Chapter 29 Development & Inheritance

Secondary oocyte must encounter sperm 12-24 hrs of passage into tube Pregnancy Window Secondary oocyte must encounter sperm 12-24 hrs of passage into tube ~72 hours prior to ovulation + day of ovulation LH spikes 24 hours prior to ovulation Sperm live 3-5 days Fertilization Sperm encounters corona radiata within an hour & releases enzymes Hyalurondiase-from acrosome of many sperm Sperm binds to zona pellucida > acrosome ruptures > membranes fuse > enters cytoplasm of egg https://www.youtube.com/watch?v=BFrVmDgh4v4

Oocyte Activation Egg membrane depolarizes: Zygote- 23 + 23 = 46 Na comes in=release of Ca from smooth ER Releases enzymes that prevent polyspermy (cortical reaction) Completion of Meiosis II = ovum Activation of enzymes=increase metabolic rate Zygote- 23 + 23 = 46 Female (x) Male (x or y)

Cleavage & Blastocyst Formation Cleavage- cell divisions, produce identical cells (blastomeres) Morula-day 3, enters uterus on day 4 Blastocyst -no longer identical cells Inner cell mass-embryo & trophoblast-provide nutrients Blastocoele-cavity

Implantation 7 days after fertilization Trophoblast secretes hyaluronidase to erode uterine lining Ectopic- implantation other than in uterus Gastrulation-day 12, inner cell mass makes 3 germ layers (ecto, meso, endo) table 29-1

1 Week 2 Migration of mesoderm around the inner Figure 29-5 Extraembryonic Membranes and Placenta Formation (Part 3 of 7). 1 Week 2 Migration of mesoderm around the inner surface of the cellular trophoblast forms the chorion. Mesodermal migration around the outside of the amniotic cavity, between the ectodermal cells and the trophoblast, forms the amnion. Mesodermal migration around the endodermal pouch creates the yolk sac. Chorion Cellular trophoblast Mesoderm Amnion Blastocoele Yolk sac Syncytial trophoblast

2 Week 3 The embryonic disc bulges into the Figure 29-5 Extraembryonic Membranes and Placenta Formation (Part 4 of 7). 2 Week 3 The embryonic disc bulges into the amniotic cavity at the head fold. The allantois, an endodermal extension surrounded by mesoderm, extends toward the trophoblast. Amniotic cavity (containing amniotic fluid) Head fold of embryo Extraembryonic membranes Amnion Allantois Yolk sac Chorion Chorionic villi of placenta Syncytial trophoblast

3 Week 4 The embryo now has a head fold Figure 29-5 Extraembryonic Membranes and Placenta Formation (Part 5 of 7). 3 Week 4 The embryo now has a head fold and a tail fold. Constriction of the connections between the embryo and the surrounding trophoblast narrows the yolk stalk and body stalk. Tail fold Body stalk Yolk sac Embryonic gut Embryonic head fold Yolk stalk

4 Week 5 The developing embryo and extraembryonic Figure 29-5 Extraembryonic Membranes and Placenta Formation (Part 6 of 7). 4 Week 5 The developing embryo and extraembryonic membranes bulge into the uterine cavity. The trophoblast pushing out into the uterine cavity remains covered by endometrium but no longer participates in nutrient absorption and embryo support. The embryo moves away from the placenta, and the body stalk and yolk stalk fuse to form an umbilical stalk. Decidua basalis Umbilical stalk Uterus Myometrium Placenta Yolk sac Chorionic villi of placenta Decidua capsularis Decidua parietalis Uterine cavity

5 Week 10 The amnion has expanded greatly, filling the uterine cavity. Figure 29-5 Extraembryonic Membranes and Placenta Formation (Part 7 of 7). 5 Week 10 The amnion has expanded greatly, filling the uterine cavity. The fetus is connected to the placenta by an elongated umbilical cord that contains a portion of the allantois, blood vessels, and the remnants of the yolk stalk. Decidua parietalis Umbilical cord Decidua basalis Placenta Amnion Amniotic cavity Decidua capsularis Chorion

Extraembryonic Membranes Yolk sac- blood cell formation Amnion- contains fluid for cushion Allantois- gives rise to urinary bladder Chorion- Chorionic villi-blood vessels for connection with mother Fetal blood has higher affinity for hemoglobin so can strip mother’s blood of O2 No mixing of maternal & fetal blood occurs bc of trophoblast separation

Placenta Highly vascular F(x): exchange of nutrients and wastes, acts as endocrine organ Connects to fetus via umbilical cord 2 umbilical A (fetus>placenta), 1 vein (brings O2 blood) Hormone Effects Human Chorionic Gonadotropin Promotes secretion of progesterone Maintains endometrial lining Human Placental Lactogen Prepares mammary glands Ensure glucose & protein available for growth Human Placental Prolactin Converts mammary glands to active Relaxin Flexibility of pubic symphysis Dilation of cervix Delays onset of labor contractions Progesterones & Estrogens Maintain endometrial lining

Extra: Read 29-8 on Genetics