Fertilization & Gastrulation Flashcards
The first trimester is characterized as _________ and the second and third trimesters are ________.
Embryonic
Fetal
What is the name of the calendar that begins from the first day of your last menstrual period and has 2 extra weeks on it?
Gestation
Menstrual
Obstetrical
What is the name of the calendar that begins on ovulation/fertilization day?
Fertilization or ovulatory calendar
What is day 14 in the Gestation/Menstrual/Obstetrical calendar?
Ovulation
This is the outside of the ovum made up of follicular cells.
Corona radiata
This is an amorphous, acellular proteoglycan meshwork surrounding the ovum.
Zona pellucida
T/F. Ovum and sperm are both haploid.
True. Ovum is 23X while sperm is 23X or 23Y
This is the space between the Zona Pellucida and the ovum where chemical reactions occur.
Perivitelline Space
What is included in the head of the sperm?
Acrosome (anterior 2/3)
Nucleus
What are the components of the sperm?
Head
Neck
Tail
What are the segments of the sperm tail?
Middle piece
Principle piece
End piece
What is unique about the middle piece of the sperm tail?
It contains mitochondria, which creates energy to move the sperm
This is the area of the uterine tube where fertilization occurs.
Ampulla (distal 2/3 of tube)
Week 1 (Day 0 to Day 7) includes what?
Starts with ovulation and continues through the process of fertilization
How long does capacitation take for the sperm that is traveling through the uterus/uterine tubes?
7 hours
This is the term for the removal of the glycoprotein coat and seminal plasma proteins from the plasma membrane of the sperm. Removing “lid” from acrosome.
Capacitation
Once capacitation occurs, the sperm is able to emit _________ to allow it to penetrate the Corona Radiata (follicular cells).
Hyaluronidase
What are the 3 main things that help sperm travel through the Corona Radiata?
- Hyaluronidase
- Movement of sperm
- Tubal mucosal proteins
Once the sperm has penetrated the Corona Radiata, it now needs to penetrate the Zona Pellucida. What enzymes are emitted from the sperm to do this?
Acrosin (main enzyme)
Esterases
Neuraminidase
Once one sperm penetrates the Zona Pellucida, enzymes are released into the Perivitelline Space to stop other sperm from penetrating. This is called…
Zona reaction
***Ensures fertilization with only ONE sperm
After the sperm has penetrated the Zona Pellucida, the plasma membranes of the sperm and oocyte will fuse. Only the head and tail of sperm enter oocyte cytoplasm, leaving behind its _________ sheath.
Mitochondrial
***This is why children inherit mitochondria only from their mother!!!
Once the sperm and oocyte have come together, there will be completion of what?
Second meiotic division
Once the sperm and oocyte have come together, there is formation of the male ________ and then fusion of the male and female ________.
Pronucleus
Pronuclei
How long does fertilization take?
Up to 24 hours (Day 0)
What are the results of fertilization?
- Completion of 2nd meiotic division
- Restoration of diploid number of chromosomes
- Determination of chromosomal sex of embryo
- Metabolic activation of oocyte (turn on different genes)
- Initiation of cleavage
After the male and female pronuclei have fused, then cleavage begins. For the first 3 days after fertilization, the embryo is called a…
Blastomere (i.e., 2-cell stage; 4-cell stage; 8-cell stage)
3 days after fertilization the blastomere becomes a…
Morula
As cleavage occurs with the blastomere, there is an (INCREASE/DECREASE) in cell number but an (INCREASE/DECREASE) in cell size.
Increase
Decrease
***Embryo size is unchanged (i.e., what fills up the Zona Pellucida)
On day 4, what happens to the morula?
It enters the uterus
What occurs 30 hours after fertilization?
Cleavage (includes all steps from zygote to morula in uterine tube)
Days 5-7 include the formation of the _________.
Blastocyst
On Day 5, fluid starts to enter and push the cells to one side, creating the ________ _______ ________. These are embryonic stem cells that can develop into any tissue type. The outer cells compose the _________ which are stem cells for placenta.
Inner cell mass (embryoblast)
Trophoblast
What occurs on Day 6?
Implantation of the blastocyst into the uterine wall
What is the difference between a day 5 and day 7 blastocyst?
Day 5 has a zona pellucida but by Day 7 it has degraded. This means the embryo has “hatched”, allowing cells to grow.
By the end of week 1, how many embryonic cell layers do we have?
One cell layer = the Inner Cell Mass
***Trophoblast cells are also present, but these contribute to the placenta, not the embryo
By the end of week 1, how many embryonic cell layers do we have?
One cell layer = the Inner Cell Mass
***Trophoblast cells are also present, but these contribute to the placenta, not the embryo
Why is it so important to know how Week 1 of development works?
– In vitro fertilization and embryo transfer (implant zygotes at 4 and 8-cell stages)
– Cryopreservation of embryos (freeze the zygotes to implant later)
– Intracytoplasmic sperm injection (directly inject sperm into cytoplasm of oocyte – used for men with low sperm count)
How do we get embryonic stem cells for research (derived from inner cell mass)?
People donate their cryopreserved embryos
What type of potency to embryonic stem cells have?
Pluripotent (form virtually any cell or tissue type)
The trophoblast release this so the body doesn’t read these new cells as foreign and try to kill them off.
Early pregnancy factor
What does the trophoblast give rise to?
Cytotrophoblast
***Stem cell layer; mitotically active – becomes placenta
What does the cytotrophoblast give rise to?
Syncytiotrophoblast
***They are multinuclear and lose their cell membrane so they can erode into endometrium
Explain what the syncytiotrophoblast function is.
– Gives off proteolytic enzymes that allow it to erode into the endometrium and implant (Day 6)
– Gives off initial signal of pregnancy, which is hCG
These can occur due to abnormal trophoblastic proliferation, causing excessive amounts of hCG to be produced.
Hydatidiform mole
This type of Hydatidiform Mole results from fertilization of an empty oocyte, followed by duplication of the sperm (“cloning”) OR from fertilization of an empty oocyte by two sperm (Zona reaction didn’t occur).
Complete mole
This type of Hydatidiform Mole results from fertilization of a normal oocyte by two sperm (Zona reaction didn’t occur).
Partial mole
What are the clinical features of a Hydatidiform Mole?
- Vaginal bleeding (looks like prune juice)
- Pelvic pressure/pain
- Enlarged uterus
- Hyperemesis gravidarum (morning sickness)
***Your body thinks you’re pregnant!
This is the term for malignant tumors that can develop from Hydatidiform Moles (3-5 percent of cases).
Choriocarcinomas
How many embryonic cell layers do we have during week 2?
Two cell layers – The inner cell mass has divided into the epiblast and hypoblast
This cell layer is only present during week 2, acting as a placeholder until week 3 hits.
Hypoblast
What does the epiblast give rise to?
- Ectoderm
- Amnion
- Amniotic cavity
The hypoblast gives rise to the ________ ________ (does not become part of embryo) which forms the prechordal plate and umbilical vesicles.
Extraembryonic endoderm
During week 2 the hypoblast cells start to migrate around the inner rim of the cytotrophoblast cells, creating a ring which is the _______ ______ _______. Then, this starts to invaginate creating two separate rings which are the ________ _______ _______ and the ________ ________ _______.
Primary umbilical vesicle
Primary umbilical vesicle
Secondary umbilical vesicle
***Primary umbilical vesicle starts to degenerate once second umbilical vesicle is formed
What does the prechordal plate (made of columnar cells) become?
Mouth
What is the term for the two cell layers in week 2?
Bilaminar disc
What is derived from the hypoblast?
Extraembryonic endoderm
What does the extraembryonic endoderm give rise to?
Prechordal plate
Primary and secondary umbilical vesicles
Extraembryonic mesoderm
This part of the extraembryonic mesoderm is a hollow cavity outside of the embryo.
Extraembryonic Coelom
This part of the extraembryonic mesoderm lines the trophoblast and covers the amnion.
Extraembryonic Somatic Mesoderm
***Think “body” –outside
This part of the extraembryonic mesoderm lines the yolk sac (umbilical vesicle).
Extraembryonic Splanchnic Mesoderm
***Think “organ” –inside
What is derived from the extraembryonic mesoderm?
- Connecting stalk
- Primitive blood
- Chorion
This is made of extraembryonic somatic mesoderm, and forms at the embryonic pole. It is the precursor to the umbilical cord and will change positions during development.
Connecting stalk
This is made of extraembryonic somatic mesoderm, cytotrophoblasts, and sycytiotrophoblasts. It is one of the layers of the placenta.
Chorion
This is made of extraembryonic splanchnic mesoderm and forms in the walls of the yolk sac (umbilical vesicles).
Primitive blood
On what days does implantation occur?
Days 6-10
This is the term for pregnancies that have abnormal implantation. They implant in places other than the uterine wall.
Ectopic pregnancies
This is a type of ectopic pregnancy that occurs when the embryo implants in the ampulla or isthmus.
Tubal pregnancy
***Rupture of this is leading reason for women to bleed to death
This is the term for when the placenta covers the internal os of the cervix (opening).
Placenta previa
If there is vaginal bleeding beyond 20 weeks, what could be the reason?
Placenta previa
In the case of placenta previa, antepartum bleeding should prompt sonographic evaluation BEFORE digital vaginal examination. Why is this?
If you perform a digital exam, you could rupture the placenta and cause the mother to hemorrhage and bleed out.
What are the types of placenta previa?
– Marginal placenta previa = placenta is close to opening
– Partial placenta previa = placenta is partially covering opening
– Total (central) placenta previa = placenta is totally covering opening
What occurs during week 3 of development?
Gastrulation
***In a normal cycle, this is when menstruation would occur
What is being developed during week 3?
CNS
Heart formation
Circulatory system
Gastrulation is the formation of what?
3 primary germ layers (trilaminar disc)
- Ectoderm
- Mesoderm
- Endoderm
In week 3, what is the ectoderm and endoderm derived from?
Ectoderm was formerly the epiblast
Endoderm is now the “true endoderm” – hypoblast was replaced by epiblast cells that signaled and become the true endoderm
What happens during week 3 in the epiblast (ectoderm)?
Primitive streak formation
What does the primitive streak consist of?
- Primitive knot (node)
- Primitive groove
- Primitive pit
What do the prechordal plate and cloacal membrane become? Why?
Prechordal plate becomes the mouth and the cloacal membrane becomes the anus. This happens because they are both made of only ectoderm and endoderm. Since mesoderm is responsible for supportive tissue (like blood) that means these areas are not receiving blood, and they die. This creates openings for the mouth and anus.
This gives rise to the diaphragm and is made of mesoderm.
Septum transversum
This type of teratoma occurs in the caudal region, and is caused by persistence of the primitive streak (over expression of cells).
Sacrococcygeal teratoma
This type of teratoma occurs in the cephalic region, and is caused by the abnormal migration of primordial germ cells.
Oropharyngeal teratoma
This is the term for a cancerous growth involving all 3 germ layers.
Teratoma
What germ layer is the notochord made of?
Mesoderm
The cells from the notochord migrate from the _______ _______ in a cephalic direction. They lie between the ectoderm and endoderm and form a tube called the ________ ________. This will then fuse with the endoderm forming the _________ _________. At this time, the amniotic cavity and primary yolk sac are in communication.
Primitive pit
Notochordal process
Notochordal plate
The notochordal plate cells will round up and form the…
Notochord proper
The notochord forms at the midline and extends from the primitive node (knot) to the ________ _______.
Prechordal plate
What are the functions of the notochord?
1) Provides template for vertebral column – **Does NOT become the vertebral column, only gives template
2) Induces neural plate formation – **Notochord gives SHH signal, which induces neural plate to form
These are rare, slow growing aggressive neoplasms of bone. Thought to arise from remnants of the notochord.
Chordomas
Where do chordomas most often occur?
Axial skeleton in spheno-occipital region of skull and sacral regions
This is an endodermal structure that lies in the posterior midline. It is diverticulum from the wall of the yolk sac. In connecting stalk.
Allantois
What is the function of the allantois?
1) Provides template for umbilical arteries and veins – **Does NOT become them, only provides template
2) Becomes urachus – **Attached to bladder
What are the different sections of mesoderm?
Paraxial (Right next to notochord)
Intermediate (Middle)
Lateral plate (Lateral to intermediate)
This section of mesoderm gives rise to somites, which become muscle, skeleton (vertebral), and dermis.
Paraxial
This section of mesoderm gives rise to urogenital structures like the kidneys and gonads.
Intermediate
This section of mesoderm gives rise to connective tissue, such as blood, lymph, mesenteries, and cardiovascular.
Lateral plate
What does the endoderm give rise to?
Trachea Lungs GI tract Thyroid Tonsils Bladder (urethra)
***More on this list, but mostly remember trachea and lungs
What does ectoderm give rise to?
Surface ectoderm – Skin, hair, nails, mammary glands, lens of eye, etc.
Neuroectoderm – Neural tube (CNS), and Neural crest (Cranial and sensory ganglia and nerves)
Which cells are the most mitotically active during implantation?
Cytotrophoblasts
