Introduction
2 Embryonic stage – from fertilization through week 8. –embryo
3 Fetal period – week nine until birth – fetus
4 Pregnancy – fertilization, implantation, embryonic and fetal development – results in birth 38 weeks later (40 weeks after last menstrual period) 3 trimesters-
5 First – all major organ systems appear – most susceptible to environmental effects
6 Second – development of organ systems
7 Third – growth of fetus
Fertilization
9 Fusion of haploid sperm nucleus with the haploid secondary oocyte nucleus to form the diploid zygote.
1 Occurs in fallopian tube -12-24 hours after ovulation
2 Only about 200 sperm reach site –Viable for 48 hours after deposition
3 Pregnancy most likely to occur –in a window that is 2 days before ovulation to 1 day after
4 Sperm swim from vagina to cervix; from here on mostly contractions of uterus and tubes that propel sperm forward
5 Prostaglandins in semen stimulate uterine motility
6 Capacitation – sperm undergo changes that prepare the membrane to fuse with oocyte
7 Cholesterol, proteins and glycoproteins are removed from head of sperm
8 Acrosome of sperm contain enzymes which penetrate
1 Corona radiata – granulosa cells surrounding secondary oocyte
2 Zona pellucida – receptors for sperm (ZP3), sperm binds to this and begins acrosomal reaction – to digest path through zona
3 First sperm to penetrate zona pellucida fuses with oöcyte nucleus –oöcyte undergoes second meiosis
4 Male pronucleus fuses with female pronucleus forming diploid zygote
Polyspermy
6 Fertilization by more than one sperm –polyspermy
9 To prevent polyspermy – oöcyte membrane depolarizes –fast block to polyspermy
10 Exocytosis of molecules which inactivate ZP3 receptors –hardens zona pellucida –slow block to polyspermy
Twins
12 Dizygotic (fraternal) twins result from release and...