The primary cilia of secretory cells in the human oviduct mucosa.

The human oviduct is lined with a simple columnar epithelium composed of ciliated cells and secretory cells. Primary cilia or solitary cilia usually extend from the apical surface of the secretory cells. The axoneme of the primary cilia is composed of nine peripheral microtubule doublets (9 + 0 pattern) that lack dynein arms and nexin links. Displacement of peripheral doublets to the central region, which is suggested to be attributable to the lack of nexin links, is one of the distinctive features of oviductal primary cilia. The basal body that extends the primary cilium connects to its paired centriole by the striated connector. The basal body is associated with the accessory structures, such as alar sheets, basal feet, and striated rootlets. Several basal feet project laterally from the basal body. The cap of the basal foot serves as the microtubule organizing center. Several striated rootlets radiate from the basal body toward the nucleus. The basal body, the paired centriole, and the basal body-associated structures are considered to play important roles in the stabilization and fixing of the cilium in the proper position on the apical cell surface.