Diarrhea is not a disease, it is a signal of various diseases, known as a symptom. There are dozens of diseases that can cause diarrhea, including digestive system diseases such as acute enteritis, acute hemorrhagic necrotizing enteritis, acute bacterial dysentery, ulcerative colitis, Crohn's disease, and intestinal tuberculosis; in addition, certain tumors in the digestive tract such as gastrinoma and VIPoma can also cause diarrhea; certain diseases outside of the digestive tract, such as hyperthyroidism and adrenal insufficiency, can also cause diarrhea. Although different diseases may present with diarrhea, their main symptoms and signs are different. Therefore, we should not make a diagnosis based solely on a single symptom, but also need to conduct a comprehensive analysis through history-taking, physical examination, laboratory tests, endoscopy, or radiographic imaging to make a diagnosis and guide treatment.
"Stomach problems" can cause diarrhea
The stomach is the largest part of the human digestive tract and is divided into the cardia, body, and pylorus. When the stomach is inflamed, ulcerated, or has tumors, it can affect the secretion of gastric acid, the bactericidal effect of gastric acid, and the digestive function of the gastrointestinal tract, making it prone to infectious and malabsorptive diarrhea. Gastrinomas can cause excessive secretion of gastric acid, affecting the digestion and absorption of the small intestine and enhancing intestinal peristalsis, leading to diarrhea with watery or fatty stools.
Duodenal diseases can cause diarrhea
The small intestine is made up of the duodenum, jejunum, and ileum. The duodenum is the first segment of the small intestine, approximately 25-30 cm long, and is the width of 12 adult fingers, hence the name "duodenum". In the middle of the duodenum, there is a papilla where the common opening of the pancreatic duct and bile duct is located. Inflammation, tumors, and stones at this site can obstruct the flow of bile and pancreatic juice, which are related to the digestion and absorption of fats, proteins, carbohydrates, and other nutrients. Therefore, obstruction of bile and pancreatic juice can lead to diarrhea. The duodenum is also a common site for gastrinomas and VIPomas, both of which can cause watery or fatty diarrhea. Although certain diseases of the duodenum can cause diarrhea, they are not very common in clinical practice.
Small intestinal diseases can cause diarrhea
The small intestine is the longest segment of the human digestive tract, with a total length of approximately 5-7 meters in adults. The duodenum is the first segment of the small intestine and is relatively short. The small intestine is mainly composed of the jejunum and ileum. The jejunum accounts for about 2/5 of the small intestine, while the ileum accounts for about 3/5. The small intestine is the main site for the digestion and absorption of nutrients such as fats, proteins, carbohydrates, and vitamins. The surface area of the small intestine, when flattened, is equivalent to the size of a standard basketball court, mainly due to its large absorption area, providing a large space for digestion and absorption of food. The small intestine has a rich blood supply, active secretion and absorption, and abundant lymphoid tissue, including isolated lymph nodes and aggregated lymph nodes, which are the main components of intestinal immunity. Due to these characteristics, inflammation of the small intestine can cause digestive and absorptive dysfunction. Surgical resection of the small intestine can also result in diarrhea. Chronic diarrhea of small intestinal origin is characterized by fatty stools.
Colonic diseases can cause diarrhea
The colon is the last segment of the digestive tract, and its main functions are water absorption, mucus secretion, storage, and processing of food residues to form feces for elimination through the anus. The colon is much thicker and structurally different from the small intestine. Its function is mainly related to the absorption of water and electrolytes from feces. In cases of chronic pseudo-obstruction, slowed intestinal motility and excessive water absorption can lead to constipation and anal fissures. Reduced water absorption can result in thin, loose stools, which can be mushy or watery. Common colonic diseases such as Crohn's disease, ulcerative colitis, colon cancer, ulcerative colonic tuberculosis, and infectious colitis can cause diarrhea. Factors that can cause diarrhea include excessive intestinal motility, excessive secretion, inflammatory exudation, or malabsorption, which increase the excretion of intestinal fluid, increase bowel movements, and result in abnormal stool consistency.
Biliary system diseases can cause diarrhea
The biliary system includes the gallbladder and bile ducts. The gallbladder is located in the gallbladder fossa below the liver and is pear-shaped, consisting of the fundus, body, and neck. Its main function is to store and concentrate bile. The bile ducts, which collect bile secreted by the liver, gradually merge into the common hepatic duct. The common hepatic duct then divides into the cystic duct and common bile duct, which open into the duodenum at the duodenal papilla. After a meal, the gallbladder contracts and releases bile into the intestines, where it mixes with pancreatic juice and food to promote fat absorption. Diarrhea after gallbladder removal is the most typical example of diarrhea caused by insufficient bile secretion. The absence of the gallbladder leads to continuous secretion of bile into the intestines. Without sufficient bile mixing with pancreatic juice and food during meals, fat absorption decreases, bowel movements increase, and stool consistency changes, resulting in fatty diarrhea. Severe cases can lead to malabsorption syndrome.
Liver diseases can cause diarrhea
The liver is the largest digestive gland in the body, weighing approximately 1500 grams in adults. It is located in the right hypochondrium and upper right abdomen, with a soft texture and rich blood supply, giving it a reddish-brown color. The liver is one of the most functionally complex organs in the body. It secretes bile, participates in the conversion of carbohydrates, fats, and proteins through the tricarboxylic acid cycle, synthesizes cholesterol, breaks down toxins or toxic substances absorbed from the intestines, metabolizes drugs (both traditional Chinese medicine and Western medicine), and manufactures or participates in the production of 14 clotting factors. It also plays an important role in bilirubin metabolism and albumin synthesis. Long-term excessive alcohol consumption can lead to liver "toxicity," resulting in fatty liver. If alcohol consumption continues, fatty liver worsens, leading to hepatocyte necrosis and fibrosis, ultimately developing into alcoholic cirrhosis and causing liver failure. All of the above functions of the liver can be impaired, resulting in bile secretion disorders, decreased detoxification of endotoxins, and the occurrence of chronic diarrhea due to intestinal infections or malabsorption caused by portal hypertension and collateral circulation.
