Diarrhea (diarrhea) is defined as an increase in the amount of stool as a result of increased peristaltic movements in the intestine, decreased absorption and/or increased secretion, an increase in the number of stools per day, and the consistency of the stool deteriorates and takes on a soft watery appearance. Normally, the number of defecations varies from person to person, but it can be from one to three times a day or even once every three days. If there are more than three watery stools a day, diarrhea can be mentioned. Along with diarrhea, there may be cramp-like pain in the abdomen and an increase in the amount of gas.
70-85% of normal stool is water. Therefore, the water content of the stool determines whether you have diarrhea or not. In twenty-four hours, about 10 liters of fluid enter the digestive tract (including drinking water and secretions), of which 9.9 liters are absorbed and 0.1 liters are excreted along with feces. 8-9 liters of these fluids are absorbed from the small intestines and 0.9-1.9 liters from the large intestines. While the absorption capacity of the small intestines is not known exactly, the colon can increase its absorption capacity up to 4-5 liters. Even very small reductions in water absorption can produce large increases in the water content of the stool. If the water content of the stool exceeds 0.3 liters, diarrhea always occurs.
Intestinal cells are capable of both secretion and absorption. Normally, the secretion rate is slower than the absorption, and the net result is absorption. Accordingly, any hormone or toxin can reduce net absorption in the gut, either by stimulating secretion or by inhibiting absorption.
The main mechanisms that cause diarrhea are:
1. The presence of osmotically active solutes that cannot be adequately absorbed in the intestinal lumen (osmotic diarrhea),
2. Active ion secretion is the inhibition of normal absorption (secretory diarrhea),
3. Intestinal motility disorder,
4. It is the morphological changes of the intestinal mucosa or the decrease in the absorption surface.
What is Osmotic Diarrhea?
Osmotic diarrhea occurs when there are non-absorbable solutes in the intestinal lumen. The main foods that increase the lumen osmolarity of the small intestine are carbohydrates. Lactose intolerance is a prime example of osmotic diarrhea. Excessive intake of non-absorbable carbohydrates, for example, excessive use of sweeteners, increases osmolarity and causes diarrhea.
Normal stool Its osmolality is close to that of plasma and is around 280-310 mOsm. A hypotonic (low osmolality compared to plasma) or hypertonic (high osmolality compared to plasma) food taken orally will be tried to be made isosmotic as it progresses down the digestive tract. If a hypertonic food is taken, fluid will be drawn into the intestinal lumen and the inside and outside of the intestinal lumen will be restored to osmotic balance. For example, if 250 mL of milk with an osmolality of 600 mOsm is drunk, its volume will have to increase to 600 mL in order for it to be expelled as 300 mOsm. If the fluid absorbed by the osmotic active substance in the intestinal lumen into the lumen is above the absorption capacity of the small and large intestines, diarrhea will occur because the water coming out will be excessive.
Osmotic diarrhea occurs due to the intake of absorbed substances, poor digestion of food and disorders in mucosal transport. In osmotic diarrhea, three important features stand out: stops starving, stool There is an "osmotic gap" of more than 100 mOsm between osmolality and plasma osmolality, and stool pH has shifted in the acid direction (<5.5).
What are Secretory Diarrheas?
These are diarrheas that occur as a result of increased water and electrolyte secretion in the intestine or decreased absorption. The main conditions that cause secretory diarrhea are; congenital disorders in ion absorption, intestinal resections, diffuse mucosal diseases that cause a decrease in the number and function of intestinal epithelial cells, and the presence of abnormal mediators (neuro-hormonal substances, bacterial enterotoxins, bile acids, etc.) that impair absorption and secretion functions.
Secretory diarrhea persists in starvation, it is large in volume and abundant water. The stool does not contain blood, fat and pus. The "osmotic gap" between fecal osmolality and plasma osmolality is below 50 mOsm.
The main conditions that cause secretory diarrhea are:
1. Infections with enteretoxin-secreting organisms:The classic disease that falls into this category is cholera. The intestinal mucosa is morphologically normal. However, due to the action of cholera toxin, the increase in intracellular cyclic adenosine monophosphate (cAMP) causes active ion secretion from enterocytes. Various microorganisms such as enterotoxigenic escherichia coli, Campylobacter jejuni, Yersinia enterocolitica, Salmonella, Shigella, Clostridium difficile can also cause secretory diarrhea through the enterotoxins they secrete.
2. Pancreatic cholera syndrome: In high concentrations in the circulation, vasoactive intestinal polypeptide (VIP) causes diarrhea by causing water and electrolyte secretion from the intestine. In adults, VAP increases, which are usually seen in tumors originating from islet cells of the pancreas, often occur in the presence of ganglioneuroma or ganglioneuroblastoma in children.
3. Idiopathic secretory diarrhea: Although these patients have clinical features of secretory diarrhea and pancreatic cholera, no tumor or VAP increase can be detected. Laparotomy or even autopsy may not find the cause. It has been reported that spontaneous recoveries may occur. Some patients may benefit from opiates.
4. Carcinoid syndrome: 70-80% of patients with carcinoid syndrome have diarrhea. Plasma levels of serotonin and substance P, which are experimentally known to cause water and electrolyte secretion in the intestine, are increased in most patients. In addition, lymphatic obstruction caused by compression of the tumoral mass and intestinal obstruction caused by fibrosis in the intestinal wall may also contribute to the formation of diarrhea.
5. Medullary carcinoma of the thyroid: Diarrhea occurs in approximately 30% of thyroid medullary carcinoma cases. The main mediator that causes intestinal secretion and therefore diarrhea is calcitonin.
6. Zollinger-Ellison syndrome (gastrinoma): In these patients, due to the high level of circulating gastrin, the amount of HCl passing into the small intestine is increased. The amount of acid reaching the jejunum can reach 24 liters per day in starvation. In addition, disorders of the brushy edges of enterocytes due to the effect of an excess of acid in the intestinal lumen can contribute to the formation of steatorrhea de diarrhea, which can occur due to the direct effect of excessive amounts of gastrin on the mucosa of the small intestine, the inactivation of pancreatic lipase with acid, and the decrease in mycelia formation by bile acids as a result of low intraluminal pH.
7. Bile acid diarrhea: It is a form of diarrhea (choleretic diarrhea) that occurs as a result of increased secretion in the colon due to impaired absorption of bile acids. The most effective drug in treatment is cholestyramine. In addition, there may rarely be an excessive increase in the concentration of bile acids excreted in faeces. Cholestyramine treatment often fails.
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