Through the ileo-cecal valve, chyme is passed into the cecum from the small intestine. At this stage, the chyme consists of undigested or indigestible food substances, secretions from the liver, pancreas, small bowel and water. In the cecum, the water is mostly removed, reducing the chyme to a semi-solid consistency which is now called faeces.
To provide lubrication for the passage of the faeces, numerous cells line the walls of the bowel and secrete a mucus substance. As a result of haustral churning, a constant sloshing effect finishes the digestive process of the chyme. Under mass peristalsis, the faeces are pushed toward the rectum and anus where they are eventually eliminated from the body. This movement is caused by the presence of food in the stomach. This activity empties the cecum and makes it ready to receive new chyme from the small intestine.
BACTERIAL ACTION IN THE BOWEL
When the bowel is healthy there is very little bacterial action in the small intestine. The large intestine, however, literally swarms with billions of these microscopic organisms. Bacterial action in the large intestine plays a major role in nutrition and digestion. These friendly bacteria synthesise valuable nutrients by digesting portions of the faecal mass. Among others, vitamin K and portions of the B complex are produced. This aspect of digestion is not completely understood and is undergoing further study. Any remaining proteins are broken down by the bacteria into simpler substances. By products of bacterial activity are numerous, such as indole, skatole, hydrogen sulphide, fatty acids, methane gas and carbon dioxide. Some of these substances are very toxic and odorous, hence the accompanying smell of faeces. The brown colour of faeces is a result of bile pigments coming from the liver. When faeces are not brown, but have a chalky appearance, there is a problem in bile secretion and digestive ability. When faeces reach the rectum they are about 70% water; 30% by weight of the mass represents bacteria while the remainder is made up of food residues, cellulose, undigested materials and dead cells discarded by the body.
The time it takes for chyme at the cecum to turn into faeces and travel to the rectum depends upon the amount of roughage in the food and the water content. Bulkier faeces travel faster as they provide substance for the bowel muscle to work upon. Otherwise a soft, fiberless stool becomes very difficult for the colon to move along. The longer it takes, the more water is absorbed, making faeces compacted and hard so that it becomes difficult to eliminate them.
Neglecting the urge to eliminate, as well as eating foods low in roughage, will lead to constipation. Laxatives, taken as an aid in elimination, either act to increase the amount of liquid retained in the faeces, or act as a lubricant to allow for easy passage. Oftentimes laxatives are compounded to be an irritant or poison and stimulate the muscle walls to cause abnormal contractions to expel the irritating substances. It is very easy to become dependent upon these drugs and thereby permanently destroy normal bowel function.
The expulsion of liquid faeces or diarrhoea, can be produced by excessive use of laxatives, nervous stress, infection or the presence of toxic substances in the bowel. Proper bowel management enhances the natural flow and rhythm of the digestive organs providing regular, painless and efficient functioning as described in this chapter.
THE SHAPE OF THE COLON
A healthy, normally functioning bowel is shaped as seen in the illustration on the next page. The cecum is located in the lower right abdomen. From there the bowel rises up into the ascending colon until it reaches the first turn toward the left. This turning point is called the hepatic flexure because of its proximity to the liver. From there the bowel travels across the abdomen beneath the stomach until it reaches the second turn called the splenic flexure. This section of the bowel, the transverse colon, is the only organ within the body that makes a transit from right to left. In a normal bowel the transverse colon makes a slightly upward grade to the splenic flexure. From the splenic flexure, the bowel moves down as the descending colon until it reaches the sigmoid colon just above the rectum. Here in the sigmoid is the holding place for faeces waiting to be eliminated. The rectum continues from the sigmoid and makes an ‘s’-like bend into the anus where the anal sphincter muscle is found.