From the time food passes into the throat, the alimentary tract takes over the process of moving the bolus (ball of food) or its digested remnants through the gut. The walls of the alimentary tract has muscular layers which contract and relax in a synchronized manner to achieve this transit. This process is known as peristalsis. As food moves through the gut and is broken down in various stages, a host of other substances is added to the mix including digestive enzymes, bile, mucus and water.
Food enters through the mouth, is digested, the nutrients absorbed and waste discarded through the anus. The time for this to occur is known as the bowel transit time. It varies even in the same person but is on average about 24 to 36 hours. At certain times it can as early as 12 hours or as late as 72 hours. The bowel transit time depends on multiple factors including the foods eaten, water and fiber intake and any periodic disruptions in bowel motility.
What is a slow bowel?
Slow bowel is not a medical term or diagnosis. Instead it is used to describe several symptoms that may or may not be associated with the same causative disease. The term slow bowel is a common term to describe symptoms primarily relating to the lower gastrointestinal tract and bowel movements. It should not be confused with lazy bowel syndrome, which is a rebound effect associated with the long term and excessive use of laxatives.
The bowels comprise the small intestine and large intestine. The small intestine starts where the stomach ends. The first and shortest part of the small intestine is known as the duodenum. The other two much longer parts of the small intestine are the jejunum and ileum. The large intestine follows through from the small intestine. It is made up of the cecum, colon and rectum. It is first important to understand how the bowel works to differentiate specific symptoms related to various bowel disorders.
Normal Activity of the Bowels
Food passes from the mouth into the throat, down the esophagus and then into the stomach. The passage of food between the esophagus and stomach is mainly controlled by the lower esophageal sphincter. Once in the stomach, the food is mixed with gastric acid and other digestive enzymes as well as mucus. Food does not immediately exit the stomach all at once. Instead small amounts of partially digested food along with the gastric juices collectively known as gastric chyme seep out of the stomach slowly – this process is known as gastric emptying.
Once in the duodenum, the chyme is exposed to more digestive enzymes, mainly from the pancreas, and bile. Gradually the liquid chyme passes through the small intestine while the digestive enzymes act on it and nutrients are absorbed into the body. The movement of this chyme is facilitated by waves of coordinated muscular contractions in a process known as peristalsis. This is discussed further under intestinal motility.
By the time intestinal chyme reaches the end of the small intestine, digestion is complete and most of the nutrients have been absorbed. From the ileum the chyme enters the cecum of the large intestine and passes into the colon as a result of peristaltic activity (colonic motility). No further chemical digestion occurs in the large intestine. Some remaining nutrients are absorbed, bacterial action may breakdown residual food material and the fluid chyme is transformed into a mushy and then solid material (feces). Various defecation reflexes then initiates the process of defecation by passing the feces in the colon into the rectum. Once the anal sphincters relax, the feces are passed out into the environment.
Slow Bowel Movement and Other Symptoms
The term ‘slow bowel’ may refer to many symptoms of lower gastrointestinal tract but the most common of these is constipation. By definition constipation is infrequent bowel movements less than three times per week associated with hard stool and straining during defecation. Constipation is a symptom and not a disease on its own. Other symptoms that may accompany constipation and therefore fall under the term of slow bowel includes :
Causes of Slow Bowels and Bowel Movements
Various physiological causes may affect bowel movements and lead to other symptoms associated with it. Physiological causes are not associated with any disease but rather normal changes or events in a person’s life. This may include lifestyle and dietary factors which are not disease processes (pathological).
- Sedentary lifestyle
- Lack of fiber intake
- Low water intake
- Excessive intake of certain foods like dairy
- Sudden changes in diet
- Stress – mental, emotional or physical
- Resisting the urge to defecate over a long period of time
- Age-related changes
A large number of cases of constipation are due to unknown causes.
Functional bowel disorders are conditions where there is no clear pathology or structural defect but the normal activity of the bowels are compromised. Irritable bowel syndrome (IBS) is the most common functional bowel disorder and in some patients it is characterized by constipation and therefore termed constipation-predominant IBS. Symptoms such as abdominal distension with no clear cause that fluctuates within a 24 hour period is known as functional bloating. It is more often seen in conditions like irritable bowel syndrome.
Pharmacological causes of constipation are often associated with certain antacids (those containing calcium or aluminum in particular), opioid painkillers, diuretics, antidepressants, iron supplements and anti-hypertensives. The long term and excessive use of laxatives may cause a rebound effect and lead to constipation.
The pathological causes of a slow bowel is numerous depending on the presentation. At times infrequent bowel movements may not fit the definition of constipation yet a person has other symptoms associated with constipation and evacuation is incomplete. Some of the causes of slow bowel movements, whether clearly defined as constipation or not, includes :
- Eating disorders
- Hypothyroidism – underactivity of the thyroid gland
- Inflammatory bowel disease (IBD) – active phases always present with diarrhea.
- Neurological disorders – affecting nerves supplying the muscles of the intestines.
- Any major illness, debility and convalescence
Article reviewed by Dr. Greg. Last updated on December 3, 2011