Anatomy and Physiology of Children and Adolescents - M. R. Sapin 2007

The Science of Viscera (Splanchnology)
Digestive System
Stomach

The Stomach serves for the Digestion of food. Within the stomach, food is mixed with digestive juices, undergoing chemical Processing (digestion) through the action of gastric juice Enzymes. Gastric juice contains Pepsin, renin, lipase, Hydrochloric acid, and mucus. The stomach also performs endocrine and absorptive Functions (absorbing sugars, alcohol, Water, and salts). The stomach walls produce the intrinsic anti-anemic factor, which facilitates the absorption of dietary vitamin B₁₂.

Shape. The human stomach resembles an elongated, curved pouch with a capacity in adults ranging from 1.5 to 4 liters. The shape and dimensions of the stomach constantly change depending on The amount of food consumed, body position, and other factors. The following PARTS OF THE stomach are distinguished. At the top is the entrance to the stomach — the cardiac orifice. The region adjacent to this opening is called the cardia (Fig. 47). To the left of the stomach's entrance is its expanded portion — the fundus, or gastric vault. The widest part, located inferior to the fundus, is called the body of the stomach. The lower convex margin forms the curved greater curvature, while the upper concave margin forms the lesser curvature. The conically narrowed right portion of the stomach forms the pylorus, which transitions into the duodenum. At this junction lies the pyloric orifice. The stomach is located in the epigastric region and the left hypochondrium. The cardiac orifice is situated at the level of the X–XI thoracic vertebrae, and the pylorus is at the level of the XII thoracic to I lumbar vertebrae.

Stomach walls. The stomach has two walls — anterior and posterior — comprising four layers: the mucous membrane (mucosa), submucosa, muscular coat (muscularis), and serous coat (serosa). The mucosa forms folds of various SHAPES AND SIZES. Longitudinal folds are oriented along the lesser curvature, while oblique and transverse folds are visible on the stomach walls. These folds are clearly observable during an internal examination of the stomach in a living person via endoscopy. When the stomach fills, the folds flatten out. In the region of the pyloric orifice, at the border between the stomach and duodenum, the mucosa forms a circular fold. Small areas bounded by grooves, known as gastric areas, are visible on the mucosal surface. On the surface of these gastric areas are depressions called gastric pits, into which 2–3 glands open, producing gastric juice. The number of gastric glands reaches 35 million. These are simple, tubular, unbranched glands. Each gland features a fundus, a neck, and an isthmus that transitions into a gastric pit. A distinction is made between proper gastric glands, located in the region of the fundus and body, and pyloric glands. Proper glands contain chief Cells, which produce digestive enzymes (pepsinogen, chymosin); parietal cells, which secrete hydrochloric acid; and mucous cells. The walls of proper glands also contain gastric endocrine cells, which produce BIOLOGICALLY ACTIVE SUBSTANCES (serotonin, endorphin, histamine, etc.). Pyloric glands, numbering about 3.5 million, are located in the region where the stomach transitions into the duodenum. Pyloric glands contain parietal and mucous cells, as well as A large number of gastric endocrine cells.

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Fig. 47. The stomach:

A. Cytology/practical/54.html">Longitudinal section of the stomach. Internal surface of the posterior wall: 1 — Esophagus; 2 — Fundus of the stomach; 3 — greater curvature; 4 — pyloric part; 5 — pyloric orifice; 6 — pyloric sphincter; 7 — mucosal folds; 8 — lesser curvature; 9 — body

B. Structure OF THE stomach wall: 1 — mucosa; 2 — gastric areas; 3 — gastric pits; 4 — muscularis mucosae; 5 — submucosa; 6 — muscular coat; 7 — solitary lymphoid nodule

The submucosa of the stomach is quite thick, allowing the mucosa to easily form folds. The muscular coat in a living person maintains stomach tone and performs peristalsis. The muscular coat consists of three layers: an outer longitudinal layer, a middle circular layer, and an inner layer of oblique fibers. The outer longitudinal layer is better developed along the greater and lesser curvatures. At the junction of the stomach and duodenum, the circular layer forms a thickening — the pyloric sphincter. When this sphincter contracts, food masses are prevented from passing from the stomach into the duodenum. Externally, the stomach is covered by a serous membrane — the Peritoneum.