Analyzing the morphological and ultrastructural features of the mammary gland during the menstrual cycle, the authors observed that in the proliferative phase, the mammary gland consisted of few developed lobules and presented a relative absence of mitotic figures. In this phase, the great majority of the epithelial cells contained small, dark, irregular, rich heterochromatinic nuclei. The mammary stroma showed similar findings, presenting dense connective tissue with few enhanced fibroblasts. During the secretory phase, the lobules were well developed and mitotic figures were usually observed. In this phase, the great majority of the ephitelial cells presented clear voluminous, rich euchromatinic nuclei; the stroma consisted of fibroblasts with voluminous nuclei full of euchromatin. There are evident modifications of the mammary tissue according to the phase of the menstrual cycle. The morphological and ultrastructural modifications indicate higher metabolical and mitotic activities during the secretory phase.
mammary gland; menstrual cycle; morphology; ultrastructure
