Stomach functions
The stomach performs not only digestive functions, but also several other important functions:
- Digestive (chemical processing): The breakdown of carbohydrates inside the food bolus by salivary enzymes continues in the stomach, but its main role is protein digestion. Pepsin hydrolyzes proteins, while hydrochloric acid (HCl) denatures them, activates pepsinogen, and creates an optimal acidic pH. In children, chymosin breaks down milk proteins. Mucus protects the organ wall, and the intrinsic factor of Castle is essential for vitamin B12 absorption.
- Absorptive: Water, salts, glucose, alcohol, and certain medications are absorbed.
- Excretory: Elimination of urea and ammonia (increases in renal failure).
- Endocrine: Production of hormone-like substances to regulate the gastrointestinal tract.
Anatomical structure and mucosal relief
Macroscopically, the stomach is divided into four parts: the cardiac (entry zone), fundus (or fornix), body (the largest part), and pyloric part (the exit region containing the pylorus — pylorus).
The inner surface exhibits a complex three-level relief:
- Ruga (plicae gastricae): form a coarse meshwork on the posterior wall, and longitudinal folds in the pyloric region specifically oriented along the lesser curvature.
- Areas (areae gastricae): mucosal areas 1–10 mm in size, separated by connective tissue grooves containing blood vessels.
- Pits (foveolae gastricae): microscopic depressions (~0.2 mm) into which the glands open (up to 10 glands per pit in the fundus region). The depth of the pits in the body and fundus is about 25% of the mucosal thickness, and they are deeper in the pyloric region.
Histology of the stomach wall
The mucous membrane (tunica mucosa) is about 1 mm thick. Its epithelium is simple columnar glandular. All cells (surface mucous cells) secrete mucus. The lamina propria consists of loose fibrous connective tissue and contains simple tubular glands with exocrinocytes and endocrinocytes. The excretory ducts of the glands are their necks (containing neck mucous cells). The muscularis mucosae consists of three layers of smooth myocytes.
The submucosa (tela submucosa) is formed by loose connective tissue with an abundance of fat cells, blood vessels, lymphatic vessels, and Meissner's nerve plexus.
The muscular coat (tunica muscularis) is unique in containing three layers of smooth muscle: inner (oblique or longitudinal), middle (circular), and outer (longitudinal). Auerbach's nerve plexus lies between them.
The serosa (tunica serosa) is the visceral peritoneum covered by mesothelium. A third nerve plexus is located beneath it.
Briefly: answers to topical questions
What types of cells are part of the proper (fundic) gastric glands and what do they secrete?
The proper (fundic) gastric glands include chief, parietal, and neck mucous cells.
- Chief cells — form secretory granules containing pepsinogen, other proenzymes, and lipases.
- Parietal (oxyntic) cells — secrete hydrogen and chloride ions (components of hydrochloric acid), bicarbonate ions, and also synthesize Castle's intrinsic anti-anemic factor.
- Neck mucous cells — are located in the neck of the gland and exhibit secretory activity.
How do the pyloric glands of the stomach differ histologically from the fundic glands?
Pyloric glands differ from fundic glands in their degree of branching, lumen width, and cellular composition.
| Sign | Fundic glands | Pyloric glands |
|---|---|---|
| Morphology | Simple tubular, practically unbranched | Simple tubular, highly branched ("bunched" appearance) |
| Lumen | Narrow | Wider |
| Cellular composition | Contain all cell types (including chief and parietal) | Mucous glands, formed by pale mucous cells (parietal cells are completely absent) |
| Staining | Basophilic and oxyphilic | Pale |
What hormones are produced by gastric endocrinocytes?
Endocrinocytes of the gastric mucosa produce a wide range of hormones to regulate GI tract function.
- G cells — produce gastrin and enkephalin.
- P cells — produce bombesin.
- D cells — produce somatostatin.
- D1 cells — produce vasoactive intestinal peptide (VIP).
- A-like cells — produce gastric glucagon.
- EC cells — secrete serotonin and melatonin.
- Enterochromaffin-like cells — release histamine.
Class and exam questions
How many layers does the muscular coat of the stomach have?
Unlike most parts of the GI tract, the muscular coat of the stomach has three layers: inner (oblique/longitudinal), middle (circular), and outer (longitudinal).
What epithelium lines the gastric mucosa?
Simple columnar glandular epithelium. All of its cells (surface mucous cells) secrete protective mucus.
What are gastric pits and what is their role?
These are depressions in the mucosal epithelium that serve as orifices for the excretory ducts of the gastric glands. There are about 3 million of them in the stomach.
What else to study on this topic
- Cellular composition of gastric glands (chief, parietal, and endocrine cells)
- Structural features of glands in different regions (cardiac, fundic, pyloric)
- Cytology and functional polarity of surface mucous cells
- Mechanism of pepsinogen activation by hydrochloric acid
- Lymphoid apparatus of the stomach (solitary follicles and infiltrates)
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