Embryology PPT 1 and 2 Flashcards
day 1
fertilization
day 2-3
cleavage
day 3
compaction
blastocyst formation
day 4
implantation begins
day 6
how many oocytes at birth
2 million
how many oocytes at puberty
40,000
how many oocytes ovulated
400
__surge causes changes within the ovary and egg for it to rupture
LH (luteinizing hormone)
Egg is surrounded by the:
Zona pelucida: layer of glycoproteins
Corona radiate: granulosa cells that surround the ovary after ovulation
Egg is swept into
oviduct (uterine tube)
Fertilization usually occurs in the
ampulla
Enters uterus
~ day 4
Implantation into uterine wall begins
~ 6th embryonic day
Begins process of cellular division (cleavage)
right after fertilization
fertilization steps (8)
1.Multiple sperm bind to corona radiate
2. Sperm passes through the corona radiata
3. Sperm binds to a ZP protein in the zona pellucida
Causes release of enzmes allowing it to burrow through ZP (acrosome reaction)
4. The cell membrane of 1 sperm fuses with cell membrane of oocyte
5. Initiates calcium influx causing the release of cortical granules (cortical reaction)
Blocks other sperm from fertilizing egg
6. Completion of 2nd meiotic division of the oocyte
7. Male and female pronuclei form fuse
8. Arrangment of the chromososmes for mitotic cell division
fertilzation usually occurs
ampulla of uterine tubes
Zygote is the result of the union of the male and female gametes
Restores 46
Maternal and paternal chromosomes are mixed
Repeated mitotic cell divisions results in an increase in
cell number (not size)
A cell formed by cleavage of a fertilized ovum is call a
blastomere
Blastomeres become __ with division
smaller
Early blastomeres are
totipotent: capable of giving rise to any cell type
in the 8 cell stage __ begins
compaction
Blastomeres tightly align by
increased cell adhesion and segregate inside vs. outside
Outer cells become
trophoblast – cells that will form placenta
Inner cells will form
embryo (inner cell mass)
When there are 16-32 blastomeres, the conceptus is referred to
a morula
inner cells and outer cells
morula enters uterus when
about 4 days after fertilization
___ are pumped into embryo creating a blastocystic cavity
Sodium and water
blastocystic cavity
- Mostly separates the embryoblast and trophoblast
- Embryo is called a blastocyst
blastocyst attaches to endometrium
~ 6 days after fertilization,
Prior to implantation, the blastocyst “hatches” from ___
zona pellucida (Enzymatically bores a whole and squeezes out)
Early ZP shedding or delayed zygote transport can cause
implantation in the wrong location (ectopic pregnancy)
Week 2: days 7-14
- Embryo becomes more deeply embedded within endometrium
- Development of trophoblast into placenta precursor
- Formation of bilaminar embryo, amniotic cavity
- ~ day 10 embyro becomes completely embedded within the endometrium
(~day7) Trophoblast proliferates and differentiates into:
cytotrophoblast and syncytiotrophoblast
Cytotrophoblast
stem cell population that adds cells to the syncytioblast
Syncytiotrophoblast
- Derived from cytotrophoblast proliferation
- Cells lose membranes and form a syncytium
- Located at the embryonic pole (adjacent to embryoblast)
- ~ day 8, begins invading into the endometrium.
- Blastocyst becomes completely embedded ~day 10
Synctytiotrophoblast comes into contact with uterine vessels and glands creating a
primitive uteroplacental circulation (lacunae filled with maternal blood)
Creates lacunae filled with maternal blood
Synctytiotrophoblast
fuse creating a lacunar network
Lacunae
Cytotrophoblast form extensions that grow into overlying synctiotrophoblast forming
chorionic villi
Villi become penetrated by __ that will eventually form blood vessels
extraembryonic mesoderm (week 2 and 3)
Embryoblast differentiate into 2 epithelial layers by
day 8
Epiblast:
columnar cells adjacent to amniotic cavity (dorsal side of embryo)
hypoblast
small cuboidal cells adjacent to exocoelomic cavity (primitive yolk sac)
- Forms into a bilaminar embryonic disc
- Located between amniotic cavity and the primary umbilical vesicle
embryoblast
Amniotic cavity forms within the
epiblast
Epiblast cells migrate forming
the amnion which encloses the amniotic cavity
Hypoblast migrate and line the blastocystic cavity forming the
exocoelomic membrane
Blastocystic cavity referred to as the
primary umbilical vesicle (primary yolk sac)
Hypoblast and cytotrophoblast produce
extraembryonic mesoderm
Extraembryonic mesoderm proliferates and
- Develops spaces within
- These spaces fuse to form the extraembryonic coelom (chorionic cavity)
precursor to the umbilical cord
Fluid filled cavity that surrounds the umbilical vesicle and amnion
Except at connecting stalk
Extraembryonic somatic mesoderm + 2 layers of trophoblast form the
chorion
chorion
Outermost fetal membrane
Contributes to the placenta
Week 3 Days (14-21) key events
- Appearance of primitive streak
- Development of the notochord and neural induction
- Differentiation of 3 germ layers (gastrulation)
Gastrulation
- Process where the bilaminar embryonic disc is converted into a trilaminar embryonic disc
- Beginning of morphogenesis: the development of the form and structure of organs and parts of the body
Gastrulation gives rise to 3 layers
ectoderm
endoderm
mesoderm