Chapter 36, Problem 20A

Summary Introduction

To explain:

The importance of regeneration of endometrium after each menstrual cycle.

Introduction:

The uterus is a hollow and muscular structure that lies in the pelvic cavity. The walls of the uterus are composed of three layers of tissues, outer perimetrium, middle myometrium, and inner endometrium. The endometrium is the inner glandular layer of the wall of the uterus. It undergoes cyclic changes during the menstrual cycle.

Explanation of Solution

After puberty, the uterus goes through the menstrual cycle. During the middle of each cycle, one ovum is released from the ovary under the influence of the hormones released by the pituitary gland. The hormones are also released by ovaries that affect the walls of the uterus. 

During the menses, the pituitary release low levels of luteinizing hormone that results in the degeneration of the corpus luteum, therefore progesterone production is reduced. The endometrium layer is degenerated due to decreased levels of progesterone hormone. The endometrium layer breaks down, and menstruation begins.

During the follicular phase, high levels of follicle-stimulating hormone stimulate ovarian follicles to secrete estrogen hormone. Oestrogen hormone stimulates the proliferation of the endometrium layer and regeneration. After the ovulation, if fertilization takes place, the endometrium layer is maintained by progesterone hormone secreted by the corpus luteum. It is because the endothelium is necessary for the implantation of the blastocyst and other events of pregnancy. The blastocyst form villi to get nourishment after the attachment to the uterine wall.

In the absence of fertilization, the corpus luteum degenerates, which leads to the disintegration of the endometrium leading to menstruation marking a new cycle.

Conclusion

Thus, the endometrium layer needs to be refreshed after every menstrual cycle because if in case fertilization occurs, the implantation of the blastocyst takes place in the endometrium. The blastocyst sinks into the pit formed in the endometrium and gets buried in the endometrium completely.