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ch29ppt - 29-1Development and Inheritance•From...

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Unformatted text preview: 29-1Development and Inheritance•From fertilization to birth–fertilization–implantation–placental development–fetal development–gestation–labor–parturition (birth)29-2Terminology of Development•Gestation period–time span from fertilization to birth (38 weeks)•Prenatal period (before birth)–embryological development•developing human for first 2 months after fertilization is known as an embryo•all principal adult organs are present–fetal development•from 9 weeks until birth is known as a fetus•by end of 3rd month, placenta is functioning•Neonatal period is first 42 days after birth–obstetrics is branch of medicine that deals with the neonatal period, pregnancy and labor29-3From Fertilization to Implantation29-4Events Before Fertilization•Haploid sperm nucleus & haploid secondary oocyte nucleus merge to form a single diploid nucleus•Occurs in uterine tube within 24 hours after ovulation (oocyte dies in 24 hours)•Events occurring before fertilization–peristalsis of uterine tube & movement of cilia transport the oocyte towards the uterus•oocyte releases chemical attractants–sperm swim towards oocyte by means of flagella•prostaglandins within the semen stimulate uterine contractions that help move sperm towards the oocyte–capacitationor final maturation of the sperm occurs within female•acrosomal membrane becomes fragile29-5Sperm Contact during Fertilization•Sperm penetrates the granulosa cellsaround the oocyte (corona radiata)•Sperm digests its way throughthe zona pellucida–when ZP3 glycoprotein binds to spermhead, it triggers the acrosomal reaction(enzyme release)•First sperm to fuse with oocyte membrane triggers the slow & the fast block to polyspermy–1-3 seconds after contact, oocyte membrane depolarizes & other cells can not fuse with it = fast block to polyspermy–depolarization triggers the intracellular release of Ca+2 causing the exocytosis of molecules hardening the entire zona pellucida = slow block to polyspermy29-6Events Within the Egg•Sperm entry, triggers oocyte to complete meiosis II and dump second polar body•Once inside the oocyte, the sperm loses its tail & becomes a male pronucleus•Fusion of male & female haploid pronuclei is the true moment of fertilization•Fertilized ovum (2n) is called a zygote–zona pellucida still surrounds it29-7Nature of Twins•Fraternal twins (dizygotic)–independent release of 2 oocytes fertilized by 2 separate sperm–as different as any 2 siblings•Identical twins (monozygotic)–2 individuals that develop from a single fertilized ovum–genetically identical & always the same sex–if ovum does not completely separate, conjoined twins (share some body structures)29-8Formation of the Morula•Rapid mitotic cell division of embryo is called cleavage•1st cleavage in 30 hours produces 2 blastomeres•2nd cleavage on 2nd day•By 3rd day has 16 cells •By day 4 has formed a solidball of cells called a morula29-9Development of the Blastocyst...
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ch29ppt - 29-1Development and Inheritance•From...

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