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MSCT > Embryology - Basic Body Plan > Flashcards

Embryology - Basic Body Plan Flashcards

1
Q

Week 1 landmark events

A

Fertilization, cleavage, blastocyst formation, implantation

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2
Q

Fertilization

A

Sperm swim through uterus and oviduct to meet the mature oocyte or ovum in the ampulla. Oocyte finishes second meiotic division and female pronucleus forms as sperm enters. Head of the sperm swells to become the male pronucleus. Diploid cell (zygote) forms.

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3
Q

Cleavage

A

Mitotic division without growth that begins as the zygote moves through the oviduct towards the uterus.

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4
Q

Blastomeres

A

Cells of the cleaving embryo, totipotent until the 4-8 cell stage (can give rise to both the embryo and fetal part of the placenta) (day 1-3)

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5
Q

Morula

A

16 cell stage, as cells divide they compact and secrete fluid to form a cavity (day 3)

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6
Q

Blastocyst

A

Embryo following cavity formation from morula, arrives in the uterine cavity 4-5 days after fertilization

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7
Q

Implantation

A

Blastocyst attaches and invades uterine wall on day 6, but continues during week 2

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8
Q

Blastomere cell types following implantation

A

Embryoblast and trophoblast

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9
Q

Embryoblast

A

Inner cell mass, form the embryo and are pluripotent stem cells

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10
Q

Trophoblast

A

Outer cell mass, surround the embryoblast and blastocyst cavity and will form the fetal part of the placenta

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11
Q

Week 2

A

Embryoblast and trophoblast each differentiate into 2 layers and 2 cavities form

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12
Q

Layers of embryoblast (bilaminar embryo)

A

Epiblast and hypoblast

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13
Q

Epiblast

A

Columnar cells that secrete fluid to form the amniotic cavity

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14
Q

Hypoblast

A

Cuboidal cells that line the blastocyst cavity to form the primitive yolk sac

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15
Q

Trophoblast layers

A

Syncytiotrophoblast and cytotrophoblast

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16
Q

Syncytotrophoblast

A

Outer layer, one cytoplasm with many nuclei, a syncytium

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17
Q

Cytotrophoblast

A

Inner layer, actively proliferating cells

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18
Q

Day 12

A

Blastocyst is completely embedded in uterine wall, lacunae (spaces in syncytotrophoblast) connect to maternal capillaries in uterine wall to establish placental blood supply. Hypoblast cells of primitive yolk sac proliferate to form extraembryonic mesoderm, where spaces start to form

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19
Q

Extraembryonic mesoderm

A

Loose connective tissue from proliferation of hypoblast cells of the primitive yolk sac

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20
Q

Day 13

A

Spaces in extraembryonic mesoderm coalesce and form the chorionic cavity, where the bilaminar embryo is now suspended by the connecting stalk. The primitive yolk sac is now called the secondary yolk sac, and chorion forms

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21
Q

Chorionic cavity

A

Formed by the coalescence of the spaces in the extraembryonic mesoderm

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22
Q

Connecting stalk

A

What suspends the bilaminar embryo in the chorionic cavity and is made of extraembryonic mesoderm

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23
Q

Secondary yolk sac

A

Primitive yolk sac turns into this following the suspension in the chorionic cavity

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24
Q

Chorion

A

Outer layer of the extraembryonic mesoderm and the trophoblast

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25
Dizygotic twins
Arise from two oocytes fertilized by two sperm, two zygotes are genetically distinct, implant separately, have separate placentas, amnions, chorions
26
Monozygotic twins
One oocyte fertilized by one sperm, one zygote that splits at some point in development, so they are genetically identical, the placentas, amnions and chorions can be shared or separate depending on when splitting occurred
27
Zygote splits at 2 cell stage
Embryos implant separately and develop like dizygotic twins (each have its own fetal membranes)
28
Splits at early blastocyst stage
Embryos share same chorion and placenta but have separate amnions
29
Splits as bilaminar embryo
Embryos share amnion, chorion and placenta
30
Hydatidiform mole
Fetal part of the placenta forms but the embryo does not, also known as a molar pregnancy
31
Complete mole
Complete lack of an embryo
32
Dispermic fertilization in complete molar pregnancy
Two sperm fertizilize an oocyte that lacks or loses its own nucleus, can result in 46,XX or 46,XY
33
Monospermic fertilization in complete molar pregnancy
One sperm fertilizes an oocyte lacking a nucleus, that then undergoes mitosis without cytokinesis, doubling parental DNA, results in 46,XX (46,YY zygote would not develop)
34
Partial moles
Dispermic fertilization of a normal oocyte, or single abnormal diploid sperm, results in triploid zygote with two sets of paternal chromosomes, 69,XXX or 69,XXY or 69,XYY
35
Week 3 major event
Conversion of the bilaminar embryo to a trilaminar embryo through gastrula toon
36
Gastrulation
Establishes the three layers that will give rise to all adult tissues and organs
37
Primitive streak
Thickened midline structure that forms around 15 days on the bilaminar embryo
38
Primitive groove
Center depression on the primitive streak
39
Primitive node
Cranial end of the bilaminar embryo expands into this
40
Primitive pit
Center depression of the primitive node
41
Body axes defined by the primitive streak
Cranial-caudal, medial-lateral, left-right
42
Layers of the trilaminar embryo
Endoderm, mesoderm, ectoderm
43
Endoderm formation
Inside layer, epiblast cells migrate to the embryonic disc to the primitive streak and down through the primitive groove to replace the hypoblast cells beneath them
44
Mesoderm formation
Middle layer, epiblast cells migrate between the newly formed endoderm and the upper epiblast cells
45
Ectoderm formation
Outside layer, remaining epiblast cells in the upper layer make this
46
Ectoderm forms...
Central and peripheral nervous systems, some head skeletal and CT, epidermis, hair, nails, sensory epithelium of nose, ear and eye
47
Mesoderm forms...
Skeletal, smooth and cardiac muscle, cartilage, bone, CT, blood, components of the kidneys and gonads (urogenital system)
48
Endoderm forms...
Epithelium of the gut and its derivatives, epithelium of the respiratory system
49
Caudal regression syndrome
AKA caudal dysplasia, impaired development of the lower half of the body due to abnormal growth and migration during gastrulation resulting in abnormal development of the caudal mesoderm
50
Risk factors for caudal regression syndrome
Maternal diabetes, Wnt family gene defects, vascular anomalies, and teratogens
51
Sirenomelia
AKA mermaid syndrome, an extreme and rare form of caudal dysplasia (though it may actually be a distinct disorder)
52
Embryonic induction
Stimulation of a specific developmental pathway in the responding tissue by a closely approximated inducing tissue
53
Embryonic induction can occur by...
Diffusion of the inducing molecule from one cell to another, contact between the extracellular matrix of one cell to another, or direct contact between the inducing and responding cells
54
Induction of the lens of the eye
Eyeball develops as a cup-shaped extension of the embryonic brain (the optic vesicle) which then comes into close contact with the surface ectoderm of the head, causing it to differentiate into the lens of the eye instead of skin through signaling molecule BMP4
55
Period of susceptibility
AKA period of maximal sensitivity, when the embryo is especially vulnerable to factors causing abnormal development around weeks 3-8 of the embryonic period when gastrulation occurs and embryonic induction initiates differentiation of different tissue types
56
Possible mechanisms for congenital anomalies
Faulty embryonic induction, defects in apoptosis, defects in migration, developmental arrest
57
Anomaly
Marked deviation from normal
58
Association
Nonrandom appearance of two or more anomalies that occur together but cause it not known
59
Congenital
Present at birth
60
Deformations
Result from mechanical forces that mold a part of the fetus over a prolonged period
61
Malformation
Structural defect in the body due to abnormal embryonic or fetal development
62
Syndrome
Group of anomalies occurring together that have a specific common cause
63
Sequence
When a primary anomaly itself determines additional defects
64
Teratogen
Any agent or factor that can disturb the development of an embryo

MSCT (28 decks)

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