Lecture 9: Fertilization and Gastrulation Flashcards
Gametes include oocytes and sperm, which are haploid cells that can undergo ______ (or fusion of nuclei of 2 sex cells)
Karyogamy
What is the difference in motility between oocytes and sperm?
Oocytes are immotile; sperm are highly motile
What is the sex chromosome constitution in sperm vs. oocytes?
Sperm: 23X or 23Y
Oocyte: 23X
In addition to their sex chromosome constitution, gamets have ____ autosomes
22
Primary oocytes remain dormant until when?
Puberty
During puberty, the ______ of the oocyte matures and completes meiosis I to form a _________ _________
Follicle
Secondary oocyte
Meiosis I of the primary oocyte at puberty produces a secondary oocyte.
The secondary oocyte begins the second meiotic division, but stops at what phase?
Metaphase
What happens to the ~2 million oocytes present in females at birth?
Most regress during childhood
No more than 40,000 remain at adolescence
~400 will form secondary oocytes and are ovulated
The oocyte is surrounded by __________ cells which are responsible for folliculogenesis
Granulosa
What 3 things are associated with the granulosa cells responsible for folliculogenesis?
Cumulous oophorus
Mural granulosa cells
Corona radiata
_________ __________ anchors the primary oocyte to the wall of the follicle
Cumulus oophorous
What lines the wall of the oocyte follicle?
Mural granulosa cells
What is firmly anchored to the zona pellucida of the oocyte?
Corona radiata
________ ________ is the thick layer of glycoproteins deep to the corona radiata of the oocyte
Zona pellucida
What are the 3 major components of a mature sperm?
Head - forms most of the bulk of the sperm and contains nucleus
Neck - junction of head and tail
Tail - provides motility to fertilization site
The head of the sperm is covered by the ________, a cap-like organell containing enzymes
Acrosome
What are the 2 major function of the acrosome of mature sperm?
Facilitates dispersion of follicular cells of corona radiata
Penetration of zona pellucida of oocyte
What is the cortical reaction and why is it so important?
Process initiated during fertilzation by the release of cortical granules from the egg
Prevents polyspermy, or the fusion of multiple sperm with one egg!
Meiosis I of the primary oocyte at puberty produces a secondary oocyte.
The secondary oocyte begins the second meiotic division, but stops at metaphase.
What stimulates the oocyte to complete meiosis II?
Fertilization
Fertilization stimulates the oocyte to complete meiosis II, resulting in fusion of ________ into a diploid aggregation of 46 chromosomes
At this point, the cell is referred to as a _________
Pronuclei
Zygote
What happens to the chromosomes once there is fusion of pronuclei and the cell becomes a zygote?
They arrange on the cleavage spindle and prepare for cleavage
There is metabolic activation and initiation of cleavage
One form of mosaicism is called _______, meaning failure of a chromosome pair to separate
Nondisjunction
When does nondisjunction occur and what does it produce?
Occurs during early cleavage
Produces an embryo with 2+ cell lines with different chromosome complements
Individuals with mosaicism are _______
Mosaics
What is the most common example of mosaicism?
Numerical mosaicism - such as trisomies
[typically trisomic mosaicism is less severe than nonmosaic condition]
Repeated mitotic divisions of the zygote produces _________
Bastomeres
How does cell number vs. cell size change during cleavage to produce blastomeres?
Increase in cell number, but decrease in blastomere size
When does production of blastomeres occur relative to fertilization?
About 30 hours after fertilization
At the 9-cell stage, the blastomeres undergo _________. At 12-32 cells, the developing human is called a ________
Compaction
Morula
During blastogenesis, after entering the uterus, the ________ _______ appears inside the morula.
Blastocystic cavity
Once the blastocystic cavity has formed inside the morula, the blastomeres make their first lineage decision to become what vs. what?
Trophoblast layer vs. embryoblast
The term _______ refers to an embryo and its membranes
Blastocyst
2 days after fertilization, the _______ ________ degenerates, which is sometimes referred to as the “hatching” of the blastocyst
Zona pellucida
Describe cell stages from day 0 through day 5 after fertilization
Day 0: pronuclear stage
Day 1: 2-cell (24 hours)
Day 2: 4-cell (48 hours)
Day 3: 8-cell (72 hours)
Day 4: morula (96 hours)
Day 5: blastocyst (120 hours) - hatching
Describe the process of in vitro fertilization and embryo transfer
Hormonal stimulation of mature oocyte formation, resulting in several mature follicles
Collection of occytes from follicles with aspirator during laparoscopy
Placement of oocytes in petri dish with capacitated sperms; in vitro fertilization of oocytes
Cleavage of zygotes in culture medium until 4-8 cell stages are reached
Transfer of 1-2 cleavage embryos into uterine cavity by way of catheter inserted through vagina and cervical canal
Assisted Reproductive Technology, or ART, consists of what 3 major methods?
Cryopreservation of embryos
Intracytoplasmic sperm injection
Assisted IVF
Describe cryopreservation of embryos
Early embryos from IVF are preserved by freezing in liquid nitrogen
Transfer of 4-8 cell embryos and blastocysts into uterus
Describe intracytoplasmic sperm injection
Sperm injected into mature oocyte, commonly done when few sperms are available
Where does fertilization occur with assisted IVF? How does this compare to the usual location of fertilization?
In the ampulla, which is the usual location of fertilization
T/F: many zygotes, morulae, and blastocysts abort spontaneously; the overall early spontaneous abortion rate is thought to be approx. 45%
True
What are 2 potential causes for spontaneous abortion?
Inadequate production of progesterone and estrogen from corpus luteum
Chromosomal abnormalities (abnormal segregation, duplication, deletions, dispermy, etc.)
How many chromosomes are present in dispermy?
69
What procedure may be required in the event of a spontaneous abortion?
Dilation and curettage (D and C)
What condition is characterized by implantation of the blastocyst outside the uterine cavity?
Ectopic pregnancy
Where do ectopic pregnancies typically occur?
In the oviduct = tubal pregnancy (mainly in ampullary region)
What are some signs of ectopic pregnancy?
Abdominal pain
Amenorrhea
Vaginal bleeding
Profuse bleeding and rupture of oviduct wall
___________ differentiation occurs 6 days after fertilization
Trophoblast
Trophoblasts differentiate into what 2 layers?
Syncytiotrophoblasts (outer layer)
Cytotrophoblasts (inner layer)
Which layer of the trophoblast will invade to produce chorionic villi?
Cytotrophoblast
__________ are a multinucleated protoplasmic mass without cell boundaries
Syncytiotrophobasts
With syncytiotrophoblasts, cells expand within the embryonic _____ and produce digestive enzymes that erode the endometrium in a process called ___________
This enables the blastocyst to burrow into the endometrium
Pole
Decidualization
Embryoblast reorganization occurs with formation of the _________ embryonic disc
Bilaminar
What are the 2 layers of the bilaminar embryonic disc?
Hypoblast (primitive endoderm)
Epiblast
Which layer of the bilaminar embryonic disc consists of a layer of columnar cells?
Epiblast (layer of columnar cells deep to hypoblast)
The columnar cells of the epiblast will give rise to what?
Embryo proper
The hypoblast, or primitive endoderm, is formed by an internal layer of _________ cells.
It is a result of the ________ of cells from the embryoblast and faces the ________ cavity.
Cuboidal
Delamination; blastocystic
What forms the 4 extraembryonic membranes and what are they?
Membranes are produced by bilaminar germinal disc and trophoblast layer
Amnion
Yolk sac
Chorion
Allantois
Which extraembryonic membrane gives rise to the embryonic portion of the placenta?
Chorion
Which extraembryonic membrane serves as a site for early blood cell and vessel formation?
Yolk sac
Which extraembryonic membrane consists of a thin layer of cells that encloses the epiblast and holds amniotic fluid?
Amnion
When does the amniotic cavity appear?
In the 2nd week
The amniotic cavity appears the 2nd week when fluid collects between the _____ and _____ cells
Epiblast; trophoblast
[the epiblast cells expand toward embryonic pole to form the amnion. The amniotic cavity will enclose the entire embryo]
The development of the yolk sac occurs as a result of proliferation of the _______ (day 8)
Hypoblast
Proliferation from the hypoblast occurs into the blastocyst cavity, forming the primary yolk sac. What is the term for the cells that line the yolk sac?
Heuser’s membrane
After formation of the Heuser’s membrane, extraembryonic ________ forms and fills the remainder of the space
Mesoderm
Extraembryonic mesoderm arises from what 2 components?
Hypoblast
Primary yolk sac
By day 12, the primary yolk sac is displaced (will degenerate) by migrating ________ cells, which form the secondary yolk sac
Hypoblast
A new space, called the _______ ______ is formed by splitting of the extraembryonic mesoderm into 2 layers
Chorionic cavity
The chorionic cavity separates the embryo with its attached amnion and yolk sac frmo the outer wall of the blastocyst = ___________
Chorion
What 2 extraembryonic germ layers are associated with the amnion?
Ectoderm
Mesoderm
What 2 extraembryonic germ layers are associated with the yolk sac?
Endoderm
Mesoderm
What extraembryonic germ layer is associated with the chorion?
Mesoderm
By day 13, the embryo proper is suspended in the chorionic cavity by the ______ _____, made up of extraembryonic mesoderm
Connecting stalk
What condition is characterized as an abnormal blastocyst with continued trophoblast development?
Hydatiform mole
What type of hydatiform mole shows some evidence of embryonic development and may appear triploid (69, XXX; 69, XXY; 69, XYY)?
Partial
With complete hydatiform mole, the oocyte lacks a female ________, and there is dispermy. No embryonic development occurs
Pronucleus
[note: dispermy = duplication of male pronucleus]
Hydatiform moles produce high levels of _____ and may produce benign or malignant tumors called _________
The placental villi will be swollen and ________
hCG; choriocarcinoma
Vesicular
The bilayer embryonic disc consists of epiblast and hypoblast.
Epiblast differentiates into what 3 structures?
Ectoderm of amnion
Embyronic ectoderm
Primitive streak
The bilayer embryonic disc consists of epiblast and hypoblast.
The hypoblast becomes the ______ of umbilical vesicle, which then differentiates into extraembryonic mesoderm
Endoderm
Extraembryonic mesoderm, embryonic mesoderm, notochordal process, and embryonic endoderm arise from what structure derived from the epiblast?
Primitive streak
________ is the process by which cells from the epiblast migrate to form the primary germ layers
Gastrulation
[primary germ layers give rise to all adult structures and establish tube-within-a-tube body plan]
Gastrulation begins during week 3 with formation of the ________ _______, which is a thin depression on the surface of the epiblast
Primitive streak
What is established once all germ layers are present in gastrulation?
Trilaminar embryonic disc
At the beginning of morphogenesis, epiblast cells move through the primitive streak to relocate between the epiblast and hypoblast layers in a process called _______
Ingression
Describe the ingression of epiblast cell relocation
Lateral –> midline –> through primitive streak –> move back to lateral
Epiblast cells displace the hypoblast, forming what germ layer?
Embryonic endoderm
Epiblast cells displace the hypoblast, forming embryonic endoderm. The cells remaining in the epiblast form what germ layer?
Embryonic ectoderm
Epiblast cells displace the hypoblast, forming embryonic endoderm. The cells remaining in between epiblast and hypoblast become what germ layer?
Embryonic mesoderm
_________ are tumors that arise from primordial germ cells (PGCs), which are migratory cells that normally populate the gonads
Teratomas
Are teratomas more common in males or females?
4x more frequent in females
[represents 3% of childhood malignancies overall]
Which germ layers are teratomas derived from?
May be derived from any one to all germ layers
Contain a range of cell types: hair, teeth, pituitary tissue, etc.
Formation of the notochordal process begins with cranial extension from the _______ ________
Primitive node
The notochordal process extends cranially from the primitive node between ectoderm and endoderm until reaching the _____ ______
Prechordal plate
T/F: by day 20, the notochordal process is complete
True
The notochordal process will form the notochord as it progresses from hollow tube –> flattened plate –> solid rod.
The notochord is a _______ derivative
Mesodermal
What is the primary inductor in the early embryo, providing the signaling required for development of axial musculoskeleton and CNS?
Notochord
The notochord contributes to the nucleus ______ in infants and children
Pulposus
The endoderm is the source of what body structures?
Epithelial linings of the respiratory and digestive tracts
Glands opening into the GI tract, glandular cells of associated organs such as the liver and pancreas
The ectoderm is the source of what body structures?
Epidermis of skin, and epidermal derivatives
CNS and PNS
Neural crest cells, eyes, and internal ears
The mesoderm is the source of what body structures?
All skeletal muscles, blood cells, the lining of blood vessels
All visceral smooth muscular coats, serial linings of all body cavities, urogenital ducts and organs
Most of the cardiovascular system
All trunk CT (including cartilage, bones, tendons, ligaments, dermis, and storm of internal organs)
