery, derived from the first part of the splenic or hepatic artery.

The posterior pancreaticoduodenal arcade is made by the posterior superior pancreaticoduodenal artery, which is the first branch of the gastroduodenal given off by the latter above the duodenum above the upper border of the head of the pancreas, where it may be hidden by connective tissue. In about 10% of cases, it has a decidedly different origin, being derived from the hepatic (4%), right hepatic (2%), aberrant right hepatic from the superior mesenteric (3%), or dorsal pancreatic (1%). After its typical origin from the gastroduodenal, the artery (1 to 3 mm in width) descends for 1 cm or more on the left side of the common bile duct and then, after crossing the latter anteriorly, descends for several centimeters along its right side before swinging to the left and downward to form the posterior arcade. The major portion of the U- or V-shaped posterior arcade lies posterior to the head of the pancreas, at a level superior to that of the anterior arcade. It comes into full view when the duodenum is mobilized and turned forward to expose its posterior surface. It is covered by a fold of connective tissue sufficiently thin that its branches can be seen. It is accompanied by a venous arcade that lies superficial to the arterial arcade and that empties directly into the portal vein. The arcade crosses the intrapancreatic part of the common bile duct (to which it supplies blood) posteriorly. Ultimately, the posterior superior pancreaticoduodenal artery unites with the inferior pancreaticoduodenal artery derived from the superior mesenteric at a higher level than that of the anterior arcade (40%), or it anastomoses with a posterior branch of a common inferior pancreaticoduodenal, the latter receiving both the anterior and posterior arcades (60%). The main branches, arising from the posterior pancreaticoduodenal arcade, are (1) several descending branches (two to three) to the first part of the duodenum, one of which may be the supraduodenal; (2) duodenal branches to the posterior surfaces of the descending, transverse, and ascending duodenum; (3) small pancreatic branches that are far less numerous and are shorter than those of the anterior arcade; (4) ascending branches (one or more) to the supraduodenal portion of the common bile duct; and (5) a cystic artery (entire or its superficial branch), which, in about 4% of cases, stems from the first part of the posterior superior pancreaticoduodenal or at its site of origin from the gastroduodenal.

In the majority of instances, the anterior and posterior pancreaticoduodenal arcades have a variant anatomic structure, in the sense that the arcades may be double, triple, or even quadruple. When multiple arcades are present, it is the outer arcade near the duodenum that usually supplies the latter with its branches, whereas the inner arcades supply only pancreatic branches and ultimately become united with other branches of the celiac trunk.

With every duodenal resection, three important vascular arrangements must be borne in mind:

• 1.

  The entire blood supply of the duodenum and head of the pancreas may be completely dissociated from the superior mesenteric. This occurs when an aberrant right hepatic from the superior mesenteric, coursing behind the head of the pancreas, gives off one or two inferior pancreaticoduodenal arteries to receive the anterior or posterior pancreaticoduodenal arcade (or both).

• 2.

  The anterior or posterior pancreaticoduodenal arcade (or both) often ends via one or more inferior pancreaticoduodenal arteries derived from the left side of the superior mesenteric or from its first, second, or third jejunal branch, a fact to be explored in every gastrojejunostomy, lest the blood supply of the duodenum be impaired and rendered insufficient for viability of that section of the gut.

• 3.

  In resections of the duodenum, extreme care should be taken to maintain an adequate blood supply to the anterior and posterior surfaces of the stumps. The duodenal branches from the pancreaticoduodenal arcades are end arteries, and if these are ligated, the suture lines pass through ischemic parts that may become necrotic and break. This can result in “blowout” of the duodenal stump; such an event has repeatedly been fatal, excessive devascularization of the stump being the direct cause of the fatal issue.

Collateral Circulation of Upper Abdominal Organs

No other region in the body presents more diversified collateral pathways of blood supply than the foregut organs, the stomach, duodenum, pancreas, spleen, liver, and gallbladder. Because of the multiplicity of its blood vessels and the loose arrangement of its connective tissue, the greater omentum is exceptionally well adapted as a terrain of compensatory circulation, especially for the liver and spleen, when either the hepatic or splenic artery is occluded. The stomach may receive its blood supply from 6 primary and 6 secondary sources; the pancreas from the hepatic, splenic, and superior mesenteric; the liver from 3 primary sources (celiac, superior mesenteric, and left gastric) and, secondarily from communications with at least 23 other arterial pathways. In view of the relational anatomy of the splenic artery, it is quite obvious that most of the collateral pathways to the upper abdominal organs can be initiated via this vessel and its branches and completed through communications established by the gastroduodenal and superior mesenteric arteries.

The most important collateral pathways in the upper abdominal organs are the following:

• 1.

  Arcus arteriosus ventriculi inferior. This infragastric omental pathway is made by the right and left gastroomental arteries as they anastomose along the greater curvature of the stomach. The arc gives off ascending gastric and descending omental arteries.

• 2.

  Arcus arteriosus ventriculi superior. This supragastric pathway with branches to both surfaces of the stomach is made by the right and left gastric arteries anastomosing along the lesser curvature. Branches of the right gastric may unite with branches from the gastroduodenal, supraduodenal, posterior superior pancreaticoduodenal, or right gastroomental arteries. Branches of the left gastric artery may anastomose with the short gastric arteries from the splenic terminals, left gastroomental, branches from the recurrent cardioesophageal branch of the left inferior phrenic, or branches of an accessory left hepatic, derived from the left gastric.

• 3.

  Arcus epiploicus magnus. This omental pathway is situated in the posterior layer of the great omentum inferior to the transverse colon. Its right limb is made by the right omental artery from the right gastroomental artery, and its left limb by the left omental artery from the left gastroomental artery. Arteries involved in this collateral route include hepatic, gastroduodenal, right gastroomental, right omental, left omental, left gastroomental, and inferior terminal branches of the splenic.

• 4.

  Circulus transpancreaticus longus. This important collateral pathway is effected by connections between the dorsal pancreatic artery and splenic artery. The dorsal pancreatic may communicate with the first part of the splenic, hepatic, celiac, or superior mesenteric, depending on which artery gives rise to the dorsal pancreatic. At the tail end of the pancreas, it communicates with the splenic terminals via the great pancreatic artery, inferior pancreatic artery, and artery to the tail of the pancreas, and at the head of the pancreas with the gastroduodenal, superior pancreaticoduodenal, or right gastroomental arteries.

• 5.

  Circulus hepatogastricus. This is a derivative of the primitive, embryonic arched anastomosis between the left gastric and the left hepatic arteries. In the adult the arc may persist in its entirety; the upper half may give rise to an accessory left gastric, and the lower half to an “accessory” left hepatic from the left gastric artery.

• 6.

  Circulus hepatolienalis. Here an aberrant right hepatic or the entire common hepatic artery, arising from the superior mesenteric artery, may communicate with the splenic artery via a branch of the dorsal pancreatic or gastroduodenal, inferior pancreatic, or artery to the tail of the pancreas.

• 7.

  Circulus celiacomesentericus. Through the inferior pancreaticoduodenal, blood may be routed through the anterior and posterior pancreaticoduodenal arcades to enter the gastroduodenal artery, from which, via the right and left gastroomental arteries, it reaches the splenic, or, via the common hepatic, it reaches the celiac.

• 8.

  Circulus gastrolienophrenicus. This connection may exist (1) via a communication between the short gastric arteries from the splenic terminals and the recurrent cardioesophageal branches of the left inferior phrenic or (2) via a communication between the latter and the cardioesophageal branches given off by the left gastric, its aberrant left hepatic branch, or an accessory left gastric from the left hepatic.

Venous Drainage of Stomach and Duodenum

Venous blood from the stomach and duodenum, along with that from the pancreas and spleen and that of the remaining portion of the intestinal tract (except the anal canal), is conveyed to the liver by the portal vein. The portal vein resembles a tree, in that its roots (capillaries) ramify in the intestinal tract, whereas its branches (sinusoids, capillaries) arborize in the liver. From its point of formation to its division within the liver into right and left branches, the portal vein measures from 8 to 10 cm in length and from 8 to 14 mm in width. Typically, the portal vein is formed by the union of the superior mesenteric vein with the splenic vein, posterior to the neck of the pancreas. Its tributaries show many variations that are extremely important in operative procedures. The inferior mesenteric vein opens most commonly into the splenic vein (38%) but, in many instances, drains into the junction point of the superior mesenteric and splenic veins (32%) or into the superior mesenteric vein (29%). Occasionally, it bifurcates, opening into both veins.

The left gastric vein accompanies the left gastric artery and runs from right to left along the lesser curvature of the stomach, at the cardioesophageal end of which it receives esophageal branches. It may empty into the junction point of the superior mesenteric and splenic veins (58%), portal vein (24%), or splenic vein (16%). The right gastric vein accompanies the right gastric artery from left to right, receives tributaries from both surfaces of the superior part of the stomach, and, usually, opens directly into the lower part of the portal vein (75%). Frequently, it enters the superior mesenteric (22%) and occasionally the right gastroomental or inferior pancreaticoduodenal veins. In some instances, it has a common termination with the left gastric vein or is not identifiable. The left gastroomental vein receives branches from the lower anterior and posterior surfaces of the stomach, greater omentum, and pancreas. It usually opens into the distal part of the splenic vein and, less frequently, into an inferior branch of the splenic vein. Short gastric veins arising from the fundus and cardiac regions of the stomach join the splenic terminals or the splenic branches of the left gastroomental veins, or they enter the splenic vein directly. The right gastroomental vein courses along the greater curvature of the stomach, where it receives branches from its anterior and posterior surfaces and from the greater omentum. Usually, it terminates in the superior mesenteric vein (83%) just before that vessel joins the portal vein. Occasionally, it enters the first part of the splenic or portal vein (2%).

The pancreaticoduodenal veins run alongside the anterior and posterior arterial pancreaticoduodenal arcades. The anterior and posterior inferior pancreaticoduodenal veins fuse into a single vein that usually joins the superior mesenteric vein below the entry of the right gastroomental vein. Frequently, the posterior arcade empties directly into the portal vein. The posterior superior pancreaticoduodenal vein typically drains to the portal vein. The cystic vein, formed by superficial and deep tributaries from the gallbladder, may enter the portal vein directly or its right branch, or drive to the liver directly. The majority of pancreatic venous branches, arising from the body and tail of the pancreas, join the splenic vein along its course, whereas others terminate in the upper part of the superior or inferior mesenteric vein or left gastroomental vein. The left inferior phrenic vein receives a tributary from the cardioesophageal region of the stomach and, usually, enters the suprarenal vein but, in some instances, joins the renal vein.

Because all larger vessels of the portal system are devoid of valves, collateral venous circulation in portal obstruction is readily effected via communications with the caval system.

Lymphatic Drainage of Stomach

The lymph from the gastric wall collects in the lymphatic vessels, which form a dense subperitoneal plexus on the anterior and posterior surfaces of the stomach. The lymph flows in the direction of the greater and lesser curvatures, where the first regional lymph nodes are situated. On the upper half of the lesser curvature (i.e., the portion near the cardia) are the left gastric lymph nodes, which are connected with the lymph nodes around the cardia. Progressing around the lesser curvature may be a few right gastric lymph nodes. Superior, inferior, and posterior to the pylorus are located the suprapyloric, subpyloric, and retropyloric lymph nodes, respectively. On the greater curvature, following the trunk of the right gastroomental artery and distributed in a chainlike fashion within the gastrocolic ligament, are the right gastroomental lymph nodes. From these nodes the lymph flows to the right toward the subpyloric nodes, which are situated anterior to the head of the pancreas, inferior to the pylorus and the first part of the duodenum. There are a few smaller left gastroomental lymph nodes in the part of the greater curvature nearest to the spleen.

For purposes of simplification, a distinction can be made between four different drainage areas into which the gastric lymph flows, although, in point of fact, these areas cannot be so rigidly separated. The lymph from the upper left anterior and posterior walls of the stomach (excluding the far left fundus and body) drains through the left gastric nodes and nodes around the cardia. From there, lymphatic fluid follows the left gastric artery and the coronary vein toward the vascular bed of the celiac artery. Included in this system are additional left gastric lymph nodes near the left crus of the diaphragm. The pyloric segment of the stomach, in the region of the lesser curvature, discharges its lymphatic fluid into the right superior pancreatic lymph nodes, partly directly and partly indirectly, via the small suprapyloric nodes. The lymphatic fluid from the left region of the fundus (i.e., adjacent to the spleen) flows along lymphatic vessels within the gastrosplenic ligament. Some of these lymphatics lead directly to the left superior pancreatic lymph nodes, and others move indirectly via the small left gastroomental lymph nodes and via the splenic nodes lying within the hilus of the spleen. Lymph from the distal portion of the inferior stomach along the right greater curvature and inferior pyloric region collects in the right gastroomental lymph nodes. From here, the lymph flows to the subpyloric nodes, which lie anterior to the head of the pancreas, partly posterior and partly inferior to the pylorus. Leading to these nodes are also a few lymphatics from that part of the greater curvature that is immediately adjacent to the pylorus. From the subpyloric lymph nodes, which are also connected with the superior mesenteric nodes by way of prepancreatic lymphatics, the lymph flows to the right superior pancreatic nodes through lymphatics situated behind the pylorus and duodenal bulb.

From the left gastric nodes, right superior pancreatic nodes, and left superior pancreatic nodes, lymphatic fluid leads to the celiac lymph nodes, situated superior to the pancreas at the base of the celiac arterial trunk and its branches. From the celiac lymph nodes, lymph flows through the gastrointestinal lymphatic trunk to reach the thoracic duct, in the initial segment of which is generally a more or less pronounced expansion, called the cisterna chyli.

The thoracic duct projects superiorly through the posterior and superior mediastinum to open into the angle formed by the left subclavian and left jugular veins, often receiving the left subclavian lymphatic trunk prior to insertion. In cases of gastric tumor, palpable metastases may sometimes develop in the left supraclavicular (Virchow) lymph nodes in this area.

Innervation of Stomach and Duodenum

The stomach and duodenum are innervated by the visceral efferent sympathetic and parasympathetic nerves, along which run visceral afferent fibers.

The sympathetic supply to the stomach emerges in the anterior spinal nerve roots as presynaptic axons projecting from cells within the intermediolateral cell column of the spinal cord, particularly from the 5th to the 9th or 10th thoracic segments. They are carried from the spinal nerves in white rami communicans that pass to the adjacent sympathetic ganglia located along the length of the sympathetic trunk. The sympathetic axons that will supply the stomach pass through the ganglia without synapsing and travel along the thoracic vertebrae as the thoracic splanchnic nerves, which pass through the diaphragm posteriorly to reach celiac ganglia. Generally, these axons will form synapses with postsynaptic nerve cells in the celiac and superior mesenteric ganglia. The postsynaptic axons of these cells are conveyed to the stomach and duodenum in the celiac plexus and the superior mesenteric plexus. We will concentrate on the former, as it is the primary nerve supply to the stomach and proximal duodenum. The axons of the celiac plexus adhere to the walls of the arteries that arise from the celiac arterial trunk; they may be referred to as the hepatic plexus, splenic plexus, or left gastric plexus, depending upon which artery they follow. The sympathetic axons of each plexus run alongside presynaptic parasympathetic axons and visceral afferent axons.

Subsidiary plexuses from the hepatic arterial plexus are continued along the right gastric and gastro­duodenal arteries and from the latter along the right gastroomental and anterior and posterior superior pancreaticoduodenal arteries. The splenic arterial plexus sends offshoots along the short gastric and left gastroomental arteries.

The left gastric plexus consists of one to four branches that accompany the artery and supply twigs to the cardiac region of the stomach and communicate with offshoots from the left phrenic plexus. Other filaments follow the artery along the lesser curvature of the stomach between the layers of the lesser omentum to supply adjacent parts of the stomach. They communicate profusely with the right gastric plexus and with gastric branches of the vagus. The nearby phrenic plexuses assist in supplying the cardiac end of the stomach. A filament from the right plexus sometimes turns to the left and passes to the region of the cardiac orifice, whereas the left phrenic plexus supplies a constant twig to the cardiac orifice. A delicate branch from the left phrenic nerve (not illustrated) supplies the cardia.

The splenic plexus gives off subsidiary nerve plexuses around its pancreatic, short gastric, and left gastroomental branches, and these supply the structures indicated by their names. A filament may curve upward to supply the fundus of the stomach.

The hepatic plexus gives off subsidiary plexuses along all its branches. These, following the right gastric artery, supply the pyloric region, and the gastroduodenal plexus accompanies the artery between the first part of the duodenum and the head of the pancreas, supplying fibers to both structures and to the adjacent parts of the common bile duct. When the artery divides into its anterior superior pancreaticoduodenal and right gastroomental branches, the nerves also subdivide and are distributed to the second part of the duodenum, the terminations of the common bile and pancreatic ducts, the head of the pancreas, and the parts of the stomach. The part of the hepatic plexus lying in the free margin of the lesser omentum gives off one or more (hepatogastric) branches that pass to the left between the layers of the lesser omentum to the cardiac end and lesser curvature of the stomach; they unite with and reinforce the left gastric plexus.

The superior mesenteric ganglion is primarily involved in supplying postsynaptic axons to the midgut organs. It does supply the distal duodenum by means of axons that follow the anterior and posterior inferior pancreaticoduodenal arteries to reach the duodenum and pancreatic head.

The parasympathetic supply of the stomach and duodenum arises in the dorsal vagal motor nucleus in the floor of the fourth ventricle. The dorsal vagal motor nuclei contribute presynaptic parasympathetic axons to the left and right vagus nerves, which leave the jugular foramen to innervate thoracic and abdominopelvic organs. We will ignore the activity of the vagus nerves in the thorax other than to mention that the left and right vagus nerves closely associate with the esophagus and interweave to produce the anterior and posterior vagal trunks, which pierce the diaphragm alongside the esophagus to enter the abdominal cavity. The anterior vagal trunk travels on the anterior aspect of the stomach and across the hepatogastric ligament to innervate some of the liver and gallbladder. Frequently, one branch, the greater anterior gastric nerve, is larger than the others. The various gastric branches can be traced for some distance beneath the serous coat before they sink into the muscle coats, and although they communicate with neighboring gastric nerves, a true anterior gastric plexus in the accepted sense of the term does not usually exist. The pyloric branches (not illustrated) arise from the anterior vagal trunk or from the greater anterior gastric nerve and run to the right between the layers of the lesser omentum before turning inferiorly through or close to the hepatic plexus to reach the pyloric antrum, pylorus, and proximal part of the duodenum. Small celiac branches run alongside the left gastric artery to the celiac plexus, often uniting with corresponding branches of the posterior vagal trunk. The posterior vagal trunk moves further posteriorly from the esophagus to run into the nearby celiac ganglion. In contrast to the presynaptic sympathetic axons entering the celiac ganglion, the presynaptic parasympathetic axons do not synapse there but instead pass through the ganglion to enter the celiac plexus. From there these axons, alongside the postsynaptic sympathetic axons from the celiac ganglion and viscerosensory axons, travel along branches of the celiac trunk, the hepatic, splenic, and left gastric plexuses, to reach the foregut organs. When these presynaptic parasympathetic axons reach the target organs, they synapse with postsynaptic parasympathetic nerve cell bodies located within the organs' walls.

Viscerosensory activity related to the stomach and duodenum is divided into two categories, visceral pain and normal visceral reflexive stimuli. The stomach is insensitive to ordinary tactile, painful, and thermal stimuli, although it responds strongly to tension, ischemia, and chemical irritations as visceral pain. Visceral pain fibers travel in a retrograde fashion along the sympathetic innervation of the stomach; therefore, visceral pain axons traveling along the left gastric, right gastric, left gastroomental, or right gastroomental plexuses would eventually reach the celiac ganglion. Without synapsing, such an axon would continue along the greater thoracic splanchnic nerves, through the sympathetic chain ganglia, and then through the white rami communicans, anterior ramus, and spinal nerve. At this time, being afferent, the axon would travel along the posterior root to reach the spinal cord. Prior to reaching the spinal cord, the axon encounters (but does not synapse within) its nerve cell body. The nerve cell bodies of these viscerosensory axons are located in the posterior (dorsal) root ganglia. Because these nerve cells are pseudounipolar, their axon extends from the target tissue to reach the cell body but also proximally to reach the posterior gray horn of the spinal cord.

Nonpainful, reflexive stimuli from the stomach travel in a retrograde manner along its parasympathetic innervation. Because all foregut organs receive their presynaptic parasympathetic innervation via the vagus nerves, reflexive visceral afferents from the stomach ascend along the vagus nerve to reach the brainstem and then project to the inferior aspect of the solitary nucleus. The cell bodies for these axons are located in the inferior vagal ganglion, which is located near the point at which the vagus nerves exit from the right and left jugular foramina.

Normal Gastric Neuromuscular Physiology

Normal gastric physiology is best described in terms of its fasting patterns and the responses of the stomach in response to food intake (the fed response).

Mechanism of Gastric Acid Secretion

The stomach has three anatomic regions, the fundus, body, and antrum. It is functionally divided into two glandular regions, the oxyntic and pyloric mucosae. The oxyntic gland mucosa contains parietal cells (that produce gastric acid (hydrogen chloride [HCl]) producing) and forms 80% of the fundus and body. The pyloric gland mucosa contains G cells and forms 20% of the antrum. Chief cells predominate at the base and secrete pepsinogen and leptin. The distinct neuroendocrine cell types and their physiologic functions are the (1) enterochromaffin cells, which contain atrial natriuretic peptide, somatostatin, serotonin, and adrenomedullin; (2) enterochromaffin-like cells, which contain histamine; (3) D cells, which contain somatostatin; and (4) cells that contain ghrelin and obestatin.

The physiologic stimulation of acid secretion is divided into three phases, the cephalic, gastric, and intestinal phases.

• 1.

  The cephalic phase is activated by the thought, taste, smell, and sight of food. Swallowing is mediated mostly by cholinergic/vagal mechanisms. The conditioned (psychic) secretion (described by Pavlov) is the principal component of the cephalic phase; hence, dogs were conditioned to associate the ringing of a bell with a meal. Anticipation of food is a powerful trigger for increasing gastric secretions. Other upregulated systems include the pancreas and gallbladder.

• 2.

  The gastric phase is due to the chemical effects of food and distention of the stomach mediated by gastrin with a marked increase in gastric blood flow supplying the metabolic requirements of the actively secreting cell types.

• 3.

  As the meal moves out of the stomach into the duodenum, the intestinal phase occurs. The buffering capacity of the lumen is reduced and the pH begins to fall. This feedback response involves several endocrine and paracrine factors, including gastric inhibitory polypeptide and cholecystokinin (CCK).

Physiologic secretion enhancers are vagal activation, food, and gastric distention. Parietal cells secrete HCl at a concentration of approximately 160 mmol, or pH 0.8, produced from the hydration of carbon dioxide to form H ⁺ and HCO3 ⁻ , catalyzed by carbonic anhydrase. The acid secretory process requires functional receptors, signaling pathways, channels, transporters, and acid-secreting pumps (H ⁺ /K ⁺ -ATPase).

Basal acid output is approximately 10% of the maximal acid output of the stimulated parietal cell. There is diurnal variation of basal acid levels, with night levels being higher than day levels.

The parietal cell contains another inhibitory receptor for prostaglandin E ₂ (PGE ₂ ) which inhibits gastric acid secretion by decreasing intracellular cyclic adenosine monophosphate levels and gastrin secretion and stimulates somatostatin secretion. Gastric acid facilitates digestion of proteins and absorption of calcium, iron, and vitamin B ₁₂ . It also suppresses growth of bacteria, preventing enteric infections and small intestinal bacterial overgrowth. Low levels of acid are related to chronic atrophic gastritis and precancerous gastric conditions. Gastric acid secretion from parietal cells is regulated by overlapping pathways that include endocrine (gastrin), paracrine (histamine and somatostatin), neural (acetylcholine), and probably autocrine (transforming growth factor alpha) factors. The source of gastric acid secretion is the parietal cell, located in the glands of the fundic mucosa. Its basolateral membrane contains receptors for histamine, gastrin, and acetylcholine; potentiated secretion may occur when all are present simultaneously. In the resting state, parietal cells are filled with secretory vesicles that form channels that drain to the apical lumen. The secretory membrane lining these structures contains the hydrogen-potassium-ATPase acid–secreting pump. This pump is always active, but it exists in a short-circuited state in resting vesicles because of inactive exchange. With stimulation, this pathway becomes active, and hydrogen-potassium exchange occurs.

With ingestion of a protein meal, gastrin is released; it enhances gastric acid secretion from parietal cells through release of histamine from enterochromaffin-like cells and has a direct effect on parietal cells.

Many dietary substances are highly effective buffers. Carbohydrates and fats inhibit acid secretion, and fat stimulates CCK and other mediators that inhibit acid secretion. Somatostatin inhibits gastric acid secretion by affecting gastrin/histamine synthesis and release. The mucosal nerves mediate the response to the cephalic phase of acid secretion and to gastric distention. Acetylcholine is the major stimulatory mediator that increases gastrin release, stimulates parietal cells, and inhibits somatostatin secretion. Other stimulatory mediators include bombesin, vasoactive intestinal peptide, and pituitary adenylate cyclase–activating polypeptide. Gastrin acts via activation of the CCK2 receptor located on parietal and enterochromaffin-like cells. Prostaglandins inhibit acid secretion and gastrin-stimulated histamine release. Gastric acid hypersecretion may be seen in chronic Helicobacter pylori infection, duodenal ulcers, Zollinger-Ellison gastrinoma, or mastocytosis or if an antrum is retained following partial gastrectomy. Rebound acid hypersecretion occurs once therapy with an H ₂ receptor antagonist or a proton pump inhibitor has ceased for 1 month or longer.

Digestive Activity of Stomach

The main role of the stomach is to prepare food for digestion and absorption by the intestine. The parietal cells produce hydrochloric acid in gastric secretions . Various neural and hormonal mediators contribute to gastric function. The acid secretory process requires functional receptors, signaling pathways, channels, transporters, and acid-secreting pumps (H+/K+-ATPase). The level of acidity depends upon the relative proportions of parietal and nonparietal secretions; hence, the more rapid the rate of secretion, the higher the level of acidity.

Rebound acid hypersecretion occurs after therapy with proton pump inhibitors or H ₂ receptor antagonists has ceased. Increased HCl secretion has been seen at night and with the acid secretory response to a meal. The alkaline tide (decrease in urinary acidity after a meal) is generally attributed to increased alkalinity of the blood resulting from the secretion of HCl. Its occurrence is influenced by the rate of formation of HCl and its absorption from the gut. Additional influencing factors include alkaline digestive secretions (mainly pancreatic), the neutralizing capacity of the food eaten, respiratory adjustments after a meal, and the diuretic effect of a meal.

Pepsin, the principal enzyme of gastric juice, is stored in the chief cells as pepsinogen. At a pH below 6.0, pepsinogen is converted to pepsin. The free pepsin activates the continued transformation of pepsinogen to pepsin. The chief cells are the most common cells in the gastric mucosa, found in the body, fundus, and antrum of the stomach, as well as in the duodenum. Pepsinogen is stimulated by acetylcholine, histamine, and CCK2 and inhibited by somatostatin.

Powerful stimuli for gastrin secretion include gastric juice rich in pepsin, hypoglycemia (vagal stimulus), or direct electrical stimulation of the vagus nerves. The pepsinogen of the gastric chief cells is also secreted internally into the bloodstream and appears in the urine as uropepsinogen.

As mentioned previously, gastric acid secretion is divided into cephalic, gastric, and intestinal phases. Mucus is excreted from neck cells and surface mucus cells in the stomach and Brunner glands after stimulation with acetylcholine, secretin, and prostaglandins. Its function is to provide a protective layer over the gastric and duodenal mucosa. Mucus slows the diffusion of acid from the lumen to the mucosa, provides lubrication for the passage of food, and maintains a near-normal pH at the mucosal surface because of its content of bicarbonate. It is dissolved by pepsin and N-acetylcysteine and easily penetrated by bile salts, ethanol, and nonsteroidal antiinflammatory drugs (NSAIDs), leading to mucosal damage. Mucosal repair is very quick and occurs through the movement of already established mature mucosal cells over the basal lamina.

Acetylcholine, histamine, endogenous nitric oxide, and PGE ₂ cause vasodilation and increased gastric blood flow; sympathetic stimulation, exogenous epinephrine, norepinephrine, and vasopressin cause vasoconstriction and decreased gastric blood flow.

Parietal cells synthesize and secrete intrinsic factor, which plays a key role in absorption of vitamin B ₁₂ in the terminal ileum. NSAIDs inhibit the cyclooxygenase (COX) enzyme in the prostaglandin production pathway and cause damage to the gastric mucosa. Currently there are two isoforms, COX-1 and COX-2. The COX-1 pathway results in production of PGE ₂ , and the COX-2 pathway is involved mainly in inflammatory events. The selective COX-2 inhibitors decrease inflammation without affecting PGE ₂ production. Mucosal defenses can also be affected by H. pylori infection.

Neuroregulation of Gastric Activity