ovary, ductless gland of the female in which the ova (female reproductive cells) are produced. In vertebrate animals the ovary also secretes the sex hormones estrogen and progesterone, which control the development of the sexual organs and the secondary sexual characteristics. The interaction between the gonadotropic hormones from the pituitary gland and the sex hormones from the ovary controls the monthly cycle in humans of ovulation and menstruation. There are two ovaries in the human, held in place on each side of the uterus by a membrane; each ovary is about the size of an almond. About 500,000 immature eggs are present in the cortex of the ovary at birth. Starting at puberty, eggs mature successively, and one breaks through the ovarian wall about every 28 days in the process known as ovulation, which continues until menopause, or cessation of reproductive functioning in the female. After its release from the ovary, the ovum passes into the oviduct (uterine or fallopian tube) and into the uterus. If the ovum is fertilized by the sperm (male reproductive cell), pregnancy ensues (see reproductive system). In flowering plants the part of the pistil containing the ova is called the ovary; the ripened ovary is the fruit.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.

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