The Stomach in the embryological developmental stage derives from the posterior foregut and has a dorsal and ventral mesogastrium. As the dorsal portion grows faster, the stomach expands, which leads to a greater and lesser curvature. In development, the stomach also moves on two rational axes:
- 90 degrees on the superior-inferior axis called the long axis
- And anti-clockwise around the posterior-anterior axis called the dorsoventral axis
This results in the stomachs greater curvature lying to the left of the midline.
A fully developed average stomach lies just below the diaphragm in the upper part of the abdominal cavity, with the greater curvature lying to the left of the midline under a portion of the liver. The prices location of the stomach is influenced by food ingestion and respiration.
Connected superiorly to the oesophagus at the gastroesophageal (GE) junction and inferiorly to the duodenum, the first part of the small intestine. The stomach is surrounded by a large number of lymph nodes and is made up of 5 regions:
- The cardia is the first part of the stomach below the oesophagus. It contains the cardiac sphincter, a thin ring of muscles that help stop contents from going back up into the oesophagus.
- The Fundus is the greater curvature area left of the midline under a portion of the liver and diaphragm.
- The body is the largest part of the stomach. In this main area of the stomach, food is mixed and starts to be broken down.
- The antrum, also known as the pyloric antrum, is the inferior curvature, and part of the stomach is where broken-down food is held until it is ready to be realised into the small intestine.
- The pylorus is the region of the stomach that connects to the duodenum. It contains the pyloric sphincter, a thick ring of muscles that acts as a valve to control the emptying of the stomach contents called chyme into the duodenum. The pyloric sphincter also prevents anything from coming back into the stomach.
The stomach is made up of several layers of tissue:
- The stomach's inner lining is a mucosa membrane, which becomes rigid when the stomach is empty. The ridges flatten out as the stomach fills with food.
- The layer covering the mucosa membrane is the submucosa, which is made up of connective tissue and contains larger blood and lymph vessels, nerve cells, and fibres.
- The layer covering the submucosa is the muscular propria or muscularis exterana, which is made up of three layers of muscle and functions as the main muscle of the stomach.
- The outer layer covering the muscular propria is the serosa, a fibrous membrane also called the visceral peritoneum.