ovary (redirected from Ovaria)

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.

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ovary

In zoology, the female reproductive organ (see reproductive system) that produces eggs and sex hormones (estrogen and progesterone). Human females have two ovaries, almond-shaped organs about 1.5 in. (4 cm) long. They contain hollow balls of cells (follicles) that hold immature eggs. About 150,000–500,000 follicles usually are present at birth; by young adulthood, only about 34,000 remain. The number continues to decrease until menopause, when the few remaining follicles decay and the ovaries shrink and produce far less estrogen. Only 300–400 follicles mature and release an egg, which develops into an embryo if fertilized or, if not, passes from the body with menstruation. In botany, an ovary is the enlarged base of a flower's female organ (pistil). It contains ovules, which develop into seeds when fertilized, and matures into a fruit.

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ovary

1. either of the two female reproductive organs, which produce ova and secrete oestrogen hormones

2. the corresponding organ in vertebrate and invertebrate animals

3. Botany the hollow basal region of a carpel containing one or more ovules. In some plants the carpels are united to form a single compound ovary

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ovary [′ōv·ə·rē]

(anatomy)

A glandular organ that produces hormones and gives rise to ova in female vertebrates.

(botany)

The enlarged basal portion of a pistil that bears the ovules in angiosperms.

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Ovary

A part of the reproductive system of all female vertebrates. Although not vital to individual survival, the ovary is vital to perpetuation of the species. The function of the ovary is to produce the female germ cells or ova, and in some species to elaborate hormones that assist in regulating the reproductive cycle.

The ovaries develop as bilateral structures in all vertebrates, but adult asymmetry is found in certain species of all vertebrates from the elasmobranchs to the mammals.

The ovary of all vertebrates functions in essentially the same manner. However, ovarian histology of the various groups differs considerably. Even such a fundamental element as the ovum exhibits differences in various groups. See Ovum

The mammalian ovary is attached to the dorsal body wall. The free surface of the ovary is covered by a modified peritoneum called the germinal epithelium. Just beneath the germinal epithelium is a layer of fibrous connective tissue. Most of the rest of the ovary is made up of a more cellular and more loosely arranged connective tissue (stroma) in which are embedded the germinal, endocrine, vascular, and nervous elements.

The most obvious ovarian structures are the follicles and the corpora lutea. The smallest, or primary, follicle consists of an oocyte surrounded by a layer of follicle (nurse) cells. Follicular growth results from an increase in oocyte size, multiplication of the follicle cells, and differentiation of the perifollicular stroma to form a fibrocellular envelope called the theca interna. Finally, a fluid-filled antrum develops in the granulosa layer, resulting in a vesicular follicle.

The cells of the theca intema hypertrophy during follicular growth and many capillaries invade the layer, thus forming the endocrine element that is thought to secrete estrogen. The other known endocrine structure is the corpus luteum, which is primarily the product of hypertrophy of the granulosa cells remaining after the follicular wall ruptures to release the ovum. Ingrowths of connective tissue from the theca interna deliver capillaries to vascularize the hypertrophied follicle cells of this new corpus luteum; progesterone is secreted here. See Estrogen, Estrus, Menstruation, Progesterone