Anatomy of the human stomach and bariatric surgery

What are the parts of the stomach and what is bariatric surgery?

The rise of bariatric surgery

Obesity is a global epidemic. The World Health Organization has estimated that in 2022 there are over 1 billion obese people globally. That includes 650 million adults and 340 million adolescents. Over 4 million people die each year due to obesity-related illnesses.

Ideally, the individual should be able to control their food intake and exercise to prevent weight gain, but it is not that simple for most people.

Many people have considered the option of a surgical procedure to lose weight.

Over 580,000 weight loss or bariatric surgeries are performed worldwide, and the numbers are increasing each year. The first procedures were done in the 1950s, and several techniques have been developed and modified since then. Understanding the anatomy of the stomach has been critical in the evolution of bariatric surgery. I thought it might be interesting to outline the four most commonly performed procedures. Before I do that, I need to answer the question, ‘What is the anatomy of the stomach?’. But if you are desperate, click on the image below to interact with the animation in 3D and then go on to read the rest of the article to learn the anatomy of the human stomach.

Anatomy of the human stomach

Where is the stomach located?

The stomach is the widest part of the alimentary tract.  It lies between the esophagus proximally and the duodenum of the small intestine distally. The stomach lies in the supracolic compartment of the abdomen, mainly in the epigastrium, and is entirely covered by peritoneum.

What are the parts of the stomach?

The stomach has two surfaces: an anterior surface and a posterior surface. The two surfaces of the stomach meet at the curvatures of the stomach.  

The lesser curvature lies superiorly, and the greater curvature lies inferiorly.

The fundus of the stomach is the dome-shaped region at the upper end of the greater curvature.  The fundus is found near the gastroesophageal junction.

The fundus then runs into the main part of the stomach, known as the body of the stomach.

The incisura is a notch found at the border of the lesser curvature of the body of the stomach. The incisura lies distal to the fundus.  

The antrum refers to the distal third of the stomach. The antrum runs into the pyloric channel and then on to the pyloric sphincter, which communicates with the duodenum.

Omentum

There are two layers of fat attached to the stomach; the lesser omentum and the greater omentum.

The lesser omentum attaches to the lesser curvature of the stomach. It runs upwards towards the liver. The lesser omentum has important structures running within its free edge, these include

• portal vein
• extrahepatic biliary tree
• hepatic artery

The greater omentum attaches to the greater curvature of the stomach. It drapes downwards over the small intestines and passes back upwards.  It becomes adhered to the peritoneum of the superior aspect of the transverse colon and transverse mesocolon. The greater omentum attaches to the posterior abdominal wall. The greater omentum is supplied by the right and left gastro-omental arteries, which are derived from the first branch of the anterior aorta.

Layers of the Stomach

The stomach wall is composed of three layers of muscle the oblique inner layer, circular middle layer, and longitudinal outer layer. Contraction and relaxation of these muscles allow the food to be turned around the stomach backwards and forwards as well as the regular peristaltic movement of the intestinal tract.

The oblique inner layer is arranged into several folds known as gastric rugae.

Histology of the stomach

The inner mucosal layer of the gastric rugae of the stomach has several folds and is organised into gastric pits lined with specialised cells.

1. Mucous cells secrete mucous that protects the stomach from the acidic content of the gastric juices.
2. Oxyntic or parietal cells secrete hydrochloric acid
3. Chief cells or zymogenic cells secrete pepsin and renin
4. Enteroendocrine cells secreted gastrin and other hormones

Functions of the stomach

1. The temporary storage of food
2. Mechanical breakdown of food by the three smooth muscle layers of the stomach which acted to churn the food to produce chyme
3. Production of gastric juice for digestion
4. Chemical digestion of food, including pepsin which breaks proteins down into polypeptides
5. Production of intrinsic factor which is required for vitamin B12 absorption in the terminal ileum
6. Secretion of the gastric hormone, which stimulates the production of gastric juice

Gastric Juice

Approximately 2 litres of gastric juices are secreted by the stomach each day.

Gastric juice contains

• water
• mineral salts
• mucus
• hydrochloric acid
• intrinsic factor
• enzyme precursors such as pepsinogen, which is activated to pepsin by the acidic environment

Blood supply of the stomach

 The stomach has an extensive blood supply from the celiac artery, also known as the celiac trunk, which is the first anterior branch of the abdominal aorta. The celiac artery immediately divides into three terminal branches:

• left gastric artery
• splenic artery
• common hepatic artery.

Each of these branches contributes to the blood supply of different parts of the stomach.

 The left gastric artery supplies the lesser curvature of the stomach.

 The splenic artery gives off a spray of branches known as the short gastric arteries, which supply the fundus of the stomach.  

The splenic artery also gives off the left gastro-omental artery (also called the left gastroepiploic artery), which supplies the greater curvature of the stomach.

 The common hepatic artery gives off the gastroduodenal artery, which passes posterior to the first part of the duodenum. The gastroduodenal artery gives off the right gastro-omental or gastroepiploic artery, which supplies the greater curvature of the stomach.

The common hepatic artery continues as the hepatic artery proper, which divides into the right gastric artery and supplies the lesser curvature of the stomach.

Summary of the blood supply of the stomach

The fundus of the stomach is supplied by the short gastric arteries.

The lesser curvature of the stomach is supplied by the right and left gastric arteries.

The greater curvature of the stomach is supplied by the right and left gastro-omental arteries.

Venous drainage of the stomach

The veins that drain the stomach correspond to the arteries.

The right gastric vein and left gastric vein drain into the portal vein. The short gastric veins and gastroepiploic veins drain into the splenic vein.  The splenic vein joins with

the inferior mesenteric vein to form the portal vein, which takes blood to the liver.  

Nerve supply of the stomach

The nerve supply to the stomach is derived from the right and left vagal nerves.

The left vagal nerve gives off several smaller fibres known as the anterior vagal trunk, which supplies the anterior part of the stomach. The posterior vagal trunk is mainly formed by fibres of the right vagus nerve, which supplies the posterior part of the stomach.

What is Bariatric Surgery?

Weight loss surgery is also known as bariatric surgery. The underlying principle of weight loss surgery is to create a smaller stomach so that the patient feels full after eating a relatively small amount of food. This way, they will eat less and lose weight.  Several techniques have been developed, most of which are now done using laparoscopy or keyhole instrumentation.

Roux- En- Y Bypass

In this procedure, a small pouch of the stomach is made by dividing the stomach into a small pouch that remains connected to the esophagus. The rest of the stomach remains connected to the duodenum. The jejeunum is then separated from the duodenum and attached to the newly created pouch of the stomach. The open distal end of the duodenum is then attached to a hole made distally in the jejunum.  

Mini Gastric Bypass

This procedure is similar to the Roux-en-Y in that the stomach is divided into two sections. A small pouch of the proximal stomach is separated from the rest of the stomach. The difference is that the jejunum remains continuous with the duodenum, but an opening is made in the jejunum, which is attached directly to the small pouch of the stomach.

Sleeve Gastrectomy

An inflatable tube is passed into the stomach towards the pylorus and is inflated. The arteries that supply the greater curvature of the stomach and fundus are divided.

The stomach is then stapled near the tube, and about 80% of the stomach is cut away and removed from the body. This creates a stomach that is smaller and tube-shaped. The hormone ghrelin is produced by the enteroendocrine cells, and it causes hunger. Removing most of the stomach has the additional benefit of reducing ghrelin levels, so patients do not feel as hungry.

Gastric Band

This procedure was introduced in the 1970s. Originally, a mesh was placed around the stomach to divide it into two sections, but the mesh eventually stretched out, and patients regained weight. The modern evolution of the mesh is an inflatable band that is placed near and stitched to the fundus of the stomach. A tube connected to the band is brought to the surface of the skin.  The pressure in the band can be altered by increasing the fluid in the band. This way, the clinician can control the amount of food the patient can eat so that they lose weight.

Click on the image to interact with the 3D model of the gastric band

Summary

 Understanding anatomy is crucial to developing new surgical techniques. Whilst there are several surgical approaches to lessen the feeling of hunger, this is major surgery and not without potentially serious complications. The patient must be given psychological help to explore underlying issues as these will not be fixed with surgery alone. A holistic approach should be adopted so that the patient feels thoroughly supported during the process. I thought this was an interesting topic, as learning anatomy becomes far more interesting when you see it through a clinical scenario.

Get in touch. Let me know if this was useful and if there are any topics you would like me to cover.

And as always… Stay Funky!

Dr Susan xx