The endometrium is the inner lining of the uterus and is one of the most important structures involved in the menstrual cycle and pregnancy. It undergoes cyclic changes throughout the menstrual cycle and is ultimately responsible for supporting the development of an embryo and fetus during pregnancy.
The endometrium is composed of two main layers: the stratum basale and the stratum functionalis. The stratum basale is the deeper layer and serves as the anchor for the endometrium within the uterus. This layer remains relatively unchanged throughout the menstrual cycle. The stratum functionalis is the upper layer and is the dynamic layer that changes in response to hormonal fluctuations during the menstrual cycle.
During the menstrual cycle, the stratum functionalis undergoes cyclical changes in preparation for possible implantation of a fertilized egg. Just before ovulation, the functional layer of the endometrium goes through specific changes, including the lengthening of uterine glands and the proliferation of tiny blood vessels. This process is called vascularization, and it results in the endometrial lining becoming thicker and enriched with blood. If fertilization occurs, the fertilized egg will implant into this thickened endometrial lining and develop into a fetus. The endometrium will continue to support the developing fetus throughout pregnancy, eventually developing into the placenta.
If fertilization does not occur, the endometrial lining will eventually shed during menstruation and the cycle will start over again. The cyclical changes in the endometrium are driven by the hormones estrogen and progesterone, which are produced by the ovaries. Estrogen causes the endometrium to thicken, while progesterone helps to prepare the endometrium for possible implantation and pregnancy.
Overall, the endometrium plays a critical role in female reproductive health and is a complex and dynamic structure that undergoes cyclical changes throughout the menstrual cycle.