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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
Q

Dizygotic twins

A

Arise from two oocytes fertilized by two sperm, two zygotes are genetically distinct, implant separately, have separate placentas, amnions, chorions

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26
Q

Monozygotic twins

A

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
Q

Zygote splits at 2 cell stage

A

Embryos implant separately and develop like dizygotic twins (each have its own fetal membranes)

28
Q

Splits at early blastocyst stage

A

Embryos share same chorion and placenta but have separate amnions

29
Q

Splits as bilaminar embryo

A

Embryos share amnion, chorion and placenta

30
Q

Hydatidiform mole

A

Fetal part of the placenta forms but the embryo does not, also known as a molar pregnancy

31
Q

Complete mole

A

Complete lack of an embryo

32
Q

Dispermic fertilization in complete molar pregnancy

A

Two sperm fertizilize an oocyte that lacks or loses its own nucleus, can result in 46,XX or 46,XY

33
Q

Monospermic fertilization in complete molar pregnancy

A

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
Q

Partial moles

A

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
Q

Week 3 major event

A

Conversion of the bilaminar embryo to a trilaminar embryo through gastrula toon

36
Q

Gastrulation

A

Establishes the three layers that will give rise to all adult tissues and organs

37
Q

Primitive streak

A

Thickened midline structure that forms around 15 days on the bilaminar embryo

38
Q

Primitive groove

A

Center depression on the primitive streak

39
Q

Primitive node

A

Cranial end of the bilaminar embryo expands into this

40
Q

Primitive pit

A

Center depression of the primitive node

41
Q

Body axes defined by the primitive streak

A

Cranial-caudal, medial-lateral, left-right

42
Q

Layers of the trilaminar embryo

A

Endoderm, mesoderm, ectoderm

43
Q

Endoderm formation

A

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
Q

Mesoderm formation

A

Middle layer, epiblast cells migrate between the newly formed endoderm and the upper epiblast cells

45
Q

Ectoderm formation

A

Outside layer, remaining epiblast cells in the upper layer make this

46
Q

Ectoderm forms…

A

Central and peripheral nervous systems, some head skeletal and CT, epidermis, hair, nails, sensory epithelium of nose, ear and eye

47
Q

Mesoderm forms…

A

Skeletal, smooth and cardiac muscle, cartilage, bone, CT, blood, components of the kidneys and gonads (urogenital system)

48
Q

Endoderm forms…

A

Epithelium of the gut and its derivatives, epithelium of the respiratory system

49
Q

Caudal regression syndrome

A

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
Q

Risk factors for caudal regression syndrome

A

Maternal diabetes, Wnt family gene defects, vascular anomalies, and teratogens

51
Q

Sirenomelia

A

AKA mermaid syndrome, an extreme and rare form of caudal dysplasia (though it may actually be a distinct disorder)

52
Q

Embryonic induction

A

Stimulation of a specific developmental pathway in the responding tissue by a closely approximated inducing tissue

53
Q

Embryonic induction can occur by…

A

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
Q

Induction of the lens of the eye

A

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
Q

Period of susceptibility

A

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
Q

Possible mechanisms for congenital anomalies

A

Faulty embryonic induction, defects in apoptosis, defects in migration, developmental arrest

57
Q

Anomaly

A

Marked deviation from normal

58
Q

Association

A

Nonrandom appearance of two or more anomalies that occur together but cause it not known

59
Q

Congenital

A

Present at birth

60
Q

Deformations

A

Result from mechanical forces that mold a part of the fetus over a prolonged period

61
Q

Malformation

A

Structural defect in the body due to abnormal embryonic or fetal development

62
Q

Syndrome

A

Group of anomalies occurring together that have a specific common cause

63
Q

Sequence

A

When a primary anomaly itself determines additional defects

64
Q

Teratogen

A

Any agent or factor that can disturb the development of an embryo

MSCT (28 decks)

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