Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Anatomy of the Stomach and Duodenum
Anatomy of the Stomach: Normal Variations and Relations
The stomach is a J -shaped reservoir of the digestive tract in which ingested food is soaked in gastric juice containing enzymes and hydrochloric acid and then is released spasmodically into the duodenum by gastric peristalsis. The form and size of the stomach vary considerably, depending on the position of the body and the degree of filling. Special functional configurations of the stomach are of interest to the clinician and radiologist ( Fig. 15.1 ).
The stomach has a ventral surface and a dorsal surface that may be vaulted or flattened and that almost make contact when the organ is empty. The stomach also has two borders, the concave lesser curvature above on the right and the convex greater curvature below on the left. The two join at the cardia, where the esophagus enters. The poorly defined cardia is the point of demarcation between both curvatures, whereas on the right the esophagus continues smoothly into the lesser curvature. On the left there is a definite indentation, the incisura cardialis (cardial or cardiac incisure, or notch), that becomes most obvious when the uppermost, hoodlike portion of the stomach (fundus, or fornix) is full and bulges upward. The major portion of the stomach (body, or corpus) blends imperceptibly into the pyloric portion, except along the lesser curvature, where a notch, the incisura angularis (angular incisure), marks the boundary between the corpus and the pyloric portion. The pylorus consists of the pyloric antrum, or vestibule, which narrows into the pyloric canal and terminates at the pyloric valve. External landmarks of the pylorus form a circular ridge of sphincter muscle and the subserosal pyloric vein.
During esophagogastroduodenoscopy, selective views can evaluate almost all these areas. For example, retroflexion of the endoscope permits visualization of the scope entering the stomach. The endoscopist can see the normal mucosa of the gastroesophageal junction as it hugs the scope, forming a fold or flap at the cardiac incisure. The pyloric channel is usually closed, and waves of contractions move aborally from the pylorus and end at the angular incisure of the pyloric antrum.
The stomach is entirely covered with peritoneum. A double layer of peritoneum, deriving from the embryonal ventral mesogastrium, extends on the lesser curvature beyond the stomach, known as the lesser omentum. It passes over to the porta hepatis and may be divided into a larger, thinner, proximal portion (hepatogastric ligament) and a smaller, thicker, distal portion (hepatoduodenal ligament), which attaches to the pyloric region and to the upper horizontal portion of the duodenum. The free edge of the hepatoduodenal ligament, through which run the portal vein, hepatic artery, and common bile duct, forms the ventral margin of the epiploic foramen of Winslow, which gives access to the lesser peritoneal sac (bursa omentalis). The greater omentum, a derivative of the embryonal dorsal mesogastrium, passes caudally from the greater curvature and contains, between its two frontal and two dorsal sheets, the inferior recess of the bursa omentalis.
The anterior surface of the stomach abuts the anterior abdominal wall, against the inferior surface of the left lobe of the liver and, to some extent in the pyloric region, against the quadrate lobe of the liver and the gallbladder. Its posterior surface is in apposition with retroperitoneal structures (pancreas, splenic vessels, left kidney, and adrenal gland) from which, however, it is separated by the bursa omentalis. The fundus bulges against the left diaphragmatic dome. On the left, adjacent to the fundus, is the spleen, which is connected to the stomach by the gastrosplenic ligament (also derived from the dorsal mesogastrium).
The four recognized principal functional types of stomach are known as orthotonic, hypertonic, hypotonic, and atonic. In the hypotonic and atonic types, the axis of the stomach is more longitudinal, whereas in the orthotonic and particularly the hypertonic types, it is more transverse.
Anatomy and Relations of the Duodenum
The duodenum, the first part of the small intestine, has a total length of approximately 25 to 30 cm (10–12 inches). It is horseshoe shaped, with the open end facing left, and is divided into four parts ( Fig. 15.2 ).
The first part of the duodenum, or the pars superior, lies at the level of the first lumbar vertebra (L1) and extends almost horizontally from the pylorus to the first flexure. As a result of its intraperitoneal position, this first duodenal portion is freely movable and can adapt its course according to the filling condition of the stomach. The anterior and superior surfaces of the first half of this duodenal segment are in close relation to the inferior surface of the liver (lobus quadratus) and the gallbladder. The radiographic designation duodenal bulb refers to the most proximal end of the pars superior duodeni, which is slightly dilated when the organ is filled and then is more sharply separated from the stomach because of pyloric contraction.
The two layers of peritoneum, which cover the anterosuperior and the posteroinferior surfaces, join together on the upper border of the superior portion of the duodenum and move as the hepatoduodenal ligament cranially toward the liver, forming the right, free edge of the lesser omentum. This ligament contains the important triad of the portal vein, hepatic artery, and common bile duct.
The second part of the duodenum, the descending portion, extends vertically from the first to the second duodenal flexure, the latter lying approximately at the level of the third lumbar vertebra (L3). The upper area of this portion rests laterally on the structures of the hilus of the right kidney; medially, its whole length is attached by connective tissue to the duodenal margin of the caput pancreatis (head of pancreas). Approximately halfway its length, the descending portion is crossed anteriorly by the parietal line of attachment of the transverse mesocolon. The common bile duct, together with the portal vein, occupies the start of the hepatoduodenal ligament, a position dorsal to the superior duodenal portion, and continues its course between the descending portion and the pancreatic head to its opening at the major duodenal papilla (Vater).
The third part of the duodenum, the inferior portion, begins at the second flexure. It begins almost horizontally (horizontal part) or sometimes in a slightly ascending direction, until it reaches the region of the left border of the aorta, where it changes direction and curves cranially to pass into the terminal duodenal segment (ascending part). Although the caudal part of the second portion and the second flexure lie over the psoas major of the right side of the body, the third duodenal portion, with its horizontal segment, passes over the vena cava and the abdominal aorta. The superior mesenteric vessels, before entering the root of the mesentery, cross over the horizontal part of the third portion near its transition to the ascending part. During its course, the third portion is increasingly covered by the peritoneum, and a complete intraperitoneal configuration is attained at the duodenojejunal flexure, which is located caudal to the mesocolon transversum at the level of the second lumbar vertebra (L2) or of the disk between L1 and L2.
As the third part of the duodenum courses up to the left of the aorta to reach the border of the pancreas, it is frequently referred to as the fourth part of the duodenum. This fourth part joins the jejunum and is fixed posteriorly by the ligament of Treitz, a suspensory muscle of the duodenum. The fourth part of the duodenum then leaves the retroperitoneal area to join the intraperitoneal jejunum. On radiographs, the duodenum usually takes the form of a C, although it may show individual variations, such as a redundant second part or a reversal of curve (see Fig. 15.2 ).
You're Reading a Preview
Become a Clinical Tree membership for Full access and enjoy Unlimited articles
If you are a member. Log in here