Movements Of The Colon

Like the stomach, the colon has movements peculiar to itself, - four very distinct modes of contraction. These are:

1. Molding movements, by which the contents are slowly compressed and molded. These movements are almost too slow to be noticed by the eye in X-Ray examinations except by observations made at intervals of a half hour or more.

2. Propulsive movements, by which the colon contents are passed along so rapidly that the eye cannot follow the movement. Movements of this sort occur regularly when the bowels are evacuated and also at other times.

3. Snake-like movements. Roeder, of Germany, has recently described movements in which the transverse or free part of the colon moves about in a manner closely resembling the contortions of a serpent. From this he concludes that the position of the transverse colon, unless it is held fast by adhesions, is not a definite one and is not a matter of much importance.

4. Reverse Peristalsis. Anti-peristalsis, that is, a reverse movement of the intestine, was first observed by Jacobi, more than twenty years ago, and has more recently been studied in cats by Cannon. These movements occur systematically while the contents of the cecum are fluid in character, and serve both to prevent the sudden and frequent discharge of the bowel contents, as in diarrhoea, and also to churn the contents of the cecum, thus bringing every portion in contact with the walls of the gut, so that absorption may be assisted.

As studied in animals, by Cannon, and in human beings by Case, the rhythmical reverse movements which occur in the colon, never in the small intestine, are interrupted at regular intervals by a downward peristalsis. These downward movements occur at intervals of about fifteen seconds.

The tight closure of the ileocecal valve alone prevents the contents of the cecum from being forced by these powerful anti-peristaltic waves backward into the small intestine. At intervals the anti-peristaltic waves cease momentarily, while the ileocecal valve relaxes, and small portions of material are passed into the cecum from the small intestine; then the anti-peristaltic waves again begin, churning the liquid material, spreading it over the surface of the cecum and ascending colon, thus encouraging absorption, while at the same time exerting a pumping action upon the venous and lymphatic, vessels, so that the contents of the cecum are rapidly dried down to the proper consistency.

It is very probable that the common practice of resisting the "call" of Nature for evacuation, may have produced abnormal conditions of the colon, by which its normal functions are obscured to a very considerable degree. The theory of anti-peristalsis, first suggested by O'Bierne, accords well with the facts of clinical experience, and may now be recognized as a fully established fact, especially since anti-peristalsis has been actually observed in man by Case on numerous occasions, in the X-ray department of the Battle Creek Sanitarium.

The Pelvic Colon

The pelvic loop of the colon, which, with the iliac colon forms what was formerly known as the sigmoid flexure, constitutes the motive part of the mechanism by means of which the feces are discharged from the body. This loop of intestine, when empty, lies low down in the pelvis, the lower end of the loop where it joins the rectum being closed by a sharp fold. There may be a sphincter at this point, although not. in a state of constant contraction. The loop fills from below as fecal matters gradually and slowly enter it from above. As it fills, the loop gradually rises, finally reaching a point at which the valve opens, so that the feces can enter the rectum. As the rectum walls become distended by the accumulation of feces, the defecating center is stimulated; and powerful nerve impulses are sent out, which cause the pelvic loop to contract, thus compressing its contents just as one compresses the contents of a rubber bulb by squeezing it with the hand. The contraction of the pelvic loop is normally so vigorous and complete that it is fully emptied of its contents. The contraction of the descending colon at the same time is normally sufficiently strong to carry the contents of the descending and iliac colon into and through the pelvic loop, so that the left half of the colon, from the splenic flexure to the anus is emptied in normal defecation. At the end of the contraction, the pelvic loop, or at least the mucous lining of the loop at its lower end, may be pushed down into the rectum like a piston, thus ensuring complete emptying of the rectum. The action of the pelvic colon thus resembles that of a bulb and piston combined, the upper part acting like a compressing bulb, while the lower part serves as a piston, thus forming a surprisingly effective mechanism for discharging the body wastes.

Careful and long-continued observations of the time required for the passage of food through the different sections of the alimentary canal, have secured very definite and exact information upon this very important subject, on which are based the figures given below.

The following table shows, according to Rosenheim, the time required for the food to reach the more important of the stations along the alimentary tube, reckoning from the time the food is eaten, since it is known that food begins to pass out of the pylorus very soon after the beginning of a meal: