diarrhea
Meaning of diarrhea: Duration does much of the diagnostic work, separating a short lived infection from a long standing problem inside the gut.
Definition of diarrhea
Diarrhea is the passage of loose or watery stools more often than is usual for a person, generally with an increase in stool volume as well. It may last a few days and settle without treatment, or continue for weeks. It is a symptom produced by many different conditions rather than a diagnosis on its own.
What is actually going wrong in the gut?
The small and large intestine handle a large volume of fluid each day, most of it secreted by the body rather than swallowed, and nearly all of it is reabsorbed before stool is formed. Diarrhea is what happens when that balance tips, and there are only a few ways it can tip.
| Mechanism | What happens | Typical causes |
|---|---|---|
| Osmotic | Something in the gut that cannot be absorbed holds water in place | Lactose intolerance, some laxatives and sugar substitutes |
| Secretory | The intestinal lining pumps fluid out faster than it takes it back | Bacterial toxins, including cholera; certain hormone producing tumors |
| Inflammatory | A damaged lining leaks fluid, blood and mucus and absorbs poorly | Invasive infection, inflammatory bowel disease, radiation injury |
| Rapid transit | Contents move through too fast for water to be reclaimed | Overactive thyroid, some surgery on the bowel, irritable bowel syndrome |
How does duration narrow the cause?
Short lived diarrhea is usually infectious, whether viral, bacterial or parasitic, and food poisoning, a recent course of antibiotics and newly started medicines account for much of the rest. Diarrhea that persists for weeks points elsewhere: celiac disease, inflammatory bowel disease, chronic pancreatic problems that leave fat unabsorbed, bile acid malabsorption, thyroid overactivity, or irritable bowel syndrome. That is why the length of the history is asked about before anything else, along with whether it wakes a person at night, whether it improves with fasting, and what the stool looks like.
Why does fluid loss matter so much?
Stool lost in quantity carries water, sodium, potassium and bicarbonate with it. Losing enough fluid and salt produces thirst, dry mouth, reduced urine output, light headedness on standing and, if it continues, disturbance of the body's salt and acid balance. The risk is greatest at the extremes of age, where reserves are smallest. Blood or mucus in the stool, fever, severe pain and weight loss are noted separately, since they suggest inflammation or invasion rather than a simple upset.
Used in a sentence
The patient reported several days of watery diarrhea accompanied by abdominal cramping.
Good to know
Diarrhea lasting less than about two weeks is generally described as acute, while diarrhea persisting beyond four weeks is described as chronic, a distinction that affects how the cause is investigated.
Word origin
Where “diarrhea” comes from
Formed from Greek dia-, meaning through, and rhein, meaning to flow.