Stomach

Anatomy

The stomach is about 25 cm long and is anatomically divided into the following parts:

• the bottom, placed above and to the left of the junction between the esophagus and stomach (esophagus-gastric);
• the cardias, corresponding to the esophagus-gastric junction;
• the body, which represents the greater portion of the stomach, and which is located between the bottom and the antrum;
• L"cave, final portion of the stomach, which extends from the small curvature to the pylorus;
• the pylorus, which represents the boundary between the stomach and the duodenum.

The stomach, as well as the other abdominal organs, is covered by the peritoneum, which is a serous and fibrous structure that has the function of protecting it and keeping it attached to the abdominal wall and to the organs close to it. The gastric wall is made up of four fundamental layers, starting from the outside and going towards the inside:

• the serous lining of the visceral peritoneum (that portion of the peritoneum attached to the organ);
• the layer muscular, which has three concentric layers of fibers (from the outside to the inside: oblique, longitudinal and circular);
• there submucosa, rich in small blood and lymphatic vessels;
• there muscularis mucosae, small layer of muscle tissue that separates the mucosa from the submucosa;
• there mucosa, which is the innermost layer of the stomach, is formed by a great variety of cells: the muciparous cells, with mucous secretion, the parietal ones, which produce hydrochloric acid, the main ones, which secrete pepsinogen, and the G cells which produce gastrin.

The pylorus continues with the duodenum, which is the first part of the small intestine. It is about 30 cm long and its wall is made up of 5 concentric layers. Starting from the outside towards the inside, the following are distinguished:

• there serous frock, represented by the visceral peritoneum;
• there muscular frock, consisting of two concentric layers of smooth muscle cells (the outer layer with a longitudinal course and the inner one with a circular course);
• there submucosal frock, mainly composed of elastic fibers, between which the duodenal glands secreting weakly alkaline (basic) and pepsinogenic mucus are located.
• there muscularis mucosae;
• there mucous cassock, consisting of epithelial cells.

The duodenal epithelium is composed of a very varied cell population: enterocytes (intestinal cells absorbing nutrients) represent the prevailing cellular element; among them are localized mucus cells, producing mucus, immune cells and endocrine cells.

Vascularization and innervation

The stomach has a rich arterial vascular network which penetrates inside the gastric wall dividing itself into smaller and smaller vessels that run along the small and large gastric curvature. The innervation is given by the vagus nerve: the importance of the integrity of the vagal innervation of the stomach in controlling the secretion acid is documented by the sharp reduction, after vagotonia (removal of the gastric portion of the vagus nerve) of the production of hydrochloric acid.

Physiology

The stomach performs numerous and important functions:

• it acts as a "container" for food from the esophagus, allowing even copious quantities of food to be ingested;
• it determines the mixing and the progression towards the duodenum of the alimentary bolus (that is the name that takes the food inside the stomach), mixed with the gastric juice;
• begins the digestion of proteins and carbohydrates, through the secreted pepsinogen and hydrochloric acid;
• it has the function of absorbing some substances;
• carries out endocrine secretion activity.

The biliary and pancreatic secretions flow into the duodenum through the ducts that put it in communication with the gallbladder and the pancreas, and the conditions of an alkaline (basic) environment are created with a high concentration of enzymes suitable for the digestion of proteins, fats and carbohydrates. The duodenum also has functions of absorption and endocrine secretion.
Important aspects of stomach physiology are peptic acid secretion, hormone secretion, motility, food digestion and other functions.