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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
(ovarium), the lower, slightly thickened, hollow part of the pistil in the flowers of angiosperm plants. The cavity of the ovary contains one or several ovules (sometimes many). After fertilization the ovules form seeds (the seeds “set”), and the ovary itself turns into the fruit.
one of the paired female sexual glands in which the eggs form and mature.
The primordial germ cells usually separate very early in the course of individual development from the somatic cells of the embryo and subsequently concentrate in one of the germ layers. The ovaries are formed in the ectoderm or entoderm in coelen-terates and in the mesoderm in all other animal phyla. In invertebrates (sponges, lower coelenterates, and acoelomate ciliated worms) the ovaries are only a temporary mass of sexual cells. In more highly developed animals they are independent organs.
Two main types of ovarian structure are distinguished. In the saccate ovaries of lower worms, echinoderms, arthropods, mollusks, and acraniates the eggs are formed in the internal lining of the organ; some time later they enter the ovarian cavity and are released through ducts. Compact ovaries are composed of internal connective-tissue stroma and an external lining from the germinal epithelium in which the eggs are formed. The mature eggs pass through a break in the ovarian wall into the common body cavity (coelom), from which they are released through oviducts completely independent of the ovaries (in annelid worms among invertebrates and in all vertebrates).
An ovary is usually one of two paired organs in bilaterally symmetrical animals and humans. However, it is sometimes unpaired: one of the ovaries may be reduced, as in gastropods and birds, or the two ovaries may fuse in the course of individual development, as in some arthropods and vertebrates (for example, lampreys and perches).
The ovaries of vertebrates are compact connective tissue bodies into which grow columns of embryonic epithelial cells that cover the ovaries on the outside. The columns of embryonic cells break down into round follicles in which a single egg and several somatic cells arranged around it (follicular cells) develop. The follicles participate in the sustenance of the growing egg and, often, in the formation of the egg membranes as well. The maturing follicle (Graafian follicle in mammals) enlarges and becomes distended by the liquid in its interior. It rises to the surface of the ovary, where it bursts and releases the mature egg. The egg passes through the oviduct, where fertilization occurs, and then enters the uterus. The corpus luteum forms on the surface of the ovary where the follicle burst (seeCORPUS LUTEUM).
In humans the ovaries are situated in the cavity of the lesser, or minor, pelvis (near its lateral walls) on both sides of the uterus, each on the posterior surface of the broad ligament of the uterus. The human ovary is typically 3–4 cm long, 2–2.5 cm wide, and 1–1.5 cm thick. It is connected to the uterus by its own ligament. Blood supply is from the ovarian arteries branching off the abdominal aorta or left renal artery and by branches of the uterine arteries. The ovary is innervated by the celiac, superior mesenteric, and hypogastric plexuses. Sex hormones, mostly estrogens and progesterone, are also formed in the ovaries. Ovarian activity is regulated by the follicle-stimulating and luteinizing hormones.
N. S. LEBEDKINA
Pathology. Salpingoophoritis is the most common ovarian disease. Ovarian apoplexy, or hemorrhage into an ovary, is usually associated with symptoms of acute abdomen. It may occur in any phase of the menstrual cycle but generally during ovulation. A rare occurrence is ovarian pregnancy. Ovarian cysts and benign epithelial tumors (cystomas) are common, but they usually do not interfere with the menstrual function of the ovaries. The most frequent complications of cysts and cystomas are twisting of the pedicle and rupture of the capsule with symptoms of acute abdomen. Endometriosis and malignant tumors may also arise in the ovaries. Ovarian cancer generally develops between the ages of 45 and 55 years, usually as a result of degeneration of a cystoma.
Emergency surgery is indicated in the presence of noninflammatory diseases of the ovaries (cysts, tumors, hemorrhages) accompanied by symptoms of acute abdomen. Preventive gynecological check-ups help in the early detection of an ovarian malignancy.
REFERENCESRukovodstvo po endokrinologii. Moscow, 1973.
Eskin, I. A. Osnovy fiziologii endokrinnykh zhelez, 2nd ed. Moscow, 1975.
A. P. KIRIUSHCHENKOV