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TOB > Embryology > Flashcards

Embryology Flashcards

0
Q

What is the zona pellicuda?

A

Glycoprotein shell surrounding the blastomeres

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1
Q

What occurs on day 2 of pregnancy?

A

Cleavage - 2 blastomeres of equal size are produced.

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2
Q

What occurs on day 3 of pregnancy?

A

A morula is formed (clump of totipotent, identical cells)

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3
Q

What occurs on day 4 of pregnancy?

A

Compaction of blastomeres occurs, formation of blastocyst (pluripotent)

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4
Q

Describe the structure of the blastocyst

A

Embryoblast - inner cell mass
Trophoblast - outer cell mass
Blastocyst cavity - space

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5
Q

What occurs on day 5 of pregnancy?

A

Blastocyst hatches from zona pellicuda. Free to move around, grow and free to implant.

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6
Q

What occurs on days 6/7 of pregnancy?

A

Implantation occurs. Conceptus has 107 cells - 8 will form the embryo cells and 99 will begin development of foetal membrane

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7
Q

What occurs on day 8 of pregnancy?

A

Beginning of the week of twos. Bilaminar disk and amniotic cavity are formed. Both embryo and placenta formation begins (placenta initially has priority).

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8
Q

What does the embryoblast differentiate into?

A

Epiblast and hypoblast

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9
Q

What does the trophoblast differentiate into?

A

Syncytiotrohphoblast and cytotrophoblast.

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10
Q

What occurs on days 9/10 of pregnancy?

A

Implantation complete - endothelium is breached. Embryonic pole and abembryonic poles are formed on day 9. Maternal blood flow is established

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11
Q

What is the embryonic pole?

A

Rapid development of syncytiotrophoblast

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12
Q

What is the abembryonic pole?

A

Primitive yolk sac formed by Heuser’s membrane, spreading across the blastocyst cavity. Yolk sac membrane is in contact with the cytotrophoblast layer

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13
Q

What occurs on day 11 of pregnancy?

A

Primitive yolk sac layer is pushed away from cytotrophoblast by acellular extraembryonic reticulum. Reticulum later converted to extraembryonic mesoderm by cell migration

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14
Q

What occurs on day 12 of pregnancy?

A

Maternal sinusoids invaded by syncytiotrophoblasts, lacunae become more continuous with sinusoids, uteroplacental circulation begins, uterine stroma prepares for embryo support

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15
Q

What occurs on day 13 of pregnancy?

A

Formation of secondary yolk sac, specialisation of existing structure. Definitive yolk sac pinches off from primitive yolk sac

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16
Q

What occurs on day 14 of pregnancy?

A

Extraembryonic spaces merge to form the chorionic cavity, connecting stalk suspends the embryo and its cavities in the chorionic cavity

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17
Q

What is the connecting stalk?

A

Column of mesoderm cells and is the future umbilical cord

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18
Q

Briefly outline the status of the embryo after two weeks

A

Conceptus has been implanted, embryo and its two cavities are suspended by connecting stalk in the chorionic cavity (supporting sac)

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19
Q

What is placenta previa?

A

Implantation in lower uterine segment - placenta eventually blocks the opening of uterus and causes severe bleeding in second part of pregnancy and even during birthing. Requires C-section.

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20
Q

What is an ectopic pregnancy?

A

Implantation at a site other than uterine body

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21
Q

Where is the optimal site of implantation?

A

Posterior uterine wall

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22
Q

Define ovary

A

Female reproductive organ. Produces oocytes

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23
Q

Define zygote

A

Fertilised oocyte

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24
Q

Define fallopian tubes

A

Tube that connects ovary to uterus. Oocyte travels along this.

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25
Q

Where is the oocyte fertilised?

A

Ampulla of fallopian tubes

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26
Q

Define uterus

A

Female reproductive organ where implantation of zygote and growth of embryo occurs

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27
Q

Define cleavage

A

Dividing of cells into two masses known as blastomeres. Occurs ~30 hrs after fertilisation

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28
Q

Define blastocyst

A

Formed from compaction of cells that make up the morula

29
Q

Define trophoblast

A

Outer cell mass which will later form supporting structures for the embryo (e.g. placenta)

30
Q

Define embryoblast

A

Inner cell mass - will later become the bilaminar disk

31
Q

Define implantation

A

Attachment of blastocyst to the wall of the uterus 6-7 days

32
Q

Define cytotrophoblast

A

Placental membrane around yolk sac

33
Q

Define syncytiotrophoblast

A

Cells that invade maternal sinusoids resulting in uteroplacental circulation

34
Q

Define bilaminar

A

Epiblast and hypoblast. Derived from the embryoblast. This will later become the trilaminar disk with the formation of the primitive streak

35
Q

Define germ layer

A

Layer from which other developed tissues originate

36
Q

Define ectoderm

A

Outermost layer of cells giving rise to epidermis and nerve tissue

37
Q

Define endoderm

A

Innermost layer of cells giving rise to gut lining

38
Q

Define dorsal surface

A

Outermost surface during early development

39
Q

Define ventral surface

A

Innermost surface during early development

40
Q

Define mesoderm

A

Middle germ layer giving rise to muscle, bone and more

41
Q

Define primitive streak

A

Narrow groove that develops on the dorsal surface of the epiblast. Important role in orientation of embryo, determining front and back

42
Q

Define gastrulation

A

Reorganisation of germ layers into ectoderm, mesoderm and endoderm

43
Q

Define trilaminar disk

A

Three germ layers. Ectoderm, mesoderm and endoderm

44
Q

What are teratogenic compounds?

A

Abnormalities of physiological development. Examples include: thalidomide, rubella, alcohol

45
Q

Give examples of ectodermal derivatives

A

skin, skin derivatives, brain and spinal cord, peripheral nerves, retina and iris of eye

46
Q

Give examples of mesodermal derivatives

A

Smooth, skeletal and cardiac muscle, connective tissue, bone, cartilage, blood and blood vessels, urinary system

47
Q

Give examples of endodermal derivatives

A

Lining of digestive tract, glands associated with digestion, other gut derivatives (e.g. lungs)

48
Q

Which period is most perilous for developing child?

A

Embryonic period (weeks 3-8)

49
Q

How does gastrulation start?

A

Appearance of primitive streak (primitive node + primitive pit). Cellular rearrangement occurs - migration/invagination

50
Q

When does the primitive streak appear?

A

Third week

51
Q

Where is the primitive node located?

A

Cranial end of the streak

52
Q

Which direction does development proceed in?

A

Cranial-caudal

53
Q

Describe migration and invagination

A

Cells on epiblast migrate towards primitive streak, invaginate into epiblast and displace hypoblast - creating mesoderm. Spread laterally and cephalad. Two gaps in mesoderm

54
Q

What is the function of the notochord?

A

Basis of the axial skeleton and drives neurulation

55
Q

What is the notochord?

A

Solid rod of cells running in the midline with an important signalling role - defines the midline

56
Q

What is the vestigial remnant of the notochord in adults?

A

Nucleus pulposus of the intervertebral discs

57
Q

Describe the status of the developing child by the end of week 3

A

Three germ layers placed anteriorly, axes are established.

58
Q

How does neurulation occur?

A

Notochord signals overlying ectoderm to thicken - edges elevate out of plane and curve towards each other creating the neural tube

59
Q

What are somites?

A

Segments of the paraxial mesoderm

60
Q

What does folding achieve?

A

Creation of a ventral body wall, embryo is suspended in amniotic sac, connecting stalk pulled ventrally, creation of coelom, 3D structure

61
Q

How many pairs of somites are there?

A

42/44 by the end of week 5, some then disappear leaving 31 pairs

62
Q

How is the coelom formed?

A

With the differentiation of mesoderm

63
Q

Give examples of derivatives of paraxial mesoderm

A

Axial skeleton, dermis, muscles of axial body wall, some limb muscles

64
Q

Give examples of derivatives of somatic mesoderm

A

Connective tissue of limbs, contributes to axial body wall

65
Q

Give examples of derivatives of splanchnic mesoderm

A

Smooth musculature, connective tissue and vasculature of gut

66
Q

Give examples of derivatives of immediate mesoderm

A

Urogenital system e.g. kidneys, ureters, gonads

67
Q

How is sclerotome formed?

A

Ventral wall of somite breaks down

68
Q

How are dermatome and myotome formed?

A

Organisation of the dorsal portion forms the dermomyotome. Myotome proliferates and migrates and the dermatome disperses

69
Q

What is the dermatome?

A

Part of somite that gives rise to the skin; strip of skin supplied by a single spinal nerve

70
Q

What is the myotome?

A

Gives rise to muscles; muscle/group of muscles supplied by a single nerve

71
Q

Briefly describe embryonic folding

A

Cephalocaudal folding. Heart lies at cranial end, moves inwards until it lies in chest area. Yolk sac extends to form a connection between yolk sac and gut

TOB (15 decks)

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