Lecture 9: Fertilization and Gastrulation Flashcards by Sarah Gillen

Gametes include oocytes and sperm, which are haploid cells that can undergo ______ (or fusion of nuclei of 2 sex cells)

Karyogamy

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What is the difference in motility between oocytes and sperm?

Oocytes are immotile; sperm are highly motile

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What is the sex chromosome constitution in sperm vs. oocytes?

Sperm: 23X or 23Y

Oocyte: 23X

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In addition to their sex chromosome constitution, gamets have ____ autosomes

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Primary oocytes remain dormant until when?

Puberty

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During puberty, the ______ of the oocyte matures and completes meiosis I to form a _________ _________

Follicle

Secondary oocyte

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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

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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

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The oocyte is surrounded by __________ cells which are responsible for folliculogenesis

Granulosa

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What 3 things are associated with the granulosa cells responsible for folliculogenesis?

Cumulous oophorus
Mural granulosa cells
Corona radiata

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_________ __________ anchors the primary oocyte to the wall of the follicle

Cumulus oophorous

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What lines the wall of the oocyte follicle?

Mural granulosa cells

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What is firmly anchored to the zona pellucida of the oocyte?

Corona radiata

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________ ________ is the thick layer of glycoproteins deep to the corona radiata of the oocyte

Zona pellucida

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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

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The head of the sperm is covered by the ________, a cap-like organell containing enzymes

Acrosome

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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

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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!

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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

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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

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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

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One form of mosaicism is called _______, meaning failure of a chromosome pair to separate

Nondisjunction

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When does nondisjunction occur and what does it produce?

Occurs during early cleavage

Produces an embryo with 2+ cell lines with different chromosome complements

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Individuals with mosaicism are _______

Mosaics

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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?

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)