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MSK Exam I > Gastrulation And Embryonic Germ Layers > Flashcards

Gastrulation And Embryonic Germ Layers Flashcards

1
Q

What is the embryonic period?

A

Weeks 3-7 during which the embryo is most susceptible to deformities

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2
Q

What are gametes?

A

Haploid cells whose genetic material fuses during fertilization

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3
Q

Describe oocytes

A

Develop in follicles and remain dormant until puberty

1-2 follicles mature each menstrual cycle -> secondary oocyte -> ovulation

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4
Q

What is the zona pellucida?

A

Thick layer of glycoproteins surrounding the oocyte

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5
Q

What are granulosa cells?

A

Responsible for follicle development

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6
Q

Which three cell types or structures are associated with the granulosa cells?

A

Cumulus oophorus, mural granulosa cells and corona radiata

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7
Q

What is the cumulus oophorus?

A

Anchor oocyte to the follicle wall

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8
Q

What are mural granulosa cells?

A

Line the wall of the follicle

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9
Q

What is the corona radiata?

A

Firmly anchored to the ZP

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10
Q

What is the acrosome reaction?

A

Sperm head releases enzymes allowing passage through the corona radiata and ZP during fertilization

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11
Q

What is the zona reaction?

A

Changes in the ZP occur resulting in an impermeable membrane to other sperm

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12
Q

What are the steps of fertilization?

A
  1. Acrosome reaction
  2. Zona reaction
  3. Fusion of egg and sperm cell membranes
  4. Sperm head and tail enter the oocyte cytoplasm
  5. Formation of female and male pronuclei
  6. Pronuclei fusion -> single diploid aggregate (the zygote)
  7. Chromosomes of the zygote are arranged on a cleavage spindle
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13
Q

What is cleavage?

A

Repeated mitotic divisions of the zygote

Begins ~30 hours after fertilization

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14
Q

What do the cells undergo at the 9 cell stage?

A

Compaction

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15
Q

The developing human is known as what at the 12-32 cell stage?

A

Morula

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16
Q

What is a blastocyst?

A

The embryo and its membranes including the trophoblast layer and embyroblast

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17
Q

When does a blastocystic cavity appear?

A

After the blastocyst enters the uterus

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18
Q

When does the ZP degenerate and cause hatching of the blastocyst?

A

After ~2 days

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19
Q

What is the difference between an early and late blastocyst?

A

Early blastocyst is still at the 2 cell stage and has the ZP attached
Late blastocyst does not have its ZP

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20
Q

Where does fertilization take place?

A

Fallopian tube

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21
Q

When the blastocyst finally arrives in the uterine cavity what occurs?

A

It attaches to the endometrium adjacent to the embryoblast and the trophoblast differentiates into a cytotrophoblast and syncytiotrophoblast
Blastocyst then burrows into the endometrium and becomes superficially implanted

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22
Q

How do syncytiotrophoblasts invade the endometrium?

A

Via enzymatic digestion

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23
Q

What will the embryoblast differentiate into during implantation on day 7?

A

Into the epiblast and hypoblast and with this differentiation the amniotic cavity forms and cells separate from the epiblast forming the amnion

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24
Q

What is the hypoblast continuous with?

A

The exocoelomic membrane

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25
Q

What is the amnion?

A

Encloses the embryo and houses amniotic fluid

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26
Q

What is the bilaminar embryonic disc?

A

When the embryoblast differentiates into epiblast and hypoblast it is referred to as the bilaminar embryonic disc

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27
Q

What is the primary umbilical vesicle?

A

Hypoblast + lining of the exocoelomic membrane

28
Q

What does the primary umbilical vesicle give rise to?

A

Extraembryonic mesoderm which is a layer of tissue that surrounds the amnion and umbilical vesicle

29
Q

What will the extraembryonic mesoderm create?

A

It will develop spaces that join and fuse to create the extraembryonic coelom which forces the primary umbilical vesicle to decrease in size

30
Q

What is the secondary umbilical vesicle?

A

Forms from hypoblast cells
Migrate inside of the primary umbilical vesicle
Site of origin of primordial germ cells

31
Q

The extraembryonic coelom separates the extraembryonic mesoderm into two structures known as what?

A

Extraembryonic somatic mesoderm and extraembryonic splanchnic mesoderm

32
Q

What is the extraembryonic somatic mesoderm?

A

Lines trophoblast and amnion

33
Q

What is the extraembryonic splanchnic mesoderm?

A

Surrounds umbilical vesicle

34
Q

What is the chorionic sac?

A

Extraembryonic somatic mesoderm + trophoblast

35
Q

What is the chorion?

A

The fetal component of the placenta

36
Q

What is gastrulation?

A

Process by which cells from the epiblast migrate to form the primary germ layers and therefore establishing the body plan

37
Q

When does gastrulation begin?

A

During week 3 with formation of the primitive streak

38
Q

What is the primitive streak?

A

Thin depression on the surface of the epiblast

39
Q

When is the trilaminar embryonic disc established?

A

Once all germ layers are present

40
Q

What does gastrulation define?

A

All body axes including cranial-caudal, dorsal-ventral, medial-lateral and left-right

41
Q

What is the notochordal process?

A

A rod of cells that defies the longitudinal axis of the embryo
Extends to the prechordal plate and site of future mouth
Will give rise to the notochord

42
Q

How is the notochordal process formed?

A

Cells migrate cranially from the primitive node and pit -> form the notochordal process

43
Q

Describe the steps for the formation of the notochordal process

A
  1. Begins with cranial extension from primitive node
  2. Forms a hollow tube (the notochordal process)
  3. Grows cranially between ectoderm and endoderm until it reaches the prechordal plate
  4. Hollows forming a canal
  5. By day 20 the notochordal process is complete
44
Q

What is the notochord?

A

A solid mesoderm rod derived from the primitive node that extends from the oropharyngeal membrane to the primitive node

45
Q

What is the function of the notochord?

A

Primary inductor (signaling center) in the early embryo
Induces the formation of the neural plate from the embryonic ectoderm
Produces signaling for development of axial musculoskeleton

46
Q

The notochord will degenerate as what structures form?

A

As the vertebral bodies form and give rise to the nucleus pulposus (intervertebral discs)

47
Q

Describe the steps for notochord development

A
  1. Floor of notochordal process fuses with underlying embryonic endoderm
  2. Fused layers degenerate allowing contact b/w notochordal canal and umbilical vesicle
  3. Floor of notochordal canal disappears and the notochordal process forms the notochordal plate
  4. Cranially notochordal plate cells proliferate and undergo infolding forming the notochord
  5. Notochord pinches off from the endoderm and the umbilical vesicle
  6. Separates the germ layers (endoderm and mesoderm)
48
Q

What is the notochordal plate?

A

Flattened grooved plate of cells in contact laterally with the embryonic endoderm

49
Q

Where does notochord formation occur?

A

In cranial regions anterior to the primitive streak

50
Q

What does the primitive streak form in caudal regions?

A

In caudal regions in swells to produce the caudal eminence (or the tail bud) which is a group fo medial mesodermal cells

51
Q

What does the caudal eminence give rise to?

A

Most caudal structures of the body

Cells will extend caudally forming a transient tail

52
Q

What does the tail bud contribute?

A

Cells to the caudal end of the neural tube and neural crest cells (caudal somites)

53
Q

What does the ectoderm form?

A

Epidermis of the skin and epidermal derivatives
CNS and PNS
Neural crest cells, eyes and internal ears

54
Q

What does the intraembryonic mesoderm form?

A

All skeletal muscle
Visceral smooth muscular coats, serosal linings of all body cavities, urogenital ducts and organs
Most of the cardiovascular system, blood cells and lining of vasculature
Cartilage, bones, tendons, ligaments, dermis and stroma of internal organs in the trunk

55
Q

What does the endoderm form?

A

Epithelial linings of the respiratory and GI tract
Glands opening into the GI tract
Glandular cells of accessory GI organs (liver and pancreas)

56
Q

What germ layer is epithelia derived from?

A

All germ layers

57
Q

What is a sacrococcygeal teratoma?

A

A germ cell tumor derived from pluripotent primitive streak cells (persistent remnants of the primitive streak)
May be derived from any/all germ layers
Surgically removed

58
Q

What is an ectopic pregnancy?

A

Implantation of the blastocyst outside the uterine cavity
2% of all pregnancies
Signs and sx: abdominal pain, profuse bleeding and rupture of the oviduct wall

59
Q

Where do ectopic pregnancies typically occur?

A

In the oviduct

60
Q

Which structures are likely to abort spontaneously?

A

Zygote, morula and blastocyst

61
Q

What are some causes for spontaneous abortions?

A

Inadequate production of progesterone and estrogen from corpus luteum
Chromosomal abnormalities: abnormal segregation, duplication, deletions, dispermy (69 chromosomes), etc

62
Q

Spontaneous abortions may require which procedure?

A

Dilation and curettage (D&C)

63
Q

Which events occur during week 1 of development?

A 
Fertilization 
Cleave and compaction 
Morula formation 
Early blastocyst formation 
Implantation (starting on day 6 but mostly in week 2) 
Late blastocyst formation
64
Q

What events occur in week 2 of development?

A

Bilaminar discs is formed (epiblast and hypoblast)
Implantation is complete
Trophoblast differentiates into cytotrophoblast and synctiotrophoblast

65
Q

What structures does the epiblast give rise to?

A

Amnion and amniotic cavity

66
Q

Which structures does the hypoblast give rise to?

A

Prechordal plate, umbilical vesicles and extraembryonic mesoderm (splanchnic and somatic)

MSK Exam I (34 decks)

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