Oogonia Flashcards
In the human, the process of oogenesis starts
early in fetal development.
The primordial germ cells proliferate and migrate from
the epithelium of the yolk sac to the genital ridge via the embryonal endoderm reaching the gonadal ridges at about the 5th week of pregnancy.
They then move inwards to form the
primitive medullary and sex cords.
At this point they lose their motility and become
oogonia which then multiply by mitosis.
Oogonia are clonally derived and intercellular cytoplasmic bridges between
oogonia, a characteristic of nest formation by premeiotic gametes, have been observed in the human.
Oogonial nests are believed to arise from daughter cells derived from the same dividing oogonium and may help
increase the store of materials and nutrients necessary for later development.
The oocytes within a cluster communicate
via the intercellular bridges.
Approximately 1000 to 2000 oogonia will arrive at the fetal ovary. They then increase dramatically in number through mitotic division to a
maximum concentration of 6-7 million oogonia by the 20th week (5th month) of gestation.
At this point mitosis stops and
no additional oogonia will develop.
Growth factors and neurotropins have been demonstrated to be important for
fetal ovary development, but information regarding their control and interactions is lacking.
Experimental evidence indicates a possible role for many factors in oocyte development and survival including
prostaglandins, members of the transforming growth factor beta (TGFB) superfamily, morphogenetic proteins (BMPs), wingless-type mouse mammary tumor virus integration site (WNT) signaling molecules and antimüllerian hormone (AMH)
