111 2 3 2 4 5 6 The Anatomy and Physiology of 7 8 the 9 1011 Ian R. Daniels and William H. Allum 1 2 3 4 5 6 7 8 9 2011 of absorption. Gastric motility is controlled by 1 Aims both neural and hormonal signals. Nervous 2 control originates from the enteric nervous sys- 3 To detail the anatomy and physiology of the tem as well as the parasympathetic (predomi- 4 stomach. nantly vagus nerve) and sympathetic systems. 5 A number of hormones have been shown to 6 influence gastric motility – for example, both 7 Introduction gastrin and cholecystokinin act to relax the 8 proximal stomach and enhance contractions 9 The stomach is the most dilated part of the in the distal stomach. Other functions of the 3011 digestive tube, having a capacity of 1000–1500 stomach include the secretion of intrinsic factor 1 ml in the adult. It is situated between the end necessary for the absorption of vitamin B12 2 of the oesophagus and the duodenum – the (Figure 2.1). 3 beginning of the small intestine. It lies in the 4 epigastric, umbilical, and left hypochondrial 5 regions of the , and occupies a recess Anatomy 6 bounded by the upper abdominal viscera, the 7 anterior and the diaphragm. It Embryology 8 has two openings and is described as having two 9 borders, although in reality the external surface Towards the end of the fourth week of embry- 4011 is continuous. The relationship of the stomach onic development, the stomach begins to differ- 1 to the surrounding viscera is altered by the entiate from the primitive foregut – a midline 2 amount of the stomach contents, the stage that tube, separated from the developing peri- 3 the digestive process has reached, the degree of cardium by the septum transversum and dor- 4 development of the gastric musculature, and the sally to the aorta. Initially a fusiform dilation 5 condition of the adjacent intestines. However, forms, beyond which the midgut opens into the 6 borders are assigned by the attachment of the yolk sac. The foregut, owing to the presence of 7 via the greater and lesser omentum, the pleuroperitoneal canals on either side, is 8 thus dividing the stomach into an anterior and connected to the dorsal wall by a 9 posterior surface. that is continuous with the dorsal mesentery of 5011 The principal function of the stomach is the mid- and hindguts. Thus a primitive mesen- 1 to mix the food with acid, mucus and pepsin tery extends from the septum transversum to 2 and then release the resulting chyme, at a con- the developing cloaca. The and ventral 311 trolled rate into the duodenum for the process pancreas (uncinate process) develop from the

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Oesophagus ventral aspect of the foregut and grow into the 1111 Fundus septum transversum, thus forming a ventral 2 mesentery – the ventral mesogastrium. As the 3 Cardia embryonic period continues the growth of the 4 two “borders” becomes notably altered and 5 the curvature of the stomach becomes apparent 6 Lesser curvature Body (Figure 2.2). The distal end rotates ventrally and 7 (Parietal cells: with the increased growth of the dorsal border 8 HCL Intrinsic factor the concavity of the lesser curvature becomes 9 apparent. With further increasing growth of 1011 Duodenum Chief cells: Pepsinogen) the entire gut and the return of the gut to the 1 the stomach becomes rotated 2 Greater along its cranial-caudal plane so that the 3 curvature “stomach sac” rotates and the original right 4 Antrum surface becomes dorsal and the left ventral. The 5 Pylorus (gastrin) position of the dorsal and ventral mesogastrium 6 is affected by the rotation (Figure 2.3). 7 Figure 2.1. The regions and functions of the stomach. (With As the dorsal mesogastrium becomes in- 8 permission from Review of Medical Physiology, WF Ganong, creased in length, it folds upon itself forming the 9 13th edition, Lange Medical Press, 1987.) lesser omentum. This lies transverse rather than 2011 1 2 Longitudinal 3 rotation axiis 4 5 6 Lesser 7 curvature 8 Stomach 9 3011 1 Greater 2 Duodenum curvature 3 ab c 4 Figure 2.2. a–c The rotation of the stomach along its longitudinal axis. 5 6 7 Cardia 8 Oesophagus 9 4011 1 Lesser 2 curvature 3 Anteroposterior axix 4 5 6 7 Greater 8 Greater curvature 9 abPylorus curvature 5011 1 Figure 2.3. The rotation of the stomach along its anteroposterior axis. (With permission from Langman’s Medical Embryology, 5th 2 edition, Williams & Wilkins, Baltimore, 1985.) 311

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111 anteroposterior and leads to the formation of incomplete duplications may be defined as 2 the lesser sac. This lies between the stomach and spherical or tubular enteric formations which lie 3 posterior abdominal wall, bounded laterally on in contiguity with the normal alimentary tract 4 the left by the dorsal mesogastrium, anteriorly and which share with it a common blood supply, 5 by the stomach and laterally on the right by the and usually a common muscle coat. These cyst- 6 developing liver. The foramen of Winslow is the like structures, or duplication cysts, usually do 7 only opening into the space and formed by not communicate with the normal lumen. They 8 the free border of the lesser omentum, between may have a mucosal lining and may be pedun- 9 the stomach and liver (Figure 2.4). culated. A duplication cyst of the stomach 1011 With the rotation of the stomach, the duo- is a communicating or non-communicating 1 denum is carried to the right. Initially the cyst lined by gastric, intestinal or pancreatic 2 duodenum is fixed by a thick mesentery to epithelium, and usually located along the 3 the posterior abdominal wall. However, with greater curvature. Occasionally it may be situ- 4 this rotation the duodenum comes to lie on ated in the wall of the pyloric region; in such 5 the posterior abdominal wall and the primitive cases encroachment on the lumen may produce 6 mesentery disappears. This results in the gastric outlet obstruction, or an appearance 7 duodenum coming to lie retroperitoneally. Sim- resembling infantile hypertrophic pyloric steno- 8 ilarly the bilary ducts and pancreas come to lie sis. In non-communicating duplication cysts, 9 within the concavity of the duodenum, the bile accumulation of acid and pepsin may produce 2011 duct having passed behind its proximal part. a local inflammatory reaction, perforation, 1 Within the folds of the dorsal mesogastrium abscess formation and peritonitis. 2 the spleen develops and this remains intimately 3 attached to the stomach. Congenital Double Pylorus, Pyloric 4 Membrane, Web or Diaphragm 5 Congenital Abnormalities Congenital double pylorus is an extremely rare 6 Pyloric Atresia condition. A pyloric membrane is defined as a 7 thin, circumferential mucosal septum in the 8 Almost all cases of gastric atresia occur in the pyloric region, projecting intraluminally per- 9 pyloric region and may present as a membrane pendicular to the long axis of the “antrum”. It 3011 occluding the lumen, as a gap in continuity, or is composed of two layers of gastric mucosa, 1 as a fibrous cord intervening between patent with a central core of submucosa and muscu- 2 portions at the gastroduodenal junction. There laris mucosae. It is generally regarded as a con- 3 is a reported association with epidermolysis genital anomaly and is usually associated with 4 bullosa. Clinically the condition presents as symptoms and signs of gastric outlet obstruc- 5 upper abdominal distension and bile-free vom- tion. 6 iting in the newborn. Maternal hydramnios 7 occurs in approximately 50% of cases. Ectopic Pancreatic Tissue 8 Aberrant pancreatic nodules have been 9 Duplications reported in the upper gastrointestinal tract. 4011 True or complete duplication of the stomach is Although usually in the duodenum they have 1 exceedingly rare. More common (but also rare) been reported in the stomach near the pylorus. 2 3 4 Dorsal mesogastrium Omental bursa 5 6 7 Stomach 8 9 Ventral 5011 abmessogastrium c 1 2 Figure 2.4.a–c The effect of rotation on the ventral and dorsal mesogastrium (a, b) and the formation of the lesser sac (omental 311 bursa) (c). (With permission from Langman’s Medical Embryology, 5th edition, Williams & Wilkins, Baltimore, 1985.)

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Macroscopic Anatomy Greater Curvature (Curvatura 1111 Ventriculi Major) 2 The stomach has two openings, two curvatures, This is directed mainly forward, and is four to 3 two surfaces and two omenta. five times longer than the lesser curvature. It 4 starts from the incisura cardiaca and arches 5 Openings backward, upward, and to the left; the highest 6 7 Gastro-oesophageal Junction point of the convexity is on a level with the sixth left costal cartilage. It then descends downwards 8 The oesophagus communicates with the stom- and forwards, with a slight convexity to the 9 ach via the cardiac orifice, which is situated on left as low as the cartilage of the ninth rib, 1011 the left of the midline at the level of T10. before turning to the right, to end at the pylorus. 1 The intra-abdominal oesophagus (antrum car- Directly opposite the incisura angularis of 2 diacum) is short and conical. After passing the lesser curvature, the greater curvature pre- 3 through the diaphragm it curves sharply to the sents a dilatation, which is the left extremity of 4 left, and becomes continuous with the cardiac the pyloric part; this dilatation is limited on the 5 orifice of the stomach. The right margin of the right by a slight groove, the sulcus intermedius, 6 oesophagus is continuous with the lesser curva- which is about 2.5 cm, from the duodenopyloric 7 ture of the stomach, while the left margin joins constriction. The portion between the sulcus 8 the greater curvature at an acute angle (incisura intermedius and the duodenopyloric constric- 9 cardiaca). tion is termed the pyloric antrum. At its com- 2011 1 Gastroduodenal Junction mencement the greater curvature is covered at its origin by peritoneum continuous with that 2 The pylorus forms the gastric outlet and com- covering the front of the organ. The left part of 3 municates with the duodenum. It lies to the the curvature gives attachment to the gastros- 4 right of the midline at the level of the upper plenic (lineal) , while to its anterior 5 border of L1 and may be identified on the portion are attached the two layers of the greater 6 surface of the stomach by a circular groove omentum, separated from each other by the 7 (duodeno-pyloric constriction). There has long right and left gastroepiploic vessels. 8 been disagreement about various aspects of the 9 structure and function of the “gatekeeper” Surfaces 3011 (Greek pyloros, from pyle = gate and ouros = 1 guard). Willis (1682) introduced the term These change with the degree of gastric disten- 2 “antrum pylori” (Greek antron = cave) to indi- sion. When the stomach is empty they may be 3 cate the part of the stomach adjoining the described as anterior and posterior surfaces, but 4 pylorus; no further demarcation was given. with distension become anterosuperior and 5 postero-inferior. 6 Curvatures 7 Anterosuperior Surface 8 Lesser Curvature (Curvatura This surface is covered by peritoneum and lies 9 Ventriculi Minor) in contact with the diaphragm, which separates 4011 This extends from the cardiac to the pyloric ori- it from the base of the left lung, the pericardium, 1 fices, thus forming the right or posterior border the seventh–ninth ribs, and the intercostal 2 of the stomach. It is a continuation of the right spaces of the left side. The right half lies in rela- 3 border of the oesophagus and lies in front of tion to the left and quadrate lobes of the liver 4 the right crus of the diaphragm. It crosses the together with the anterior abdominal wall. The 5 body of L1 and ends at the pylorus. A well- transverse colon may lie on the front part of this 6 demarcated notch, the incisura angularis, is seen surface when the stomach is collapsed. 7 distally although its position varies with the state 8 of distension of the stomach. Attached to the Postero-inferior Surface 9 lesser curvature are the two layers of the hepato- This surface is covered by peritoneum, except 5011 gastric ligament (lesser omentum). Between over a small area close to the cardiac orifice; this 1 these two layers are the left gastric artery and the area is limited by the lines of attachment of the 2 right gastric branch of the hepatic artery. gastrophrenic ligament, and lies in apposition 311

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111 with the diaphragm, and frequently with the epiploic foramen (of Winslow). The remainder 2 upper portion of the left suprarenal gland. Other of the lesser omentum, extending from the left 3 relations are to the upper part of the front of end of the porta hepatis to the lesser curvature, 4 the left kidney, the anterior surface of the pan- contains the right and left gastric arteries and 5 creas, the left colic flexure, and the upper layer the accompanying veins, as well as lymph 6 of the transverse mesocolon. The transverse glands, lymph vessels and branches of the ante- 7 mesocolon separates the stomach from the rior and posterior vagus nerves. 8 duodenojejunal flexure and small intestine. 9 Thus the abdominal cavity is divided into supra- 1011 and infra-colic compartments. This is formed along the greater curvature of the 1 The anterior boundary of the lesser sac stomach by the union of the peritoneal coats 2 (omental bursa) is formed by this surface. This of the anterior and posterior gastric surfaces. 3 potential space can be accessed via an opening On its left it shortens into the gastrosplenic 4 on the free border of the lesser omentum, omentum, containing the short gastric branches 5 which contains the common hepatic artery, of the splenic artery between its two layers. On 6 the common bile duct and the portal vein (the the right it is continued for 3.0 cm along the 7 foramen of Winslow). lower border of the first part of the duodenum. 8 From its origin the greater omentum hangs 9 Parts of the Stomach down in front of the intestines as a loose apron, 2011 extending as far as the transverse colon, where 1 The stomach is divided into a pyloric part and its two layers separate to enclose that part of the 2 body by a plane passing through the incisura colon. The upper part of the greater omentum 3 angularis on the lesser curvature and the left contains the greater part of the right and left 4 limit of the opposed dilatation on the greater gastroepiploic arteries and their accompanying 5 curvature. The body is further subdivided into veins, lymph vessels, lymph glands, nerve fila- 6 the fundus and cardia by a plane passing hori- ments, fat and areolar tissue. 7 zontally through the cardiac orifice. Distally a 8 plane passing from the sulcus intermedius at Blood supply 9 right angles to the long axis of this portion 3011 further subdivides the pyloric portion. To the 1 right of this plane lies the pyloric antrum. At Arterial Supply (Figure 2.5) 2 operations, a slight groove may be seen in the The coeliac artery, the artery of the foregut, sup- 3 serosal surface at the gastroduodenal junction. plies the stomach by its three branches. It arises 4 A small, superficial subserosal vein, lying within from the front of the aorta between the crura 5 this groove and vertically across the front of the of the diaphragm and is a short wide trunk, 6 gut may be evident. This is the prepyloric vein surrounded by the coeliac lymph nodes and 7 (of Mayo) and drains into the right gastric vein. flanked by the coeliac ganglia of the sympathetic 8 At operation, palpation of this area reveals system. The main branches are the left gastric 9 the pyloric ring between the thick walls of the artery, the hepatic artery and the splenic artery. 4011 pyloric region and the thin walls of the duode- 1 num. The Left Gastric Artery. 2 This runs to the left, gives off an ascending 3 Omenta oesophageal branch, and supplies the upper 4 part of the stomach. However, it may arise 5 Lesser Omentum directly from the aorta (5–6.7%), and may 6 This extends from the inferior and posterior provide one or both of the inferior phrenic 7 surfaces of the liver to the stomach and proxi- arteries or a common trunk for the two. Dupli- 8 mal 3.0 cm of the duodenum. The free border of cate arteries have been reported and sometimes 9 the lesser omentum between the porta hepatis an enlarged (accessory) branch (8–25% of indi- 5011 and the duodenum contains the hepatic artery, viduals) is found. This branch may replace the 1 the portal vein, the common bile duct, lymph left hepatic artery (11–12% of individuals). The 2 glands, lymph vessels and nerves. Behind this left gastric artery turns downwards between 311 free edge is the opening into the lesser sac or the layers of the lesser omentum and runs to the

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Oesophageal branches Oesophageal hiatus of diaphragm 1111 Short gastric arteries 2 Right gastric artery 3 4 5 Left gastric artery 6 Aorta 7 Doeliac artery 8 9 1011 1 2 Splenic artery Hepatic artery 3 4 Gastroduodenal artery Left gastroepiploic artery 5 6 7 8 9 2011 1 Right gastroepiploic artery 2 Superior pancreaticoduodenal artery 3 4 Figure 2.5. The arterial supply of the stomach. (With permission from Clinical Anatomy for Medical Students, 6th edition, RS Snell, p. 207, Fig. 5–14, Lippincott Williams & Wilkins, Philadelphia, 2000.) 5 6 7 8 right along the lesser curvature. Having divided the anterior and posterior gastric walls, anasto- 9 into two parallel branches, these divide further mosing with branches from the right gastro- 3011 supplying the anterior and posterior gastric epiploic artery. The gastroduodenal artery 1 walls. These vessels anastomose freely with descends behind the first part of the duodenum, 2 arteries from the greater curvature. Around the which it supplies by multiple small branches. 3 incisura angularis, the two main branches then The terminal divisions are the superior pancre- 4 anastomose with the two branches of the right aticoduodenal artery, supplying the second part 5 gastric artery. The hepatic artery may arise of the duodenum and head of the pancreas, and 6 directly from the left gastric. the right gastroepiploic artery. The right gas- 7 troepiploic artery passes along the greater cur- 8 The Hepatic Artery vature of the stomach between the layers of the 9 This is the second branch of the coeliac trunk greater omentum and gives off branches to 4011 and passes downwards as far as the first part of the anterior and posterior gastric walls before 1 the duodenum. At the opening into right border anastomosing with the left gastroepiploic artery. 2 of the lesser sac it turns forwards (epiploic fora- 3 men) and curves upwards between the two lay- The Splenic Artery 4 ers of the lesser omentum towards the porta This passes to the left along the upper border of 5 hepatis, to supply the liver. The gastroduodenal the pancreas, behind the peritoneum and the 6 and right gastric arteries are given off as it turns stomach, to supply the spleen. Division into 7 into the lesser omentum. The right gastric artery the terminal branches close to the spleen is 8 passes to the left between the two layers of the called a magistral splenic (~1–2 cm from the 9 lesser omentum, and runs along the lesser cur- hilum), but earlier division is called a distribut- 5011 vature of the stomach before dividing into two ing splenic. During its course it gives off 1 branches that anastomose with the branches of branches to the pancreas; just before entering 2 the left gastric artery. It also gives off branches to the splenic hilum it gives off the short gastric 311

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111 arteries supplying the gastric fornix, and the left 4. Hepatogastric trunk (hepatic and left 2 gastroepiploic artery. The latter passes down- gastric) 3 wards and to the right along the greater curva- 5. Splenogastric trunk (splenic and left 4 ture of the stomach, between the two layers of gastric) 5 the greater omentum, to anastomose with the 6. Coeliacomesenteric trunk (superior 6 right gastroepiploic artery at the mid-portion mesenteric in conjunction with hepato- 7 of the greater curvature. It gives off branches to splenogastric trunk) 8 the anterior and posterior gastric walls, which 9 anastomose with branches of the gastric arter- 7. Coeliacocolic trunk (middle or accessory 1011 ies along the lesser curvature. These arterial middle colic arising from the coeliac 1 arcades ramify through the submucosa, forming trunk is extremely rare). 2 a rich arterial network from which branches A posterior gastric artery, a branch of the 3 arise to supply the mucous membrane. There- splenic, is reported to be present in 48–68% of 4 fore the mucosa is not supplied by end arteries, individuals and forms another source of the 5 with the possible exception of the mucosa along blood supply to the superior portion of the pos- 6 the lessercurvature, which appears to receive its terior gastric wall. It may also supply a superior 7 arterial supply directly from branches of the polar artery to the spleen. These vessels have a 8 right and left gastric arteries. “hidden” posterior location and may be over- 9 Multiple variations of the splenic artery are looked, leading to the possibility of dangerous 2011 reported. Commonly it may divide into two bleeding if damaged. 1 branches that reunite with the splenic vein 2 passing through the loop thus formed. It may Venous Drainage 3 give rise to branches normally derived from 4 other vessels, such as the left gastric, middle The gastric veins are similar in position to 5 colic and left hepatic. The short gastric arteries that of the arteries along the lesser and greater 6 may arise from the gastroepiploic artery, the curvatures. These veins drain either directly 7 splenic artery proper, the splenic branches of or indirectly into the portal system. The major 8 the splenic artery, or any combination thereof. veins are: 9 Similarly the left gastroepiploic artery may orig- 1. Left gastric vein. This runs to the left 3011 inate from one of the splenic branches. In a along the lesser curvature, receiving the 1 third of cases the dorsal pancreatic artery may oesophageal veins below the oesophageal 2 also arise from the splenic artery. hiatus in the diaphragm. It usually drains 3 directly into the portal vein at the supe- 4 Multiple small branches from the hepatic and rior border of the pancreas. 5 gastroduodenal arteries supply the first 2 cm 6 of the duodenum. This part of the duodenum 2. Right gastric vein. This runs along the 7 occupies the embryological transition zone lesser curvature to the right towards 8 between the coeliac and superior mesenteric the pylorus. Posterior to the first part of 9 vascular supplies, and the vessels, which supply the duodenum it joins the portal vein. It 4011 it vary considerably in their size and mode of also receives the prepyloric vein which 1 origin. This variation in blood supply may receives the veins from the first 2 cm of 2 partly account for the frequency of ulceration. the duodenum. 3 The coeliac trunk may lack one or more of its 3. Left gastroepiploic vein. This passes to 4 main branches. These may arise from the aorta the left along the greater curvature and 5 or the superior mesenteric, either indepen- with the short gastric veins drains into 6 dently or in conjunction with another branch. the splenic vein or its tributaries. The 7 The following variations have been reported: splenic vein is joined with tributaries 8 from the pancreas as well as the inferior 9 1. Hepatosplenogastric trunk mesenteric vein; these ultimately form 5011 2. Hepatosplenic trunk (hepatic and the portal vein with the superior mesen- 1 splenic) teric vein. 2 3. Hepatosplenomesenteric trunk (hepatic, 4. Right gastroepiploic vein. This runs to 311 splenic and superior mesenteric) the right as far as the head of the pan-

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creas. Usually it joins the superior part of the body of the stomach. These 1111 mesenteric vein and thus drains into drain into the left gastric nodes lying 2 the portal vein. However, considerable along the left gastric artery. These nodes 3 variations may occur and the right gas- are joined by lymphatics coming down 4 troepiploic may enter the portal vein from the lower part of the oesophagus, 5 directly, or it may join the splenic vein. and their efferents proceed to the coeliac 6 There is no gastroduodenal vein. nodes. 7 • Zone 2. This is from the distal part of 8 Lymphatic Drainage the lesser curvature, including the lesser 9 curvature of the pyloric region, to the 1011 The gastric lymphatics arise in the subepithelial suprapyloric nodes along the right 1 interglandular tissue of the mucosa. They pass gastric artery. Efferent channels from the 2 outwards between the glands to communicate suprapyloric nodes drain to the hepatic 3 with each other in the periglandular plexus and ultimately to the coeliac and aortic 4 and from here the channels proceed into the nodes. 5 subglandular plexus between the glands and • Zone 3. This zone includes the pyloric 6 muscularis mucosae. Short vessels passing part of the stomach as well as the right 7 through the muscularis mucosae form the half of the greater curvature. The lym- 8 submucous plexus. Larger vessels draining this phatics from these areas drain into the 9 plexus then pass through the muscular coats right gastroepiploic nodes in the gastro- 2011 before communicating with the networks colic ligament, lying along the right gas- 1 among the muscle fibres, and opening into the troepiploic vessels, and into the pyloric 2 subserous plexus. From this subserosal plexus, nodes on the anterior surface of the head 3 valved collecting vessels radiate to the curva- of the pancreas. The direction of lymph 4 tures of the stomach to enter the omenta. flow is from above downwards, towards 5 The lymphatics of the stomach can be divided the pylorus and the nodes between the 6 into three systems: head of the pancreas and second part of 7 8 1. Intramural. This consists of three net- the duodenum. From these groups, col- 9 works; submucosal, intermuscular and lectively called the subpyloric glands 3011 subserosal. The submucosal lymphatic 1 channels communicate freely through- 2 out the submucosa of the stomach and 3 to a lesser degree with the submucosal 4 lymphatics of the duodenum; they also 5 communicate freely with the intermus- 6 cular and subserosal networks. 7 2. Intermediary. This consists of numerous Zone 4 Zone 1 8 small channels between the subserosal 9 network and the extramural collecting 4011 systems. 1 3. Extramural. This consists of four major Zone 2 2 zones of lymphatic drainage, corre- 3 sponding to the arterial supply of the 4 stomach. Ultimately all zones drain into 5 the coeliac nodes around the coeliac 6 arterial trunk on the anterior aspect of 7 the aorta. 8 The lymphatic drainage of the stomach can be Zone 3 9 divided into four zones [1]. (Figures 2.6 and 2.7): 5011 Figure 2.6. Zonal drainage of the gastric lymphatics. (With 1 • Zone 1. This comprises the upper two- permission from Last’s Anatomy, 10th edition, p. 245, Fig. 5.27, 2 thirds of the lesser curvature and a large CS Sinnatamby (ed), Churchill Livingstone, London, 2001.) 311

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111 Lymphatics from lower third of oesophagus 2 3 ‘Short gastric’ nodes 4 5 Splenic nodes 6 7 8 Left gastric nodes 9 1011 Right gastric nodes 1 2 Coeliac nodes 3 4 5 Hepatic nodes 6 7 8 Gastroduodenal nodes Left gastroepiploic nodes 9 2011 1 2 Right gastroepiploic nodes 3 4 Figure 2.7. The nodal lymphatics. (With permission from Clinical Anatomy for Medical Students 6th edition, RS Snell, p. 207, Fig. 5 5–15, Lippincott Williams & Wilkins, Philadelphia, 2000.) 6 7 8 (which also drain the first part of the has led to the concept of a three-part autonomic 9 duodenum), efferent vessels pass along control system consisting of cholinergic, adren- 3011 the gastroduodenal artery to the hepatic ergic and peptidergic nerves. These peptides are 1 nodes along the hepatic artery, and unique with a dual localisation in endocrine 2 thence to the coeliac nodes. cells and peripheral nerves in the walls of the 3 • Zone 4. This comprises the left half of gastrointestinal tract. 4 the greater curvature and the gastric 5 fornix. The lymph vessels from here Parasympathetic Nerve Supply 6 pass to the left gastroepiploic nodes, 7 lying along the left gastroepiploic artery. The anterior and posterior vagal trunks and 8 These drain to the pancreatico-lienal their branches form the parasympathetic nerve 9 nodes along the splenic artery, before supply to the stomach. Afferent fibres are also 4011 terminating in the coeliac nodes. present in the vagi. 1 2 Nerves Anterior Vagus 3 This is derived mainly from the left vagus 4 The autonomic nervous system consists of two nerve but also includes fibres from the right 5 components, cholinergic – mostly parasympa- vagus and also some sympathetic fibres from 6 thetic, and adrenergic – mostly sympathetic the splanchnic nerves. It enters the abdominal 7 nerves. However, a third component of the cavity through the oesophageal hiatus in the 8 autonomic system, which is neither cholinergic diaphragm. It is usually single but may be 9 nor adrenergic, has been recognised within the divided into multiple trunks. Having given off 5011 gastrointestinal tract – the peptidergic system. several fine branches to the lower end of the 1 They release a purine nucleotide as the active oesophagus and cardiac part of the stomach, the 2 substance. An increasing number of peptides anterior trunk breaks up into its main branches. 311 that are released have been recognised and this Latarjet’s classic description of the nerves is that

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2 · UPPER GASTROINTESTINAL SURGERY three main sets of branches are present [2] part of the stomach. The second division, 1111 (Figure 2.8) These are: through the hepatic branches, supplies the 2 pylorus and first part of the duodenum, i.e. 3 • Set 1. This consists of four to five direct the “sphincteric” part of the stomach. 4 branches, emanating “one below the 5 other” to supply the upper part of Posterior Vagus 6 the lesser curvature. These nerves do not This is mainly formed by fibres from the right 7 form a plexus. A few filaments from the vagus nerve and enters the abdomen posterior 8 sympathetic supply join these direct to the oesophagus. After entering the abdomen 9 branches via the coeliac plexus. One of it divides into two main branches: the coeliac 1011 the branches in this group is very distinct and the posterior gastric. It then continues 1 and Latarjet called it the “principal ante- along the lesser curvature innervating the pos- 2 rior nerve of the lesser curvature”. It terior gastric wall although only extending to 3 innervates the area from the cardia to the incisura angularis. The lowest branch is 4 the pylorus. sometimes referred to as “the posterior nerve of 5 • Set 2. Branches from the vagal supply to Latarjet”. These nerves do not innervate the 6 the liver. There are usually three to five pylorus and prepyloric region. 7 nerves and they descend in the lesser 8 omentum, on to the superior margin of Sympathetic Nerve Supply 9 the pylorus and first part of the duode- 2011 This is derived almost entirely derived from num. 1 the coeliac plexus. The gastric branches of the • Set 3. These consist of vagal filaments 2 coeliac plexus accompany the vessels supplying from the hepatic branches. These accom- 3 the stomach – the left gastric, hepatic and pany the sympathetic nerves along the 4 phrenic arteries. Others accompany the splenic, right gastroepiploic artery and provide 5 right gastric and gastroepiploic vessels. Fibres vagal fibres to the inferior margin of the 6 from the coeliac plexus accompany the left infe- pylorus. 7 rior phrenic artery, pass anterior to the lower 8 Latarjet divided the nerves of the anterior oesophagus and communicate with the anterior 9 vagus into two distinct functional divisions. The vagus before being distributed to the cardia and 3011 first division, consisting of the direct branches, fornix. Other fibres travel with the left gastric 1 supplies the fornix and body, i.e. the “reservoir” artery and divide into three groups: 2 1. Those passing with the oesophageal and 3 Anterior vagal 4 trunk superior branches of the left gastric Posterior vagal artery to the cardia and proximal part of 5 trunk the body of the stomach. These commu- 6 nicate with branches of the anterior and 7 Coeliac branch posterior vagal trunks. 8 2. Those passing with the main branch of 9 the left gastric artery along the lesser cur- 4011 Hepatic 1 branch vature to supply the anterior and poste- rior surfaces of the body of the stomach 2 Pyloric and antrum. 3 branch 4 3. Those passing through the lesser 5 omentum towards the porta hepatis. 6 These communicate with hepatic 7 branches of the anterior vagal trunk 8 Fibres from the coeliac plexus pass along the 9 Figure 2.8. The anatomy of the nerves of Laterjet. (With hepatic artery and are distributed with its 5011 permission from Clinical Anatomy for Medical Students, 6th branches. They reach the pyloric region of 1 edition, RS Snell, p. 246, Fig. 5–28, Lippincott Williams & Wilkins, the stomach with the right gastric and right 2 Philadelphia, 2000.) gastroepiploic arteries. 311

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111 Preganglionic sympathetic fibres end in the Muscularis Externa 2 coeliac ganglia. The efferent fibres emerging 3 from the coeliac ganglia to accompany the arter- Since the time of Willis (1682), there has been 4 ies are postganglionic. Afferent visceral fibres disagreement about the muscular layers of the 5 from the stomach travel the same course in stomach. The muscularis externa is composed 6 reverse, to ganglion cells in the posterior spinal of smooth, unstriped or involuntary fibres and 7 nerve roots. However, these do not synapse in is made up of three layers: an external longitu- 8 the sympathetic ganglia. dinal, middle circular, and an inner oblique 9 layer. These inner oblique fibres are arranged in 1011 Peptidergic System inverted U-shaped bundles over the anterior 1 Peptidergic cells are derived embryologically and posterior gastric walls. They loop over the 2 from neuroectoderm and are referred to as fornix and extend as far as the incisura angu- 3 APUD cells because they synthesize monoa- laris. Hence these fibres have no effect on 4 mines through a process of amine precursor the distal stomach. In this area, including the 5 uptake and decarboxylation (APUD). They are pyloric region, the muscularis externa is com- 6 also referred to as neuroendocrine cells. A posed of outer longitudinal and inner circular 7 large number of biologically active peptides layers. 8 have been detected in these APUD cells within 9 the gut. These peptides include gastrin, vasoac- Submucous Coat 2011 tive intestinal peptide (VIP), somatostatin, This is a layer of loose areolar tissue with some 1 enkephalin, neurotensin and substance P. elastic fibres that lies between the muscularis 2 Most of these monoamines have several mol- mucosae and the muscularis externa. It is 3 ecular forms or sizes, e.g. gastrin-14, gastrin-17, rich in mast cells, macrophages, lymphocytes, 4 gastrin-34. Some are released into the circula- 5 tion, producing their biological effects in distant eosinophilic leucocytes and plasma cells. 6 target organs (endocrine), whilst others act Within this layer the vessels and nerves divide 7 locally in the vicinity of their site of origin before entering the mucous membrane. It con- 8 (paracrine) and some function as neurotrans- tains arteries, veins, lymphatics and Meissner’s 9 mitters (neurocrine). nerve plexuses. These plexuses form part of the 3011 autonomic nervous system and contain post- 1 Microscopic Anatomy ganglionic sympathetic fibres as well as pre- and 2 postglanglionic parasympathetic fibres. 3 The wall of the stomach and the proximal Unlike the duodenum (glands of Brunner), in 4 3.0 cm of the duodenum are composed of four the stomach the submucous layer does not 5 coats. From without inwards these are the contain any glands. However, it is wider than 6 serous, muscular, submucous and mucous that of the duodenum and extends into the 7 coats. The mucous coat is separated from the rugae of the stomach, forming the core of each 8 luminal contents by a layer of gastric mucus. mucosal fold. 9 4011 Serous Coat (Adventitia) Mucosa 1 This is formed by the peritoneum, which is a This consists of three components, the muscu- 2 thin layer of loose connective tissue covered laris mucosae, the lamina propria, and the 3 with . It is attached to the muscu- epithelial lining. 4 lar coat, except at the greater and lesser curva- 5 tures, where it is continuous with the greater Muscularis Mucosae 6 and lesser omentum respectively. Owing to its 7 peritoneal attachments the proximal 3.0 cm of This is a thin layer of smooth muscle that forms 8 the duodenum, i.e. the proximal half of the first the border between the mucosa and submucosa. 9 part of the duodenum, the duodenal bulb, is It has outer longitudinal and inner circular 5011 mobile. It shares the peritoneal covering of the fibres and fibres extend from the inner layer 1 pyloric region of the stomach and is unlike through the lamina propria around the gastric 2 the remainder of the duodenum, which is glands and toward the gastric lumen. These may 311 retroperitoneal. compress the glands and aid their emptying.

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Lamina Propria Mucosal Zones 1111 This layer consists of a delicate network of col- 2 lagenous and reticular fibres and a few fibrob- The mucous membrane of the entire stomach is 3 lasts or reticular cells. It lies between the lined by glands that open into the gastric pits. 4 muscularis mucosae and the surface epithelial The blind ends of the glands extending into 5 cells with their glands and extends into the area the mucosa are slightly expanded and coiled, 6 between the necks of the glands forming a sometimes dividing into two or three branches 7 basement membrane. It is thin in the fundus (Figure 2.9). The gastric mucosa can be divided 8 and body, where the gastric glands are numer- into three zones, based on the predominant cell 9 1011 ous and closely packed, but is more prominent types within the glands (Tables 2.1 and 2.2). 1 in the cardiac and pyloric zones. It also contains 2 plasma cells, mast cells, eosinophilic leucocytes 3 and lymphocytes. Local accumulations of lym- 4 phocytes may occur in the cardiac and pyloric Surface 5 regions. Strands of smooth muscle from the mucous cells 6 muscularis mucosae traverse this layer, which Gastric pit 7 also contains fine capillaries, lymphatic vessels 8 and nerve fibres. 9 2011 Lamina 1 Epithelial Lining propria 2 A layer of simple columnar cells covers the 3 entire luminal surface of the mucosa. However, Mucous neck cells 4 the surface contains numerous tubular invagi- 5 nations – gastric pits or foveolae. The pits are 6 deeper in the pyloric region than elsewhere in 7 the remainder of the stomach, extending at least 8 halfway to the muscularis mucosae. They are 9 V-shaped, tapering off into the glands that open 3011 into them. 1 The mucus-secreting columnar cells lining 2 the luminal surface and the pits are joined by 3 tight junctions. This may act as one of the mech- Parietal cells 4 anisms to protect the underlying layers against 5 luminal acid. The supranuclear portions of the 6 cells contain dense, homogeneous, spherical or 7 ovoid granules consisting of a type of mucigen, 8 which upon release into the lumen gives rise to 9 the layer of mucus that covers the luminal 4011 surface of the mucosa. In the cells of the gastric 1 pits, the granules become progressively less 2 abundant at deeper levels, and in the bottom of Chief cells 3 the pits they form only a thin layer immediately 4 beneath the cell surface. These cells continue 5 into the necks of the gastric glands. Under phys- 6 iological conditions, the surface mucous cells 7 are continuously desquamated into the lumen Argentaffin cell 8 and are completely replaced every 3 days. Newly 9 formed cells appear in the deeper parts of the Figure 2.9. The gastric glands. (Reproduced with permission 5011 foveolae and in the necks of the glands; these from Applied Physiology for Critical Care, MA Glasby, CL-H 1 are slowly displaced upward and continually Huang, 1st Edition, 1995, Fig. 34.1, p. 337, Butterworth 2 replace those lost on the surface. Heinemann Oxford.) 311

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111 Table 2.1. Summary of the mucosal zones 1. Chief, zymogenic or peptic cells. Their 2 Oxyntic zone These glands produce nearly all the secretory granules contain the precur- 3 enzymes and hydrochloric acid secreted in sors of pepsin. 4 the stomach as well as producing mucus 2. Parietal or oxyntic cells. These are most 5 Cardiac zone These glands secrete mucus numerous in the necks of the glands, but 6 Pyloric zone These glands secrete mucus. They also do not border directly onto the lumen, 7 produce endocrine, paracrine or neurocrine being separated from it by the peptic 8 regulatory peptides by virtue of the APUD cells contained in their glands cells. They are triangular in shape, with 9 the apex projecting towards the lumen 1011 between the sides of two peptic cells. 1 These cells are intensely acidophilic, and Table 2.2. The secretory epithelial cells and their roles 2 contain the gastric proton pump mecha- 3 Four major types of secretory epithelial cells cover the nism that produces the hydrochloric 4 surface of the stomach and extend down into gastric acid. They may also contain intrinsic 5 pits and glands: factor. 6 Mucous cells: secrete alkaline mucus that protexts 3. Neck mucous cells. These cells resemble 7 the epithelium against shear stress and acid the mucous cells of the cardiac and 8 Parietal cells: secrete hydrochloric acid pyloric zones. They lie between the pari- 9 Chief cells: secrete pepsin, a proteolytic enzyme etal cells in the necks of the glands but are 2011 smaller than the surface mucous cells. 1 G cells: secrete the hormone gastrin Their mucigen granules are larger and 2 less dense than those of the surface cells. 3 4. Neuroendocrine cells. These are small, 4 granulated cells that occur sporadically 5 within the gastric mucosa. They synthe- 6 Cardiac Zone sise and store serotonin (5-hydroxy- 7 tryptamine, 5-HT). They are much more 8 This is a narrow, ring-shaped area around numerous in the pyloric zone. 9 the gastro-oesophageal junction, containing the 3011 cardiac glands. These glands have wide lumina 1 and shallow pits and are composed of mucus- Pyloric Zone 2 secreting cells. This zone may contain a few APUD cells that synthesise monoamines. In the This comprises the distal third of the stomach 3 and extends further along the lesser curvature 4 transitional area, where this zone is continuous with the oxyntic zone, a few parietal cells may than the greater. The pits are the deepest within 5 the stomach and extend into the mucous mem- 6 be present. The glands of the cardiac zone secrete mucus. brane for half its thickness. These glands branch 7 more extensively and the tubules are coiled. 8 They contain the following types of cells: 9 Oxyntic Zone 4011 This comprises the proximal two-thirds or 1. Mucous cells. These are similar to the 1 more of the stomach. The glands are known as neck mucous cells of the oxyntic glands 2 fundic glands, proper gastric glands or princi- and constitute the majority of cells in 3 pal gastric glands. One of their most important the pyloric glands. They have a pale cyto- 4 properties is the secretion of gastric acid. The plasm containing indistinct granules, 5 term oxyntic (Greek: acid- forming) is also used the nucleus is often flattened against the 6 as an indicator of this glandular zone. The base of a cell, and short microvilli 7 mucosa here is much deeper than in the cardiac covered by a layer of mucus are present 8 zone and contains a greater number of glands. on the luminal surface. 9 The pits are shallow, but the glands extending 2. Parietal cells. A few isolated parietal cells 5011 from the bottoms of the pits are longer than the may be present among the mucous 1 pits are deep. cells. Parietal cells also occur in the tran- 2 Each principal gastric gland is composed of sitional region between the pyloric and 311 four kinds of cells: oxyntic zones.

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3. Neuroendocrine cells. These cells are important role in protecting the epithelium 1111 much more numerous in the pyloric from acid and other chemical insults. It is made 2 than in the cardiac and oxyntic zones up of glycoprotein subunits bound by disul- 3 although when compared with the phide bonds and forms a water-insoluble gel 4 mucous cells they are still relatively few that is impermeable to H+ ions. Production is 5 in number. With light microscopy they stimulated by luminal acid and vagal activity, 6 have been called enterochromaffin cells. and is increased by prostaglandins. Therefore 7 With electron microscopy their cyto- aspirin non-steroidal anti-inflammatory drugs 8 plasmic granules are clearly visible after (NSAIDs) increase the damage to the stomach 9 staining with chromium or silver salts. by inhibiting prostaglandin formation as well 1011 On the basis of their staining reactions, as by crystallising out in the gastric cells. 1 the cells have been divided into two Bicarbonate is also secreted from parietal 2 types: argentaffin cells, in which the cells. These epithelial barrier cells are very 3 granules reduce silver without pretreat- adherent due to tight junctions between them. 4 ment, and argyrophilic cells, in which a After epithelial disruption the cells migrate 5 reducing substance is required before along the exposed basement membrane to fill 6 the granules will react with silver. in the defect and then stick tightly together. 7 The mucosal zones of the stomach are not Gastric cells also can turn over rapidly in 8 sharply defined, the glands of one region mingle response to injury, as there is a rich mucosal 9 with those of the adjoining region and interme- blood flow providing oxygen, bicarbonate and 2011 diate glands may be present between the nutrients and removing acid. Blood flow is 1 mucosal zones. normally increased simultaneously with acid 2 secretion and is reduced by aspirin and alcohol. 3 4 Physiology Pepsinogen Secretion 5 The chief cells secrete pepsinogens, contained in 6 Gastric Secretions zymogen granules. These are the precursors of 7 the pepsins (proteases) in gastric juice. Once 8 The cells of the gastric glands secrete about 2500 secreted, pepsinogen I is activated by the pres- 9 ml of gastric juice daily. This contains a variety ence of gastric acid into the active protease 3011 of substances and gastric enzymes, whose role pepsin. This is an endopeptidase that is largely 1 is to kill ingested bacteria, aid protein digestion, responsible for the initiation of protein diges- 2 stimulate the flow of bilary and pancreatic juices tion into smaller peptides and polypeptides. It 3 and provide the necessary pH for pepsin to splits the long amino acid chains in the region 4 begin protein degradation (Table 2.3). of peptide bonds containing aromatic amino 5 6 Mucus Secretion acids. It acts at pH 1.5–2.5 and above pH 5.4 is inactivated. It is released mainly by vagal stim- 7 The most abundant epithelial cells are mucus- ulation but also by histamine gastrin secretion, 8 secreting columnar cells, which cover the entire alcohol, cortisol, caffeine and acetazolamide. 9 luminal surface and extend down into the Pepsinogen release may also occur during 4011 glands as “mucous neck cells”. These cells periods of hypoglycaemia and prolonged 1 secrete bicarbonate-rich mucus that coats and increased intracranial pressure. 2 lubricates the gastric surface, and serves an 3 Hormone Secretion 4 5 Table 2.3. Contents of normal (fasting) gastric juice The principal hormone secreted from the 6 Cations: Na+, K+, Mg2+, H+ gastric epithelium is gastrin, a peptide that is 7 – 2– 2– important in control of acid secretion and Anions: Cl , HPO4 , SO4 8 Pepsins: I–III gastric motility (see below). 9 Gelatinase 5011 Mucus Other Secretions 1 Intrinsic factor Gastric epithelial cells secrete a number of other 2 Water enzymes, including an acid-resistant lipase and 311

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111 gelatinase. The lipase hydrolyses triglycerides The H+ is obtained from the ionisation of 2 of medium- and short-chain fatty acids into water, which is then actively transported into 3 glycerol and free fatty acids. the gastric lumen in exchange for K+ that has 4 Intrinsic factor, a glycoprotein secreted by been recycled from the membrane. Chloride 5 parietal cells, is necessary for intestinal absorp- ions are also actively transported into the – 6 tion of vitamin B12. It acts by combining with gastric lumen. The resulting OH ion is neu- 7 the vitamin B12 and is necessary for its attach- tralised by the carbonic acid buffer system to 8 ment to receptors in the terminal ileum. Lack of form a bicarbonate ion that diffuses into the 9 intrinsic factor due to reduction in parietal cell interstitium to be replaced by a further Cl– ion. – – 1011 mass following gastric surgery, or the produc- There is a HCO3 –Cl exchange mechanism 1 tion of antibodies to the cells, called pernicious within the interstitium, but Cl– also enters the 2 anaemia, leads to megaloblastic anaemia. cell with Na+. The carbonic acid is replenished 3 Secretion of intrinsic factor occurs following by the hydration of CO2, which is produced 4 vagal, gastrin or histamine stimulation of the by cellular metabolism from the abundance of 5 parietal cells. carbonic anhydrase within the mucosa. After a 6 meal this results in the development of a nega- 7 tive respiratory quotient; thus arterial CO2 is 8 The Formation and Secretion of higher than venous and the gastric venous – 9 Gastric Acid return is alkaline with a high HCO3 content. 2011 1 Stimulation of the parietal cells results in acid 2 secretion (Figure 2.10). These cells contain Gastric Hormones multiple tubulovesicular structures within their 3 Gastrin 4 cytoplasm that on stimulation move to the 5 mucosal membrane and fuse with it, producing Experiments in the early twentieth century 6 a microvillous appearance that increases the using injected extract of pyloric mucosa stimu- 7 surface area. This results in the presence of lated secretion of gastric acid and pepsinogen. + + + 8 the H -K ATPase that transports the H onto This action was thought to be hormonal in 9 the luminal surface. This secretion is isotonic origin and the active substance was called 3011 with other fluids and its pH is <1. gastrin [3]. However, this theory was initially 1 disputed because this action was similar to that 2 of histamine and the isolation of gastrin was not 3 Gastric Interstitial performed until the late 1960s when two related juice fluid 4 heptadecapeptides were identified from hog

5 – – antral mucosa. These heptadecapeptides were 6 Cl Cl isolated in the pyloric zone. The highest density H O + CO 7 2 3 of gastrin-producing G cells occurs in the distal 8 Carbonic 3.0 cm of the stomach, where the concentration 9 anhydrase of gastrin is 500 times higher than in the body 4011 H2 CO3 of the stomach. The first part of the duodenum 1 also contains a significant level of G cells. These 2 cells originate from neuroectoderm together + + – 3 K H + HCO3 HCO3 with other cells of the APUD series. 4 Microscopically they are piriform in shape A 5 + + – and located in the mid and deep zones of the 6 H H OH pyloric mucosal glands. Electron microscopy 7 shows that they possess microvilli extending 8 into the lumen and that secretory granules are H O 9 2 present in the basal parts of the cells. This allows 5011 for secretion of hormone into the bloodstream 1 Parietal cell in response to luminal stimuli. 2 There are two main types of gastrin, gastrin I 311 Figure 2.10. Hydrochloric acid production from the parietal cell. and gastrin II, produced predominantly by the

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G cells of the pyloric mucosal zone. Other Although initially thought only to suppress 1111 sources are the duodenal G cells, D cells in the the secretion of growth hormone, it also pos- 2 islands of Langerhans in the pancreas, and iso- sesses a wide variety of inhibitory actions on 3 lated G cells in the proximal-acid-producing other pituitary and extrapituitary secretions. It 4 region of the fornix and body of the stomach. suppresses the release of thyroid-stimulating 5 Gastrin 17 (17 amino acids) is the predomi- hormone by the pituitary, the release of gluca- 6 nant form in the pyloric antrum, and is further gon, insulin and exocrine secretions by the 7 subdivided into a non-sulphated gastrin I and a pancreas, the secretion of cholecystokinin, 8 sulphated gastrin II form. There is also a “big” motilin and secretin by the intestine, and the 9 gastrin (G34) containing 34 amino acids and a secretion of gastrin, gastric acid and pepsin by 1011 “big big” gastrin with many more amino acids. the stomach. 1 “Mini” gastrin containing 14 amino acids can Somatostatin suppresses gastric acid secre- 2 also be isolated, but is less active than G17. tion by direct action on the parietal cells of the 3 The common factor in all the molecules is the cardiac and oxyntic mucosal zones. Thus by 4 C-terminal tetrapeptide Tyr-Met-Asp-Phe-NH2. lowering the pH, it also inhibits the secretion of 5 Fasting levels of gastrin are increased gastrin through a feedback loop of low pH sup- 6 by achlorhydria associated with pernicious pressing both gastric acid and gastrin secretion. 7 anaemia, any form of surgical vagotomy, 8 Zollinger–Ellison syndrome (gastrinoma), Vasoactive Intestinal Peptide (VIP) 9 chronic renal failure and massive small bowel 2011 resection. Vasoactive intestinal peptide (VIP) is a polypep- 1 Its physiological and pharmacological effects tide with strong vascular effects isolated from 2 are summarised in Table 2.4. small intestine. It has been subsequently 3 demonstrated in central and peripheral neu- 4 Somatostatin rones, suggesting a neurotransmitter function. 5 In the peripheral autonomic system VIP 6 Somatostatin is a tetradecapeptide that was nerves occur in various regions, including the 7 initially found to inhibit the release of growth superior and inferior mesenteric ganglia, and 8 hormone (GH) from the pituitary gland. the submucous (Meissner’s) and myenteric 9 However, it has subsequently been identified (Auerbach’s) plexuses of the intestinal wall. 3011 widely in the central nervous system, the gas- Structures believed to exert a sphincteric func- 1 trointestinal tract and other organs, with the tion receive a particularly rich supply of VIP 2 highest concentration being found in the pan- nerves, more so than the smooth muscle of 3 creas. In the stomach it is found in the pyloric adjacent regions. Among these are the oesoph- 4 and oxyntic mucosal zones but not in the agogastric junction, the pyloric “sphincter”, 5 cardiac zone. Within the pancreas it is isolated sphincter of Oddi, internal anal sphincter, and 6 from the islet D cells. the openings of the ureters and urethra into the 7 trigonum of the bladder. 8 Table 2.4. The physiological and pharmacological effects of In the stomach these nerves are found around 9 gastrin oxyntic and pyloric mucosal glands. In the duo- 4011 denum VIP (and substance P) is present in 1 Gastrin causes: Parietal cells to stimulate acid secretion Pepsin and intrinsic factor secretion nerves in the villi and muscularis mucosae and 2 Increased mitotic activity in the stomach around blood vessels and between the lobules of 3 and small bowel mucosa Brunner’s glands. Its actions include vasodilata- 4 Contraction of the lower oesophageal tion, thus lowering blood pressure, increased 5 sphincter cardiac output, glycogenolysis and relaxation of 6 The release of insulin, glucagon and smooth muscle. In the stomach there is signifi- 7 calcitonin cant inhibition of gastric secretion associated 8 Pancreatic stimulation and bile flow with VIP release. It probably acts as a neuro- 9 Small bowel secretion transmitter in a paracrine, rather than in an 5011 Gastric and small bowel motility to endocrine, way. The VIP neurones have been 1 increase The gastrocolic reflex shown to be under dual (both vagal and 2 splanchnic) control of the autonomic system. 311

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111 Substance P slightly. Sugars are absorbed to an extent and 2 this varies with the sugar and its concentration. 3 In the gastrointestinal tract nerve fibres and Galactose is most readily absorbed followed by 4 neurones containing substance P (11-amino- glucose, lactose, fructose and finally sucrose. 5 acid peptide) are encountered along its entire Low concentrations of sugars are absorbed very 6 length. However, they are least prominent in the slowly. Ethyl alcohol is absorbed fairly rapidly 7 oesophagus and upper part of the stomach, but as are other lipid-soluble compounds including 8 the highest concentrations occur in the duode- aspirin and other NSAIDs. These substances are 9 num. These neurones are located mainly in the also well-recognised causes of gastric irritation 1011 myenteric plexuses. Here the nerve fibres richly and their use (especially overuse) is commonly 1 innervate the circular musculature. However, associated with development of gastritis and 2 the longitudinal muscle contains only a sparse gastric ulcers. The stomach absorbs water 3 network of fibres. Substance P may also be readily with half the ingested volume absorbed 4 vasoactive as the nerve fibres are also found in in about 20 minutes. 5 close contact with blood vessels. 6 In the stomach substance P is found in the Regulation of Gastric Secretion 7 oxyntic zone in a few, thin fibres only and in 8 fibres interconnecting in the pyloric antrum. In and Motility 9 the duodenum substance P (and VIP) is present Gastric function is classified into three phases in 2011 in nerve networks in the villi as well as in the which secretory and motor activities are closely 1 muscularis mucosae and around blood vessels. linked. 2 It has been found to cause contraction of the 3 muscularis mucosae. Control of Gastric Acid Secretion 4 Acid secretion may be divided into two 5 Other Gastric Hormones phases interprandial, when acid secretion is 6 Encephalin 1–5 mmol/h, and stimulated where acid secre- 7 These are endogenous opiate-like compounds tion is maximally 20–35 mmol/h. This is further 8 forming two pentapeptides, endorphin and subdivided into cephalic, gastric and intestinal 9 enkephalin. They can be isolated throughout phase. Normal subjects maximally secrete 3011 the gastrointestinal tract, although the highest 0.5 mmol/h/kg body weight) 1 concentration is found in the pyloric antrum. 2 The role of these peptides is not clear. Interprandial 3 Resting secretion occurs in the absence of all 4 Galanin intestinal stimulation. However, to abolish 5 Galanin may act as a regulatory factor in the all gastic acid secretions, a bilateral vagotomy 6 control of gastrointestinal motility. It is usually (truncal) and excision of the pyloric antrum 7 found in close association with VIP-containing would be necessary. 8 nerves. 9 Stimulated Secretion 4011 Neurotensin The Cephalic Phase (Figure 2.11). The cephalic 1 This is secreted by N cells in ileal mucosa. phase is initiated by seeing, smelling and antic- 2 However, small traces occur in the pyloric ipating food. These influences act on the limbic 3 mucosal zone. The neurotensin level rises after system and hypothalamus and these nuclei 4 a meal, but its function is still unclear. It may stimulate the dorsal motor nucleus of the vagus. 5 inhibit pentagastrin-stimulated gastric acid and This stimulus is transmitted thought the vagus 6 pepsin secretion after a meal as well as delaying nerve to the enteric nervous system, resulting in 7 gastric emptying, resulting in the controlled release of acetylcholine in the vicinity of G cells 8 release of chyme into the small intestine. and parietal cells. Binding of acetylcholine to 9 its receptor on G cells induces secretion of the 5011 hormone gastrin, which, in concert with acetyl- 1 Absorption from the Stomach choline and histamine, stimulates parietal cells 2 The stomach absorbs very few substances. Fats to secrete small amounts of acid. Additionally, 311 are not absorbed. Polypetides are absorbed only a low level of gastric motility is induced.

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G cell 1111 2 3 ACh (N) 4 5 6 ACh (M) GRP 7 X (vagus) 8 Gastrin Thought Sight 9 Smell 1011 X (vagus) Taste 1 of food 2 3 4 Parietal ACh ACh 5 cell (M) (N) 6 a HCl 7 8 Distension of 9 pyloric antrum 2011 1 2 X (vagus) Amino acids 3 SMP 4 MP X (vagus) 5 6 Distension 7 G cell fundus and body of stomach 8 9 3011 Gastrin 1 SMP 2 MP X (vagus) 3 4 X (vagus) Parietal 5 cell 6 7 8 b HCl 9 4011 Figure 2.11. The cephalic (a) and gastric phases (b) of acid secretion. X, vagus; ACh (N), acetylcholine (nicotinic receptor); ACh (M), 1 acetylcholine (muscarinic receptor); GRP, gastrin-releasing peptide; SMP, submucous plexus; MP, myenteric plexus. (Reproduced with 2 permission from Applied Physiology for Critical Care, MA Glasby, CL-H Huang, 1st edition, 1995, Fig. 34.3, p. 340, Butterworth 3 Heinemann, Oxford.) 4 5 6 The release of acetylcholine and bombesin mine) stimulated by the release of histamine 7 (gastrin-releasing peptide) initiates gastrin from mast cells close to the parietal cells. The 8 release from the G cells. The gastrin passes via histamine sensitises the parietal cell to the 9 the portal circulation to stimulate the parietal action of gastrin and acetylcholine. The H2 5011 cells. It potentiates the effect of vagal stimula- receptor blockers (cimetidine and ranitidine) 1 tion, thus resulting in increased acid secretion. act on these receptors, thus reducing acid 2 The parietal cells also have H2 receptors (hista- secretion. 311

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111 The Gastric Phase (Figure 2.11). When food Collectively, enteric hormones and the 2 enters the stomach several additional factors enterogastric reflex put a strong brake on gastric 3 come into play, foremost among them being secretion and motility. As the ingesta in the 4 distension and mucosal irritation. Distension small intestine is processed, these stimuli 5 excites stretch receptors and irritation activates diminish, the damper on the stomach is 6 chemoreceptors in the mucosa. These events are released, and its secretory and motor activities 7 sensed by enteric neurones, which secrete addi- resume. 8 tional acetylcholine, further stimulating both G 9 cells and parietal cells. Gastrin from the G cells Gastric Motility and Hunger Contraction 1011 feeds back to the parietal cells, stimulating it 1 even further, mediated by vagovagal reflexes Resting Electrical Activity Within the 2 through the dorsal motor nucleus. Additionally, Stomach 3 activation of the enteric nervous system and A pacemaker in the longitudinal muscle close to 4 release of gastrin cause vigorous smooth muscle the greater curve of the cardia controls the fre- 5 contractions. The net result is that secretory and quency of contractions. It depolarises at a rate 6 motor functions of the stomach are fully turned of 3/minute, and each wave – the gastric slow 7 on – acid and pepsinogen are secreted, pepsino- wave (or basal electrical rhythm) – increases 8 gen is converted into pepsin and vigorous sodium permeability across the cell membrane 9 grinding and mixing contractions take place. and the impulse spreads through the longitudi- 2011 However, acid secretion may be inhibited nal and circular muscles via low resistance junc- 1 during the gastric phase by local mechanisms. tions. These junctions make up about 12% of the 2 If the antral pH falls to 1–1.5, inhibition of membrane surface. 3 gastrin release occurs. This is mediated by two In the empty stomach (approximately 50 ml 4 mechanisms – the effect of luminal acid on the volume), the resting potential is low (–50 mV) 5 microvilli of the G cell and the stimulation of and although the waves pass at a rate of 6 somatostatin from D cells in the antrum, which 3/minute, not all of these waves are equal in 7 acts inhibits directly on the G cells and parietal amplitude and do not set off an action poten- 8 cells by a local paracrine effect. tial. However, when the critical firing level is 9 passed the resulting action potential sets off an 3011 The Intestinal Phase. As chyme is emptied into excitation–contraction coupling and a contrac- 1 the small intestine control is necessary to limit tion spreads throughout the stomach. 2 gastric empting. This probably allows the duo- 3 denum time to neutralize the acid and efficiently Intragastric Pressure 4 absorb incoming nutrients. Hence, this phase of Intragastric pressure remains relatively con- 5 gastric function is dominated by the small intes- stant at 5 mmHg (0.7 kPa) because as food 6 tine sending inhibitory signals to the stomach passes into the stomach, the musculature of the 7 to slow secretion and motility. Two types of fundus and body relaxes via a feedback loop – 8 signals are used: nervous and endocrine. Dis- receptive relaxation. In addition, as wall tension 9 tension of the small intestine, as well as chemi- rises so does the radius, thus keeping the intra- 4011 cal and osmotic irritation of the mucosa, is gastric pressure constant (law of Laplace). 1 transduced into gastric-inhibitory impulses However, above 1000 ml, the radius cannot 2 in the enteric nervous system – this nervous increase in size so the wall tension and intra- 3 pathway is called the enterogastric reflex. Fat gastric pressure rises. 4 and carbohydrate in the chyme cause the release Thus volumes above 1000 ml lead to stimula- 5 of GIP (gastric inhibiting peptide), which tion of stretch receptors within the stomach 6 inhibits gastrin secretion. Secondly, enteric hor- wall. 7 mones such as cholecystokinin and secretin are 8 released from cells in the small intestine and Gastric Tone 9 contribute to suppression of gastric activity. In most instances gastric hypotonicity is of 5011 Gastrin also causes the release of calcitonin idiopathic origin and presumably of little clini- 1 from the C cells of the thyroid gland, which cal significance. More severe degrees, some- 2 inhibits further release of gastrin via a feedback times progressing to acute gastric dilatation, 311 loop. may occur in a variety of conditions, e.g. post-

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2 · UPPER GASTROINTESTINAL SURGERY operatively, after severe trauma and in elec- distension – via a vagal feedback loop, increased 1111 trolyte disturbances. duodenal osmolarity – via osmoreceptors, the 2 A short, transversely situated, “steerhorn” presence of acid in the duodenum – via a local 3 stomach, on the other hand, is now known to be enteric neuronal pathway, and the release of GIP 4 the result of gastric hypertonicity. In these cases and chalesystokinin by fat in the duodenum. 5 immediate emptying of liquid barium usually In addition, sympathetic stimuli reduce 6 commences in the erect position, before the gastric emptying via the limbic and hypothala- 7 onset of peristalsis or cyclical contractions of mic nuclei. 8 the pyloric sphincteric cylinder. 9 Hunger Contractions 1011 Control of Gastric Motility When the stomach is empty there can be periods 1 of increased gastric motility several hours after 2 As the volume of the stomach passes 1000 ml a meal. With stimulation of the hypothalamus 3 the intragastric wall tension rises. This activates the individual feels hungry. This leads in a 4 stretch receptors, again through a vagovagal rise in vagal stimulation and causes increased 5 reflex arc, which cause depolarisation in the gastric motility. Contraction of the empty stom- 6 longitudinal and circular smooth muscles. ach leads to a rise in intragastric pressure that 7 However, this leads to every slow wave being can stimulate tension and pain receptors in the 8 above the critical firing level. An action poten- gastric wall, simulating mild pain or discomfort. 9 tial is therefore propagated with each slow wave 2011 and a contraction passes from the fundus Changes in Physiology and 1 through the body to the pyloric antrum. These 2 now occur three times per minute and the force Function Related to Disease 3 of the contraction also increases along the 4 stomach. Initially low in the fundus, where Nausea, Retching and Vomiting 5 the muscular layer is thinnest, at the pylorus The mechanism of vomiting in mammals is 6 intragastric pressure may reach 40–50 mmHg complex and in spite of experimental studies 7 (5.3–6.7 kPa). some aspects are still not fully understood. It is 8 The pyloric sphincter is not a high-pressure usually accepted that the vomiting sequence 9 zone and is open in the resting phase. As a con- consists of three successive phases: nausea ini- 3011 traction wave arrives it contracts. However, tially, followed by retching, often leading to 1 since the canal was open before the rise in intra- forcible expulsion of gastric contents through 2 gastric pressure some of the chyme passes the mouth, i.e. ejection or vomiting. During 3 through the pylorus (5–15 ml) before the gastric these stages a coordinated sequence of move- 4 slow wave reaches it. When the slow wave ments occurs, involving, amongst others, the 5 reaches the antrum and pylorus they contract upper small bowel, stomach, oesophagus, 6 together – terminal contraction, and the pylorus diaphragm, voluntary abdominal muscles and 7 closes. This phase of the contraction acts to glottis. The complex movements of the ejection 8 recirculate or “churn” the gastric contents. Only phase occur with extreme rapidity. The action is 9 when duodenal pressure drops due to relaxation controlled by the vomiting centre present bilat- 4011 does the pyloric pressure drop. erally in the medulla oblongata at the level of 1 the olivary nuclei, and close to the tractus soli- 2 Factors Modifying Gastric Motility tarius at the level of the dorsal vagal nuclei. A 3 Both vagal stimuli and gastrin increase antral complex pathway mediated via efferents in the 4 motility and influence emptying. However, after fifth, seventh, ninth, tenth and twelfth cranial 5 a truncal vagotomy, the force of the antral pump nerves leads to contraction of the intercostal 6 is reduced and gastric emptying time is pro- muscles, diaphragm and abdominal muscles. 7 longed, hence the need for a drainage procedure Afferent impulses pass via the vagus (tenth 8 after a truncal vagotomy. cranial nerve) and sympathetic nerves to the 9 The force of the pump is also moderated by vomiting centre. However, other impulses reach 5011 the volume and composition of the chyme. via the labyrinth, the limbic system and the 1 Hormonal and neuronal mechanisms also reg- chemoreceptor trigger zone. This is situated in 2 ulate gastric emptying. These include duodenal the lateral wall of the fourth ventricle. 311

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THE ANATOMY AND PHYSIOLOGY OF THE STOMACH

111 Nausea is the conscious recognition of the tion of the hyoid bone, which opens the upper 2 subconscious excitation of an area known as oesophageal sphincter and closes the glottis, the 3 the medulla oblongata closely associated with soft palate rises to close the posterior nares and 4 the vomiting centre and can be initiated by then a downward contraction of the diaphragm 5 impulses from the gastrointestinal tract, the with simultaneous contraction of the abdominal 6 lower brain in association with motion sickness wall muscles raises intragastric pressure. With 7 or cortical impulses. Vomiting without the pro- the sudden relaxation of the lower oesophageal 8 dromal phase of nausea can occur, indicating sphincter, expulsion occurs. 9 that only certain portions of the vomiting centre 1011 are associated with it. 1 Questions 2 The Process of Vomiting 3 If the upper gastrointestinal tract becomes 1. Outline congenital abnormalities. 4 excessively irritated, over-distended or over- 2. Describe lymph drainage of stomach and 5 stimulated, vomiting may occur. Initially anti- relate this to surgical excision. 6 peristaltic waves begin and may occur as far 7 down as the ileum. These waves travel at 2–3 3. Describe nerve supply. 8 cm/s; thus within a few minutes a large volume 4. Name cells of the gastric wall and their 9 of intestinal contents may be pushed back into functions. 2011 the stomach and duodenum causing distension. 1 This may result in retching. 2 3 Retching Phase References 4 The retching phase is characterized by a series 1. Eker R. Carcinomas of the stomach: investigation of the 5 of violent spasmodic abdomino-thoracic con- lymphatic spread from gastric carcinomas after totle 6 tractions with the glottis closed. During this and partial gastrectomy. Acta Chir Scand 1951;101: 7 time the inspiratory movements of the chest 112–26. 8 wall and diaphragm are opposed by the expira- 2. Latarjet A, Wertheimer P. L’énervation gastrique. Données expérimentales. Déductions cliniques. J Méd 9 tory contractions of the abdominal muscula- Lyon 1921;36:1289–302. 3011 ture. At the same time movements of the 3. Edkins J. The chemical mechanism of acid secretion. 1 stomach and its contents take place. Whereas a J Physiol 1906;34:133–44. 2 patient will complain of disagreeable sensations 3 during nausea, speech is not possible during 4 retching. The characteristic movements furnish 5 a ready diagnostic sign of the retching phase. Further Reading 6 The Vomiting Act Sinnatamby CS (ed). Last’s anatomy. Regional and applied. 7 10th edn. London: Churchill Livingstone, 2001. 8 Once the act of vomiting has been triggered, a Snell RS Clinical anatomy for medical students. 6th ed. 9 deep inspiratory movement occurs, with eleva- Philadelphia: Lippincott Williams & Wilkins, 2000. 4011 1 2 3 4 5 6 7 8 9 5011 1 2 311

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