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MSK Exam 1 > Gastrulation & Embryonic Germ Layers > Flashcards

Gastrulation & Embryonic Germ Layers Flashcards

1
Q

How many hours after fertilization does repeated mitotic divisions of the zygote occur?

A

30hrs

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2
Q

At __-cell stage, zygote undergoes compaction (day 3)

A

9 cell

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3
Q

Morula forms on day __, during the __-__ cell stage

A
  • 4
  • 12-32
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4
Q

When does the blastocystic cavity appear?

A

After the blastocyst enters the uterus, which is typically day 5

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5
Q

What is the term used to describe the degeneration of the zona pellucida, allowing the transition from blastocyst to late blastocyst?

A

Hatching

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6
Q

What day does the embryoblast reorganize into the epiblast and hypoplast?

A

During implantation, on day 7

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7
Q

What does the trophoblast differentiate into?

A

Cytotrophoblast and syncytiotrophoblast

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8
Q

What is the role of syncytiotrophoblasts?

A
  • invade the endometrium
  • allows proper development of placenta
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9
Q

What is the role of cytotrophoblasts?

A
  • produce digestive enzymes to degrade/erode the endometrial wall
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10
Q

What day is implantation of the blastocyst into the endometrial wall complete?

A

Day 10

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11
Q

What day does the amniotic cavity form?

A

Day 8

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12
Q

What type of cells create the amnion?

A

Epiblast cells

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13
Q

What is the role of the amnion (considered an extraembryonic membrane)?

A
  • encloses the embryo
  • houses amniotic fluid
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14
Q

1 of __ extraembryonic membranes will enclose the embryo by the 8th week

A

4

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15
Q

Amniotic cavity forms as fluid collects between ___ and ___ cells

A

Epiblast and Trophoblast

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16
Q

____ ___ develops from lacunae that join and fuse to create ___ ___

A
  • Extraembryonic Mesoderm
  • Extraembryonic coelom (chorionic cavity)
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17
Q

What cells form the primary yolk sac (Heuser’s membrane)?

A

Hypoblasts

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18
Q

What are the features of a late blastocyst?

A
  • contains more cells than a morula
  • has an embryoblast, the precursor of the embryo
  • has cytotrophoblast cells
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19
Q

What tissue is directly responsible for the degradation of endometrial epithelium during implantation?

A

Cytotrophoblast

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20
Q

Ectopic pregnancy is most commonly found in the:

A

Proximal uterine tube

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21
Q

Reorganization of the embroyblast into the epiblast and hypoblast during implantation (formation of bilaminar disc) establishes the __-__ axis

A

Dorsal-Ventral

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22
Q

What day does implantation occur?

A

Day 7

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23
Q

What day does the first migration wave of hypoblast cells occur?

A

Day 8

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24
Q

What is the result of the first migration wave of hypoblast cells?

A

Formation of the primary yolk sac (Heuser’s membrane)

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25
Q

What day(s) does the second wave of hypoblast cells occur?

A

12-13

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26
Q

What is the result of the second migration wave of hypoblast cells?

A

Formation of the secondary/definitive yolk sac; primary yolk sac will degenerate

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27
Q

Yolk sac is source of:

A
  • Hematopoesis
  • Primary germ cells (produce gametes)
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28
Q

Chorionic Cavity (extraembryonic coelom) separates embryo with its amnion and yolk sac from the ___

A

Chorion (outer wall of blastocyst)

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29
Q

What are the 4 extraembryonic membranes?

A
  • Amnion
  • Yolk Sac
  • Chorion
  • Allantios
30
Q

Chorionic cavity (extraembryonic coelom) separates extraembryonic mesoderm into:

A

(1) Extraembryonic Somatic Mesoderm
(2) Extraembryonic Splanchnic Mesoderm

31
Q

What does the Extraembryonic Somatic Mesoderm line?

A

Trophoblast and Amnion

32
Q

What does the Extraembryonic Splanchnic Mesoderm surround?

A

Umbilical vesicle

33
Q

What is the Chorion (chorionic sac) composed of?

A
  • Extraembryonic somatic mesoderm
  • Trophoblast layers
34
Q

What is the role of the Chorion?

A
  • connects developing fetus to mother
  • contributes to fetal side of placenta
35
Q

What is the connecting stalk composed of?

A

Extraembryonic (somatic) mesoderm

36
Q

What is the role of the connecting stalk?

A
  • attaches the early embryo to the placenta
  • precursor to the umbilical cord
37
Q

What is the first major event of week 3?

A

Gastrulation

38
Q

Gastrulation begins with the midline formation of raised thickening of ___ cells which is known as the __ __

A
  • Epiblast
  • Primitive streak
39
Q

What day does the primitive streak (primative pit/node/groove) form?

A

Day 15

40
Q

What are the 3 main functions of Gastrulation?

A
  • Forms trilaminar disc
  • Establishes our “tube within a tube”
  • Defines major body axes: Cranial-caudal, left-right, dorsal-ventral
41
Q

Gastrulation

A
  • Movement of epiblast cells (EMT) through the primitive streak to create the primary germ layers
42
Q

What are the 5 main subdivisions that the intraembryonic mesoderm reorganize into?

A
  • Cardiogenic mesoderm
  • Paraxial mesoderm (somites)
  • intermediate mesoderm
  • Lateral plate mesoderm
  • Notochordal process (Notochord)
43
Q

What is the order of mesoderm subdivisions (from cranial -> caudal) during the mid-primitive streak stage?

A

(1) Prechordal Plate
(2)Cardiogenic mesoderm (divides into two sections that “sandwich” the prechordal plate)
-CELLS LINING PRIMITIVE STREAK-
(3) Notochord
(4) Head Mesoderm
(5) Somites
(6) Intermediate Mesoderm
(7) Lateral Plate Mesoderm

44
Q

What are the first and second cells that form during intraembryonic mesoderm reorganization (early primitive streak phase)?

A

(1) Cardiogenic mesoderm
(2) Extraembryonic mesoderm

45
Q

What is present on the surface ectoderm during the fully elongated streak stage (cranial -> caudal)?

A

(1) Placodal Ectoderm (surrounds Neural Crest & Neural Plate)
(2) Neural Crest
(3) Neural Plate
(4) Primitive Streak (same order cells as mid-primitve streak stage)

46
Q

Sacrococcygeal Teratoma

A
  • Germ cell tumor (benign or malignant)
  • Derived from pluripotent primitive streak cells
  • Persistent remnants of primitive streak (normally this closes off entirely)
  • Rare, most affects females
  • May be derived from any/all germ layers
  • Surgically excised
47
Q

What day does the Notochordal Process form?

A

Day 17

48
Q

How is the Notochordal Process formed?

A

(1) Cells from primitive node and pit migrate cranially (towards prechordal plate)
(2) Grows in length as primitive node cells are added to proximal end, associated with regression of primitive streak
(3) Formation of hollow tube

49
Q

List the steps that are involved in the formation of Notochordal Process -> flattened plate -> solid rod Notochord

A

(1) Ventral floor of the tube (notochordal process) fuses with underlying endoderm
(2) Two layers break down, leaving behind the flattened notochord plate
(3) Notochordal plate completely detaches from the endoderm
(4) Free ends of notochordal plate fuse as it rolls up into space (of mesoderm) between ectoderm and endoderm
(5) Changing into a solid rod, the Notochord forms

50
Q

Notochord is ___ in origin

A

Mesodermal

51
Q

What days does the transformation of the notochordal process -> notochordal tube occur?

A

Days 16-22

52
Q

Notochord

A
  • Solid mesodermal rod derived from the primitive node/pit
  • Extends from the oropharyngeal membrane to the primitive node
  • Functions as the primary inductor (signaling center) in the early embryo
  • Degenerates as the vertebral bodies form
53
Q

What are the two main signaling roles of the Notochord?

A
  • Induces the formation of the neural plate from the embryonic ectoderm
  • Provides signaling for development of axial musculoskeleton
54
Q

What does the Notochord give rise to?

A

Nucleus Pulposus (intervertebral discs) of embryo, fetus and young children

55
Q

What does the Ectoderm give rise to?

A
  • Epidermis of the skin
  • Epidermal derivatives (hair follicles, nails, glands)
  • CNS
  • PNS
  • Neural crest cells
  • Eyes
  • Internal ears
56
Q

What does the Mesoderm (intraembryonic) give rise to?

A
  • All skeletal muscle
  • Vertebrae
  • Visceral smooth muscular coats
  • Serosal linings of all body cavities
  • Urogenital organs (i.e kidneys)
  • Most of the cardiovascular system
  • Cardiac muscle
  • Blood cells
  • Lining of vasculature
  • Cartilage
  • Bones
  • Tendons
  • Ligaments
  • Dermis
  • Stroma of internal organs in the trunk
57
Q

What does the Endoderm give rise to?

A
  • Epithelial linings of the GI and respiratory tracts
  • Glands opening into the GI tract
  • Glandular cells of accessory GI organs (liver, pancreas)
  • Thymus
  • Urethra
58
Q

__ comes from ALL germ layers!

A

Epithelia

59
Q

Notochord formation occurs in ___ regions, __ to the primitive streak

A
  • Cranial
  • Anterior
60
Q

Primitive Streak represents about 10-20% of embryos length at day __

A

Day 2

61
Q

What day does the Primitive Streak disappear by?

A

Day 26

62
Q

What is the Caudal Eminence (tail bud) formed from?

A

Remnants of the primitive streak that swell and produce a caudal midline mass of mesoderm

63
Q

What day does the Caudal Eminence form?

A

Day 20

64
Q

Cells extend ___ to form a transient tail (from caudal eminence)

A

Caudally

65
Q

Tail bud contributes cells to the caudal end of the ___ ___ & ___ ___ __, caudal somites

A
  • Neural tube
  • Neural crest cells
66
Q

Gastrulation occurs during a period of development called:

A

Primary Body Development
(primitive streak gives rise to the 3 primary germ layers which subsequently assemble into organ rudiments)

67
Q

Formation of the rudimentary tail occurs after gastrulation is complete, during a period of development called:

A

Secondary Body Development
(differs from primary body development because it involved direct formation of organ rudiments from the tail bud without the prior formation of distinct germ layers)

68
Q

Caudal Dysplasia

A
  • Arises from problems in gastrulation which occurs at the caudal end of the embryo
69
Q

What end of the embryo does Gastrulation occur?

A

Caudal end (this is where primitive streak develops)

70
Q

Chorionic Villi

A
  • Components of the fetal portion of the placenta

MSK Exam 1 (6 decks)

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