NURS 247 Ch 10 Fetal Development and Genetics Review Questions and Answers

Duration of pregnancy40 wks 9 calendar months 266-280 days 3 stages of fetal development 1. Pre embryonic stage 2. Embryonic stage 3. Fetal stage Summary of preembryonic stage1. Fertilization takes place in the ampulla of the fallopian tube 2. Union of sperm and ovum forms zygote 46 chromosomes 3. Cleavage cell division continues to form a morula (mass of 16 cells) 4. The inner cell mass is called a blastocyst, which forms the embryo and amnion 5. The outer cell mass is called a trophoblast, which forms the placenta and chorion 6. Implantation occurs 7-10 days after conception in the endometrium Preembryonic stage-fertilization through sec wk -AKA conception -union of ovum + sperm -fertilization occurs 2 wks p last normal menstrual period Preembryonic stage -prior to fertilization-ovum + spermatozoon undergo meiosis -primary oocyte completes 1st meiotic division bf ovulation -primary + sec spermatocytes undergo meiotic division in testes Preembryonic stage -zona pellucida200 million sperm/ml + are in ejaculated semen, only one able to enter ovum to fertilize it -others are blocked by this clear protein layer -layer disappears in 5 days -sperm reaches plasma membrane -ovum resumes meiosis & forms nucleus with 1/2 # of chromosomes (23) -ovum nucleus + sperm nucleus make contact- they lose nuclear membranes + combine maternal + paternal chromosomes -B/c ea nuclear contains a haploid # of chromosomes (23), union restores to diploid # (46) -resulting zygote begins process of a new life Preembryonic stage Zygote-genetic info from ovum + sperm establishes physical characteristics of individual -sex is deter