Disorders of the motor function of the intestine

Diarrhea: definition and pathogenetic classification

Diarrhea (from Greek diarrheo — to flow through) is a typical form of digestive system pathology. Its main clinical criteria include increased frequency of bowel movements (more than 2–3 times a day) and a change in stool consistency to liquid or mushy.

Depending on the leading mechanism of development, four types of diarrhea are distinguished:

• Exudative. Occurs as a result of excessive exudate formation by the intestinal mucosa. Typical examples include infectious and non-infectious enteritis and colitis.
• Secretory. Results from excessive fluid secretion directly into the intestinal lumen. This form is characteristic of cholera, viral enterocolitis, AIDS, and VIPoma (hyperproduction of vasoactive intestinal peptide by a pancreatic tumor).
• Hyperosmolar. Develops due to significant hyperosmolarity of the intestinal contents. It occurs in malabsorption of chyme components or upon overdose of saline laxatives.
• Hyperkinetic. Forms as a consequence of a combination of hypersecretion and increased intestinal peristalsis. It is observed in irritable bowel syndrome and various forms of enterocolitis.

Systemic consequences of recurrent diarrhea

Profuse or recurrent diarrhea poses a serious threat to homeostasis and can lead to a number of severe systemic disorders:

1. Body hypohydration. Fluid loss can reach extreme degrees of dehydration—exicosis (e.g., in severe cholera courses).
2. Hypovolemia. Occurs due to the loss of a large amount of fluid and a decrease in circulating blood volume (CBV).
3. Arterial hypotension. Is a direct result of decreased CBV, falling cardiac output, and a reduction in total peripheral vascular resistance.
4. Electrolyte balance and acid-base state (ABS) disorders. The nature and severity of these shifts directly depend on the specifics of the underlying disease that caused the diarrhea.

Obstipation (constipation): types and mechanisms of development

Constipation is a typical form of pathology combined with prolonged stool retention (up to 3 days or more) and difficulty in bowel emptying. Like diarrhea, obstipation is accompanied by digestive and absorptive disorders.

The classification of constipation includes four main varieties (alimentary, neurogenic, mechanical, and rectal). Let us examine their mechanisms of origin in more detail:

• Alimentary (low-volume) constipation. The main cause is a small volume of intestinal contents. This is caused by chronic malnutrition, insufficient fluid intake, dietary fiber deficiency (vegetables and fruits), and a diet consisting predominantly of easily digestible food.
• Neurogenic constipation. Subdivided into two forms with opposite pathogenetic links:
• Spastic: occurs due to an excessive increase in parasympathetic neurogenic influences on the intestinal wall (e.g., in neuroses). This causes prolonged contraction of the intestinal muscular wall, slowing down food movement and evacuation.
• Atonic: associated with a decrease in neuroeffector parasympathetic influences on the intestinal musculature. Often observed after abdominal surgeries or with improper use of anticholinergic drugs.
• Rectal constipation. Results from pathological processes in the rectum accompanied by pronounced pain syndrome (e.g., in anal fissures or paraproctitis). The pathogenesis is that severe pain reflexively suppresses the normal defecation reflex.
• Mechanical constipation. Distinguished in the general classification of typical motility disorder forms as an independent variety of obstipation.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Mechanisms of exicosis development in severe infectious intestinal diseases.
• The effect of vasoactive intestinal peptide (VIP) on the secretory function of the digestive tract.
• Pathogenesis of acid-base state (ABS) disorders during massive loss of intestinal juice.
• The role of anticholinergic drugs in the development of atonic constipation.
• Mechanical constipation: etiology, pathogenesis, and differences from other forms of obstipation.

Other topics in "Chapter 24. Typical Forms of Digestive System Pathology"

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