Collagen organisation in the cervix and its relation to mechanical function.

The organisation of collagen fibrils within the cervices from non-pregnant humans and rats and day 22 pregnant rats was measured using X-ray diffraction. This technique yields the direction of preferred orientation of the collagen fibrils and an orientation distribution function. In the human cervix there are three distinct zones which blend smoothly into each other on passing radially outward from the canal. Adjacent to the canal and in the outermost zone the fibrils are oriented predominantly longitudinally, that is parallel to the canal. In the middle zone the fibrils have a preferred orientation in a circumferential direction. A similar structure is seen in the non-pregnant rat cervix. The collagen fibrils in the day 22 pregnant rat showed no preferred orientation and are therefore randomly oriented within the tissue. The directions in which the collagen fibrils are oriented determine the directions in which the tissue can best withstand tensile stress.