Tiêu chảy là bệnh được đặc trưng bởi phân lỏng, tăng khối lượng phân, tăng tần số đi đại tiện, tiêu chảy có hai dạng là tiêu chảy cấp tính và tiêu chảy mạn tính. Lượng nước trong phân > 98%.

I.                   Hậu quả: mất nước, mất điện giải, suy dinh dưỡng.

II.                Phân loại: Có 2 cách:

1.      Cấp, mạn.

2.      Do tăng tiết, do tăng thẩm thấu, do tăng nhu động, do viêm-nhiễm.

III.             Nguyên nhân:

1. Do tăng tiết: Secretory diarrhea

Secretory diarrhea means that there is an increase in the active secretion, or there is an inhibition of absorption. There is little to no structural damage. The most common cause of this type of diarrhea is a cholera toxin that stimulates the secretion of anions, especially chloride ions. Therefore, to maintain a charge balance in the lumen, sodium is carried with it, along with water.

2. Do tăng thẩm thấu: Osmotic diarrhea

Osmotic diarrhea occurs when too much water is drawn into the bowels. This can be the result of maldigestion (e.g., pancreatic disease or Coeliac disease), in which the nutrients are left in the lumen to pull in water. Osmotic diarrhea can also be caused by osmotic laxatives (which work to alleviateconstipation by drawing water into the bowels). In healthy individuals, too much magnesium or vitamin C or undigested lactose can produce osmotic diarrhea and distention of the bowel. A person who does not have lactose intolerance can have difficulty absorbing lactose after an extraordinarily high intake of dairy products. In persons who do not have fructose malabsorption, excess fructose intake can still cause diarrhea. High-fructose foods that also have a high glucose content are more absorbable and less likely to cause diarrhea. Sugar alcohols such as sorbitol (often found in sugar-free foods) are difficult for the body to absorb and, in large amounts, may lead to osmotic diarrhea.

                   3. Do tăng nhu động: Motility-related diarrhea

Motility-related diarrhea is caused by the rapid movement of food through the intestines (hypermotility). If the food moves too quickly through the GI tract, there is not enough time for sufficient nutrients and water to be absorbed. This can be due to a vagotomy or diabetic neuropathy, or a complication of menstruation. Hyperthyroidism can produce hypermotility and lead topseudodiarrhea and occasionally real diarrhea. Diarrhea can be treated with antimotility agents (such as loperamide).

                   4. Do viêm nhiễm: Inflammatory diarrhea

Inflammatory diarrhea occurs when there is damage to the mucosal lining or brush border, which leads to a passive loss of protein-rich fluids, and a decreased ability to absorb these lost fluids. Features of all three of the other types of diarrhea can be found in this type of diarrhea. It can be caused by bacterial infections, viral infections, parasitic infections, or autoimmune problems such as inflammatory bowel diseases. It can also be caused by tuberculosis, colon cancer, and enteritis.