L6 - MSK - Fertilization and Gastrulation Flashcards
What happens within Week 1?
Formation of the inner cell mass
What happens within Week 2?
Formation of epiblast and hypoblast
What happens in Week 3?
Gastrulation
Where are the mitochondria on the sperm?
Middle Piece of Tail contains Mitochondrial sheath
What covers the nucleus of the Sperm?
Acrosome
What contains enzymes which are used to get into egg?
Acrosome
What contains the follicular cells of the egg?
Corona Radiate
What is Step 1 of Fertilization?
- Capacitation: Glycoprotein coat and seminal plasma proteins removed from plasma membrane of sperm. - Passage of sperm through corona radiata - Hyaluronidase
What is Step 2 of Fertilization?
Penetration of Zona Pellucida - esterases, acrosin ** , neuramindase - Zona Reaction - block polyspermy
Where does Fertilization occur?
Fallopian Tube
Where does Blastocyst form?
Uterus
What is Step 3 of Fertilization?
- Fusion of plasma membranes of oocyte and sperm - Head and tail of sperm enter oocyte cytoplasm
What is Step 4 of Fertilization?
- Completion of second meiotic division - Formation of male pronucleus - Fusion of male and female pronuclei
What are the results of fertilization?
1 - Completion of 2nd meiotic division 2 - Restoration of diploid number of chromosomes (46 chromosome!) 3 - Determination of chromosomal sec of embryo 4 - Metabolic activation of oocyte 5 - Initiation of cleavage
What occurs during Cleavage?
- Increase in cell number, but decrease in cell size - Embryo size Unchanged - Morula development (Day 3) *Occurs ~30hrs after fertilization
When does a Blastocyst form?
Day 5-7
How many layers are present at the end of week 1?
One layer. Inner cell mass (ICM)
What is the Trophoblast? What week does it occur? What does it give rise to?
Early pregnancy factor Week 1 Gives rise to: Cytotrophoblast Syncytiotrophoblast
What is the Cytotrophoblast?
Triggered by Trophoblast Week 1 - stem cell layer - mitotically active
What is the Syncytiotrophoblast?
Triggered by Trophoblast Week 1 - Proteolytic Enzymes, chorionic gonadotropin - Responsible for implantation and initial signal of pregnancy
What are 3 types of Assisted Reproductive Technologies?
- In Vitro Fertilization and Embryo Transfer 2. Cryopreservation of Embryos 3. Intracytoplasmic sperm Injection
What are Embryonic Stem Cells?
- Derived from the inner cell mass - Pluripotent : form virtually any cell or tissue type - Therapeutic cloning or somatic nuclear transfer
What forms when there is abnormal trophoblastic proliferation and excessive amounts of hCG produced?
Hydatidiform Mole
A Complete Hydatidiform Mole results from?
- Fertilization of an empty oocyte, followed by duplication of the sperm 2. OR from fertilization of an empty oocyte by two sperm
Partial Hydatidiform Mole results from?
Fertilization of a normal oocyte by two sperm
What are the clinical features of Hydatidiform Moles?
- Vaginal bleeding 2. Pelvic pressure or pain 3. Enlarged Uterus 4. Hyperemesis Gravidarum
What is Choriocarcinomas?
Malignant tumor that develops from hydatidiform mole?
What are the parts of the Epiblast? When is it formed?
Epiblast is part of the Inner Cell Mass and made up of 3 parts: 1. Ectoderm 2. Amnion 3. Amniotic Cavity Made during Week 2
What are the parts of the Hypoblast? When is it formed? Does it remain?
- Endoderm a. Prechordal Plate b. Primary and secondary yolk sac (umbilical vesicle) c. Extraembryonic Mesoderm Formed Week 2 Only present during Week 2. Is a placeholder until Week 3 Extraembryonic
When does Morula enter Uterine Cavity?
Day 4
When does implantation occur?
Day 6: Implantation of Blastocyst into Uterus
What happens between Day 5 and Day 7 to the Blastocyst?
- Degeneration of Zona Pellucida (“Hatching”) - Embryonic Pole Forms - Blastocyst cavity enlarges - trophoblast thins (will form placenta)
What is the Bilaminar Embryonic Disc? When does it form?
Made up of epiblast and Hypoblast. Week 2.
What are the pre-mouth cells?
Prechordal Plate
What are the parts of the Extraembryonic Mesoderm?
- Extraembryonic Coelom - Hollow Cavity outside of Embryo 2. Extraembryonic Somatic Mesoderm - Lining the Trophoblast and covering the Amnion 3. Extraembryonic Splanchnic Mesoderm - Lining the yolk sac (umbilical vesicle)
What makes the belly button?
Connecting Stalk
What are the derivatives of the Extraembryonic Mesoderm?
- Connecting Stalk 2. Primitive Blood 3. Chorion
What is the extraembryonic somatic mesoderm that forms at embryonic pole and position changes during development?
Connecting Stalk
What forms in the wall of yolk sac and is extraembryonic splanchnic mesoderm? Does it remain?
Primitive Blood *Replaced in Week 3
What is Chorion?
- Extraembryonic somatic mesoderm - Cytotrophobast - Syncytiotrophoblast *Layer of Placenta
Week 2 Abnormal Implantation
Ectopic -Tubal Pregnancy: have to remove so mom survives - Placenta Previa: placenta too close to internal of cervix
What do you NOT do if Placenta Previa is suspected?
Digital Vaginal Examination -Can cause severe hemorrhage from palpitation of the placenta since it’s too close to opening of cervix
What are the 3 types of Placenta Previa? Symptoms? Treatment?
- Marginal 2. Partial 3. Total (Central) - Vaginal bleeding beyond 20 weeks gestation - Antepartum bleeding should prompt sonographic evaluation *do not stick fingers into vaginal for exam –> C-Section reduces risk of hemorrhage
What 3 layers are present during Week 3?
- Ectoderm 2. Mesoderm 3. Endoderm
What is the formation of 3 primary germ layers?
Gastrulation
What is the earliest form of the embryonic vertebrae?
Primitive Streak
What are the 3 parts of the Primitive Streak?
Primitive Knot (node) Primitive Groove Primitive Pit
What forms into the diaphragm?
Septum Transversum
Where does the anus form?
cloacal membrane
How do the anus and mouth form?
Degeneration = opening Only Ectoderm and Endoderm present NO Mesoderm
What does Ectoderm make?
Skin Hair CNS Eyes
What does Mesoderm make?
*Supporting Muscle Bone Blood Heart Spleen
What does Endoderm make?
GI Liver Stomach Lungs Bladder
What disorder does a persistence of a primitive streak cause?
Sacrococcygeal teratoma (SCT)
What does abnormal migration of primordial germ cells cause?
Oropharyngeal teratoma
Where germ cell layer does Notochord come from? Where does it extend from? What is it a template for? What does it induce?
Mesoderm Midline Extends from primitive node anterior to prechordal plate Template for Vertebral Column (Does NOT become it) Induces Neural Plate (Sonic Hedgehog)
What are the steps for the formation of Notochord?
- Cells migrate from Primitive Pit in cephalic direction 2. between ectoderm and endoderm, form tube called Notochordal Process 3. process fuses with endoderm, forming Notochordal Plate 4. Primary Yolk Sac and Amniotic Cavity Communicate 5. Notochordal Cells round up, form Notochord Proper
Clinical Significance: What is Chordomas?
- Rare slow growing aggressive neoplasms of bone - Arise from remnants of Notochord - Occur in axial skeleton in Spheno-Occipital region of skill and sacral regions
What is the Allantois?
- Posterior midline - Diverticulum from wall of yolk sac - Endoderm - Template for umbilical arteries and vein - Becomes urachus (attached to bladder)
What will the Allantoic Diverticulum in body stalk become?
Umbilical Cord
What are the 3 parts of Mesoderm?
- Paraxial 2. Intermediate 3. Lateral Plate
What does the Paraxial of Mesoderm become?
Somites - muscle - Skeleton (Vertebral) - Dermis
What does the Intermediate Mesoderm become?
- Urogenital - Kidneys - Gonads (ovaries and testes)
What does the Lateral Plate of the Mesoderm become?
- Connective Tissue - Blood - Lymph - Mesenteries - Cardiovascular
When does the Primitive Streak form?
Week 3
What main structures does the Endoderm become?
Epithelial Parts of: Lungs GI Tract Bladder Thyroid Gland Tonsils
- Follicular Cells of Corona Radiata
- Cytoplasm
- Nucleus
- Zona Pellucida
1-8
- Acrosome
- Head
- Nucleus covered by acrosome
- Neck
- Middle Piece of Tail
- Mitochondrial Sheath
- Principal piece of Tail
- End piece of Tail
Where does Fertilization most commonly occur?
In the Ampulla of the Uterine Tube
What enzyme is released by sperm during Capacitation?
What does it allow for?
Hyaluronidase
Allows sperm to enter into the perivitelline space
How many cells is a Morula?
Is Zona Pellucida still present?
12-32 cells
Yes
When is Blastocyst fully implanted in the uterus?
Day 9
When does Blastocyst attach to endometrium of uterus?
Day 6
What is the first layer the sperm break through?
corona radiata
What is the second layer the sperm break through?
Zona Pellucida
What 2 layers does the Trophoblast differentiate into?
When?
Cytotrophoblasts - inner cell layer, stem cells
Syncytiotrophoblasts - outer later, starts implantation, initial sign you’re pregnant*
~Day 6
What is located btween the epiblast and cytotrophoblasts?
Amniotic Cavity
What is the layer of cells deep to the hypoblast?
What does it form?
What does it surround?
What does it help make up (along with hypoblast)?
Epiblast
forms the embryo
surrounds amniotic cavity
makes up the bilaminar embryonic disc (along with Hypoblast)
Extraembryonic coelom
Cavity outside the embryo that dives the mesoderm into:
- Extraembryonic somatic mesoderm
- Extraembryonic splanchnic mesoderm
Extraembryonic somatic mesoderm
- lines cytotrophoblast layer of trophoblasts, more outer layer
(think somatic means body so on the outside)
Extraembryonic splanchnic mesoderm
-surrounds umbilical vesicle and is the more inside layer
(think splanchnic means viscera so on the inside)
Chorion
extraembryonic somatic mesoderm (outside layer) + trophoblast (cytotrophoblast + syncytiotrophoblast layers)
What cells can form a Teratoma during Gastrulation?
What are the most common?
- germ cell tumor from primitive streak cells that can be from any one (or all) germ layers; can contain hair, teeth, etc
- Sacrococcygeal are most common
What are the first cells to migrate through the Primitive Streak?
What cells do they kick out?
What layer/cells do they become?
Epiblast cells migrate through the streak, kick the Hypoblast cells out, form Endoderm
At what end does the Primitive Streak form?
The Caudal End of Bilaminar Disc
Where does the formation of the Notochordal Process begin?
What is the process structure?
Begins at the primitive node
Forms a hollow tube (nortochordal process)
What is the signal center in the embryo?
Notochord
What does the Notochord degenerate into?
Degenerates as vertebral bodies and makes nucleus pulposus (soft filling inside intervertebral disc)
Describe the process of Gastrulation.
● First cells of epiblast to migrate and replace hypoblast layer = endoderm
● Next set of cells of epiblast to migrate and sit on top of newly made endoderm = mesoderm
● Last set of cells that sit on very top of newly formed mesoderm = ectoderm
