The three-dimensional organization of the smooth musculature in the ampulla of the human fallopian tube: a new morpho-functional model.

The three-dimensional organization of the smooth musculature around the human ampulla is revealed by means of scanning electron microscopy after NaOH maceration and ultrasonic microdissection of the interstitial connective tissue. The muscular wall of the ampulla appears as a continuous network of randomly anastomosed smooth muscle cell bundles that showed a multidirectional arrangement. The smooth muscle cell bundles modify their orientation along their course, intertwine repeatedly with each other and dichotomize, generating new bundles with a different orientation from that at the origin. These results demonstrate that the myosalpinx of the human ampulla is not organized into clear cut longitudinally, circularly or spirally arranged layers, as suggested in previous light microscopy studies. In contrast, the presence of a network of multidirectional smooth muscle cell bundles revealed in this study suggests that there is no morphological evidence for unidirectional peristalsis, and that the musculature is probably structurally designed to stir rather than push the tubal contents. These morphological findings better explain the random pattern of propagation of the contraction waves and the electrical impulses through the smooth musculature of the human ampulla, as postulated in early experimental physiological studies. Further, they suggest a specific function for the ampullar musculature which may not be only strictly related to tubal content transport.