Organization of collagen fibers in the intestine

The characteristic extinction pattern which is observed when the submucosa is viewed in the optical polarizing microscope has been analyzed in terms of the configuration and orientation of the 4 micron diameter collagen fibers. It is shown that the observed polarization effects are produced by periodic variations in orientation of fully birefringent fibers. The fiber configuration required to produce the observed polarization effects is a tilted wave configuration with a crimp period of approximately 20 micron. In the model, the tilted waveform fibers are crimped in register and form parallel arrays. The arrays are oriented in layers at approximately +30 degrees and -30 degrees to the longitudinal direction and are mirror images of each other. Analysis of the extinction pattern shows that the model satisfactorily accounts for the observed polarization effects at several different angles of the crossed polaroids. The calculated strain necessary to straighten the wavy fibers of the model correlates well with the observed strain to uncrimp the collagen fibers in the intestine. This suggests that the initial response to stress is gradual uncrimping of the collagen fibers, and concurrently, a decrease in the angle between biaxially oriented fibers, rather than extension of the straight fibers.