The human intestine is divided into two main regions: the small intestine and the large intestine. The majority of digestion and absorption processes occur in various parts of the small intestine. The large intestine, also known as the colon, is the last part of the digestive system. It is responsible for the absorption of water, and the formation and expulsion of feces.
The colon can be further subdivided into five regions: cecum, ascending colon, transverse colon, descending colon, and sigmoid colon. The cecum is the first part of the colon, and is involved in digestive processes. Closely associated with the cecum is the appendix, whose biological functions in the human body are not entirely clear. The ascending colon is connected to the small intestine through the cecum.
The process of reabsorption of water and formation of feces occurs as the digested food and waste material move through the ascending, transverse and descending colon segments. The descending colon ends in the sigmoid colon, which is connected to the rectum. The feces are stored in the rectum till the time of defecation.
Obstruction of the Colon
Obstruction to the flow of digested material and feces could occur in any part of the large intestine, namely the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and even the rectum. The blockage in the colon may be partial in some cases, and complete in others. Most cases of blocked colon are caused by mechanical obstructions to the movement of digested material. Regardless of the type and location of blockage, a blocked colon is a medical emergency, and should receive immediate medical attention.
Signs and Symptoms
A blocked colon produces a variety of signs and symptoms. Some of these include:
- Constipation and diarrhea: A blockage in the colon, either complete or partial, could result in constipation or diarrhea. Severe constipation caused by a blocked colon is also referred to as obstipation. The size and shape of stools change in cases of a blocked colon. A complete block in the colon may stop the defecation process entirely, and can be life-threatening. Diarrhea is caused by a partial obstruction of the colon, which allows liquid material to pass through.
- Nausea and vomiting: When the blockage in the colon backs up digestive waste products as far up as the small intestine, nausea and vomiting may occur.
- Cramps: Abdominal pain or cramps may also be present in cases of blocked colon.
- Failure to pass gas: The obstruction in the colon may even block the passage of gas, leading to difficulty in passing gas. This can be accompanied by abdominal distension and bloating.
- Melena: A blocked colon may also lead to bleeding in the gastrointestinal tract. This results in black, tarry stools (technically referred to as melena). In some cases, fresh blood may also be expelled through the anus. This condition is referred to as hematochezia.
- Borborygmi: Borborygmi is the technical term for the rumbling sounds produced in the bowel. Borborygmi may increase and then decrease as the obstruction in the colon becomes worse.
Read more on small volume bowel movement.
Causes of Blocked Colon
Colon blockage can occur in a variety of conditions. Many of the causes of a blocked colon are similar to the causes of blockage in the small intestine. The following are some of the more common causes of a blocked colon:
Hernia refers to conditions in which a tissue or an organ starts bulging out of an abnormal opening in the structures that contain that tissue or organ. Hernia of the colon may sometimes become trapped within some weak spot in the abdominal wall, leading to obstruction of the colon. This type of trapped hernia that cannot be pushed back into its normal position is referred to as incarcerated hernia.
Intussusception refers to a condition in which a part of the colon folds back into another part of the intestine. This causes obstruction to the movement of waste material in the colon. Newborns and infants are relatively more susceptible to intussusception than older adults.
Volvulus refers to a condition in which the stomach or the intestine twists on itself, leading to an obstruction. Volvulus of the large intestine may sometimes occlude the small intestine as well. The terminal ends of the large intestine, the cecum and the sigmoid colon, are relatively more prone to twisting than other parts of the colon.
Tumors and polyps
The growth of tumors and polyps within the lumen of the intestine could lead to a blocked colon. There are usually no incriminating symptoms when the tumor or polyps are small. Once they reach a size where occlusion of the intestinal lumen begins, constipation, diarrhea, and hematochezia may occur. This is likely the case with malignant tumors of the colon (such as colon cancer and colorectal cancer).
Inflammatory bowel disease
The walls of the colon are likely to undergo hypertrophy in individuals suffering from chronic inflammatory bowel disease (such as Crohn’s disease and ulcerative colitis). The thickening of the walls of the colon may also cause obstruction to the passage of food waste.
Diverticula are small outgrowths or pouches arising from the walls of the colon. Chronic inflammation of the diverticula (technically known as diverticulitis) can lead to scar formation and obstruction in the colon.
Impaction of feces refers to a hardening of the stools. Impacted feces are common in elderly individuals. Impacted feces makes defecation painful, which causes the affected individuals to try to avoid defecation. This can lead to a blocked colon.
Acute colonic pseudo-obstruction
Acute colonic pseudo-obstruction refers to a sudden distention of the proximal regions of the colon. This condition, also referred to as the Ogilvie’s syndrome, is painless. Ogilvie’s syndrome can occur in a variety of conditions, including diabetes, trauma, uremia, surgery, burns, dehydration, and after using certain medications.
Read more about bowel motility disorders.
Hirschsprung’s disease refers to a congenital defect that is characterized by the formation of a megacolon (a dilated colon). The megacolon does not have proper reflex contractile activity due to dysfunctional ganglion cells. This disrupts the colonic motility and causes obstruction of the colon due to accumulation of the feces.
Ischemic bowel disease
Ischemia or infarction of the colon can also cause obstruction due to impaired intestinal motility and edema.
Presence of a foreign body within the colon could also lead to a blocked colon. Movement of digested material through the colon may also be affected by conditions that involve regions outside the colon, such as large tumors present in the vicinity. Impaction of gallstones within the lumen of ileum may also cause a blocked colon.