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 stool frequency (more than 2–3 times a day) and a change in consistency to liquid or loose.
Depending on the leading pathogenetic mechanism, four types of diarrhea are distinguished:
- Exudative. Occurs as a result of excessive exudate production 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 VIPomas (vasoactive intestinal peptide-secreting tumors of the pancreas).
- Hyperosmolar. Develops due to significant hyperosmolarity of the intestinal contents. It occurs in malabsorption syndromes or with an overdose of saline laxatives.
- Hyperkinetic. Forms as a result of a combination of hypersecretion and increased intestinal peristalsis. It is observed in irritable bowel syndrome (IBS) and various enterocolitides.
Systemic Consequences of Recurrent Diarrhea
Profuse or recurrent diarrhea poses a serious threat to homeostasis and can lead to several severe systemic complications:
- Body Dehydration. Fluid loss can reach extreme degrees of dehydration, known as exicosis (e.g., in severe cholera).
- Hypovolemia. Arises due to the loss of a large volume of fluid and a decrease in circulating blood volume (CBV).
- Arterial Hypotension. A direct result of decreased CBV, falling cardiac output, and reduced total peripheral vascular resistance.
- Electrolyte Imbalance and Acid-Base Disturbances. The nature and severity of these shifts directly depend on the underlying disease causing the diarrhea.
Constipation (Obstipation): Types and Pathogenetic Mechanisms
Constipation is a typical pathological state characterized by prolonged stool retention (3 days or more) and difficult bowel evacuation. Like diarrhea, constipation is accompanied by digestive and absorptive disorders.
Constipation classification includes four main types (alimentary, neurogenic, mechanical, and rectal). Let us examine their mechanisms in detail:
- Alimentary (Low-Volume) Constipation. The main cause is the small volume of intestinal contents. This is caused by chronic malnutrition, insufficient fluid intake, dietary fiber deficiency (lack of vegetables and fruits), and a diet consisting primarily of easily digestible foods.
- Neurogenic Constipation. Divided into two forms with opposite pathogenetic links:
- Spastic: occurs due to excessive parasympathetic neural influences on the intestinal wall (e.g., in neuroses). This causes prolonged contraction of the intestinal smooth muscle, slowing down food transit and evacuation.
- Atonic: associated with decreased neuroeffector parasympathetic effects on the intestinal musculature. Frequently observed after abdominal surgeries or with improper use of anticholinergic drugs.
- Rectal Constipation. The result of pathological processes in the rectum accompanied by prominent pain (e.g., anal fissures or paraproctitis). The pathogenesis involves strong pain reflexively suppressing the normal defecation reflex.
- Mechanical Constipation. Classified within general motility disorders as an independent form of obstipation.