Divisions

The stomach begins as a dilation in the tubular embryonic foregut during the fifth week of gestation. By the seventh week, it descends, rotates, and further dilates with a disproportionate elongation of the greater curvature into its normal anatomic shape and position. Following birth, it is the most proximal abdominal organ of the alimentary tract. The most proximal region of the stomach is called the cardia, which attaches to the esophagus. Immediately proximal to the cardia is a physiologically competent lower esophageal sphincter. Distally, the pylorus connects the distal stomach (antrum) to the proximal duodenum. Although the stomach is fixed at the gastroesophageal (GE) junction and pylorus, its large midportion is mobile. The fundus represents the superiormost part of the stomach and is floppy and distensible. The stomach is bounded superiorly by the diaphragm and laterally by the spleen. The body of the stomach represents the largest portion and is also referred to as the corpus. The body also contains most of the parietal cells and is bounded on the right by the relatively straight lesser curvature and on the left by the longer greater curvature. At the angularis incisura, the lesser curvature abruptly angles to the right. It is here that the body of the stomach ends and the antrum begins. Another important anatomic angle (angle of His) is that formed by the fundus with the left margin of the esophagus (Fig. 49-1).

FIGURE 49-1 Divisions of the stomach.

(From Yeo C: Shackelford’s surgery of the alimentary tract, ed 6, Philadelphia, 2007, WB Saunders.)

Most of the stomach resides within the upper abdomen. The left lateral segment of the liver covers a large portion of the stomach anteriorly. The diaphragm, chest, and abdominal wall bound the remainder of the stomach. Inferiorly, the stomach is attached to the transverse colon, spleen, caudate lobe of the liver, diaphragmatic crura, and retroperitoneal nerves and vessels. Superiorly, the GE junction is found about 2 to 3 cm below the diaphragmatic esophageal hiatus in the horizontal plane of the seventh chondrosternal articulation, a plane only slightly cephalad to that containing the pylorus. The gastrosplenic ligament attaches the proximal greater curvature to the spleen.

Blood Supply

The celiac artery provides most of the blood supply to the stomach (Fig. 49-2). There are four main arteries—the left and right gastric arteries along the lesser curvature and the left and right gastroepiploic arteries along the greater curvature. In addition, a substantial quantity of blood may be supplied to the proximal stomach by the inferior phrenic arteries and by the short gastric arteries from the spleen. The largest artery to the stomach is the left gastric artery, and it is not uncommon (15% to 20%) for an aberrant left hepatic artery to originate from it. Consequently, proximal ligation of the left gastric artery occasionally results in acute left-sided hepatic ischemia. The right gastric artery arises from the hepatic artery (or the gastroduodenal artery). The left gastroepiploic artery originates from the splenic artery and the right gastroepiploic originates from the gastroduodenal artery. The extensive anastomotic connection between these major vessels ensures that in most cases, the stomach will survive if three out of four arteries are ligated, provided that the arcades along the greater and lesser curvatures are not disturbed. In general, the veins of the stomach parallel the arteries. The left gastric (coronary) and right gastric veins usually drain into the portal vein. The right gastroepiploic vein drains into the superior mesenteric vein and the left gastroepiploic vein drains into the splenic vein.

FIGURE 49-2 Blood supply to the stomach and duodenum showing anatomic relationships to the spleen and pancreas. The stomach is reflected cephalad.

(From Yeo C: Shackelford’s surgery of the alimentary tract, ed 6, Philadelphia, 2007, WB Saunders.)

Lymphatic Drainage

The lymphatic drainage of the stomach parallels the vasculature and drains into four zones of lymph nodes (Fig. 49-3). The superior gastric group drains lymph from the upper lesser curvature into the left gastric and paracardial nodes. The suprapyloric group of nodes drains the antral segment on the lesser curvature of the stomach into the right suprapancreatic nodes. The pancreaticolienal group of nodes drains lymph high on the greater curvature into the left gastroepiploic and splenic nodes. The inferior gastric and subpyloric group of nodes drains lymph along the right gastroepiploic vascular pedicle. All four zones of lymph nodes drain into the celiac group and into the thoracic duct. Although these lymph nodes drain different areas of the stomach, gastric cancers may metastasize to any of the four nodal groups, regardless of the cancer location. In addition, the extensive submucosal plexus of lymphatics accounts for the fact that there is frequently microscopic evidence of malignant cells several centimeters from gross disease.

FIGURE 49-3 Lymphatic drainage of the stomach.

Innervation

As shown in Figure 49-4, the extrinsic innervation of the stomach is parasympathetic (via the vagus) and sympathetic (via the celiac plexus). The vagus nerve originates in the vagal nucleus in the floor of the fourth ventricle and traverses the neck in the carotid sheath to enter the mediastinum, where it divides into several branches around the esophagus. These branches coalesce above the esophageal hiatus to form the left and right vagus nerves. It is not uncommon to find more than two vagal trunks at the distal esophagus. At the GE junction, the left vagus is anterior, and the right vagus is posterior (LARP).

FIGURE 49-4 Vagal innervation of the stomach. The line of division for truncal vagotomy is shown; it is above the hepatic and celiac branches of the left and right vagus nerves, respectively. The line of division for selective vagotomy is shown; this is below the hepatic and celiac branches.

(From Mercer D, Liu T: Open truncal vagotomy. Oper Tech Gen Surg 5:8–85, 2003.)

The left vagus gives off the hepatic branch to the liver and then continues along the lesser curvature as the anterior nerve of Latarjet. Although not shown, the so-called criminal nerve of Grassi is the first branch of the right or posterior vagus nerve; it is recognized as a potential cause of recurrent ulcers when left undivided. The right nerve gives a branch off to the celiac plexus and then continues posteriorly along the lesser curvature. A truncal vagotomy is performed above the celiac and hepatic branches of the vagi, whereas a selective vagotomy is performed below. A highly selective vagotomy is performed by dividing the crow’s feet to the proximal stomach while preserving the innervation of the antral and pyloric parts of the stomach. Most (90%) of the vagal fibers are afferent, carrying stimuli from the gut to the brain. Efferent vagal fibers originate in the dorsal nucleus of the medulla and synapse with neurons in the myenteric and submucosal plexuses. These neurons use acetylcholine as their neurotransmitter and influence gastric motor function and gastric secretion. In contrast, the sympathetic nerve supply comes from T5 to T10, traveling in the splanchnic nerve to the celiac ganglion. Postganglionic fibers then travel with the arterial system to innervate the stomach.

The intrinsic or enteric nervous system of the stomach consists of neurons in Auerbach’s and Meissner’s autonomic plexuses. In these locations, cholinergic, serotoninergic, and peptidergic neurons are present. However, the function of these neurons remains poorly understood. Nevertheless, a number of neuropeptides have been localized to these neurons; these include acetylcholine, serotonin, substance P, calcitonin gene–related peptide (CGRP), bombesin, cholecystokinin (CCK), and somatostatin. Consequently, it is an oversimplification to think of the stomach as only containing parasympathetic (cholinergic input) and sympathetic (adrenergic input) supply. Moreover, the parasympathetic nervous system contains adrenergic neurons and the sympathetic system also contains cholinergic neurons.

Gastric Morphology

The stomach is covered by peritoneum, which forms the outer serosa of the stomach. Below it is the thicker muscularis propria, or muscularis externa, which is made up of three layers of smooth muscles. The middle layer of smooth muscle is circular and is the only complete muscle layer of the stomach wall. At the pylorus, this middle circular muscle layer becomes progressively thicker and functions as a true anatomic sphincter. The outer muscle layer is longitudinal and continuous with the outer layer of longitudinal esophageal smooth muscle. Within the layers of the muscularis externa is a rich plexus of autonomic nerves and ganglia, called Auerbach’s myenteric plexus. The submucosa lies between the muscularis externa and mucosa and is a collagen-rich layer of connective tissue that is the strongest layer of the gastric wall. In addition, it contains the rich anastomotic network of blood vessels and lymphatics and Meissner’s plexus of autonomic nerves. The mucosa consists of surface epithelium, lamina propria, and muscularis mucosae. The latter is on the luminal side of the submucosa and is probably responsible for the rugae that greatly increase epithelial surface area. It also marks the microscopic boundary for invasive and noninvasive gastric carcinoma. The lamina propria represents a small connective tissue layer and contains capillaries, vessels, lymphatics, and nerves necessary to support the surface epithelium.

Gastric Microscopic Anatomy

Gastric mucosa consists of columnar glandular epithelia. The cellular populations (and functions) of the cells forming this glandular epithelium vary based on their location in the stomach (Table 49-1). The glandular epithelium is divided into cells that secrete products into the gastric lumen for digestion (parietal cells, chief cells, mucus-secreting cells) and cells that control function (gastrin-secreting G cells, somatostatin-secreting D cells) cells. In the cardia, the mucosa is arranged in branched glands and the pits are short. In the fundus and body, the glands are more tubular and the pits are longer. In the antrum, the glands are more branched. The luminal ends of the gastric glands and pits are lined with mucus-secreting surface epithelial cells, which extend down into the necks of the glands for variable distances. In the cardia, the glands are predominantly mucus-secreting. In the body, the glands are mostly lined from the neck to the base with parietal and chief cells (Fig. 49-5). There are a few parietal cells in the fundus and proximal antrum, but none in the cardia or prepyloric antrum. The endocrine G cells are present in greatest quantity in the antral glands.

Table 49-1 Gastric Cell Types, Location, and Function

FIGURE 49-5 Cells residing within a gastric gland.

(From Yeo C: Shackelford’s surgery of the alimentary tract, ed 6, Philadelphia, 2007, WB Saunders.)

Gastrin

Gastrin is produced by G cells located in the gastric antrum (see Table 49-1). It is synthesized as a prepropeptide and undergoes post-translational processing to produce biologically reactive gastrin peptides. Several molecular forms of gastrin exist. G-34 (big gastrin), G-17 (little gastrin), and G-14 (minigastrin) have been identified. However, 90% of antral gastrin is released as the 17–amino acid peptide, although G-34 predominates in the circulation because its metabolic half-life is longer than that of G-17. The pentapeptide sequence contained at the carboxyl terminus of gastrin is the biologically active component and is identical to that found on another gut peptide, CCK. CCK and gastrin differ by tyrosine sulfation sites. The release of gastrin is stimulated by food components in a meal, especially protein digestion products. Luminal acid inhibits the release of gastrin. In the antral location, somatostatin and gastrin release are functionally linked, and an inverse reciprocal relationship exists between these two peptides.¹

Gastrin is the major hormonal regulator of the gastric phase of acid secretion following a meal. Histamine, released from enterochromaffin-like (ECL) cells, is also a potent stimulant of acid release from the parietal cell. Gastrin also has considerable trophic effects on the parietal cells and gastric ECL cells. Prolonged hypergastrinemia from any cause leads to mucosal hyperplasia and an increase in the number of ECL cells and, under some circumstances, is associated with the development of gastric carcinoid tumors.²

The detection of hypergastrinemia may suggest a pathologic state of acid hypersecretion but generally is the result of treatment with agents to lower acid secretion, such as proton pump inhibitors. Table 49-2 lists common causes of chronic hypergastrinemia. Hypergastrinemia that results from the administration of acid-lowering drugs is an appropriate response caused by loss of feedback inhibition of gastrin release by luminal acid. Lack of acid causes a reduction in somatostatin release, which in turn causes increased release of gastrin from antral G cells. Hypergastrinemia can also occur in the setting of pernicious anemia or uremia, or following surgical procedures such as vagotomy or retained gastric antrum after gastrectomy. In contrast, gastrin levels increase inappropriately in patients with gastrinoma (Zollinger-Ellison syndrome [ZES]). These gastrin-secreting tumors are not located in the antrum and secrete gastrin autonomously.

Table 49-2 Causes of Hypergastrinemia

Gastrin initiates its biologic actions by activation of surface membrane receptors. These receptors are members of the classic G protein–coupled seven–transmembrane-spanning receptor family and are classified as type A or B CCK receptors. The gastrin or CCK-B receptor has high affinity for gastrin and CCK, whereas the type A CCK receptors have an affinity for sulfated CCK analogues and a low affinity for gastrin. Binding of gastrin with the CCK-B receptor has been associated with elevated intracellular calcium levels.

Somatostatin

Somatostatin is produced by D cells and exists endogenously as the 14– or 28–amino acid peptide. The predominant molecular form in the stomach is somatostatin-14. It is produced by diffuse neuroendocrine cells located in the fundus and antrum. In these locations, D cell cytoplasmic extensions have direct contact with the parietal cells and G cells, where it presumably exerts its actions through paracrine effects on acid secretion and gastrin release.³ Somatostatin is able to inhibit parietal cell acid secretion directly but can also indirectly inhibit acid secretion through inhibition of gastrin release and downregulation of histamine release from ECL cells. The principal stimulus for somatostatin release is antral acidification, whereas acetylcholine from vagal fibers inhibits its release.

Somatostatin receptors are also seven–transmembrane-spanning receptors. Binding of somatostatin with its receptors is coupled to one or more inhibitory guanine nucleotide–binding proteins. Parietal cell somatostatin receptors appear to be a single subunit of glycoproteins with a molecular weight of 99 kDa, with equal affinity for somatostatin-14 and somatostatin-28. Somatostatin can inhibit parietal cell secretion through G protein–dependent and G protein–independent mechanisms. However, the ability of somatostatin to exert its inhibitory actions on cellular function is primarily thought to be mediated through the inhibition of adenylate cyclase, with a resultant reduction in cyclic AMP levels.

Gastrin-Releasing Peptide

Bombesin was discovered in 1970 in an extract prepared from skin of the amphibian Bombina bombina (European fire-bellied toad). Its mammalian counterpart is gastrin-releasing peptide (GRP). GRP is particularly prominent in nerves ending in the acid-secreting and gastrin-secreting portions of the stomach and is found in the circular muscular layer. In the antral mucosa, GRP stimulates gastrin and somatostatin release by binding to receptors located on the G and D cells, respectively. It is rapidly cleared from the circulation by a neutral endopeptidase and has a half-life of approximately 1.4 minutes. Peripheral administration of exogenous GRP stimulates gastric acid secretion, whereas central administration in the ventricles inhibits acid secretion. The inhibitory pathway activated is not mediated by a humoral factor, is unaffected by vagotomy, and appears to involve the sympathetic nervous system.

Histamine

Histamine plays a prominent role in parietal cell stimulation. Administration of histamine 2 (H₂) receptor antagonists almost completely abolishes gastric acid secretion in response to gastrin and acetylcholine. This suggests that histamine may be a necessary intermediary of gastrin- and acetylcholine-stimulated acid secretion. Histamine is stored in the acidic granules of ECL cells and in resident mast cells. Its release is stimulated by gastrin, acetylcholine, and epinephrine following receptor-ligand interactions on ECL cells. In contrast, somatostatin inhibits gastrin-stimulated histamine release through interactions with somatostatin receptors located on the ECL cell. Thus, the ECL cell plays an essential role in parietal cell activation that possesses stimulatory and inhibitory feedback pathways that modulate the release of histamine and therefore acid secretion.

Ghrelin

Ghrelin is a 28–amino acid peptide predominantly produced by endocrine cells of the oxyntic mucosa of the stomach, with substantially lower amounts from the bowel, pancreas, and other organs. Removal of the acid-producing part of the stomach decreases circulating ghrelin by 80%. Ghrelin appears to be under endocrine and metabolic control, has a diurnal rhythm, likely plays a major role in the neuroendocrine and metabolic responses to changes in nutritional status, and may be a major anabolic hormone.

In human volunteers, ghrelin administration enhances appetite and increases food intake. In patients who have undergone a gastric bypass, ghrelin levels are 77% lower than those of matched obese controls, a finding not seen after other forms of antiobesity surgery. Although the mechanism responsible for suppression of ghrelin levels after gastric bypass is unknown, this suggests that ghrelin may be responsive to the normal flow of nutrients across the stomach. Other studies have suggested that ghrelin leads to a switch toward glycolysis and away from fatty acid oxidation, which would favor fat deposition. It appears that ghrelin is upregulated in times of negative energy balance and downregulated in times of positive energy balance, although the precise role of ghrelin in energy metabolism remains unclear. Ghrelin may come to have a role in the treatment and prevention of obesity.

Stimulated Acid Secretion

Activation and Secretion by the Parietal Cell

The two second messengers principally involved in stimulation of acid secretion by parietal cells are intracellular cyclic AMP (cAMP) and calcium. Synthesis of these two messengers in turn activates protein kinases and phosphorylation cascades. The intracellular events following ligand binding to receptors on the parietal cell are shown in Figure 49-7. Histamine causes an increase in intracellular cAMP, which activates protein kinases to initiate a cascade of phosphorylation events that culminate in activation of H⁺, K⁺-ATPase. In contrast, acetylcholine and gastrin stimulate phospholipase C, which converts membrane-bound phospholipids into inositol triphosphate (IP₃) to mobilize calcium from intracellular stores. Increased intracellular calcium activates other protein kinases that ultimately activate H⁺, K⁺-ATPase in a similar fashion to initiate the secretion of hydrochloric acid.

FIGURE 49-7 Intracellular signaling events in a parietal cell. As shown, histamine binds to H₂ receptors, stimulating adenylate cyclase through a G protein–linked mechanism. Adenylate cyclase activation causes an increase in intracellular cAMP levels, which in turn activates protein kinases. Activated protein kinases stimulate a phosphorylation cascade, with a resultant increase in levels of phosphoproteins that activate the proton pump. Activation of the proton pump leads to extrusion of cytosolic hydrogen in exchange for extracytoplasmic potassium. In addition, chloride is secreted through a chloride channel located on the luminal side of the membrane. Gastrin binds to type B cholecystokinin receptors and acetylcholine binds to M3 receptors. Following the interaction of gastrin or acetylcholine with their receptors, phospholipase C is stimulated through a G protein–linked mechanism to convert membrane-bound phospholipids into inositol triphosphate (IP3). IP3 stimulates the release of calcium from intracellular calcium stores, leading to an increase in intracellular calcium that in turn activates protein kinases, which activate the H⁺,K⁺-ATPase. ATP, Adenosine triphosphate; ATPase, adenosine triphosphatase; cAMP, cyclic adenosine monophosphate; Gi, inhibitory guanine nucleotide protein; Gs,stimulatory guanine nucleotide protein; PIP2, phosphatidylinositol 4,5- diphosphate; PLC, phospholipase C.

(From Yeo C: Shackelford’s surgery of the alimentary tract, ed 6, Philadelphia, 2007, WB Saunders.)

H⁺, K⁺-ATPase is the final common pathway for gastric acid secretion by the parietal cell. It is composed of two subunits, a catalytic α-subunit (100 kDa) and a glycoprotein β-subunit (60 kDa). During the resting, or nonsecreting, state, gastric parietal cells store H⁺, K⁺-ATPase within intracellular tubulovesicular elements. Cellular relocation of the proton pump subunits through cytoskeletal rearrangements must occur in order for acid secretion to increase in response to stimulatory factors. The subsequent insertion and heterodimer assembly of the H⁺, K⁺-ATPase subunits into the microvilli of the secretory canaliculus causes an increase in gastric acid secretion. A KCl efflux pathway must exist to supply potassium to the extracytoplasmic side of the pump. Cytosolic hydrogen is secreted by H⁺, K⁺-ATPase in exchange for extracytoplasmic potassium (see Fig. 49-7), which is an electroneutral exchange and therefore does not contribute to the transmembrane potential difference across the parietal cell. Secretion of chloride is accomplished through a chloride channel moving chloride from the parietal cell cytoplasm to the gastric lumen. The secretion or exchange of hydrogen for potassium, however, does require energy in the form of adenosine triphosphate (ATP) because hydrogen is being secreted against a gradient of more than a million-fold. Because of this large energy requirement, the parietal cell also has the largest mitochondrial content of any mammalian cell, with a mitochondrial compartment representing 34% of its cell volume. In response to a secretagogue, the parietal cell undergoes a conformational change, and a several-fold increase in the canalicular surface area occurs (Fig. 49-8). In contrast to stimulated acid secretion, cessation of acid secretion requires endocytosis of H⁺, K⁺-ATPase, with regeneration of cytoplasmic tubulovesicles containing the subunits, and this occurs through a tyrosine-based signal. The tyrosine-containing sequence is located on the cytoplasmic tail of the β-subunit and is highly homologous to the motif responsible for internalization of the transferrin receptor.

FIGURE 49-8 Diagrammatic representation of resting and stimulated parietal cells. Note the morphologic transformation between the nonsecreting parietal cell and stimulated parietal cell, with increases in secretory canalicular membrane surface area.

More than 1 billion parietal cells are found in the normal human stomach and are responsible for secreting about 20 mmol/hr of hydrochloric acid in response to a protein meal. Each individual parietal cell secretes 3.3 billion hydrogen ions/second, and there is a linear relationship between maximal acid output and parietal cell number. However, gastric acid secretory rates may be altered in patients with upper gastrointestinal (GI) disease. For example, gastric acid is often increased in patients with duodenal ulcer or gastrinoma, whereas it is decreased in patients with pernicious anemia, gastric atrophy, gastric ulcer, or gastric cancer. The lower secretory rates observed in gastric ulcer patients are typically for proximal gastric ulcers, whereas distal, antral, or prepyloric ulcers are associated with acid secretory rates similar to those in duodenal ulcer patients.

Gastric acid thus plays a critical role in the digestion of a meal. It is required to convert pepsinogen into pepsin, elicits the release of secretin from the duodenum, and limits colonization of the upper GI tract with bacteria.

Pharmacologic Regulation

The diversity of mechanisms that stimulate acid secretion has resulted in the development of many site-specific drugs aimed at decreasing acid output by the parietal cell. The best-known site-specific antagonists are the group collectively known as the H₂ receptor antagonists. The most potent of the H₂ receptor antagonists is famotidine, followed by ranitidine, nizatidine, and cimetidine. The half-life for famotidine is 3 hours and approximately 1.5 hours for the others. All undergo hepatic metabolism, are excreted by the kidney, and do not differ much in bioavailability.

The newest class of antisecretory agents is the proton pump inhibitors (PPIs). These substituted benzimidazoles, of which omeprazole is a prime example, inhibit acid secretion more completely because of their irreversible inhibition of the proton pump. These PPIs are weak acids with a pK_a of 4 and therefore become selectively localized in the secretory canaliculus of the parietal cell, which is the only structure in the body with a pH lower than 4. After oral administration, these agents are absorbed into the bloodstream as prodrugs and then selectively concentrate in the secretory canaliculus. At low pH, they become ionized and activated, with the formation of an active sulfur group. Because the proton pump is located on the luminal surface, the transmembrane pump proteins are also exposed to acid or low pH. The cysteine residues on the α-subunit form a covalent disulfate bond with activated benzimidazoles, which irreversibly inhibits the proton pump. Because of the covalent nature of this bond, these PPIs have more prolonged inhibition of gastric acid secretion than H₂ blockers. In order for recovery of acid secretion to occur, new protein pumps need to be synthesized. As a result, these agents have a longer duration of action than their plasma half-life, with the intragastric pH being maintained higher than 3 for 18 hours or longer.

One notable side effect of all antisecretory agents is the elevation of serum gastrin levels. Serum gastrin levels are higher after treatment with PPIs than with H₂ receptor antagonists. This effect is accompanied by hyperplasia of G cells and ECL cells when these agents are administered chronically. Chronic administration of omeprazole has been found to cause ECL hyperplasia that could progress to carcinoid tumors in rats.³ This effect, however, was not specific for omeprazole and was reproduced by other agents that caused prolonged inhibition of acid secretion and resultant hypergastrinemia.

Other Gastric Secretory Products

Fasting Gastric Motility

The electrical basis of gastric motility begins with the depolarization of pacemaker cells located in the midbody of the stomach, along the greater curvature. Once initiated, slow waves travel at 3 cycles/minute in a circumferential and antegrade fashion toward the pylorus. In addition to these slow waves, gastric smooth muscle cells are capable of producing action potentials, which are associated with larger changes in membrane potential than slow waves. In comparison to slow waves, which are not associated with gastric contractions, action potentials are associated with actual muscle contractions. During fasting, the stomach goes through a cyclical pattern of electrical activity composed of slow waves and electrical spikes, which has been termed the myoelectric migrating complex (MMC). Each cycle of the MMC lasts 90 to 120 minutes. The net effects of the MMC are frequent clearance of gastric contents during periods of fasting. The exact regulatory mechanisms of MMC activities are unknown, but these activities remain intact after vagal denervation.

Postprandial Gastric Motility

Ingestion of a meal results in a decrease in the resting tone of the proximal stomach and fundus, referred to as receptive relaxation and gastric accommodation, respectively. Because these reflexes are mediated by the vagus nerves, interruption of vagal innervation to the proximal stomach, such as by truncal vagotomy or proximal gastric vagotomy, can eliminate these reflexes, with resultant early satiety and rapid emptying of ingested liquids. In addition to its storage function, the stomach is responsible for the mixing and grinding of ingested solid food particles. This activity involves repetitive forceful contractions of the mid and antral portions of the stomach, causing food particles to be propelled against a closed pylorus, with subsequent retropulsion of solids and liquids. The net effect is a thorough mixing of solids and liquids and sequential shearing of solid food particles to smaller than 1 mm.

The emptying of gastric contents is under the influence of well-coordinated neural and hormonal mediators. Systemic factors, such as anxiety, fear, depression, and exercise, can affect the rate of gastric motility and emptying. Additionally, the chemical and mechanical properties and temperature of the intraluminal contents can influence the rate of gastric emptying. In general, liquids empty more rapidly than solids and carbohydrates empty more readily than fats. An increase in the concentration or acidity of liquid meals causes a delay in gastric emptying. In addition, hot and cold liquids tend to empty at a slower rate than ambient temperature fluids. These responses to luminal stimuli are regulated by the enteric nervous system. Osmoreceptors and pH-sensitive receptors in the proximal small bowel have also been shown to be involved in the activation of feedback inhibition of gastric emptying. Inhibitory peptides proposed to be active in this setting include CCK, glucagon, vasoactive intestinal peptide, and gastric inhibitory polypeptide.

Abnormal Gastric Motility

Symptoms of abnormal gastric motility are nausea, fullness, early satiety, abdominal pain, and discomfort. Although mechanical obstruction can and should be ruled out with upper endoscopy or radiographic contrast studies, objective evaluation of a patient with a suspected motility disorder can be accomplished with gamma scintigraphy, real-time ultrasound, and magnetic resonance imaging (MRI). Gastric motility disorders usually encountered in clinical practice are gastric dysmotility following vagotomy, delayed gastric emptying associated with diabetes mellitus, and gastric motility dysfunction related to H. pylori infection. Vagotomy results in loss of receptive relaxation and gastric accommodation in response to meal ingestion, with resultant early satiety, postprandial bloating, accelerated emptying of liquids, and delay in emptying of solids. Clinical manifestations of diabetic gastropathy, which can occur in insulin-dependent or insulin-independent patients, closely resemble the clinical picture of postvagotomy gastroparesis. Furthermore, structural changes have been identified in the vagus nerve of patients with diabetes, suggesting that a diabetic autonomic neuropathy may be responsible. However, the metabolic effects of diabetes have also been implicated. Specifically, hyperglycemia has been shown to cause a decrease in contractility of the gastric antrum, increase in pyloric contractility, and suppression of the migrating motor complex (MMC). Suppression of MMC activity is thought to be responsible for the accumulation of gastric bezoars seen in some diabetic patients. In contrast, hyperinsulinemia, which is often associated with non–insulin-dependent diabetes, may play a role in the gastroparesis seen in non–insulin-dependent diabetes because it also leads to suppression of MMC activity.⁴

H. pylori–infected patients with nonulcer dyspepsia have also been demonstrated to have impaired gastric emptying accompanied by a reduction in gastric compliance.⁵ In rats, lipopolysaccharide derived from H. pylori causes a reduction in gastric emptying of a liquid meal for up to 12 hours by an unknown mechanism. Regardless of the cause of gastroparesis, treatment consists of prokinetic agents, such as metoclopramide and erythromycin, which have been shown to have some benefit, although the evidence is more compelling in diabetics.

Gastric-Emptying Studies

There are a number of ways to assess gastric emptying. The saline load test is perhaps the simplest and is accomplished by instilling a known volume of saline into the stomach and aspirating the amount remaining at a certain time. Alternatively, fluoroscopic procedures can also provide information on gastric emptying and may reveal mechanical causes that could contribute to a delay, such as gastric outlet obstruction. However, computerized radionucleotide scans are more commonly used to assess gastric emptying. This can be done with radiolabeled liquids or with a radiolabeled solid meal. After a mechanical obstruction has been ruled out, gastric emptying studies using these radionucleotide scans can be particularly helpful for patients with gastric atony from an associated illness such as diabetes or in postgastrectomy patients.

Helicobacter pylori Infection

It is now believed that 90% of duodenal ulcers and approximately 75% of gastric ulcers are associated with H. pylori infection. When this organism is eradicated as part of ulcer treatment, ulcer recurrence is extremely rare. H. pylori is a spiral or helical gram-negative rod with four to six flagella that resides in gastric-type epithelium within or beneath the mucus layer. This location protects the bacteria from acid and antibiotics. Its shape and flagella aid its movement through the mucus layer and it produces enzymes that help it adapt to this hostile environment. Most notably, it is a potent producer of urease, which is capable of splitting urea into ammonia and bicarbonate, creating an alkaline microenvironment in the setting of an acidic gastric milieu. The secretion of this enzyme, however, facilitates detection of the organism. H. pylori is microaerophilic and can only live in gastric epithelium. Thus, it can also be found in heterotopic gastric mucosa in the proximal esophagus, Barrett’s esophagus, gastric metaplasia in the duodenum, within a Meckel’s diverticulum, and heterotopic gastric mucosa in the rectum.

The mechanisms responsible for H. pylori–induced GI injury remain to be fully elucidated, but three potential mechanisms have been proposed:

Peptic ulcers are also strongly associated with antral gastritis. Studies done before the H. pylori era have demonstrated that almost all peptic ulcer patients have histologic evidence of antral gastritis. It was later found that the only patients with gastric ulcers and no gastritis were those ingesting aspirin. It is now recognized that most cases of histologic gastritis are caused by H. pylori infection. Even 25% of patients with an NSAID-associated ulcer have evidence of a histologic antral gastritis, as opposed to 95% of those with non–NSAID-associated ulcers. In most cases, the infection tends to be confined initially to the antrum and results in antral inflammation. Other evidence supporting a causal role for H. pylori in histologic gastritis comes from two separate volunteer physicians who ingested inocula of H. pylori after first confirming normal gross and microscopic gastric mucosa. Both developed gastric H. pylori infection. Acute inflammation was observed histologically on days 5 and 10. By 2 weeks, it had been replaced by chronic inflammation with evidence of a mononuclear cell infiltration. These two reports provide documentation that H. pylori can cause histologic gastritis. However, histologic gastritis does not necessarily equate with symptoms of dyspepsia.

H. pylori infection usually occurs in childhood, and spontaneous remission is rare. There is an inverse relationship between infection and socioeconomic status. The reasons for this remain poorly understood but seem to be the result of factors such as sanitary conditions, familial clustering, and crowding. This likely explains why developing countries have a comparatively higher rate of H. pylori infection, especially in children.

A number of studies have demonstrated what appears to be a steady linear increase in the acquisition of H. pylori infection with age, especially in the United States and northern European nations. In the United States, H. pylori prevalence also varies among racial and ethnic groups.

H. pylori infection is associated with a number of common upper GI disorders, but most infected individuals are asymptomatic. Normal U.S. blood donors have an overall prevalence of about 20% to 55%. H. pylori infection is almost always present in the setting of active chronic gastritis and is present in most duodenal (>90%) and gastric (60% to 90%) ulcer patients. Noninfected gastric ulcer patients tend to be NSAID users. There is weaker association with nonulcer dyspepsia. In addition, most gastric cancer patients have current or past H. pylori infection. Although the association between H. pylori and cancer is strong, no causal relationship has been proven. H. pylori–induced chronic gastritis and intestinal metaplasia, however, are thought to play a role. There is also a strong association between +lymphoma and H. pylori infection. Regression of these lymphomas has been demonstrated after eradication of the organism.

Limited data are available to estimate the lifetime risk of PUD in patients with H. pylori infection. In a longitudinal study from Australia with a mean evaluation period of 18 years, 15% of H. pylori–positive subjects developed verified duodenal ulcer as compared with 3% of seronegative individuals. In a 10-year study of asymptomatic gastritis patients, 11% of patients with histologic gastritis developed PUD over a 10-year period, compared with only 1% of those without gastritis. Another factor implicating a causative role for H. pylori and ulcer formation is that eradication of H. pylori dramatically reduces ulcer recurrence. Many prospective trials have shown that patients with H. pylori infection and non-NSAID ulcer disease who have documented eradication of the organism almost never (<2%) develop recurrent ulcers.

Nonsteroidal Anti-inflammatory Drugs

Hospitalizations for bleeding upper GI lesions have increased together with the increased use of NSAIDs. The risk for bleeding and ulceration is proportional to the daily dosage of NSAIDs. The risk also increases with age older than 60 years, patients having a prior GI event, or concurrent use of steroids or anticoagulants. Consequently, the ingestion of NSAIDs remains an important factor in ulcer pathogenesis, especially in regard to the development of complications and death. More than 3 million people in the United States use NSAIDs daily. When compared with the general population, NSAID users have a 2- to 10-fold increased risk for GI complications.

The risk for mucosal injury or ulceration is roughly proportional to the anti-inflammatory effect associated with each NSAID. In comparison to H. pylori ulcers, which are more frequently found in the duodenum, NSAID-induced ulcers are more often found in the stomach. H. pylori ulcers are also almost always associated with chronic active gastritis, whereas gastritis is not frequently found with an NSAID-induced ulcer, occurring only about 25% of the time. When NSAID use is discontinued, the ulcers usually do not recur.

Acid

Acid plays an important but likely noncausative role in the formation of ulcers. In duodenal ulcers, there is a large overlap of acid levels between ulcer patients and normal subjects. Almost 70% of patients with duodenal ulcers have an acid output within the normal range. Acid levels alone provide little information and, as such, acid secretory testing is of little value in establishing a diagnosis of duodenal ulcer.

For types I and IV gastric ulcers, which are not associated with excessive acid secretion, acid acts as an important cofactor, exacerbating the underlying ulcer damage and attenuating the ability of the stomach to heal. For patients with type II or III gastric ulcers, gastric acid hypersecretion seems to be more common, and consequently they behave more like duodenal ulcers.

Clinical Manifestations

Diagnosis

History and physical examination are of limited value in distinguishing between gastric and duodenal ulceration. Routine laboratory studies include a complete blood count, liver chemistries, and serum creatinine, serum amylase, and calcium levels. A serum gastrin level should also be obtained in patients with ulcers that are refractory to medical therapy or require surgery. An upright chest radiograph is usually performed when ruling out perforation. The two principal means of diagnosing duodenal ulcers are upper GI radiography and fiberoptic endoscopy. Upper GI is less expensive, and most (90%) ulcers can be diagnosed accurately by this means. However, about 5% of ulcers that appear radiographically benign are malignant. H. pylori testing should also be done in all patients with suspected PUD.

Upper Gastrointestinal Radiography

Diagnosis of duodenal ulcer by upper GI radiography requires the demonstration of barium within the ulcer crater, which is usually round or oval and may or may not be surrounded by edema. This study is useful to determine the location and depth of penetration of the ulcer and the extent of deformation from chronic fibrosis. A characteristic barium radiograph of a peptic ulcer is shown in Figure 49-9. The ability to detect ulcers on radiography requires the technical skills and abilities of the radiologist but is also dependent on the size and location of the ulcer. With single-contrast radiographic techniques, as many as 50% of duodenal ulcers may be missed, whereas with double-contrast studies, 80% to 90% of ulcer craters can be detected.

FIGURE 49-9 There is a large benign-appearing gastric ulcer protruding medially from the lesser curvature of the stomach (arrow), just above the gastric incisura.

(Courtesy Dr. Agnes Guthrie, Department of Radiology, University of Texas Medical School, Houston.)

Treatment

Complicated Ulcer Disease

Ulcer disease was once very much the purview of the general surgeon, with ulcer surgery forming a major part of general surgery practice. With the shift in understanding of the disease from one primarily of aberrant acid physiology to one of infectious disease, this has changed significantly, with the overwhelming majority of ulcer patients being treated and cured medically. The surgeon’s role now is primarily to treat the approximately 20% of patients who have a complication from their disease, which includes hemorrhage, perforation, and obstruction (Box 49-2). Frequently included in discussions of complicated ulcer disease is the intractable ulcer. Although intractable disease no doubt exists, its definition is nebulous and exactly when and what type of surgical intervention it requires remain primarily a matter of judgment.

For H. pylori–negative patients, an acid-reducing procedure should also be performed, such as truncal or parietal cell vagotomy.

Hemorrhage

Upper GI bleeding remains a relatively common problem, with an annual incidence of approximately 1/1000.¹¹ Most nonvariceal bleeding (70%) is attributable to peptic ulcers. Most bleeding will stop spontaneously and requires no intervention; persistent bleeding, however, is associated with a 6% to 8% mortality.

The primary clinical criteria that predict persistent bleeding or rebleeding after initial cessation of bleeding, and thus increased mortality, are increased age, decreased hemoglobin (<10 g/dL) at presentation, shock, melena, and need for blood transfusion. Patients who meet any of these criteria should be considered as high risk.¹¹

Almost all patients with an acute upper GI bleed should have endoscopy within 24 hours. Although the data are not conclusive, early endoscopy has been shown to be a cost-effective strategy by triaging patients to more rapid intervention, if warranted, and by identifying low-risk patients without the need for prolonged observation (and therefore earlier hospital discharge).

The initial approach to an upper GI bleed is similar to the approach to a trauma patient. Large-bore IV access, rapid restoration of intravascular volume with fluid and blood products as the clinical situation dictates, and close monitoring for signs of rebleeding are all essential to effective management of these patients. The role of nasogastric (NG) lavage remains an area of debate; however, it can be useful as a predictor of high-risk patients and as an aid for later endoscopic intervention. Patients with bright red blood on NG lavage, as opposed to clear or coffee ground lavage, are at much higher risk for persistent bleeding or rebleeding and warrant endoscopic intervention. Furthermore, the NG tube can be used to lavage the stomach and duodenum prior to endoscopy, removing clot and old blood that could obscure visualization of the source of bleeding. Given its relatively low risk and potential benefit, NG tube placement should be part of the treatment algorithm for these patients once appropriate intravascular access has been established and resuscitation begun.

Patients who are noted to have active bleeding, via an arterial jet or oozing, an adherent clot, or a visible vessel within the ulcer, are at high risk and intervention is required. Patients without active bleeding, no visible vessel, and a clean ulcer base are low risk and do not require further intervention. All patients undergoing endoscopic examination should be tested for their H. pylori status. For the high-risk patient requiring intervention, the best initial approach is endoscopic control, which results in primary hemostasis in approximately 90% of patients. The most common method of control is injection of a vasoconstrictor at the site of bleeding. However, with this method alone, primary hemostasis rates are high but up to 30% of patients have rebleeding. This has led to the development of new techniques, including use of a second vasoconstrictor or sclerosing agent, thermal coagulation, and placement of clips at the site of bleeding. A 2007 meta-analysis has compared the use of epinephrine alone to epinephrine plus any second technique.¹² A dual approach, when compared with epinephrine alone, showed better primary hemostasis, reduction in rebleeding rate, lower rate of surgery, and decreased mortality.

Importantly, both thermal coagulation and mechanical clips, in single-method comparisons with epinephrine, have shown significant superiority with respect to primary hemostasis and rebleeding. A meta-analysis comparing either of these two techniques alone to the use of dual methods has shown no significant difference, except in cases of active arterial bleeding, in which case use of a second method was superior. Although the cost and complications from epinephrine remain small, the use of dual methods does have slightly higher, although still less than 1%, complication rates (e.g., necrosis, perforation), than any single technique. Current 2003 guidelines for endoscopic control of bleeding advocate the use of epinephrine plus an additional method.¹¹ As more data become available, it may be demonstrated that thermal or mechanical treatment alone can be used for most patients. For patients who have rebleeding, repeat endoscopy does not increase their mortality and should be attempted prior to surgical intervention.

All high-risk patients should be placed in a monitored setting, preferably an intensive care unit, until all bleeding has stopped for 24 hours. As part of the 2003 consensus guidelines, all high-risk patients should be placed on an IV PPI, with an initial bolus followed by continuous infusion or intermittent dosing for up to 72 hours. When compared with a histamine blocker and placebo, the IV PPI showed lower rebleeding rates, lower rate of emergency surgery, and decreased mortality.¹³ Patients deemed high risk based on clinical factors who are awaiting endoscopy should probably begin therapy, even prior to endoscopy.

Despite the use of PPIs and improved methods of endoscopic control, 5% to 10% of patients will have persistent bleeding that requires surgical intervention. The vessel most likely to be bleeding is the gastroduodenal artery because of erosion from a posterior ulcer. The duodenum is opened longitudinally, with the incision carried across the pylorus. The vessel is oversewn, with a three-point U stitch technique, which effectively ligates the main vessel along with any smaller branches. One must be careful to avoid incorporating the common bile duct into the stitch. The duodenotomy is closed transversely to avoid narrowing (Fig. 49-10).

FIGURE 49-10 A-E, Heineke-Mikulicz pyloroplasty.

(From Soreide JA, Soreide A: Pyloroplasty. Oper Tech Gen Surg 5:65–72, 2003.)

< div class='tao-gold-member'>

Only gold members can continue reading. Log In or Register to continue