The causes of chronic constipation are very complicated and can be grouped into two main categories: first, secondary constipation, which is commonly caused by a low-fiber diet, intestinal tumors, drugs or certain diseases such as metabolic and endocrine diseases, systemic diseases, neurological or psychiatric diseases. If no clear secondary factors or diseases are found to cause the onset of constipation, primary constipation (or functional constipation or idiopathic constipation) can be diagnosed. According to its pathological hearing changes, primary constipation or functional constipation can be mainly divided into the following three types: (a) Colonic transmission dysfunction – slow transmission type of constipation This type is also known as colonic weakness, refers to the intestinal contents from the proximal to the colon and distal rectum through the time slower than normal. This type occurs mostly in young and middle-aged women (mean age of onset 25 years) and presents with decreased frequency of bowel movements, less bowel movements, hard stools; no stools or hard stools on anorectal examination, while the external anal sphincter retracts and forceful defecation function normally; prolonged passage time of the whole stomach or colon; lack of evidence of outlet obstruction type of constipation, such as normal balloon expulsion test and normal anorectal manometry. Although in some patients, the slow passage of bowel contents may be related to dietary culture, for most patients, the pathophysiological mechanism of this type is not currently known. Manometry studies suggest that reduced colonic dynamics is responsible for the colonic transmission dysfunction. Current studies of the lesions underlying slow colonic transmission using advanced microscopic techniques have revealed abnormalities in the intestinal interosseous plexus and alterations in enteric neurotransmitters, such as accumulation of neurofilament protein aggregates and interstitial hyperplasia, and increases in the inhibitory neuromediators nitric oxide (NO) and vasoactive intestinal peptide (VIP), which may be associated with colonic motility disorders. Slow-transmission constipation can be subdivided into two types: n Colonic weakness: associated with reduced high-amplitude transmission contractions, this peristaltic sequence is usually considered to be the mechanism by which the colonic contents undergo group motility. Therefore, lack of this peristaltic sequence may manifest as prolonged retention of residual fecal masses in the right hemicolectum. nDisorders of terminal colon motility: Under normal conditions, terminal colon motility constitutes a mechanical barrier to the movement of intestinal contents, and abnormal and uncoordinated terminal colon motility may lead to the development of constipation. In this type of constipation, the slow passage of intestinal contents slows down the filling rate of the colon, which in turn leads to decreased responsiveness or even retardation of the rectum. At the same time, the water in the intestinal contents is excessively absorbed, resulting in dry stools, which aggravates the difficulty of defecation. (ii) Outlet obstruction type constipation This type is also often called “outlet obstruction”, “emptying obstruction” or “emptying obstruction”, “anal spasm ” or “pelvic floor dysfunction”. The abnormalities leading to functional outlet obstruction include transverse muscle dysfunction, rectal smooth muscle dynamics, rectal sensory impairment, internal anal sphincter dysfunction, temporary anatomic obstruction such as intra-rectal mucosal or total intra-rectal condyloma, anterior rectal distension, sacro-rectal separation, and pelvic floor hernia. Patients with this type may have a history of transvaginal delivery or pelvic surgery prior to the onset of constipation. In this type of patients, the pelvic floor muscles and external anal sphincter are not fully relaxed or paradoxically contracted during defecation, resulting in obstruction of fecal passage; some patients have impaired or lost defecation reflex, which reduces the sensitivity of rectal defecation and leads to the accumulation of fecal masses in the rectum, resulting in constipation; other causes of outlet obstruction include perineal descent syndrome or abdominal muscle weakness. However, many underlying factors can be involved in functional outlet obstruction, so it is difficult to determine the causal relationship between them and chronic constipation. In addition, the main causative factors of functional outlet obstruction vary from patient to patient, and many patients cannot be explained by a single lesion; a detailed analysis of the test results obtained is necessary to understand the underlying cause of constipation in each patient. Exit obstruction constipation is characterized by normal or only mildly slowed transmission times throughout the colon, but excessive retention of residual material in the rectum. In this case, the bowel contents cannot be completely evacuated from the rectum. Patients often present with straining to defecate, a feeling of incomplete defecation or downward movement, low defecation volume, and a desire to defecate or lack of desire to defecate; anorectal finger examination may reveal a large amount of mud-like stool in the rectum, and the external sphincter of the rectum may show paradoxical contraction during forceful defecation; the total gastrointestinal or colonic transit time is normal, and most markers are retained in the rectum; anorectal manometry may reveal paradoxical contraction of the anal sphincter during forceful defecation or abnormal sensory threshold of the rectal wall, etc. Patients with this type often complain of time-consuming and laborious defecation or incomplete defecation. (iii) Mixed type, i.e., a combination of colonic transmission dysfunction and functional outlet obstruction, and the patient has the characteristics of both types of constipation. The above three types are suitable for functional constipation, but also for chronic constipation caused by other etiologies, such as diabetes mellitus, scleroderma combined with constipation, and drug-induced constipation is mostly slow transmission type. Constipation-predominant irritable bowel syndrome (IBS): is a chronic functional bowel disease characterized by abdominal discomfort or pain with altered bowel habits and abnormal bowel movements, with no lesions on barium enema or colonoscopy, and no evidence of systemic disease. The constipated type of irritable bowel syndrome may have outlet dysfunction combined with slow-transit constipation, mostly in young women, most prominently manifested by abdominal pain, and its colonic transit time may approximate that of healthy individuals. Because this type often coexists with emptying disorders, care should be taken to differentiate irritable bowel syndrome, which is predominantly constipating, from emptying disorders alone.