General Motility Disorders: Diarrhea and Constipation

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  • 0:20 What Is Diarrhea?
  • 0:39 What Is Osmotic and…
  • 1:52 Other Types of…
  • 3:39 Testing For and…
  • 4:56 What Is Constipation…
  • 5:48 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
This lesson will discuss diarrhea and constipation. More interestingly, we'll actually discuss the many different forms of diarrhea, such as osmotic and secretory. We'll also learn what melena and hematochezia mean.

Potentially Deadly Simple Problems

A great many song, commercial, and joke has been made about the contents that will be expelled, no pun intended, in this lesson.

All joking aside, what we'll talk about may look simple but has a lot more consistencies to it than most people expect and can actually be deadlier than you suspect.

What Is Diarrhea?

Diarrhea is a type of bowel movement resulting in watery stools. You knew that. But believe it or not, what you may not know is there's actually more than one type of diarrhea. The next time you get diarrhea, try to figure out which type you have as you're sitting on the toilet. At least it'll make the experience a bit more fun!

What Is Osmotic and Secretory Diarrhea?

So, there's osmotic diarrhea, which can occur if things that can't be absorbed by the intestines draw water out of the body or cause the retention of water within the intestinal lumen, the open part of the intestines. Eating too many grapes or enjoying lactose intolerance are two prime examples of this type of diarrhea. The good thing about this type of diarrhea is that many times you'll just get it out of your system once or twice, and it will stop on its own until the next time you drink too much grape juice. In a basic sense, osmotic diarrhea occurs because the pump pushing water into the body is not strong enough to do so against the larger forces of osmosis holding the water back in the lumen.

But when the pump actually actively pumps water out of the body and into the intestines, then it's called secretory diarrhea. It's actually not that big of a secret. In this type of diarrhea, the water is being secreted out into the intestines. The end result is a massive and potentially deadly secretion of water and resulting dehydration of the body. Causes of secretory diarrhea include bacterial toxins, such as the cholera toxin, certain laxatives, and even tumors.

Other Types of Diarrhea, Melena, and Hematochezia

There are other types of diarrhea, including exudative and inflammatory, where there's blood, mucus, and pus in the stool that can be associated with inflammatory bowel disorders, such as ulcerative colitis and Crohn's disease. These things can increase the fluid content of the stool and even the osmotic forces, predisposing to diarrhea. If that wasn't bad enough, the inflammation in these diseases causes irritant receptors in the bowel to constantly fire off signals telling your brain you need to always go to the bathroom, even if only a tiny bit of bloody mucus ends up coming out.

If the blood coming out of the rear end is bright red, it's called frank blood or hematochezia. Again, hematochezia is fresh, bright red blood being passed as a result of bleeding occurring in the lower gastrointestinal tract, such as the colon. It can also occur if there is massive upper GI bleed. This should be contrasted with melena. Melena is dark tarry, digested blood coming from the upper digestive tract, such as the stomach and duodenum.

Finally, certain neurological and metabolic conditions, stress, or even some types of food and drugs can decrease the amount of time ingested food and water has for absorption into the body, leading to diarrhea due to what's known as motility disorder. In this case, the pump works just fine; it's simply that the digestive content is rushing by way too quickly for the pump to catch it all. This occurs because the muscles of the GI tract do not contract and relax back and forth properly like a jaw in order to 'chew' the food in the intestines. Instead, they quickly flush the food down through the entire tract like a conveyor belt.

Testing and Treating Diarrhea

Prolonged or severe diarrhea can cause the loss of bicarbonate, potassium, and magnesium from the body. Sodium levels may increase or decrease, depending on the cause. All of this can actually cause serious problems, such as arrhythmias of the heart and metabolic acidosis.

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