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CHAPTER 22: THE REPRODUCTIVE SYSTEMS

VI.DEVELOPMENT DURING PREGNANCY

Pregnancy includes a sequence of events including fertilization, implantation, embryonic growth, and fetal growth that finally results in birth.

A.Fertilization = fusion of genetic material from sperm and ovum into a single nucleus;

See Fig 22.36, page 916.

1.Sperm become fully capacitated within the female reproductive tract (i.e. acrosome secretes digestive enzymes to break through corona radiata).

2.Secondary oocyte is ovulated from ovary surrounded by a zona pellucida and corona radiata (nutritive granulosa cells).

3.Usually in the fallopian tube, sperm bind to the zona pellucida, but only one sperm penetrates and enters the secondary oocyte (i.e. syngamy):

a.depolarization of oocyte cell membrane;

b.calcium ions rush in (and from within);

c.granules are released from oocyte;

d.causing oocyte cell membrane to become impermeable to other sperm.

e.Prevents polyspermy.

4.Once the sperm has entered a secondary oocyte:

a.Meiosis II occurs (forming female pronucleus = 23 chromosomes [i.e. haploid; 1n]);

b.Sperm's tail is shed (forming male pronucleus = 23 chromosomes [i.e. haploid; 1n]);

c.Pronuclei fuse forming a segmentation nucleus

( = 46 chromosomes; 2n);

d.Zygote = segmentation nucleus, cytoplasm, and the zona pellucida.

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