The main functions of the uterus are receiving the embryo, sheltering the fetus during pregnancy and delivering the newborn at term. The uterus is a pear-shaped, muscular, hollow organ with a triple-layered wall: an outer tunica serosa, the perimetrium, a thick tunica muscularis, the myometrium, and an inner tunica mucosa, the endometrium. The endometrium is the layer in which the implantation takes place. This layer experiences morphologic and functional changes that are closely associated with the cyclic release of sexual hormones. In absence of periodic hormonal influence, i.e., before puberty or following menopause, this tissue has a constant morphology and thickness. Following the menarche the uterus prepares itself in each menstrual cycle for receiving a fertilized oocyte. This takes place via the proliferation and differentiation of the endometrium. If the implantation does not occur, the functional (outermost) layer of the endometrium is shed and expulsed, leading to menstruation.
Functional anatomy of the endometrium
The endometrium consists of a single-layered prismatic epithelium with or without cilia (depending on how far along the menstruation cycle is) and its basal lamina, uterine glands, and a specialized, cell-rich connective tissue (stroma) containing a rich supply of blood vessels. One recognizes the spiral arteries (end branches of the uterine arteries as well as a venous outflow system.
- Cyclic alterations of the uterine glands and blood vessels during the course of the menstruation, as preparation for the implantation
- Location where the blastocyst is normally implanted
- Location where the placenta develops