Gastrulation and Embryonic Germ Layers Flashcards
Zona Pellucida
Thick layer of glycoproteins that surrounds oocyte
Purpose of Zona Pellucida
Helps with sperm recognition and binding
Granulosa cells
Responsible for follicle development
Cumulus oophorous
Anchor oocyte to follicle wall
Mural granulosa cells
Line wall of follicle
Corona radiata
Firmly anchor to zona pellucida; sperm must cross this layer to fertilize the oocyte
What are the 3 types of granulosa cells?
Corona radiata, mural granulosa cells, cumulus oophorous
List the 7 steps of fertilization
- Acrosome reaction
- Zona reaction
- Fusion of egg and sperm cell membranes
- Sperm head and tail enter ooctye cytoplasm
- Formation of female and male pronuclei
- Pronuclei fuse to form zygote
- Chromosomes of zygote align on cleavage spindle
What is the acrosome reaction?
Sperm head releases enzymes
Why is the acrosome reaction important?
It allows the sperm to pass through the corona radiata and zona pellucida
What is the zona reaction?
Changes in the zona pellucida
Why is the zona reaction important?
It prevents the oocyte from being fertilized by more than one sperm by making the zona pellucida impermeable
What happens after fertilization?
Cleavage
What is cleavage?
Begins 30 hours after fertilization
Repeated mitotic divisions of zygote
After 8 cells have been created, what happens?
Compaction
What is compaction?
Cells squeezing in, taking smaller and more irregular shapes to fit inside
Once 12-32 cells have been created what do you form?
Morula
After the morula is formed, what happens next?
Blastogenesis
What is blastogenesis?
Formation of a blastocyst and degradation of the zona pellucida
What is does a blastocyst include?
Embryo and its membranes
- Trophoblast layer
- Embryoblast layer
How long after initial penetration of the oocyte with the sperm does it take for blastocyst formation?
5-6 days
Describe spontaneous abortions?
45%; occurs to zygotes, morulae, blastocysts;
Happens due to chromosomal abnormalities, inadequate hormone release
Usually before you know you are pregnant
Where does the blastocyst attach?
Endometrial wall adjacent to its embryoblast layer
What does the trophoblast layer differentiate into?
Cytotrophoblast and syncytiotrophoblast
What does the cytotrophoblast do?
Release enzymes
What does the syncytiotrophoblast do?
Use enzymatic degradation to invade endometrial wall to become superficially implanted
What does the embryoblast layer differentiate into?
Epiblast and hypoblast
What does the hypoblast do?
Continuous with exocoelomic membrane; lines cytotophoblast to create chorion
What does the epiblast do?
Forms amniotic cavity and amnion
Why is the epiblast important?
It protects the developing fetus
What is the amnion?
Encloses embryo and houses amniotic fluid
What is the bilaminar embryonic disc?
Epiblast + Hypoblast
*Day 6-10
What is the primary umbilical vessel?
Hypoblast + lining of exocoelomic membrane
What does the primary umbilical vessel give rise to?
Extraembryonic mesoderm
What is the extraembryonic mesoderm?
Layer of tissue that surrounds amnion and umbilical vessel
What happens to spaces in the extraembryonic mesoderm?
The spaces join and fuse to create the extraembryonic coelom
What does the extraembryonic coelom do?
Forces the primary umbilical vessel to decrease in size
What is the secondary umbilical vessel?
Forms from hypoblast cells, migrates inside of primary umbilical vesicle and it is the site of origin for primordial germ cells
What does the extraembryonic coelom separate the extraembryonic mesoderm into?
Extraembryonic somatic mesoderm and the extraembryonic splanchic mesoderm
Extraembryonic somatic mesoderm
Lines trophoblast and amnion
Extraembryonic splanchic mesoderm
Surrounds umbilical vessel
Chorion sac
Fetal component of placenta
What is the chorion sac made of
Extraembryonic somatic mesoderm and trophoblast
What is an ectopic pregnancy?
Implantation of the blastocyst outside the uterine cavity, usually in the oviduct
Signs and symptoms of ectopic pregnancy
Profuse bleeding, abdominal pain, ruptured oviduct and occasional loss of ovary
2% of all pregnancies
What is gastrulation?
Formation of trilaminar embryonic disc of primary germ layers
When does gastrulation take place?
Week 3 of development
What defines body axes; such as cranial-caudal, dorsal-vental, left-right?
Gastrulation
First step in gastrulation?
Epiblast cells thicken to create the primitive streak and primitive node
Cells in the middle of primitive streak and node die to become what?
Primitive groove and primitive pit
What cells migrate into primitive groove?
Epiblast cells
The hypoblast during gastrulation will become what?
Endoderm
The epiblast layer during gastrulation will become what?
Ectoderm
The cells that are migrating into the primitive groove and towards the cranial end become what?
Mesoderm
What is the function of the notochord?
Primary signaling center in the embryo
What is saccrococcygeal Teratoma?
Tumor made of pluripotent primitive streak cells
Mostly occurs in female and tumor grows at sacral end
