They are two small, oval-shaped structures (similar to an almond), 2 or 3 centimeters long (in an adult woman), located in the pelvis, one on each side of the uterus. Internally, they are located at the end of the fallopian tubes, not exactly joined to them. This, because the ovaries are suspended in the pelvic cavity and are held on to the tubes only by a thin ligament. These small “mounts” make the ovaries be considered organs of certain mobility. If we perform a transverse cut in them, we will notice that after the epithelium that lines it, there is an area called peripheral area or cortex, and is the precise place where the thousands of female sexual cells live and mature.Then we find its innermost part, known as medulla. It contains the fibrous tissue, vessels and ovarian nerves. Inside, each ovary houses approximately 200,000 immature sexual cells, which develop and are discarded during the female fertile period (from the first menarchy or menstruation until menopause). However, despite the great amount of sexual cells ready to be developed and fertilized, only a small amount manages to be expulsed from the ovary in its mature stage (around 400 in a woman’s lifetime). The amount of fertilized ovules is even lower because a great number of them are expulsed along with the uterine lining (endometrium) during menstruation.
Ovules are the largest human cells. Their diameter reaches 0.13 millimeters, easily visible under a microscope. They have no movement of their own, nor do they have any structures that ease their transportation, like the tail of a spermatozoon. For this reason, from the moment one of them is expulsed from the ovary, it is helped by the fimbriae (part of the fallopian tubes) in order for them to freely advance through the oviducts and uterus.The nucleus of the ovule is the region where half of the genetic information necessary to form a new being is housed. On the outside, this sexual cell is surrounded by several layers, which have different functions. The zona pellucida or pellucida layer is formed around the developing ovule; its consistency is similar to a gel and is mainly made up of glucoproteins whose function is to protect it and ease the union with the male sexual cells. Further out, a layer of follicular cells is found which is arranged in a circular fashion, which is known as the corona radiata; after them, another portion of cells make up the granular zone.