Ovaries and Female Reproduction

The earliest indirect reference to the ovary appeared in Aristotle’s The History of Animals. Although not recognizing the existence of the ovaries, Aristotle did describe the process of spaying sows, then a common agricultural practice. Camels were also spayed to “quench in them sexual appetites and stimulate in them growth and fatness.” Aristotle’s understanding of the ovaries in the reproductive process was limited by the prevailing belief in the “seed and soil” concept of reproduction. The male provided the “seed,” with the female playing a passive role, providing the “soil” in which the seed would grow. Aristotle saw a connection between the “seed” and the male’s semen. However, the existence of spermatozoa only became evident in 1677, when first visualized under Leeuwenhoek’s microscope. Interest in the ovary and female reproductive system was resumed during the sixteenth through the nineteenth centuries and was focused upon its anatomy and, later, various disorders afflicting it.

In this image of the female reproductive system, the ovaries are depicted as blue-green structures. At the time of ovulation, the egg travels through the Fallopian tube to the uterus, where it is potentially fertilized by a sperm cell.

The loss of the ovaries was known for some time to result in atrophy of the uterus and loss of sexual function. In 1900, Emil Knauer showed that the ovaries exerted control over the female reproductive system. After transplanting ovaries to experimental animals, he prevented the symptoms associated with their removal. Josef von Halban extended these studies the same year when he demonstrated that transplantation of ovaries into an immature spayed guinea pig permitted the animal to attain normal puberty. Thus, the ovaries were found to not only maintain the female genital tract but were also responsible for its development.

On the basis of these findings, the existence of an internal secretion from the ovary - a single hormone - was postulated. Identification of this substance required the development of a sensitive assay, which Edgar Allen and Edward Doisy perfected in 1923, that was capable of detecting estrogen, the female sex hormone, in the blood and urine of pregnant and non-pregnant females. In 1926, Siegfried Loewe detected the presence of a female sex hormone in the urine of menstruating females, noting that the concentration of this hormone varied with the phase of the menstrual cycle.