Why do diarrhea and constipation occur alternately? First of all, we should know that the nerves that regulate the intestinal tract (and also other internal organs) are called “vegetative nerves”, and the connection between the central nervous system, especially the higher nervous activity of the brain, and the internal organs is regulated directly or indirectly through these vegetative nerves. The so-called “indirectly” means that the intermediate effect is exerted through the secretory function of endocrine glands. There are two types of plant nerves: sympathetic nerves and parasympathetic nerves, whose roles are both different and complementary. For example, sympathetic nerves can inhibit the motor and secretory functions of the intestine, while parasympathetic nerves can enhance the motor and secretory functions of the intestine. When an “organic” or “functional” change occurs in a part of the intestine, it will stimulate the vegetative nerves, and the vegetative nervous system transmits these continuous stimulation signals to the cerebral cortex, which can lead to the regulation of the cerebral cortex over time. Disorder, the parasympathetic nerve center will take the opportunity to release from the control of the cerebral cortex, increased excitability, governed by it to accelerate intestinal movements, the patient appears diarrhea; the nerve excitement for too long, can be due to “fatigue” and gradually decline and turn to inhibition, the intestinal muscles will slowly relax, peristalsis weakened, the result and cause constipation. This constipation is clinically known as “flaccid constipation”, while some diseases due to strong stimulation of the parasympathetic nerve center by the stimulus and in a state of extreme excitement, so that the distal colon continues to spasm, resulting in “spasmodic constipation”. These patients often pass very fine ribbon-like stools or goat’s egg-like stools. The spasm of the colon continues to deepen, intestinal peristalsis increases again, and the stool turns from constipation to diarrhea, and so on and so forth. It can be seen that in patients with intestinal motility disorders, sometimes constipation (slow bowel movement), sometimes diarrhea (rapid bowel movement), or alternating constipation and diarrhea will occur. So, which diseases will have alternating diarrhea and constipation? 1, intestinal tuberculosis. This disease is usually seen in young and middle-aged people, more women than men, and the lesions are mainly located in the ileocecal region, but can also involve the colon and rectum. There are three main types of intestinal tuberculosis, namely ulcerative intestinal tuberculosis, hyperplastic intestinal tuberculosis and mixed intestinal tuberculosis. Sometimes, diarrhea alternates with constipation. Hyperplastic intestinal tuberculosis is mainly constipation. 2. Fecal mass filling. In constipation, the abdomen is vaguely distended and painful, and every time there is an intention to have a bowel movement, but it cannot be done as desired. A long hard lump can be felt in the left lower abdomen, and sometimes watery diarrhea may occur suddenly. When the fecal mass is exhausted, the mass in the lower left abdomen disappears rapidly and the diarrhea stops. In fact, this lump is a manifestation of fecal masses retained in the intestinal cavity. This diarrhea is pseudo-diarrhea. 3, colon cancer. In the middle-aged and elderly people are more often. Whether it occurs in the transverse colon, left curved colon, right curved colon, etc., it can show significant weight loss, significant anemia, weakness and pain of different degrees in the abdomen. For example, in transverse colon cancer, there is often a movable mass around the umbilicus that is not associated with stool. In the early stage of left flexural colon cancer, although there are symptoms of alternating constipation and diarrhea in the case of incomplete intestinal obstruction, the abdominal masses are not easily palpable. Such as right varicose colon and cecum cancer masses can be easily found in the right side of the abdomen. IBS is a common functional bowel disease characterized by abdominal pain or abdominal discomfort with changes in bowel habits without organic lesions. It is mainly divided into diarrhea type, constipation type and mixed type. Diarrheal IBS is often characterized by rapid defecation, with dilute watery stools, usually 3 – 5 times a day, and in a few severe episodes up to 10 times a day, with mucus, but no pus and blood. Some patients have alternating diarrhea and constipation. Constipation type IBS often has difficulty in defecation, dry stool, small amount, in the shape of sheep feces or fine rod. 5. Intestinal obstruction. Intestinal obstruction can be caused by intussusception and roundworm obstruction, which are common in children, and hernia, intestinal adhesion disease and tumor, which are common in middle-aged and elderly people. In case of incomplete intestinal obstruction, alternating constipation and diarrhea are also common because of the inflammation of the intestine proximal to the obstruction. When the intestinal lumen obstruction gradually increases, blood in the stool and pseudo-diarrhea can occur. 6, cirrhosis of the liver. Those with chronic hepatitis are susceptible. 2 – 3 times a day stool, always thin, sometimes can appear oil-like stool. A few days of stool can not be solved by the fecal mass, mostly hard, light yellow and undigested food for more. 7. Regional ileitis. The patient is between 20 – 40 years old, characterized by fever and paroxysmal abdominal cramps, constipation and diarrhea alternately. x-ray can be seen in the ileum is knotted, small intestine curvature swollen, the proximal side of the cecum can be stump barium shadow and stenosis. These diseases not only have symptoms of alternating constipation and diarrhea, but also have different degrees of abdominal pain. Therefore, when using antidiarrheal drugs, analgesics and laxatives, caution must be exercised to avoid delaying causal treatment. In addition, constipated patients may have diarrhea after taking certain drugs, and often have dry stools or even constipation after stopping the drugs; constipated patients may have diarrhea when using enemas for laxative purposes, and often have constipation after stopping the enemas.