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Survey of Embryonic Development Diagrams showing the size of a human conceptus from fertilization to the early fetal stage Embryo Fertilization 1-week conceptus 2-week conceptus 3-week embryo 4-week embryo 5-week embryo 6-week embryo 7-week embryo 8-week embryo 9-week fetus 12-week fetus Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Sperm penetration and the cortical reaction (slow block to polyspermy Sperm Corona radiata Zona pellucida First polar body Oocyte in second meiotic division (b) Sperm nucleus Acrosome Acrosomal reaction Granulosa cells of corona radiata Zona pellucida Extracellular space Oocyte plasma membrane Cortical granule Oocyte cytoplasm (a) Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Fusion of oocyte and sperm plasma Cortical reaction membranes Sperm nucleus engulfed by oocyte cytoplasm Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Events immediately following sperm penetration Sperm Daughter cells Extracellular space Second meiotic division of oocyte Second meiotic division of first polar body (g) Detached sperm tail (h) Sperm pronucleus (a) Corona radiata Zona pellucida Ovum nucleus Polar bodies (b) Anaphase of first cleavage division (f) Sperm and ovum chromosomes Male pronucleus Mitotic spindle Centriole Female pronucleus (e) (c) Zygote (d) Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Cleavage from zygote to blastocyst (a) Zygote (b) 4-cell stage (fertilized 2 days egg) Sperm (c) Morula 3 days Degenerating zona pellucida Blastocyst cavity (d) Early blastocyst 4 days Inner cell mass Blastocyst cavity Trophoblast (e) Implanting blastocyst 6 days (b) Fertilization (sperm meets egg) (a) (c) Uterine tube Ovary Oocyte (egg) (d) Uterus (e) Ovulation Endometrium Cavity of uterus Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Hormonal changes during pregnancy Relavtive blood levels Human chorionic gonadotropin Estrogens Progesterone 0 4 8 Ovulation and fertilization Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn 12 16 20 24 Gestation (weeks) 28 32 36 Birth Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Implantation of the blastocyst Endometrium Uterine endometrial epithelium Inner cell mass Trophoblast Blastocyst cavity Lumen of uterus (a) Endometrial stroma with blood vessels and glands Syncytiotrophoblast Cytotrophoblast Inner cell mass (future embryo) Lumen of uterus (b) Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn (c) Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Formation of the three primary germ layers Amniotic sac Bilayered embryonic disc Yolk sac (b) . . . turned 90˚(c) 3-D view (d) Section view in (e) Amniotic sac (amnion) Yolk sac Left Future opening between mouth and pharynx Head Cut edge of amnion Tail (a) Embryo (See Figure 28.7b) Yolk sac Primitive Epiblast streak Hypoblast (e) Bilayered embryonic disc, Right lateral-superior view Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Formation of the three primary germ layers Head Cut edge of amnion Primitive streak Yolk sac (cut edge) Epiblast Hypoblast Left Right Sections Endoderm (g) 14–15 days Ectoderm Primitive streak Tail (f) Bilayered embryonic disc, superior view Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn (h) 16 days Mesoderm Definitive endoderm Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Neurulation Head Left Cut edge of amnion (a) 17 days Surface ectoderm Neural plate Future Amnion neural Amniotic cavity crest Neural plate Right Ectoderm Notochord Mesoderm Primitive streak Notochord Endoderm Tail Yolk sac Cut edge of amnion Neural Neural plate fold (b) 19 days Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Primitive node Primitive streak Neural groove Neural crest Neural groove Notochord Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Tissues derived from the three germinal layers • Ectoderm: nervous tissues, epidermis and melanocytes. • Mesoderm: bones, muscles, mesenchyme, reproductive system, urinary system. • Endoderm: digestive system, respiratory system, endocrine system. Events of placentation, early embryonic development, and extraembryonic membrane formation Amniotic cavity Endometrium Maternal blood vessels Proliferating syncytiotrophoblast Cytotrophoblast Amniotic cavity Bilayered embryonic disc: • Epiblast • Hypoblast Endometrial epithelium Lacuna (intervillus space) containing maternal blood Chorionic villus Primary germ layers: • Ectoderm Amnion • Mesoderm • Endoderm Yolk sac Forming body stalk Allantois Chorion Extraembryonic mesoderm Chorion being formed Extraembryonic coelom Lumen of uterus (a) 71/2-day implanting blastocyst Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn (b) 12-day implanted blastocyst (c) 16-day embryo Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Embryonic membranes • Amnion: encases and protects embryo against mechanical and temperature trauma. • Yolk sac: transfers nutrients to embryo. Replaced by placenta in humans. • Allantois: repository of embryo wastes. Replaced by placenta in humans. Events of placentation, early embryonic development, and extraembryonic membrane formation Decidua basalis Maternal blood Chorionic villus Umbilical blood vessels in umbilical cord Amnion Amniotic cavity Yolk sac Extraembryonic coelom Chorion Lumen of uterus Decidua capsularis (d) 41/2-week embryo Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Events of placentation, early embryonic development, and extraembryonic membrane formation Placenta Decidua basalis Chorionic villi Yolk sac Amnion Amniotic cavity Umbilical cord Decidua capsularis Extraembryonic coelom Uterus Lumen of uterus (f) 13-week fetus Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Events of placentation, early embryonic development, and extraembryonic membrane formation Maternal arteries Maternal veins Myometrium Stratum basalis of endometrium Maternal portion of placenta (decidua basalis) Chorionic villus containing fetal capillaries Maternal blood in lacuna (intervillus space) Fetal arteriole Fetal venule Amnion Umbilical cord Fetal portion of placenta (chorion) Umbilical arteries Umbilical vein Connection to yolk sac (g) Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings.
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