Posts Tagged ‘Colon structure’

Colon Wall Muscles in Diverticular Disease

Sunday, September 2nd, 2012

MUSCLE LAYERS

Between the mucus producing lining and the outer layer of the colon wall, there are two major muscle systems. The inner circular muscles surround the colon, contraction can close the colon or they can act in waves to propel contents along. Between the appendix at the beginning and the rectum at the end of the colon, longitudinal muscles are gathered into three bands known as taenia. This arrangement allows contractions to shorten the colon and propel faeces without compressing them. Coordination between the two types of muscle can produce a variety of movements. An earthworm moving along soil is a good example to observe a similar system.

MOVEMENTS ALONG THE COLON

In the caecum, repeated circular muscle contractions mix the liquid contents (chyme). These change into backwards and forwards segmenting and propulsive movements to dry and move the mushy contents along the ascending and transverse lengths of the colon. Longitudinal muscles become more involved as faeces become more solid in the second, left side, of the colon. Occasional powerful contractions sweep faeces into the descending and sigmoid areas. Faeces are stored with the sigmoid area acting as a vertical warehouse with supporting arcs of circular muscle. Strong contractions of longitudinal muscles produce a concertina effect to push out colon contents on defaecation. The first half of the colon is controlled automatically by the vagus nerve from the brain. The left side has some local nerve reflexes and a person can have some influence such as when to defaecate.

CHANGES WITH DIVERTICULAR DISEASE

Changes in the colon musculature in diverticular disease (DD) were described even before the early 20th century when DD was rare, (1) and in many reports since. Muscle abnormality and dysfunction persisted in the colon after resection of the areas with diverticula (2). Long sections of the left colon can change in appearance without any diverticula which may only occur years later. The muscular abnormalities are the primary pathogenic mechanisms of DD (3). DD is only diagnosed when diverticula are observed, changes in muscles have had little attention especially in areas without diverticula. (more…)