Gastric Absorption and the Mucosal Barrier
Under normal physiological conditions, the stomach rapidly absorbs water and low-molecular-weight electrolytes. It also exhibits a high rate of alcohol and various toxic agents absorption. However, when structural damage to the gastric wall occurs, barrier function declines. The primary consequence is enhanced penetration of macromolecules, particularly antigenically foreign proteins, into the internal environment of the body. This inevitably triggers immunopathological processes, ranging from classic allergic reactions to severe autoimmune responses.
The gastric barrier consists of mucus, bicarbonates (which neutralize acid), and a strict pH gradient (from 2.0 in the lumen to 7.0 at the epithelial membrane). The barrier can be disrupted by Helicobacter pylori, ethanol, NSAIDs, bile salts, or an excess of lipid peroxidation products. Aggressive factors cause a sharp spike in hydrogen ion concentration within cells, epithelial cell death, destruction of tight junctions, edema, and hemorrhage.
Disorders of Intestinal Digestive Function
Digestive pathology arises from combined or isolated secretory dysfunctions of the digestive glands. Consequently, the two main types of digestion are impaired: luminal (in the intestinal lumen) and membrane-bound (surface digestion).
Key causes of impairment:
- Pancreatic achylia: loss of the exocrine function of the pancreas. It results from reduced glandular mass (pancreonecrosis, tumor, resection), duct obstruction, or dyskinesia (smooth muscle spasm).
- Bile secretion disorders: bile deficiency in the small intestine due to liver and biliary tract diseases.
- Decreased secretion of Brunner's glands: lack of protective mucus and bicarbonates in the duodenum. Causes include mucosal atrophy, wall ischemia, acute enteritis, and intoxications.
- Goblet cell dysfunction: impaired mucus secretion in intestinal crypts and villi.
Absorption Disorders and Malabsorption Syndrome
Impairments in luminal and membrane-bound digestion naturally lead to the development of malabsorption syndrome. Its primary threats to the body include total energy and substrate deficiency, as well as the risk of intestinal autoinfection and toxemia.
Absorption of hydrolysis products is impaired due to the following factors:
- Digestive insufficiency: defects in nutrient breakdown.
- Accelerated transit: reduced contact time between chyme and the mucosa (observed in diarrhea, irritable bowel syndrome).
- Mucosal atrophy: a physical reduction in the absorptive surface area.
- Mucosal screening (shielding): an excess of inflammatory exudate or mucus preventing nutrient contact with the villi (typical for acute intestinal infections).
- Decreased intestinal length: consequences of surgical resection for necrosis or tumors.
- Vascular disorders: microcirculatory disturbances in the intestinal wall, including ischemia, venous congestion, and stasis.