The Colon Normal and Pathologic Anatomy

The distinctive haustral contour of the large intestine is provided by three bands of longitudinal muscle—the taeniae coli. Since the taeniae are shorter than the length of the colon itself, their tethering action in relation to the circular muscle results in the characteristic haustral sacculations. The colonic haustra are thus organized into three distinct rows, each of which has characteristic anatomic relationships.1

The development and action of the taeniae have been carefully studied by Lineback.2 In the embryo, the outer layer of muscle originates in the caudal end of the bowel and extends upward until it eventually encases the colon. The three taenial bands are well marked by the 100-mm stage. Haustra are not generally seen in infancy, however (Fig. 15-1). It is not until the third year of life that the disproportionate increase in length between the colon and its longitudinal muscle bands results in the colon's being consistently bunched up, forming its characteristic saccular haustrations (Fig. 15-2).

Internally, the colon presents a relatively smooth surface, except for the semicircular folds of the haustral pouches. Section of a longitudinal muscle band at the level of a haustration obliterates the haustration and causes the bowel segment to lengthen. The taeniae function not only as shortening bands for the colon but as strong, fixed longitudinal cables on which the circular fibers are fixed (Fig. 15-3). The waves of contraction in the circular muscle occur independently and asynchronously in each of the three intertaenial regions,2,3 and it is this contraction that further produces the haustral clefts. The contribution ofboth the longitudinal muscle bands and the contraction of the circular muscle to the formation of the haustral folds accounts to some degree for their variable appearance on barium enema exami-nation.1,4

In the routine interpretation of barium enema studies, little attention is ordinarily directed to the organi-

Redundant Colon Picture

Fig. 15—1. Long, redundant ahaustral colon in an infant.

Since the colon grows in length faster than the development of the taeniae, the latter come to act as tethering cables to accordion the contour of the large intestine.

Fig. 15—1. Long, redundant ahaustral colon in an infant.

Since the colon grows in length faster than the development of the taeniae, the latter come to act as tethering cables to accordion the contour of the large intestine.

zation of the large intestine into three constituent rows of haustra. Indeed, the overlapping of the contours of the sacculations is generally considered a bothersome feature in contrast to the more readily apparent outlines of the stomach or small bowel loops. Careful evaluation

Wrinkle Skin Anatomy

Fig. 15—2. The "wrinkled" skin of the shar-pei dog can be likened to the haustral configuration of the colon. Foreshortening of redundancy results in multiple folds or sacculations.

Intestinal Haustral Contractions

Fig. 15—3. Interconnections of colonic muscle between the layers.

Longitudinal muscle fibers (y) of the taenia turn at right angles and fuse with the circular muscle layer (x). This linkage provides a point for contraction, limiting the formation of interhaustral clefts to the zones between adjacent taeniae. (Reproduced from Lineback.2)

Fig. 15—3. Interconnections of colonic muscle between the layers.

Longitudinal muscle fibers (y) of the taenia turn at right angles and fuse with the circular muscle layer (x). This linkage provides a point for contraction, limiting the formation of interhaustral clefts to the zones between adjacent taeniae. (Reproduced from Lineback.2)

of the anatomic profiles of the haustra, however, provides a precise basis for the radiologic analysis of a variety of abdominal diseases. In cases of extrinsic mass impressions on the colon or extension of an adjacent process to the large intestine, detailed analysis of the specific group of haustral sacculations first or principally involved leads to more precise localization and thereby identification of the primary process.5 Basic to an appreciation of pathologic alterations, however, is an understanding of the normal haustral anatomy and relationships.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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