Ultrastructural changes in the cervical epithelium during the estrous cycle of the marsupial Monodelphis domestica (grey short-tailed opossum)

Ultrastructural changes in the cervical epithelium related to the estrous cycle have been studied in the South American marsupial Monodelphis domestica. The two cervices protrude with prominent papillae into the sinus vaginalis. At times of simple columnar at others of more pseudostratified character consists of two types of cells, ciliated and secretory cells. The mucosal epithelium is uniform in its entire length and shows no division into an endo- and ectocervix. The mucosa of the cervix differs from the uterine endometrium. There are no glandular structures, but the luminal epithelium shows deep invaginations underlined by dense connective tissue. The most conspicuous changes include the height and the differentiation of the cervical epithelium which attains its maximum development during estrus, where secretory cells are fully packed with large secretory granules and ciliated cells are well developed. After extruding their granules, secretory cells may transform into ciliated cells, while ciliated cells show the phenomenon of deciliation in which cilia packets are shed into the cervical lumen. This transformation process takes place mainly during post- and metestrus. The presence of solitary cilia is only noticeable during pro-estrus, being in contrast to the uterine epithelium where they appear during the whole estrous cycle.