The proliferative phase typically occurs after menstruation and lasts between 6 to 13 days in a standard 28-day cycle. This phase involves the reconstruction of the endometrium, guided by estrogen produced by the developing ovarian follicle.
Notably, the stratum basale, the basal layer of the endometrium, including the basal parts of the uterine glands, remains unaffected by menstruation. Stem cells in this layer undergo mitosis, regenerating the stratum functionalis and thickening the endometrium.
During this phase, the endometrium becomes denser as short, straight endometrial glands develop. Along with the coiling and lengthening arterioles, these glands penetrate the stratum functionalis, enhancing vascularization within the endometrium. As a result, the endometrium regains its velvety texture, doubling its thickness to approximately 4–10 mm.
The proliferative phase culminates in ovulation, triggered by a surge in luteinizing hormone released by the anterior pituitary gland. This phase sets the stage for potential fertilization and pregnancy.
The proliferative phase is the second phase of the uterine menstrual cycle. It begins after menstruation and lasts approximately 6 to 13 days in a typical 28-day cycle.
During this phase, the uterine endometrium rebuilds itself under the influence of estrogen released by the growing follicles in the ovaries.
The basal layer of the endometrium, known as the stratum basale, including the basal parts of the uterine glands, survives menstruation intact.
The cells in the stratum basale rapidly divide, creating a new stratum functionalis layer.
As the endometrium thickens, endometrial glands develop, and arterioles coil and lengthen, penetrating the newly formed stratum functionalis.
As a result, the endometrium becomes velvety, thick, and well-vascularized, roughly doubling in thickness to about 4–10 mm.
In the meantime, events in the ovaries result in the maturation of the dominant follicle into a Graafian follicle.
As a result, the proliferative phase concludes with ovulation, triggered by a surge in luteinizing hormone levels released by the anterior pituitary gland.
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