CLINICAL ANATOMY OF THE ESOPHAGUS, STOMACH, DUODENUM, LIVER, BILIARY TRACT AND PANCREAS

Prof.Dr. Turgut IPEK, M.D.

ESOPHAGUSThe esophagus is a muscular tube that startsas the continuation of the pharynx and ends as the cardia of the stomach.The esophagus is firmly attached at its upperend to the cricoid cartilage and at its lowerend to the diaphragm.

Three normal areas of esophagus narrowingare evident on the barium esophagogram orduring esophagoscopy. The uppermostnarrowing is located at the entrance into theesophagus and is caused by thecricopharyngeal muscle. Its luminal diameteris 1.5 cm, and it is the narrowest point of theesophagus.

The middle narrowing is due to an indentationof the anterior and left lateral esophageal wallcaused by the crossing of the left main stembronchus and aortic arch. The luminaldiameter is 1.6 cm.

The lowermost narrowing is at the hiatus of the diaphragm and is caused by thegastroesophageal sphincter mechanism. Theluminal diameter at this point variessomewhat depending on the distention of theesophagus by the passage of food, but has been measured at 1.6 to 1.9 cm.

The cervical portion of the esophagus is approximately 5 cm long and descends between thetrachea and the vertebral column from the level of siwth cervical vertebrae to the level of the interspacebetweenthe first and second thoracic vertebraeposteriorly or of the suprasternal notchanteriorly.Laterally, on the left and right sides of thecervical esophagus are the carotid sheaths and thelobes of the thyroid gland.

The thoracic portion of the esophagus is approximately 20 cm long. It starts at thethoracic inlet. In the upper portion of thethorax, it is in intimate relationship with theposterior wall of the trachea and theprevertebral fascia. Just above the trachealbifurcation, the esophagus passes to the rightof the aorta.

Dorsally, the thoracic esophagus follows thecurvature of the spine and remains in close contactwith the vertebral bodies. From the eighth thoracicvertebrae downward, the esophagus moves verticallyaway from the spine to pass through the hiatus of thediaphragm. The thoracic duct passes through thehiatus of the diaphragm on the anterior surface of thevertebral column behind the aorta and under the rightcrus. In the thorax the thoracic duct lies dorsal to theesophagus between the azygos vein on the right andthe descending thoracic aorta on the left.

The abdominal portion of the esophagus is approximately 2 cm long. It starts as theesophagus passes through the diaphragmatichiatus and is surrounded by thephrenoesophageal membrane.

The musculature of the esophagus can be dividedinto an outer longitudinal and an inner circular layer. The upper 2 to 6 cm of the esophagus contains onlystriated muscle fibers. From there on smooth musclefibers gradually become more abundant. Most of theclinically significant esophageal motility disordersinvolve only the smooth muscle in the lower two-thirds of the esophagus. When a surgical esophagealmyotomy is indicated, the incision needs to extendonly this distance.

Contraction of the longitudinal muscle fibersshortens the esophagus. The circular musclelayer of the esophagus is thicker than theouter longitudinal layer.

The cervical portion of the esophagus receives itsmain blood supply from the inferior thyroid artery. The thoracic portion receives its blood supply fromthe bronchial arteries, with 75 percent of individualshaving one right-sided and two left-sidedbranches. Two esophageal branches arise directlyfrom the aorta. The abdominal portion of theesophagus receives its blood supply from theascending branch of the left gastric artery and frominferior phrenic arteries.

Blood from the cappillaries of the esophagusflows into a submucosal venous plexus andthen into a periesophageal venous plexus fromwhich the esophageal veins originate. In thecervical region, the esophageal veins emptyinto the inferior thyroid vein; in the thoracicregion into the bronchial, azygos, orhemiazygos veins; and in the abdominalregion into the coronary vein.

The parasympathetic innervation of the pharynx andesophagus is provided mainly by the vagus nerves.The cricopharyngeal sphincter and the cervicalportion of the esophagus receive branches frombothrecurrent laryngeal nerves, which originate from thevagus nerves

- the right recurrent nerve at the lower margin of thesubclavian artery, the left at the lower margin of theaortic arch.

The lymphatics located in the submucosa of the esophagus are so dense and interconnectedthat they constitute a single plexus.In hte upper two-third of the esophagus thelymphatic flow is mostly cephalad, and in thelower third caudad.

The efferent lymphatics from the cervicalesophagus drain into the paratracheal anddeep cervical lymph nodes, and those fromthe upper thoracic esophagus empty mainlyinto the paratracheal lymph nodes. Efferentlymphatics from the lower thoracic esophagusdrain into the subcarinal nodes and nodes in the inferior pulmonary ligaments.

STOMACHThe fundus is lined by a highly specializedepithelium that secretes HCL, pepsin , and intrinsicfactor. The mucosa of the antrum participates in theprocess of gastric acid secretion by releasing thesecretagogue, gastrin, into the circulation.The stomach, therefore, can be considerer as twoorgans: its proximal portiın is designed for storageand digestion, and its distal part is adapted to the role of mixing and evacuation.

Blood Supply and LymphaticsThe lesser curve of the stomach is supplied primarilyby the left gastric artery, which arises from the celiacaxis. The right gastric artery, arising from theascending hepatic artery, is usually a small vesselthat provides branches to the first part of theduodenum and the pylorus. Right and leftgastroepiploic aretries arise from the gastroduodenaland splenic arteries, respectively. They from an arcade along the greater curve, the right providingblood to the antrum and the left supplying the lowerportion of the fundus.

The short gastric arteries arising from thesplenic artery are small and relativelyinsignificant in terms of the amount of bloodthat they deliver to the most proximal portionof the body of the stomach.

The lymphatic drainage of the stomach follows thedistribution of the blood supply.Lymph from the upper lesser curvature of thestomach drains into the left gastric and paracardialnodes. The antral segment on the lesser curve drainsinto the right suprapancreatic nodes. Lesions high on the greater curvature flow into the left gastroepiploicand splenic nodes, while the distribution of flowalong the right gastroepiploic enters nodes at thebase of the vascular pedicle serving this area.

InnervationMotor aspects as well as secretory aspects of gastricfunction are controlled by the autonomic nervoussystem. The vagus nerves provide a predominantpart of this innervation. Each vagus has a singlebranch within the abdomen: the hepatic arising fromthe left anterior vagus, and the celiac from the rightposterior vagus. Each vagus terminates in theanterior and posterior nerves of Laterjet, respectively.

Knowledge of the anatomy of these nerveshas resulted in a new technique, highlyselective vagotomy, for treatment of pepticulcer. In this procedure, the antral branchescalled the “crow’s foot” are preserved, whilethe more proximal branches are divided as they enter the stomach.

The right posterior vagus may occasionallygive off a small branch that courses to the leftbehind the esophagus to join the cardia. Thisbranch has been termed the “criminal nerve of Grassi” in recognition of its important role in the etiology of recurrent ulcer when it is leftundivided.

MorphologyThe gastric glands consist of six major celltypes: surface, mucous neck, progenitor, chief, parietal, and endocrine cells.

SphinctersThe entrance of ingestants into the stomach is controlled by a highly specialized 5-cm areaof smooth muscle, termed the loweresophageal sphincter. This sphincter, whichpresents a high-pressure zone between theesophagus and stomach, relaxes to allow thepassage of foodstuffs. It then contracts toprevent the regurgitation of gastric contentsinto the esophagus.

SMALL INTESTINEThe small bowel extends from the pylorus tothe cecum. Carefulestimates provide a duodenal length of 20 cm, a jejunal length of 100 to 100 cm, and an ileal length of 150 to160 cm. The jejunoileum extends from theperitoneal fold that supports the duodenal-jejunal junction (the ligament of Treitz) downward to the ileocecal valve.

The jejunum has a larger circumference and is thicker than the ileum, and it may be identified at operation because of this and also because the mesenteric vessels usually from only one or two arcades and send out long straight vasa recta to the mesenteric border of jejunum. By contrast, the blood supply to the ileum may have four or five separate arcades, the vasa recta are shorter, and, most important, there is usually much more fat in the mesentery of the ileum than in that of the jejunum.

Except for the proximal duodenum, which is supplied by branches of the celiac axis, theblood supply of the small bowel is entirelyfrom the superior mesenteric artery, which is the second major branch of theinfradiaphragmatic aorta. The superiormesenteric artery also supplies the appendix, cecum, and ascending and proximaltransverse colons.

Venous drainage of the segments of the smallbowel is in parallel with the arterial supply. The superior mesenteric vein joins the splenicbehind the neck of the pancreas to from theportal vein.

The small bowel contains major deposits of lymphatic tissue, particularly in the Peyer’spatches of the ileum.The small bowel mucosa is characterized bytransverse folds (plicae circulares or valves of Kerckring), but actually these are absent in the duodenal bulb and in the distal ileum.

The innervation of the small bowel comes bothsympathetic and parasymphatetic systems. Parasympathetic fibers come from the vagus andtraverse the celiac ganglia. They affect secretion andmotility and probably all phases of bowel activity. Vagal afferent fibers are present but apperently do not carry pain impulses. The symphatetic fiberscome from the three sets of splanchnic nerves. Painfrom the intestine is mediated through general visceral afferent fibers in the symphatetic system.

HistologyThe wall of the small bowel has four layers- theserosa, the muscularis, the submucosa, and themucosa.The crypts of Lieberkühn contain four types of cells-goblet cells that secrete mucus, enterochromaffincells whose endocrine function is unknown, Panethcells that secrete zymogen granules and whosefunction is also unknown, and undifferentiatedepithelial cells whose function is to provide for cellrenewal. The major known functions of the villi aredigestion and absorbtion.

LIVERTrue division into right and left lobes is in line withfossa for the inferior vena cava posteriorly and thegallbladder fossa anteroinferiorly.

Biliary DrainageThe anterior and posterior sectoral ducts in the rightlobe join to form the right hepatic duct, while themedial and lateral segmental ducts in the left lobeterminate in the left hepatic duct in the porta hepatis.

Blood SupplyThe afferent blooh supply to the liver arisesfrom two sources: (1) the hepatic artery, which carries oxygenated blood and accountsfor approximately 25 percent of hepatic bloodflow, and (2) the portal vein, which accountsfor approximately 75 percent of hepatic bloodflow and drains the splanchnic circulation.

The common hepatic artery originates fromthe celiac axis and, after contributing thegastroduodenal and right gastric artery, ascends in the hepatoduodenal ligament to theleft of the common bile duct and anterior in the portal vein. It bifurcates into a right andleft branch to the left of the main lobarfissure.

Intrahepatic anastomoses between the rightand left hepatic arteries do not occur. Thecystic artery is usually an extrahepatic branchof the right hepatic artery.The portal venous system contains no valves. It returns to the liver the blood that the celiac, superior mesenteric, and inferior mesentericarteries supply to the gastrointestinal tract, pancreas, and spleen.

In the porta hepatis the vein divides into twobranches, which course to each lobe. Theaverage length of the main portal vein is 6.5 cm, and the average diameter is 0.8 cm.The hepatic venous systembegins as a centralvein of the liver lobule and represents the onlyvessel in human beings into which thesinusoids empty. The major hepatic veins areclassified as right, left and middle.

In human beings there are no valves in the hepatic venous system. Total hepatic blood flow can measured by means of hepatic vein catheterization and the use of the Fickprinciple. The average value is 1500 mL/min/1.73 m2 of body surface.

GALLBLADDER AND EXTRAHEPATIC BILIARY SYSTEMGallbladder

The gallbladder is a saclike, hollow organ measuringabout 10 cm in length that lies in a fossa on theundersurface of the liver.The gallbladder is attached to the liver by looseareolar tissue rich in small blood vessels andlymphatics.The gallbladder has a fundus, body, infundibulum, and neck.

The infundibulum, also known Hartmann’s pouch, is a small bulbous diverticulum, typically lying on thainferior surface of the gallbladder.The cystic duct is the tubular structure that connectsthe gallbladder to the common bile duct. The so-called spiral valves of Heister are situated within thecystic duct; they appear to play an important role in the passage of bile into and out of the gallbladder.

The major blood supply to the gallbladder is throughthe cystic artery, which is typically a branch of theright hepatic artery.The cystic artery runs close to the cystic duct in thetriangle of Calot. This anatomic area is defined bythe edge of the liver, the common hepatic bile duct, and cystic duct. The venous drainage of thegallbladder is variable and generally does not runparallel with the arteries. Drainage is into the rightbranch of the portal vein.

The wall of the gallbladder is richlyinnervated with sympathetic andparasympathetic nerve fibers. The sensationof pain is mediated by visceral, sympatheticfibers. The motor stimulus for gallbladdercontraction is carried through the vagusnerves and the celiac ganglion

Bile DuctThe biliary tract has its origin within the small intra hepaticbile ducts. Using the classic definitions, the extrahepaticbiliary tract begins with the right and left hepatic duct. Thecommon hepatic duct makes up the left border of the triangleof Calot, and is continuous with the common bile duct, andthe division, which is fairly arbitrary, occur at the level of thecystic duct. The common bile duct is approximately 8 cm in length and courses from the junction with the commonhepatic duct, through the substance of the pancreas andultimately drains into the duodenum. The common bile ductempties into the duodenum at the papilla of Vater.

AnomaliesAnomalies of the gallbladder include ectopiclocations, disorders of number of gallbladders(agenesis or multiple), or defects in gallbladder formation and development. Perhaps the most common anomaly is that of the gallbladder being located intrahepatically.

PANCREASIt is arbitrarily divided into a head with its incinateprocess, a neck, a body, and a tail.There are usually no tributaries between the anteriorsurface of the superior mesenteric and portal veinsand the posterior surface of the neck.Bile and Pancreatic DuctsThe common bile duct passes posterior to the headof the pancreas on its way to the duodenum, and is partially ar completely covered by the pancreas in over 70 percent of cases.

The main pancreatic duct (Wirsung) arises in the tail of the pancreas and enters theduodenal wall caudal to the bile duct.The ampulla of Vater is a dilatation of thecommon pancreaticobiliary channel within thepapilla and is distal to the junction of the twoducts. An ampulla is present in about 90 percent of cases, and it usually is quite short(5 mm or less).

The accessory pancreatic duct (Santorini) usuallydrains the anterior and superior portion of the headof the pancreas. In 60 percent of cases, it enters theduodenum about 2 cm cranial and slightly anterior tothe papilla of Vater, through the minor papilla.Numerous variations of ductal anatomy occur, but only pancreas divisum, which occurs in up to 10 percent of normal people, mat occasionally cause disease.

Blood SupplyThe blood supply to the head of the gland comesfrom the superior pancreaticoduodenal artery, whicharises from the gastroduodenal artery and dividesinto anterior and posterior branches.The dorsal pancreatic artery usually arises from theproximal 2 cm of the splenic artery and, aftersupplying some branches to the head, passes to theleft to supply the body and tail of the gland. There it is called the transverse pancreatic artery. Numerousbranches from the splenic artery anastomose with thetransverse artery and also supply the body and tail.

The head of the pancreas is drained by veins which parallelthe arteries. The superior pancreaticoduodenal, rightgastroepiploic, and a colic vein join to form a majorgastrocolic trunk on the anterior surface of the head. Thistrunk empties into the superior mesenteric vein just before it passes under the neck of the pancreas, and may be a usefulanatomic landmark to identify the vessel during pancreaticsurgery.Venous drainage of the body and tail of the pancreas is directly to the splenic vein, and through the inferiorpancreatic vein to the inferior or superior mesenteric veins.

LymphaticsLymphatic drainage of the pancreas is richand, in general, follows venous drainage in alldirections. The superior nodes, loceted alongthe superior border of the pancreas, collectlymph from the anterior and superior upperhalf of the gland.

The inferior nodes, along the inferior marginof the head and body, drain the anterior andposterior lower half. Anterior nodes drain theanterior surface of the head of the pancreas. They are located beneath the pylorus, anteriorly in the groove between the pancreasand duodenum, and the root of the mesenteryof the transverse colon.

Posterior nodes drain the posterior surface of thehead. They are found posteriorly in the groovebetween the pancreas and duodenum, along thecommon bile duct, the aorta as high as the origin of the celiac axis artery, and at the origin of thesuperior mesenteric artery. Splenic nodes drain thetail of the pancreas. Lymphatic drainage is importantin regard to the spread of pancreatic cancer, whicharises most commonly in the head of the gland.

NervesThe pancreas receives symphatetic fibers via thesplanchnic nerves and parasymphatetic innervationby way of the vagus nerves (celiac division of theposterior vagus trunk). The splanchnic nerves alsocarry visceral afferent pain fibers which pass throughthe celiac plexus and ganglia. I t is not knownwhether afferent fibers of the vagus are involved in pancreatic pain. Because pancreatic cancer andchronic pancreatitis are often accompanied bysignificant pain, efforts to relieve it sometimesinclude destruction of the celiac ganglia, withvariable success.

ReferencesPeters JH, DeMeester TR Esophagus andDiaphragmatic Hernia. Principles of Surgery Ed. Schwartz JI McGraw Hill 1994, 1043-1122.