Egg cell

Source: Wikipedia, the free encyclopedia.
"Ova" redirects here. For other uses, see Ova (disambiguation).
Not to be confused with Egg.
Egg cell
A human egg cell with surrounding corona radiata
Details
Identifiers
Latinovum
GreekΩάριο (oário)
MeSHD010063
FMA67343
Anatomical terms of microanatomy
Human egg cell

The egg cell or ovum (pl.: ova) is the

oogamous. A nonmotile female gamete formed in the oogonium of some algae, fungi, oomycetes, or bryophytes is an oosphere.[2] When fertilized, the oosphere becomes the oospore.[clarification needed
]

When egg and sperm fuse during

diploid cell (the zygote
) is formed, which rapidly grows into a new organism.

History

While the non-mammalian animal egg was obvious, the doctrine ex ovo omne vivum ("every living [animal comes from] an egg"), associated with

Oskar Hertwig in 1876.[5][6]

Animals

In animals, egg cells are also known as ova (singular ovum, from the

egg').[7] The term ovule in animals is used for the young ovum of an animal. In vertebrates, ova are produced by female gonads (sex glands) called ovaries. A number of ova are present at birth in mammals and mature via oogenesis
.

Studies performed on humans, dogs, and cats in the 1870s suggested that the production of

ovarian stem cells exist within the mammalian ovary. Whether or not mature mammals can actually create new egg cells remains uncertain and is an ongoing research question.[8][9]

Mammals including humans

Diagram of a human egg cell
Ovum and sperm fusing together
The process of fertilizing an ovum (top to bottom).

In all

mammals except monotremes
, the ovum is fertilized inside the female body.

The human ova grow from primitive germ cells that are embedded in the substance of the ovaries. Each of them divides repeatedly to give secretions of the uterine glands, ultimately forming a blastocyst.[10]

The ovum is one of the largest

cells in the human body, typically visible to the naked eye without the aid of a microscope or other magnification device.[11] The human ovum measures approximately 120 μm (0.0047 in) in diameter.[12]

Ooplasm

Ooplasm is like the yolk of the ovum, a cell substance at its center, which contains its

germinal disc.[13]

The ooplasm consists of the

hyaloplasm, often called the formative yolk; and the nutritive yolk or deutoplasm, made of rounded granules of fatty and albuminoid substances imbedded in the cytoplasm.[13]

Mammalian ova contain only a tiny amount of the nutritive yolk, for nourishing the embryo in the early stages of its development only. In contrast, bird eggs contain enough to supply the chick with nutriment throughout the whole period of incubation.[13]

Ova development in oviparous animals

In the

amphibians and reptiles), the ova develop protective layers and pass through the oviduct to the outside of the body. They are fertilized by male sperm either inside the female body (as in birds), or outside (as in many fish). After fertilization, an embryo develops, nourished by nutrients contained in the egg. It then hatches from the egg, outside the mother's body. See egg
for a discussion of eggs of oviparous animals.

The egg cell's

mitochondria are the sole means the egg can reproduce by mitosis and eventually form a blastocyst
after fertilization.

Ovoviviparity

There is an intermediate form, the ovoviviparous animals: the embryo develops within and is nourished by an egg as in the oviparous case, but then it hatches inside the mother's body shortly before birth, or just after the egg leaves the mother's body. Some fish, reptiles and many invertebrates use this technique.

Plants

Nearly all land plants have alternating

fertilization, the ovule develops into a seed containing the embryo.[14]

In

plant ovary develops into a fruit to facilitate the dispersal of the seeds. Upon germination, the embryo grows into a seedling.[14]

Gene expression pattern determined by histochemical GUS assays in Physcomitrella patens. The Polycomb gene FIE is expressed (blue) in unfertilized egg cells of the moss Physcomitrella patens (right) and expression ceases after fertilization in the developing diploid sporophyte (left). In situ GUS staining of two female sex organs (archegonia) of a transgenic plant expressing a translational fusion of FIE-uidA under control of the native FIE promoter

In the

GUS staining reveals. Soon after fertilisation the FIE gene is inactivated (the blue colour is no longer visible, left) in the young embryo.[15]

Other organisms

In algae, the egg cell is often called oosphere.[citation needed] Drosophila oocytes develop in individual egg chambers that are supported by nurse cells and surrounded by somatic follicle cells. The nurse cells are large polyploid cells that synthesize and transfer RNA, proteins, and organelles to the oocytes. This transfer is followed by the programmed cell death (apoptosis) of the nurse cells. During oogenesis, 15 nurse cells die for every oocyte that is produced.[16] In addition to this developmentally regulated cell death, egg cells may also undergo apoptosis in response to starvation and other insults.[16]

See also

References

  1. ^ "Ovum". Biology Dictionary. BiologyOnline. 7 October 2019. Retrieved 21 January 2023.
  2. ^ "Oosphere Meaning". YourDictionary. Retrieved 12 April 2021.
  3. PMID 22827343
    .
  4. ^ ""Conclusio" from Carl Ernst von Baer's De Ovi Mammalium et..." (jpeg).
  5. ^ Needham, Joseph (1959). A History of Embryology (2nd, revised ed.). Cambridge, England, UK: Cambridge University Press.
  6. S2CID 86828337
    .
  7. ^ Lewis, Charlton T.; Short, Charles (1879). "ōvum". A Latin Dictionary. Perseus Digital Library.
  8. S2CID 207156647
    .
  9. PMID 30601039
    .
  10. ISBN 9780122272455
    . Retrieved 3 November 2013.
  11. ISBN 978-1-86891-380-0
    .
  12. ISBN 0-8153-3218-1
    .
  13. ^ a b c "The Ovum". Gray's Anatomy. Retrieved 18 October 2010.
  14. ^
    ISBN 978-0-471-24520-9
    .
  15. PMID 19542356
    .
  16. ^
    PMID 15355784
    .

External links
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