Diarrhea: Definition, Types & Causes

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  • 0:00 Diarrhea Defined
  • 3:01 Causes of Diarrhea
  • 3:35 Types of Diarrhea
  • 5:20 Lesson Summary
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Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

Did you know there is more than one reason for diarrhea, that there is more than one kind of diarrhea, and that there is way more than one way to define diarrhea? Learn more in this lesson.

Diarrhea Defined

You know that feeling? You know the one. When you're out at a restaurant, on a train or just walking in the middle of the street and you realize that you have to go. Now. And not number one, but number two. Yep. It's because your stomach is churning, and your worst fear may come to pass if you lose control. It's diarrhea. What exactly is diarrhea anyway? Diarrhea is an increased frequency of bowel movements with a concomitant passage of liquefied stool. This is the standard definition of diarrhea, anyway. It comes from the prefix of 'di-', which means two or twice as much, and '-rrhea', which means a profuse flow of something. There's actually a more proper medical definition of what we just call 'the runs.' Another way to define diarrhea is a reversal of the net absorption of water and electrolytes in the intestinal tract to their secretion and excretion out of the body, meaning, instead of absorbing water and electrolytes into our body, we are now ridding ourselves of more of them. There's a third way to look at and define diarrhea, also from a medical perspective. Diarrhea can be seen as a stool volume of greater than 10mL/kg/d in infants and young children, or a stool weight of more than 200g/d in teenagers and adults. Who knew there could be so many ways to describe so many of our memories on the toilet? In essence, diarrhea is really an increase in the water content of the stool. That's the important part of it. This, in turn, causes stool frequency to increase.

One other thing. As with any topic in medicine, there are catches and exceptions to just about every rule and definition. For instance, the definition of a stool weight of more than 200g/d in teenagers and adults is applicable in most scenarios, but not all. This is because something called normal output diarrhea exists. This is where the stool output is less than 200g/d, but the person experiences hyper-defecation, abnormally increased frequency of defecation, as a result of things like anorectal disease, functional bowel disorders, and hormonal problems. However, from some perspectives, normal output of diarrhea is actually a misnomer because true diarrhea entails an excess of water being excreted and expelled. This is what causes the liquefied stool. The three disorders I just mentioned may not have excess water being expelled, and instead will only increase the frequency of defecation, hyper-defecation, or loss of control of defecation, incontinence, without a change in the consistency of the stool itself. Thus, the definitions for diarrhea all depend on how picky you want to be about the language you use.

Causes of Diarrhea

Anorectal disease, functional bowel disorders, and hormonal problems are some of the less frequent causes of diarrhea, actually. More common causes for diarrhea include:

  • Bacteria, such as salmonella,
  • Viruses, such as rotovirus,
  • Parasites or protozoa, like Giardia,
  • Drugs,
  • Cancer,
  • Intestinal disorders, like irritable bowel, ulcerative colitis, and Crohn's Disease, and
  • Food, be it due to overconsumption of certain foods, intolerance or allergy.

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