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BISC 333 > Quiz 2 > Flashcards

Quiz 2 Flashcards

1
Q

Where does fertilization occur in the mammalian reproductive tract?

A
  • the egg is fertilized in the ampulla of the oviduct (fallopian tube)
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2
Q

During early mammalian development, where does implantation of the blastocyst occur?

A
  • the blastocyst implants in the uterine wall (where gastrulation occurs)
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3
Q

What are 5 key events that take place between fertilization and implantation during early mammalian development?

A
  1. Ovulation (an oocyte is expelled from the ovary)
  2. Oocyte is swept into the oviduct by fimbriae
  3. Fertilization occurs in the ampulla of the oviduct
  4. Embryo moves along the oviduct via cilia; cleavage occurs
  5. Embryo reaches the uterus and implants into the uterine wall; gastrulation occurs
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4
Q

What are three challenges involved in studying embryonic development in mammals?

A
  1. Small egg size (difficult to manipulate experimentally)
  2. Low egg/zygote production (difficult to obtain enough material for biochemical studies)
  3. Development occurs internally in the mother (more difficult to experimentally mimic an internal vs. external environment)
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5
Q

Why is the mouse often used as a model organism for mammalian development?

A
  1. Short life cycle for a mammal
  2. Genome has been sequenced
  3. Forward and reverse genetic approaches can be taken to study the roles of genes on developmental processes
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6
Q

What type of cleavage do mammals have?

A

Isolecithal egg- Holoblastic, rotational cleavage

  • successive divisions occur in separate planes
  • first cleavage is meridional
  • second cleavage, one blastomere undergoes meridional cleavage and the second blastomere undergoes equatorial cleavage
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7
Q

What are some distinguishing features of mammalian cleavage?

A
  • slow cell division
  • asynchrony of early cell division (embryos do not increase exponentially, but frequently contain odd numbers of cells)
  • transition from maternally to zygotically produced gene products
  • compaction
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8
Q

What is compaction?

A
  • takes place after the 3rd cleavage (8 cell stage)
  • contact between blastomeres is maximized and they form a compact ball of cells called the morula (outside cells form tight junctions, inside cells form gap junctions)
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9
Q

What do the internal cells of the mammalian morula give rise to?

A
  • embryo proper

- descendants of the embryo proper will give rise to the inner cell mass

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10
Q

What do most of the external cells of the mammalian morula give rise to?

A
  • trophoblast or trophoectoderm
  • descendants of the trophoectoderm give rise to the chorion (extra-embryonic structures) (the chorion is the fetal portion of the placenta, required for implantation)
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11
Q

What is cavitation in mammalian development?

A
  • the trophoblast cells fill the interior of the compacted morula with fluid to create the blastocoel
  • this positions the inner cell mass (embryoblast) to one side
  • after cavitation, the embryo is now considered a blastocyst
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12
Q

What happens to labeled cells if you place them inside the unlabeled cells of a secondary embryo?

A
  • if a marked blastomere is inserted into the interior of a morula, it and its progeny become part of the inner cell mass
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13
Q

What happens to the labeled cells if you placed them outside the unlabeled cells of a secondary embryo?

A
  • if a marked blastomere is placed on the outside of a host morula, it and its descendants contribute to the trophoblast
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14
Q

What does the specification of cells as either inner cell mass or trophoectoderm depend on?

A
  • their position in the developing embryo
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15
Q

What is the inside-outside model?

A
  • proposes that cell position on the outside and inside of the late morula determines its fate in the blastocyst
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16
Q

What is the cell-polarity model?

A
  • proposes that, at the 8-cell stage, cell polarity and cleavage patterns lead to the establishment of outside and inside cells at the 16-cell stage and later
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17
Q

What causes the expansion of the mouse blastocyst as it travels through the oviduct to the uterus?

A
  • Na/K pumps on the trophoblast PM pump Na into blastocoel cavity
  • This generates an osmotic gradient, drawing water into the blastocoel and increasing hydrostatic pressure
  • This leads to the enlargement and rounded ball shape of the embryo
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18
Q

What happens when the blastocyst adheres to the oviduct walls?

A
  • ectopic or tubal pregnancy
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19
Q

Why is an ectopic pregnancy dangerous?

A
  • the implantation of the embryo into the oviduct can cause a life-threatening hemorrhage
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20
Q

What proteins are involved in the hatching of the mouse blastocyst?

A
  • strypsin

- plasmin

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21
Q

Why does the mouse blastocyst hatch prior to implantation?

A
  • the presence of the zona pellucida prevents adherence to the oviduct and uterine wall
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22
Q

What are the three stages involved in implantation?

A
  • apposition
  • adhesion
  • invasion
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23
Q

What is apposition?

A
  • the initial adhesion of blastocyst to endometrial surface (this is an unstable stage since the blastocyst could still detach)
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24
Q

What is adhesion?

A
  • occurs when a stronger connection is established between embryo and endometrium
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25
Q

What is invasion

A
  • stage involves trophoblastic cells invading endometrium
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26
Q

How does the uterine lining (endometrium) “catch” the blastocyst?

A

Via a series of receptor and molecular interactions

  • the extracellular matrix of the uterine epithelium contain collagen, laminin, fibronectin, hyaluronic acid, and heparan sulfate receptors
  • the trophoblast cell contain integrins that will bind to the uterine collagen, fibronectin, and laminin, and they synthesize heparan sulfate proteoglycan precisely prior to implantation
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27
Q

What proteases do the trophoblast cells secrete once the blastocyst makes contact with the endometrium?

A
  • collagenase, stromelysin, and plasminogen activator
28
Q

What is the function of the proteases that trophoblasts cells secrete?

A
  • they digest the extracellular matrix of the uterine tissue, enabling the blastocyst to bury itself within the uterine wall
29
Q

What structural changes have evolved so that the mammalian embryo can obtain nutrients directly from its mother.

A
  • dramatic restructuring of the maternal anatomy (such as expansion of the oviduct to form the uterus)
  • the development of a fetal organ capable of absorbing maternal nutrients (chorion)
30
Q

Which part of the placenta represents the maternal portion?

A
  • Decidua

- rich in the blood vessels that will provide oxygen and nutrients to the embryo

31
Q

Which part of the placenta represents the fetal portion?

A
  • Chorion
  • derived primarily from embryonic trophoblast cells and supplemented with mesodermal cells derived from the inner cell mass
  • induces the uterine cells to form the decidua
32
Q

What is the bilaminar embryonic disc?

A
  • aka blastodisc
  • the two layers composed of the epiblast and hypoblast
  • evolved from the embryoblast
33
Q

How does the hypoblast form?

A
  • the first form of segregation of cells within inner cell mass gives rise to the hypoblast
  • prior to gastrulation, the hypoblast cells delaminate from inner cell mass to line blastocoel cavity and form the primitive gut
34
Q

What does the hypoblast give rise to?

A

hypoblast -> extraembryonic endoderm -> yolk sac

35
Q

How does the epiblast form?

A
  • the epiblast is derived from the remaining inner cell mass above the hypoblast
36
Q

What does the epiblast give rise to?

A
  • the epiblast will give rise to the embryonic epiblast and the amniotic ectoderm
37
Q

What is the function of amniotic fluid?

A
  • shock absorber for the developing embryo

- prevents desiccation

38
Q

Cytotrophoblast

A
  • original type of extraembryonic cells dervied form the trophoblast
  • contain proteolytic enzymes that digest the uterine wall and remodel the uterine blood vessels so that the maternal blood bathes fetal blood vessels
39
Q

Syncytiotrophoblast

A
  • multinucleate (syncytium)

- produce finger-like processes allowing further progression into uterine wall by digesting uterine tissue

40
Q

What is the closing plug?

A
  • a blood clot known as a closing plug (or fibrin plug) seals the site of the initial penetration of blastocyst into endometrium
41
Q

What is the polar trophoectoderm?

A
  • located nearest to the inner cell mass

- post-implantation, gives rise to polyploid trophoblast giant cells

42
Q

What is the mural trophoectoderm?

A
  • located opposite and farthest from the inner cell mass

- becomes the ectoplacental cone and the extra-embyonic ectoderm, both which give rise to placenta

43
Q

What is the function of the polyploid trophoblast giant cells?

A

They secrete various proteins

  • extracellular matrix components
  • cell adhesion molecules
  • cytokines
  • hormones to promote embryo implantation and maternal adaptations during pregnancy
44
Q

What is the function of the yolk sac in mammals?

A
  • the yolk sac acts as a source of primordial germ cells (embryonic precursors of sperm and egg cells) and hematopoiesis
  • the placenta solely carries out supporting nutrition of developing human embryo
45
Q

What is the function of the yolk sac in reptiles and birds?

A
  • has a function associated with nutrition
46
Q

What is the connecting stalk?

A
  • derived from extraembryonic mesoderm

- joins the embryo to the cytotrophoblast

47
Q

What does the connecting stalk become during mammalian embryo development?

A
  • becomes the umbilical cord
48
Q

Which structure during gastrulation gives rise to the left-right and A/P axes of developing mammalian embryo?

A
  • Primitive streak gives rise to L/R and A/P body axes, and marks the beginning of gastrulation
49
Q

What is the bilaminar embryonic disc?

A
  • refers to the epiblast and the hypoblast, evolved from the embryoblast
  • the two layers are sandwiched between two ballons: the primitive yolk sac and the amniotic cavity
50
Q

What does the bilaminar embryonic disc determine?

A
  • Determines the D/V axis
  • epiblast is dorsal
  • hypoblast is ventral
51
Q

What structure in mammalian development is analogous to the amphibian blastopore?

A

Primitive groove (the depression that forms within the primitive streak)

  • results from the active involution of cells forming the primitive streak
  • marks the cephalocaudal axis of the embryo
52
Q

What structure in mammalian development is analogous to the amphibian dorsal lip of the blastopore?

A

Hensen’s node (primitive knot)- regional tickening of cells at the top (anterior) of the primitive groove through which gastrulating cells migrate anteriorally to form tissues in the future head and neck
-major organizing center for the early chick embryo

53
Q

How does Henson’s node form during gastrulation?

A
  • via regional thickening of cells at the anterior end of the primitive streak, where cells are also moving inwards
54
Q

During chick embryo gastrulation, what do the migrating epiblast cells give rise to?

A
  • cells migrating through Hensen’s node travel anteriorly (cephalically) to form the head processes and the notochord
  • remaining cells travel through the streak migrate ventrally and laterally to become mesoderm and endoderm precursors
55
Q

Why are the cells migrating in between hypoblast and epiblast layers coated with hyaluronic acid?

A
  • this acts to keep them separate while they migrate

- they synthesize this as they leave the primitive streak

56
Q

What else it the D/V axis of the embryo defined by?

A
  • the embryonic-abembryonic axis of the blastocyst
57
Q

What does the embryonic region include?

A
  • inner cell mass
58
Q

What does the abembryonic region include?

A
  • part of the blastocyst opposite the inner cell mass
59
Q

Why does the primitive endoderm of the mouse embryo migrate?

A
  • to cover inner surface of mural trophectoderm to become the parietal endoderm
  • to cover the egg cylinder and epiblast to become the visceral endoderm
60
Q

What are 4 differences between human embryo development and mouse embryo development?

A
  1. The mouse embryo has a unique “cup shape”
  2. The mouse embryo undergoes a process called turning
  3. Gastrulation in humans is more reminiscent of chick embryo development
  4. Mouse embryos (implantation is often initiated in the mural trophectoderm), Human embryos (initial contact occurs through the polar trophectoderm)
61
Q

What is “turning”?

A
  • the mouse embryo initially develops inside-out, ectoderm is internal and surrounded by the mesoderm and endoderm
  • after gastrulation, turning results in an inversion of the germ layers with ectoderm on the outside, endoderm on the inside and mesoderm in the middle
62
Q

How is the proamniotic cavity created during mouse embryo development?

A
  • the epiblst proliferation/elongation develops an internal cavity = proamniotic cavity
  • this gives the embryo a cup-shaped form
  • this cavity forms by programmed cell death (apoptosis)
63
Q

How is the A/P axis formed in mouse embryos?

A
  • inhibitory signals from the extraembryonic ectoderm restrict anterior fate to the distal region
  • epiblast signals endoderm at the end of the cup = specification of distal visceral endoderm (DVE)
  • DVE proliferates, extends and moves to one side = anterior visceral endoderm (AVE)
  • the AVE prevents the primitive streak from forming at the anterior end
  • AVE signals the epiblast to induce anterior ectoderm
  • the primitive streak then forms on the opposite side of the epiblast, marking the posterior end of the embryo
64
Q

What is situs inversus?

A
  • individuals have organs that are positioned in a mirror image from normal positions
65
Q

What is situs solitus?

A
  • the normal position of the thoracic and abdominal organs

BISC 333 (4 decks)

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