test 2 Flashcards
Fertilization occurs where
- ampullary region of the fallopian tube
Sperm + Oocyte =
Zygote
Reaches 2 cell stage about how long after fertilization
- 30 hours post fertilization
- happens in fallopian tube
Reaches 4 cell stage about how long after fertilization
- 40 hours
- happens in Fallopian tube
Reaches 12-16 cell stage about how long after fertilization
- 72 hours (3 days)
- happens in Fallopian tube
mitotic divisions
Series of mitotic divisions occurs.
Cells increase in number
Become smaller with each division
Cells are called BLASTOMERES
8 cell stage
Cells are loosely arranged until 8 cell stage.
After the 3rd cleavage, cells have maximized contact with each other.
Start to undergo compaction
Cells separate into inner and outer cells.
16 cell stage
called a MORULA
Had defined inner and outer cells.
Inner cells = inner cell mass (will become the embryo)
Outer cells = outer cell mass (will become the trophoblasts, which will be the placenta)
What happens when the morula makes wits way into the uterus
Fluid penetrates into the intercellular spaces of Inner Cell Mass.
Spaces become a single cavity
BLASTOCELE
Enlarges and becomes a BLASTOCYST
Embryo is called a BlastocystEarly Embryonic Development process (6 steps)
- fertilization (12-24 hours after ovulation)
- cleavages (first cleavage completed about 30 hours after fertilization)
- Morula (3-4 days after fertilization)
- Blastocyst (4.5-5 days after fertilization)
- Implantation (6 days after fertilization)
Blastocyst is comprised of:
Trophoblast – outer covering
Formed from cells of the outer cell mass.
Cells flatten and eventually form the epithelial wall of the blastocyst
Blastocele – Internal fluid filled space
Embryoblast – Inner cell mass
Located at one pole
Trophoblast and part of inner cell mass will become and the rest of the inner cell mass will become?
- the placenta
Rest of inner cell mass will become the embryo
Around day 6 after fertilization
implantation occurs
Trophoblastic cells over the embryoblast pole penetrate between the epithelial cells of the uterine wall.
L-Selectin (Trophoblasts) and carbohydrate receptor on uterine epithelium mediate attachment and capture of the capture and holding of the leukocytes from the blood onto the endothelial cells
Blastocyst remains free in the uterus for 2 days
Blastocyst attaches to
uterine epithelium, and subsequently the endometrium
Oriented so the inner cell mass is near the endometrium
At day 8
- the Blastocyst is partially embedded
The Trophoblast cells over the embryoblast differentiate into 2 layers:
Syncytiotrophoblast – multi-nucleated, outer zone
no cell boundries
Cytotrophoblast – mononucleated cells, inner layer (look like normal cells)
distinct cells
Cells from cytotrophoblast divide and migrate into the syncytiotrophoblast
Fuse and lose individual cell membrane – multi-nucleated
Both layers become part of the chorion (one of the fetal membranes)
Inner cell mass –embryoblast, differentiates too
Hypoblast layer (Entoderm)
Layer of small cuboidal cells adjacent to the blastocyst cavity
Epiblast layer (Ectoderm)
Layer of high columnar cells adjacent to amniotic cavity
Forms a flat disc
Small cavity appears within the epiblast
Enlarges to become amniotic cavity
Day 11-12
Completely embedded
Cells of the Synctiotrophoblast penetrate deeper into endothelial lining of maternal capillaries
Capillaries are congested and dilated
Called SINUSOIDS
Causes blood to flow through the trophoblastic system
Beginning of the uteroplacental circulation (primitive placenta)
Cytotrophoblast proliferates to form:
Amnion
Thin Protective membrane that surrounds the developing embryo.
Amniotic Cavity
Space, eventually filled with fluid.
What starts at day 8
GASTRULATION: Process for establishing 3 germ layers
Inner cell mass differentiates into:
Ectoderm
Endoderm
Mesoderm
These are the major embryonic tissues from which all tissues and organs of the body develop.
Gastrulation: Cells of the epiblast migrate to the primitive streak
Regulated by fibroblast growth factor 8 (FGF8)
Made by streak cells
Down-regulated with E-Cadherin (causing things to be loose)
Protein normally holds epiblasts together
Loss of E-Cadherin allows cells to detach and move
Arrive and become “flask-like”
Detach from epiblast and slip beneath it
Epiblast is the source of the germ layers.
Inward movement / cause invagination
Cells displace the hypoblast
Creates Endoderm
Others lie between the epiblast and the new endoderm
Mesoderm
Cells remaining in the epiblast
Ectoderm
Around 14 days after fertilization after gastrulation
Inner Cell Mass now called an Embryonic Disc as amniotic cavity starts to form.
Ectoderm – Layer of cells of the inner cell mass closest to the amniotic cavity.
Endoderm – layers of inner cell mass that borders the blastocele.
Mesoderm – Lies between the ectoderm and endoderm.
Ectoderm Becomes:
Skin, teeth, mouth glands, nervous system, some endocrine glands.
Endoderm Becomes:
Epithelium of digestive tract, respiratory system, bladder, reproductive organs, urethra
