Human Anatomy and Physiology (with Age-Related Features of the Child's Body) - Sapin M. R., Sivoglazov V. I. 2002

The Doctrine of Viscera (Splanchnology)
Digestive System
Stomach

The human stomach serves as a reservoir for ingested food, mixes it with digestive juices, and performs chemical Processing (Digestion) of food via the components of gastric juice. The juice contains Pepsin, renin, lipase, Hydrochloric acid, and mucus. The Stomach also performs endocrine and absorptive Functions (absorbing sugars, alcohol, Water, and salts). The walls of the stomach produce the intrinsic anti-anemic factor, which facilitates the absorption of dietary vitamin B₁₂.

The human stomach resembles a chemical retort or a pear, though its shape constantly changes depending on The amount of food consumed, body posture, and other factors. The capacity of an adult stomach ranges from 1.5 to 4 liters.

At the top is the entrance to the stomach — the cardiac orifice — and the adjacent cardiac region (Fig. 42). To the left of it, the stomach expands to form the fundus (or vault), which extends downward and to the right into the body of the stomach. The lower convex margin of the stomach forms the greater curvature, while the upper concave margin forms the lesser curvature. The narrow right part of the stomach forms the pylorus, which leads through the pyloric orifice into the duodenum.

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Fig. 42. 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. Diagram of the stomach wall Structure: 1 — mucous membrane, 2 — gastric areas, 3 — gastric pits, 4 — muscular layer of the mucosa, 5 — submucosa, 6 — muscular coat, 7 — solitary lymphoid nodule

The stomach is located in the epigastric region and the left hypochondrium. The cardiac orifice lies at the level of the X—XI thoracic vertebrae, and the pylorus is at the level of the XII thoracic — I lumbar vertebrae.

The stomach has two walls: anterior and posterior. Both walls transition into one another along the greater and lesser curvatures. The stomach walls consist of four layers: the mucous membrane (mucosa), submucosa, muscular coat, and serous coat (serosa). The mucous membrane forms longitudinal folds (along the lesser curvature), as well as oblique and transverse folds. These folds are clearly visible in living individuals during endoscopy and smooth out when the stomach fills. In the region of the pyloric orifice, the mucosa forms a circular fold. The polygonal areas of the mucosa separated by grooves are called gastric areas. On the surface of these areas are gastric pits—depressions, into each of which open 2—3 glands that produce gastric juice. The number of gastric glands reaches 35 million. These are simple, tubular, unbranched glands. Each gland has a fundus, a neck, and an isthmus that transitions into the gastric pit. A distinction is made between proper gastric glands, located in the fundus and body of the stomach, and pyloric glands. Proper gastric glands contain chief Cells that produce digestive Enzymes (pepsinogen, chymosin), parietal cells that secrete hydrochloric acid, and mucous cells. The walls of proper gastric glands also contain gastric endocrine cells (enteroendocrine cells) that produce BIOLOGICALLY ACTIVE SUBSTANCES (serotonin, gastrin, histamine, etc.).

Pyloric glands are located in the region where the stomach transitions into the duodenum; their number reaches 3.5 million. Pyloric glands contain parietal cells, mucocytes, and A large number of gastrointestinal enteroendocrine cells.

The submucosa of the stomach is well developed. The muscular coat forms three layers: an outer longitudinal layer, a middle circular layer (most developed in the pyloric region), and an inner oblique layer. The first two layers are continuations of the corresponding layers of the esophageal muscular coat. Furthermore, the circular layer forms a thickening at the gastroduodenal junction—the pyloric sphincter. When the sphincter contracts, the passage of food from the stomach into the duodenum is blocked. The stomach Muscles maintain its tone and perform peristalsis in living individuals.

Externally, the stomach is covered by the Peritoneum, meaning it is situated intraperitoneally.

Age-related Features of the stomach

The newborn's stomach is spindle-shaped. The cardiac part, fundus, and pyloric region are poorly defined, and the pylorus is wide. By the end of the first year of life, the stomach lengthens, and between the ages of 7 and 11, it acquires the adult shape. The formation of the cardiac part is completed only by the beginning of the second childhood period (8 years). The stomach volume in a newborn is about 50 cm³. By the end of the first year of life, stomach volume increases to 250—300 cm³. At 2 years, the volume is 490—500 cm³; at 3 years, 580—680 cm³; and by 4 years, up to 750 cm³. By the end of the second childhood period (12 years), the volume increases to 1300—1500 cm³. In formula-fed infants, the stomach is distended, particularly in the anterior wall region. A significant portion of the newborn's stomach (cardia, fundus, and part of the body) is located in the left hypochondrium and covered by the left lobe of the Liver. The greater curvature adjoins the transverse colon. As the left lobe of the liver decreases in size, the stomach moves closer to the anterior abdominal wall and shifts into the epigastric region.

The inlet of the stomach in a newborn is at the level of the VIII—IX thoracic vertebrae, and the pyloric orifice is at the level of the XI—XII thoracic vertebrae. As the child grows and develops, the stomach descends. At 7 years of age, in the upright position, the stomach inlet is projected between the XI—XII thoracic vertebrae, and the outlet between the XII thoracic and I lumbar vertebrae. In old age, the stomach descends even further. The mucous membrane of the newborn's stomach is relatively thick, with high folds. The number of gastric pits is about 200 thousand. By the age of three, the number of such pits reaches 720 thousand; by two years, 1,300 thousand; and by 15 years, 4 million.

The number of gastric glands in a newborn is about 500 thousand. Their number in children increases rapidly: in a two-month-old infant, the number of glands reaches 1.8 million; in two-year-old children, 8 million; in six-year-olds, 10 million; and in an adult, about 35 million.

The muscular coat of the newborn's stomach is poorly developed. It reaches its maximum thickness by 15—20 years of age.