Human Reproductive Endocrinology Females So what happens after sex Conception fertilization occurs in the oviduct also called fallopian or uterine tube About 24 hours later zygote starts to divide This phase of rapid cell division is called Cleavage Day 3 morula forms ball of cells that becomes hollow Day 6 hollow ball of cells called a blastocyst inner cell mass trophoblasts Blastocyst produces human chorionic gonadotropin hcg Day 7 blastocyst implants into wall of uterus So what happens after sex Conception fertilization occurs in the oviduct also called fallopian or uterine tube About 24 hours later zygote starts to divide This phase of rapid cell division is called Cleavage Day 3 morula forms ball of cells that becomes hollow Day 6 hollow ball of cells called a blastocyst inner cell mass trophoblasts Blastocyst produces human chorionic gonadotropin hcg Day 7 blastocyst implants into wall of uterus The hcg from the blastocyst signals the corpus luteum to NOT degenerate Day 7 12 blastocyst implants into wall of uterus So what happens after sex Trophoblasts dissolve away layers of endometrium which will heal and grow back Trophoblast cells epiblast cells endometrial cells will eventually form the placenta visible week 5 fully formed month 3 or 4 Inner cell mass will flatten out and form disk Epiblast cells will give rise to embryo Hypoblast cells will give rise to tissues that support the developing embryo So what happens after sex Day 7 12 Epiblast will give rise to embryo more on that in a minute Hypoblast will give rise to tissues that support the developing embryo Extraembryonic membranes begin to form will become more complex Chorion Amnion Gas exchange Cavity contains amniotic fluid Will surround cushion embryo Yolk sac More fluid no yolk in mammals Site of early blood cell production Allantois coming soon Becomes part of umbilical cord and helps nourish embryo fetus So what happens after sex Day 7 12 Epiblast will give rise to embryo more on that in a minute Hypoblast will give rise to tissues that support the developing embryo Extraembryonic membranes begin to form will become more complex Chorion Amnion Gas exchange Cavity contains amniotic fluid Will surround cushion embryo Yolk sac More fluid no yolk in mammals Site of early blood cell production Allantois coming soon Becomes part of umbilical cord and helps nourish embryo fetus So what happens after sex Day 13 Epiblast will give rise to embryo Gastrulation the details Cells of the epiblast divide migrate and differentiate Primitive streak forms Dorsal cells are future ectoderm Migrate into streak Cells pass to bottom and become endoderm Cells that break off and migrate to the middle become mesoderm Gastrulation results in a disk made of 3 layers of embryonic cells ectoderm mesoderm and So what happens after sex endoderm Day 14 21 The layers of the embryonic disk begin to form other structures Extraembryonic membranes continue to develop Chorion trophoblast and mesoderm Gas exchange Amnion mesoderm and ectoderm Cavity contains amniotic fluid Will surround cushion embryo Yolk sac hypoblast and mesoderm More fluid no yolk in mammals Site of early blood cell production Allantois endoderm and mesoderm Becomes part of umbilical cord and helps nourish embryo fetus Gastrulation results in a disk made of 3 layers of embryonic cells ectoderm So what happens after sex mesoderm and endoderm Day 14 21 The layers of the embryonic disk begin to form other structures Extraembryonic membranes continue to develop Organogenesis week 3 through week 8 Embryonic disk grows layers move Neural tube becomes central nervous system Notocord contributes to spinal column intervertebral disks Somites contribute to vertebrae ribs and others Coelom becomes abdominal and thoracic cavities Archenteron becomes digestive tract Head and bottom visible by week 4 All major organs visible by week 8 not completely functional though Now called a fetus zygote to week 8 Week 4 Week 8 Know where the following tissues come from Nervous system Skeletal system Liver Touch receptors in skin Circulatory system Lining of reproductive system Lining of mouth Muscular system Most of reproductive system So what happens after sex First Trimester the first three months 12 or 13 weeks Everything we just talked about Second Trimester the second three months Baby grows and becomes very active Mom may feel baby move during the second month Placenta takes over estradiol and progesterone production corpus luteum finally degenerates Babies prematurely born toward the end of this period 24 weeks have a fair survival rate if a high quality NICU is available a very low survival rate Babies born before 24 weeks have Third Trimester Baby grows Everything gets crowded Labor usually occurs around 40 weeks about 9 months
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