Gastroenterology training and education

Discuss the parts of stomach?

• Stomach is divided into five parts- cardia, fundus, body, pyloric part and pylorus
• Cardia- this is the part of the stomach attached to the oesophagus. This is the area just distal to the z line
• Fundus- this is the dilated portion to the left and superior to the cardiac orifice and is marked off from the remainder of the body by a plane passing horizontally through the cardiac orifice
• Body- Lies between the fundus and pyloric antrum
• Pyloric part- it consists of a wide portion, the antrum and a narrow portion, the pyloric canal. Incisura angularis (angular notch) is a sharp angulation of the lesser curvature. This indicates the junction of the body and pyloric part of the stomach.
• Pylorus- this is a strong ring of smooth muscle, which controls the exit of stomach contents in the duodenum

Stomach also has two curvatures- the lesser and greater curvature.

Discuss the blood supply of stomach?

Stomach is supplied from the coeliac axis.
The left (direct branch of coeliac artery) and right (branch of hepatic artery) gastric arteries supply the lesser curvature. The right and left gastric artery anastomoses
The right (branch of gastroduodenal artery arising from hepatic artery) and left (branch of splenic artery) gastroepiploic arteries supply the greater curvature. The left and right gastroepiploic artery anastomoses
The short gastric arteries arising from the splenic artery also supply the proximal greater curvature and fundus.

Discuss the lymphatic supply of stomach?
There are four major areas of lymphatic drainage, all draining into coeliac nodes
Towards lesser curvature:

• left gastric nodes: it lies along the left gastric artery and drain a large part of the body of the stomach. Efferent’s from here follow the left gastric blood vessels and go to the coeliac nodes.
• right gastric nodes: drain a small portion of the pylorus. Efferent’s go to hepatic nodes and eventually to coeliac nodes.

Towards greater curvature:

• pancreaticosplenic nodes: drain the spleen, pancreas, and the left fundus and body of the stomach. They send lymph to the coeliac nodes.
• right gastroepiploic nodes: drain the body and pyloric portion of the stomach. Efferent’s go from here to the pyloric nodes, located on the anterior surface of the head of pancreas close to the pylorus. Pyloric nodes drain into the hepatic nodes, and finally the coeliac nodes.

Discuss the greater and lesser omentum?
Omentum is a double layered fold of peritoneum. Lesser omentum connects the lesser curvature to the liver. The greater omentum hangs down from the greater curvature and connects the stomach to the diaphragm, spleen and the transverse colon.

Discuss the histology of stomach?

Like other parts of GIT, stomach has 4 layers:

• Mucosa
  • Columnar epithelium
  • Lamina propria- loose network of connective tissue
  • Muscularis mucosae- thin layer of smooth muscle between lamina propria and submucosa
• Submucosa- fibrous connective tissue containing blood vessels, lymphatic channels, Meissner’s plexus and oesophageal glands
• Muscularis propria- 3 muscle layers- inner oblique, middle circular layer and outer longitudinal layer of muscles. Auerbach’s myenteric plexus lies between middle circular and outer longitudinal layer
• Serosa Oesophagus lacks a serosal layer unlike the rest of the GIT

Discuss the epithelial cell layer?

The epithelium of the stomach forms deep pits. These pits form ducts whose walls are lined with various gastric glands:

• Goblet cells- this makes up the surface layer of the simple columnar epithelium. These cells secrete mucus, which protects the mucosa from the gastric acid
• Parietal cells- are found along the neck and lower walls of the ducts. They secrete HCL and intrinsic factor
• Chief cells- line the lower walls of the ducts. These cells are found in the fundus only. They secrete pepsinogen for protein digestion
• Enteroendocrine (APUD) cells- secrete hormones like gastrin, histamine etc. These hormones diffuse directly into the blood vessels unlike the secretion of the other cells above which enter the stomach and mix with food

Discuss the gastric acid secretion?
Parietal cells bear receptors for three stimulators of acid secretion:

• Acetylcholine (muscarinic type receptor)
• Gastrin
• Histamine (H2 type receptor)

H+/K+ ATPase or “proton pump” located on the parietal cells is the final common pathway for HCL secretion from parietal cells. Proton pump inhibitors act on this final common pathway and produces powerful acid suppression.