Mechanisms and classification of motor disorders
In pathological physiology, typical disorders of gastric motor function are classified according to the leading mechanism of their occurrence. There are three main targets whose damage leads to motility disorders: the muscular wall, the sphincter apparatus, and the peristaltic process itself.
Changes in wall tone. Normally, the stomach maintains a certain muscular tension. Pathology leads to hypertonus (increased tension) or hypotonus (decreased tension). The extreme degree of hypotonus is atony—complete absence of muscle tone. It is atony that provokes peristole disorders. The term peristole originates from the Greek words peri (around) and stello (to squeeze). This is a crucial tonic contraction of the musculature that ensures the tight enveloping of food contained in the stomach.
Sphincter pathology. Disorders affect the cardiac and pyloric sphincters. Their tone may be excessively decreased or excessively increased. The most severe variant is prolonged spasm. If it occurs in the cardiac region, cardiospasm develops; if in the pyloric region, pylorospasm.
Peristalsis failures. The movement of the peristaltic wave can be excessively accelerated (hyperkinesis) or, conversely, slowed down (hypokinesis).
Etiology: why is motility impaired?
The causes (etiology) of evacuation function disorders are divided into three large groups: neural regulation disorders, humoral regulation failures, and organic pathological processes.
- Neural regulation disorders. The autonomic nervous system directly controls the stomach. Enhancement of motility occurs with increased tone of the vagus nerve (n. vagus). Suppression of motor function is associated with activation of the sympathetic nervous system.
- Humoral regulation disorders. Biologically active substances can both stimulate and stop contractions.
- Inhibition of motility is caused by: high concentration of hydrochloric acid (HCl) in the stomach, as well as an excess of secretin and cholecystokinin.
- Stimulation of motility is observed with a reduced HCl content, as well as against the background of an excess of gastrin and motilin.
- Organic changes. Structural defects of the stomach—erosions, ulcers, scars, or tumors—inevitably alter contractility. Depending on the localization and severity of the process, they can either weaken or enhance motility.
Pathogenesis and consequences: evacuation disorders
Whatever the primary mechanism (wall tone disruption, sphincter spasm, or peristalsis disorder), they all share a common outcome. The pathogenesis of disorders is based on combined or separate disorders of stomach wall tone and peristalsis, which ultimately leads to impaired evacuation function.
There are two types of disorders of chyme (food mass) evacuation from the stomach into the duodenum:
- Accelerated evacuation.
- Delayed evacuation.
Clinical manifestations. One of the most frequent manifestations of evacuation disorders is a feeling of heaviness and fullness in the stomach, which occurs even after taking a small amount of food. This clinical syndrome is based on a specific mechanism: a decrease in the tone and motility of the antral region of the stomach.
Briefly: answers to topical questions
What is the pathogenesis of eructation and vomiting in gastric evacuation function disorders?
In the "vicious circle" syndrome, the disturbance of food mass evacuation from the stomach is due to food being retained in the stomach, duodenum, and the afferent loop of the jejunum. Food in the loop decomposes and enters the stomach back, leading to eructation and vomiting. Vomiting develops as a result of activation of the vomiting center neurons in the medulla oblongata and includes combined phenomena:
- Antiperistalsis — enhancement of antiperistalsis of the stomach wall.
- Muscle contraction — simultaneous contraction of the diaphragm and abdominal wall muscles.
- Muscle relaxation — relaxation of the muscles of the cardiac part of the stomach and esophagus.
What is dumping syndrome and how is it related to accelerated gastric evacuation?
Dumping syndrome is a typical evacuation disorder characterized by rapid evacuation of gastric contents into the small intestine. Accelerated passage of insufficiently processed chyme triggers a chain of pathological reactions:
- Hyperosmolality — development of rapid hyperosmolality of the intestinal contents.
- Hypovolemia — food hyperosmia causes an influx of fluid into the intestinal lumen.
- Arterial hypotension — activation of the release of biologically active substances against the background of hypovolemia.
- Glycemic fluctuations — intensive glucose absorption causes hyperglycemia and hyperinsulinemia, leading to late hypoglycemia.
How to remember humoral regulation: "Secretin and cholecystokinin inhibit, gastrin and motilin stimulate (motivate)." High acidity (HCl) inhibits motility, while low acidity stimulates it.
Class and exam questions
What is peristole and how does atony affect it?
Peristole is a tonic contraction of the gastric musculature that ensures tight enveloping of food. In atony (complete absence of muscle tone), peristole disorders occur, and the stomach loses its ability to tightly fit around food masses.
What is the ultimate result of any gastric motility disorders?
All changes in wall tone, sphincters, and peristalsis lead to impaired evacuation function. Chyme evacuation into the duodenum is either pathologically accelerated or slowed down.
How does the autonomic nervous system affect peristalsis?
Increased vagal tone (n. vagus) leads to enhanced motility. Activation of the sympathetic nervous system, by contrast, suppresses gastric motor function.
Can organic changes in the stomach enhance motility?
Yes, pathological processes (erosions, ulcers, scars, tumors) can both weaken and enhance motility. The ultimate effect depends on the exact localization and severity of the pathological process.
What else to study on this topic
- Pathogenesis of cardiospasm and pylorospasm development
- The effect of ulcers and scars on local gastric motility
- Mechanisms of humoral inhibition of peristalsis
- The relationship between gastric juice acidity (HCl) and chyme evacuation rate
- The role of the antral region in generating the feeling of heaviness
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