How many eggs when born? How many will we have by adulthood?
the amt we're born with is the amt we'll always have!
How does the egg start off?
it is stuck in prophase as a primary oocytye; during menstruation, a single primary oocyte is released from the ovaries, and then goes thru meiosis I, starts meiosis II, and gets halted as a secondary oocyte
How does fertilization happen?
when a haploid sperm cell combines with a secondary oocyte, allowing it to complete meiosis II, formiung the ovum: this is a cortical rxn
cortical rxn after combination of sperm and secondary oocyte
causes a change in cell polarity; it then deposits calcium on the surface of the ovum, preventing the other sperm from fertilizing the same egg
What happens after the cortical rxn?
the male and female pronuceli unite!
pronucleus
nucleus of a haploid gamete
What happens after getting the diploid zygote from the 2 pronuclei fusion?
the zygote moves along the fallopian tubes, going through a series of cell divisions (known as an embryo as soon as it divides the first time)
embryo cell and volume info
cell # increases as cell volume remains the same; the zona pellucida prevents volume increasing
So what happens as a result of cell volume remaining the same in spite of cell# increasing?
this increases the ratio of SA to vol, this gives the cell an increased area for gas exchange, and other processes to occur; but cell differentiation has yet to occur at embryo stage!
during what point post-fertilization does cleavage occur?
days 1-3
morula
a solid ball of cells (16 to 20); located close to each other which helps w/ communication; once in this stage, the cell undergoes blastulation
blastulation
(free for days 5-7 and implanted by week 2) formation of the blastula (aka: blastocyst)--a sphere of cells surrounding a fluid-filled cavity
blastocoel
fluid-filled cavity surrounded by cells in the blastula