Figure 2.

The changes in the uterine mucus (endometrium) during the menstrual cycle. In the proliferative (follicular) phase, the production of estrogen increases, but it decreases in the secretory (luteal) phase. The production of progesterone is high in the secretory phase and low in the proliferative phase. The production of LF is positively correlated with the estrogen level and negatively with the progesterone level. During menstruation, pH in the genital tract increases to 7.3–7.4, but glycogen production by epithelial cells is low, so the population of lactobacilli in the vagina and uterine cervix is low. Under such conditions, the genital tract is particularly prone to infection.