The Pyloric Sphincteric Cylinder in Health and Disease

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Chapter 3 (page 10)

Chapter 3

The Walls of the Stomach and Duodenum

At upper abdominal operations, with the organs in situ, a slight groove may be seen in the glistening serosal surface at the gastroduodenal junction. In the groove a small, superficial subserosal vein, lying vertically across the front of the gut, may be evident; this is the prepyloric vein, draining into the right gastric vein (Chap. 7). The groove and the prepyloric vein indicate the position of the pyloric ring. At palpation a sudden transition is felt at the ring between the thick walls of the pyloric region and the thin walls of the duodenum.

The wall of the pyloric part of the stomach and of the proximal 2.0 to 3.0 cm of the duodenum is composed of four coats. From without inwards these are the serous, muscular, submucous and mucous coats. The mucous coat is separated from the luminal contents by a layer of gastric mucus.

Serous Coat

The serous coat or adventitia is formed by the peritoneum; it is a thin layer of loose connective tissue, covered on its outer aspect with mesothelium. It is closely attached to the subjacent muscular coat, except at the greater and lesser curvatures, where the connection is more lax and where it is continuous with the greater and lesser omentum respectively.

The lesser or gastro-hepatic omentum extends from the inferior and posterior surfaces of the liver to the stomach and proximal 2.0 to 3.0 cm of the duodenum. The portion of the lesser omentum between the porta hepatis and the duodenum contains the hepatic artery, the portal vein, the common bile duct, lymph glands, lymph vessels and nerves. On the right it ends in a rounded margin; immediately posterior to the free right edge is the opening into the lesser sac or epiploic foramen. The remainder of the lesser omentum, extending from the left end of the porta hepatis to the lesser curvature, contains the right and left gastric arteries and the accompanying veins, as well as lymph glands, lymph vessels and branches of the anterior and posterior vagus nerves.

The greater omentum is formed along the greater curvature of the stomach by the meeting of the peritoneal coats of the anterior and posterior gastric surfaces. On its left it shortens into the gastro-splenic omentum, containing the short gastric branches of the splenic artery between its two layers. On the right it is continued for 2.0 to 3.0 cm along the lower border of the first part of the duodenum. From its origin the greater omentum hangs down in front of the intestines as a loose apron, extending as far as the transverse colon, where its two layers separate to enclose that part of the colon. The upper part of the greater omentum contains the greater part of the right and left gastroepiploic arteries and their accompanying veins, lymph vessels, lymph glands, nerve filaments, fat and areolar tissue. On its surface it may have loose accumulations of histiocytes.

There is some doubt whether the subserous lymphatics are continuous with those of the duodenum (Chap. 7); the question is of importance in the spread of pyloric carcinoma (Chap. 33). Owing to its peritoneal attachments the proximal 2.0 to 3.0 cm of the duodenum, i.e. the proximal half of the first part of the duodenum, known as the duodenal bulb, is mobile. It shares the peritoneal covering of the pyloric region of the stomach, unlike the remainder of the duodenum, which is fixed to the posterior abdominal wall in a retroperitoneal position; consequently only the ventral and right lateral surfaces of the remainder of the duodenum are clothed by peritoneum; the duodenal curve abuts against the head of the pancreas.

Muscular Coat or Muscularis Externa

There has long been disagreement among anatomists about the muscular build of the stomach. Some of the uncertainties can be traced back to the time of Willis (1682). On the one hand there were those who believed the stomach to be a simple, undifferentiated muscular chamber. On the other hand several authorities found that the stomach consisted of a number of different muscular divisions or regions. A huge literature has accumulated on this and related questions, the historical perspectives being fully dealt with by Cunningham (l906), Forssell (l913), Horton (l928) and Torgersen (l942).

The gastric muscular coat or muscularis externa is composed of smooth, unstriped or involuntary fibres. It is made up of three layers, viz. an external longitudinal, a middle circular and an inner oblique layer. The oblique fibres are arranged in inverted U-shaped bundles which loop over the fornix and extend downwards in the anterior and posterior gastric walls as far as the incisura angularis. Consequently the oblique fibres take no part in the muscular build of the distal part of the stomach, including the pyloric region; the muscularis externa here is composed solely of outer longitudinal and inner circular layers.

Cunningham (l906) studied the muscular anatomy of the stomach in man and the anthropoid ape in great detail. He pointed out that normally post-mortem changes set in rapidly, causing the muscular walls to relax, which hampered investigations in fresh specimens. However, by fixing a stomach in "its natural form and natural bed", it was possible to obtain hardened specimens suitable for dissection.

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