Fertilization and Gastrulation Flashcards
When is it most likely for something to go wrong in human development?
The first 8 weeks (aka the embryonic trimester)
When does the Obstetrical calendar start? When does the calendar assume fertilization occurs?
Obstetrical Calendar starts 1st day of LMP
Fertilization starts 14 days after 1st day LMP (Approximates with ovulation, assumes the earliest possible point for fertilization)
Where does the Ovulatory Calendar start?
Fertilization (Two weeks after the obstetrical calendar starts)
What is the Zona Pellucida made of?
Glycoprotien Meshwork
Where does most fertilization occur?
The Ampulla (distal 1/3 of the fallopian tube)
What all occurs in week 1? (5 things)
- Fertalization
- Cleavage
- Blastocyst formation
- Inner Cell Mass (Embryoblast)
- Implantation
What is another name for the inner cell mass?
Embryoblast
What is capacitation?
What does this allow for?
The removal of a glycoprotien coat and seminal plasma protiens from the plasma membrane of the sperm for fertilization
-passage of sperm through corona radiata
The Acrosome Reaction
What does a sperm use to penetrate the corona radiata?
Hyaluronidase
What does a sperm use to penetrate the zona pellucida?
Esterases, acrosin, and neuraminidase
What does the Zona Pellucida do to prevent polyspermy?
Changes conformation - the meshwork becomes rigid
What technique might be performed to induce pregnancy in a couple for which the male has a low sperm count?
Intracytoplasmic sperm injection
Make up for the diminished liklihood of a sperm contacting an egg by directly injecting the sperm into the egg.
Going from exterior to interior, what are the layers of a human oocyte?
- Corona Radiata
- Zona Pellucida
- Perivitelline Space
- Plasma membrane of oocyte
- Cytoplasm of oocyte
What does the perivitelline space assist in?
What does it do?
The zona reaction
Releases granules to block polyspermy
What is the name of the cell that divides in cleavage?
Blastomere
When does cleavage begin to occur?
At about 30 hours
When does the dividing embryo become a morula?
Day 3
When does the embryo become an early blastocyst?
What changes to make this structure?
Day 5
A fluid filled cavity (blastocystic cavity) is formed
When does the embryo enter the uterine body?
Day 3-4
When does implantation typically occur?
Around day 6
What stage is the developing embryological structure in by day 7 (end of week 1)?
What are the main structures of this structure?
Late Blastocyst
Inner cell mass, blastocyst cavity, and trophoblast ring
What two structures does the trophoblast give rise to, and what do those structures do?
Cytotrophoblast
This is a mitotically active stem cell layer, forms the syncytiotrophoblast. Stays on the outside
Syncytiotrophoblast
Contains proteolytic enzymes and hCG - responsible for implantation and initial pregnancy signaling.
Conceptually, the trophoblast gives rise to the placenta.
What does the inner cell mass give rise to?
The embryo!
Where do we get Embryos for Stem Cell Therapy?
From Cryo-preserved embryos
At what point does the Zona Pellucida disappear?
What this called?
By day 7
“Hatching of the embryo”
What immunosupressant protien to the trophoblasts produce?
When do we start to see this be produced?
Early pregnancy factor
After about 10 days
What is Hydatidiform Mole?
What causes the complete version?
What causes the partial version?
Abnormal proliferation of trophoblasts.
Complete: An empty oocyte getting fertalized, and then duplicating the sperm OR an empty oocyte getting fertalized by two sperm
Partial: Normal egg fertalized by two sperm
What would you call a malignant tumor which has developed from a hyatidiform mole?
Where do these types of tumors like to metastasize? (6 places)
Choriocarcinoma
- Liver
- Lung
- Vagina
- Intestine
- Bone
- Brain
What are the clinical features of Hydatidiform Mole?
- Vagnial Bleeding (villi can sometimes be seen)
- Pressure or pain of the pelvis
- Enlarged Uterus
- Hyperemesis Gravidarum
- Excess hCG
What two structures make up the Week 2 Inner Cell Mass?
Epiblast and Hypoblast
(In week 2 the inner cell mass differentiates into the epiblast and hypoblast)
What three structures are formed from the Epiblast?
Ectoderm
Amnion
Amnionic Cavity
What does the Hypoblast give rise to?
What three structures does that in turn give rise to?
The Extraembryonic Endoderm
- Prechordal Plate
- Primary and secondary yolk sac (aka umbilical vesicle)
- Extraembryonic Mesoderm
Where would one find Extraembryonic Somatic Mesoderm?
Lining the trophoblast and covering the amnion
(Next to ectoderm)
Where would one find Extraembryonic Splanchnic Mesoderm?
Lining the yolk sac
(Next to endoderm)
What does the prechordal plate become?
What other function does it have?
The mouth
Organizes the head
When is the Hypoblast present?
The hypoblast is only present during week 2!
The hypoblast is only present during week 2!!
The hypoblast is only present during week 2!!!
(She said this three times during lecture, so make sure you’ve got this one on lock)
What is extraembryonic coelom?
The hollow space outside of the embryo.
What is the Connecting Stalk made of?
Extraembryonic Somatic Mesoderm
What is the Primitive Blood made of?
Extraembryonic Splanchnic Mesoderm
What is the Chorion made of?
What is it?
Extraembryonic somatic mesoderm
Cytotrophoblast
Syncytiotrophoblast
The Chorion is one of the layers of the placenta.
Where might an Ectopic Pregnancy implant?
In the Uterine Tube, or in the Abdomen
What is placenta previa?
What is the main clinical manefestation?
Partial or complete blockage of the cervix by the placenta.
Vaginal bleeding beyond 20 weeks gestation.
What happens in week 3?
Gastrulation
It’s also the week that mom often knows she’s pregnant
Week 3 = 3 layers
What systems are beginning to develop in week 3?
Heart and CNS
Women often realize they’re pregnant during what phase of embryological development?
Gastrulation - Week 3
What sort of things come from the Ectoderm?
Skin, hair, nails, brain, spinal cord.
What sorts of things develop from the Mesoderm?
Muscle, bone, blood, heart, spleen
What sorts of structures come from the Endoderm?
Lungs, GI tract, bladder, glands (eg. thyroid)
Cells of the epiblast push down and encounter signals that cause them to differentiate into what?
True endoderm and mesoderm
The epiblast replaces all of the cells of the hypoblast!
What do you call the cells of the epiblast that remain on top of the tri-laminar disc?
Ectoderm
The primitive streak forms in which half of the epiblast?
The caudal end.
What does the Lateral Plate of the mesoderm give rise to?
Connective tissue
(Blood, Lymph, Mesenteries, and Cardiovascular)
What does the Intermediate Mesoderm give rise to?
Urogenital Structures
(Like the kidneys and gonads)
What three types of Mesoderm are present during gastrulation?
Paraxial Mesoderm
Intermediate Mesoderm
Lateral Plate
What does the heart form from?
The cardiogenic area.
What layers make up the prechordal plate and the cloacal membrane?
When do these two structures develop?
Just ectoderm and endoderm.
There is no mesoderm, and no blood supply
Week 2, before gastrulation occurs.
What is the Septum Transversum?
What layer is it made of?
The future Diaphragm.
Mesoderm
What causes sacrococcygeal and orapharyngeal teratomas?
A remnant of the primitive streak
OR
Abnormal Migration of Stem Cells
What layer does the notochord come from?
Mesoderm
What three things does the notochord do?
Induces the midline for the embryo
Serves as a template for the vertebral column (does not itself form the vertebral column)
induce the formation of the neural plate and CNS
What connects the amniotic cavity to the yolk sac?
What is that opening called?
The notochordal process fuses with the endoderm, coming from the primitive pit. This creates an opening into the yolk sac through that pit.
Neurenteric Canal
For the Allantois
What layer is it formed of?
What is it the template for?
What does it become?
Endoderm
Umbilical arteries and vein (does not become these structures, but provides a template)
Becomes the Urachus
What cancer can come from the notocord?
Where do these neoplasms form?
What germ layer will these have come from?
Chordomas
Spheno-occipital region of skull, and sacrum
Mesoderm
What does the Paraxial Mesoderm give rise to?
Somites
(Define the muscle, skeleton and skin)
What do Somites become? (3 things)
What germ layer do they come from?
Vertebral Skeleton (Scleratome)
Muscle (Myotome)
Dermis (Dermatome)
Mesoderm
What does the Intermediate Mesoderm become?
Kidneys
Gonads
What structures arise from the Lateral Plate Mesoderm?
How is the Lateral Plate Mesoderm Divided?
Blood, Lymph, Mesentaries, Cardiovascular
Somatic / Splanchnic
Somatic is next to ectoderm, Splanchnic is next to endoderm
What supplies the extraembryonic mesoderm to support the placenta in week 3?
The Primitive Streak
Some of the differentiating epiblast cells push down, become mesoderm, and then leave the embryo via the connecting stalk to supply the placenta. These mesoderm cells are now called “extraembryonic”
