1. Chapter 29 Development & Inheritance

2. Secondary oocyte must encounter sperm 12-24 hrs of passage into tube
Pregnancy Window
Secondary oocyte must encounter sperm 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

3. 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 = 46
Female (x)
Male (x or y)

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

16. Extra:
Read 29-8 on Genetics