[endo- + ¹metro- + -ium]
The mucous membrane that lines the uterus. It consists of two highly vascular layers of areolar connective tissue: the basilar layer, which is adjacent to the myometrium; and the functional layer, which is adjacent to the uterine cavity. Simple columnar epithelium forms the surface of the functional layer and the simple tubular uterine glands. Straight arteries supply blood to the basilar layer; spiral arteries supply the functional layer. Both estrogen and progesterone stimulate the growth of endometrial blood vessels.
Beginning with menarche and ending at menopause, the uterine endometrium passes through cyclical changes that constitute the menstrual cycle. These changes are related to the development and maturation of the graafian follicle in the ovary, the discharge of the ovum, and the subsequent development of the corpus luteum in the ovary.
If the ovum is not fertilized or the zygote not implanted, the functional layer of the endometrium is shed in menstruation.
The cycle then begins again, with the functional layer regenerated by the basilar layer.
Following implantation of the zygote, the endometrium becomes the maternal portion of the placenta; it fuses with the chorion of the embryo. After birth, the uterine lining is shed.
SEE: fertilization for illus
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