On the concept of stem cell and a model of functional-morphological structure of the endometrium.

The paper discusses the fundamentals of a functional-morphological model of the structure of human endometrial ephitelium during two phases of the menstrual cycle. The model is based on the hypothesis that endometrial epithelium comprises populations of stem cells, capable of long-term self maintenance and producing differentiated epithelial cells, which can be divided according to the model, into three types: estradiol-sensitive cells, estradiol- and progesterone-sensitive cells and progesterone-sensitive cells. The significance of changes in blood-estradiol and progesterone levels during the menstrual cycle required for conversion of one type of the cells into another is considered, and histochemical characterization of different types of cells is given.