Anatomy

The stomach is a dilated portion of the gastrointestinal tract which has three main functions; storage of food, mixing food with gastric secretions and control of the rate of release of food to the small intestine for further digestion and absorption. It is a J-shaped organ and much of it lies under the cover of the lower ribs. It has an anterior and posterior surface, two openings (the proximal cardiac and the distal pyloric orifices) and two curvatures (greater and lesser) (Figure 2.1). Although relatively fixed at both ends, the intervening part is mobile and can undergo considerable variation in shape. The stomach is usually divided into the following parts:

Fundus - dome shaped and projects upwards and to the left of the cardiac orifice. Body - extends from the level of the cardiac orifice to the incisura angularis (a constant notch at the junction of the lesser curve and antrum). The incisura is an important endoscopic landmark. Antrum - extends from the incisura to the proximal part of the pylorus.

Pylorus - the most tubular part of the stomach and its thick muscular wall forms the physiological and anatomical pyloric sphincter, marked by a slight constriction on the surface of the stomach. The pylorus, which is approximately 2.5 cm long, joins the first part of the duodenum.

The cardiac orifice is where the abdominal part of the oesophagus enters the stomach. Although no anatomical sphincter is present, a physiological mechanism exists which prevents gastro-oesophageal regurgitation.

The lesser curvature forms the right border of the stomach, extending from the cardiac orifice to the pylorus. The greater curvature extends from the left of the cardiac orifice, over the fundus to the inferior part of the pylorus. Peritoneum completely surrounds the stomach and leaves its curvatures as double layers called omenta which contain fat, lymph nodes and vessels. The lesser omentum extends from the lesser curve to the liver. The gastrosplenic omentum extends from the upper part of the greater curve to the spleen, while the greater omentum runs to the transverse colon from the lower part.

The mucous membrane of the gastric body is thrown into numerous longitudinal folds or rugae. This facilitates flattening of the mucosa when the stomach is distended by food. The mucosal surface contains millions of gastric pits or foveolae that lead to mucosal glands. The mucosal surface is composed of columnar, mucin-secreting epithelium (surface mucus - foveolar cells), while deeper in the gastric pits are mucus neck cells. The gastric glands vary depending on their anatomic region (Figure 2.1):

Cardia: mucin-secreting cells.

Fundus/body: parietal cells (acid), chief cells (pepsin) and scattered endocrine cells. Antrum/pylorus: endocrine (mostly gastrin G cells) and mucin-secreting cells.

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