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ovum[o´vum] (pl. o´va) (L.)
the female reproductive or germ cell which after fertilization is capable of developing into a new member of the same species; called also egg. The term is sometimes applied to any stage of the fertilized germ cell during cleavage and even until hatching or birth of the new individual. The human ovum consists of protoplasm that contains some yolk, enclosed by a cell wall consisting of two layers, an outer one (zona pellucida) and an inner, thin one (vitelline membrane). There is a large nucleus (germinal vesicle) within which is a nucleolus (germinal spot). adj., adj o´vular.
centrolecithal ovum one with the yolk concentrated at the center of the egg, surrounded by a peripheral shell of cytoplasm, and with an island of cytoplasm surrounding the nucleus, such as that of an arthropod.
holoblastic ovum one that undergoes total cleavage.
isolecithal ovum one with a small amount of yolk evenly distributed throughout the cytoplasm.
meroblastic ovum one that undergoes partial cleavage.
primitive ovum (primordial ovum) any oocyte very early in its development.
telolecithal ovum one with a comparatively large amount of yolk massed at one pole, such as that of a reptile or bird.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
an ovum in which the yolk is evenly distributed throughout the cytoplasm.
Farlex Partner Medical Dictionary © Farlex 2012
ovum(o'vum) plural.ova [L., egg]
1. The female reproductive or germ cell.
2. A cell that is capable of developing into a new organism of the same species. Usually fertilization by a spermatozoon is necessary, although in some lower animals ova develop without fertilization (parthenogenesis). See: conception; fertilization; menstrual cycle; menstruation
An ovum with a small yolk portion that is distributed throughout the protoplasm. Synonym: isolecithal ovum
An ovum having a large central food yolk, as in a bird's egg.
An ovum that undergoes complete cleavage, as opposed to partial or meroblastic cleavage.
The female gamete, required for reproduction. The ovum develops from an oogonium within the graafian follicle of the ovary and matures through the meiotic process of oogenesis. A mature ovum is about 0.13 to 0.14 mm (0.0051 to 0.0055 in) in diameter. At ovulation, the ovum is bounded by a translucent cellular membrane (the zona pellucida), which is connected to a layer of follicular cells (the corona radiata); these cells enclose the cytoplasm, nuclei, and chromatin material. The exact time during which a human ovum is capable of fertilization and further development before degenerating is not known; however, it is probably 24 hr. See: illustration; oogenesis; ovulation
isolecithal ovumAlecithal ovum.
A secondary oocyte that has completed its second meiotic division as a result of contact with a sperm. The nucleus of the mature ovum becomes the female pronucleus.
An ovum in which only the protoplasmic region undergoes cleavage, characteristic in ova containing a large amount of yolk.
An ovum ready for fertilization.
A germ cell that arises very early in the development of the embryo, usually in the yolk sac endoderm, migrates into the urogenital ridge, and is the precursor for the functional gamete.
An ovum in which the yolk is fairly abundant and tends to concentrate in one hemisphere.
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