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CM Week 2 > Embryology: formation of the basic body plan > Flashcards

Embryology: formation of the basic body plan Flashcards

1
Q

When do embryologists measure the age of the embryo?

A

the estimated time of fertilization

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2
Q

When do clinicians describe pregnancy?

A

by trimesters, 3 month period stating with the date of onset of the last menstrual period (LMP) and ending with birth (40 weeks LMP or 38 weeks following fertilization)

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3
Q

When is the basic body plan set up?

A

during the first 3 weeks after fertilization or 5 weeks LMP

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4
Q

What occurs during the first week of fertilization?

A

fertilization, cleavage, blastocyst formation and implantation.

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5
Q

During the 1st week of fertilization what happens after ovulation?

A

The ovum is swept into the oviduct by its fimbriae (finger like projections) and travels to the ampulla, widened part of the oviduct where it is fertilized.

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6
Q

What is a one cell embryo called?

A

zygote

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7
Q

After fertilization what happens to the embryo?

A

undergoes mitotic divisions without growth (cleavage) and moves towards the uterus.

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8
Q

What are the cells of the cleaving embryo called?

A

blastomeres

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9
Q

How long are blastomeres totipotent?

A

totipotent until the 4-8 cell stage.

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10
Q

What does totipotent blastomere mean?

A

The cells can give rise to both the embryo and the fetal part of the placenta.

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11
Q

What is a 16 cell embryo called?

A

morula

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12
Q

What is blastocyst formation?

A

as the cells of the morula divide the compact (move closer together) and secrete fluid to form a cavity (cavitate)

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13
Q

After blastocyst formation what is the embryo called and where does it go?

A

blastula or blastocyst. it arrives in the uterine cavity by 4-5 days after fertilization.

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14
Q

What happens by day 6 of fertilization?

A

the blastocyst attaches to and begins to invade the uterine wall-implantation

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15
Q

What day after fertilization does implantation continue through?

A

Day 10

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16
Q

What happens by day 9 after fertilization?

A

embroyoblast and trophoblast each differentiate into 2 layers

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17
Q

What does the embroyoblast layer contain?

A

they are epiblast, columnar cells that secrete fluid to and from the amniotic cavity, and the hypoblast cuboidal cells that line the blastocyst cavity converting it into the primitive yolk sac.

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18
Q

What does the trophoblast layer contain?

A

syncytiotrophoblast one cytoplasm with many nuclei (a syncytium) and the cytotrophoblast.

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19
Q

What do syncytiotrophoblast cells produce?

A

human chorionic gonadotrophin (hCG)

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20
Q

What does hCG do?

A

supports the uterine lining na maintains pregnancy. it is the basis of many pregnancy tests.

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21
Q

By day 12 after fertilization what happens?

A

spaces in the syncytiotrophoblast called lacunae (lakes) connect to capillaries in the interim wall to establish the placental blood supply. The hydroblast cells linen the primitive yolk sac ;proliferate to form loose connective tissue ( extrambryonic mesoderm) within which spaces appear that join to form the chorionic cavity.

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22
Q

By day 13 after fertilization what happens?

A

the bilaminar embryo is suspended within the chorionic cavity. the primitive yolk sac I snow the secondary or definitive yolk sac.

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23
Q

Summarize what happens by the end of week 2 of fertilization.

A

the embryo has 2 layers (bilaminar): epiblast and hypoblast
the trophoblast has 2 layers: syncytiotrophoblast and cytotrophoblast
2 cavities form: the amniotic cavity and the chorionic cavity
the yolk sac is the blastocyst cavity lined with hypoblast cells

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24
Q

What happens during weeks 3 after fertilization?

A

gastrulation establishes the 3 germs layers

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25
Q

What are the 3 germs layers that give rise to all adult tissues?

A

ectoderm, mesoderm, and endoderm

26
Q

What cells give rise to germ layers?

A

epiblast cells

27
Q

What cells give rise to form the yolk sac?

A

hypoblast cells

28
Q

What does the ectoderm form?

A

(everything external) central and peripheral nervous systems (exception as they are on the inside) epidermis, hair, and nails, sensory epithelium of nose ear and eye

29
Q

What does the mesoderm form?

A

(everything middle) skeletal, smooth and cardiac muscle
cartilage, bone connective tissue, blood
kidneys and gonads

30
Q

What does the endoderm form?

A

(everything inside)
epithelium of the gut and its derivatives (liver, gallbladder, pancreas)
epithelium of the respiratory system.

31
Q

When does the trilaminar (3 layer) embryo undergo folding?

A

17-22 days after fertilization

32
Q

What formations does folding result in?

A

formation of the gut tube from the top of the yolk sac, formation of the lateral and anterior body walls, and formation of the body cavity which now encloses the gut tube. Called the (gut) tube within a (body wall) tube body plan

33
Q

What does folding enclose in relation to the embyro?

A

the embryo within the amniotic cavity

34
Q

What does the neural tube form?

A

central nervous system, brain, and spinal cord

35
Q

Where does the neural tube develop from?

A

the ectoderm overlying a midline mesodermal situation called the notochord or notochordal process.

36
Q

What does the notochord secrete?

A

factors (signaling molecules) important for tissue patterning, causing the overlying ectoderm to become neuroectoderm

37
Q

When the neuroectoderm folds what does it form?

A

neural tube

38
Q

What is the neural crest and what does it do?

A

Cells on the top of the neural tube, the cells migrate away early in development to form the peripheral nervous system and some other structures.

39
Q

What does the notochord become after folding?

A

the nucleus pulpous of the intervertebral discs

40
Q

What disorder impairs development of the lower half of the body?

A

Caudal regression syndrome (caudal dysplasia)

41
Q

What body parts could caudal dysplasia affect and what is the underlying mechanism?

A

lower limbs, lumbar and sacral vertebrae, lower gut urinary and genital tracts
Underlying mechanism is abnormal gastrulation resulting in not enough caudal mesoderm which is the last mesoderm to form

42
Q

What genetic and environmental factors are implicated in caudal dysplasia?

A

maternal diabetes, Went gene defects, vascular anomalies, and teratogens

43
Q

What is sirenomelia (mermaid syndrome)?

A

an extreme and rare form of caudal dysplasia. most obvious defect is fusion of the 2 lower limbs at the midline, also deformed left kidney and small right kidney and anomalies to terminal digestive urinary and genital tracts

44
Q

What is sacrococcygeal teratoma?

A

a disorder relation to abnormal gratulation. it is a tumor that develops at the base of the coccyx. It is a germ cell tumor that is thought to be derived from the primitive streak. Occur more in females, nonmalignant, can grow quite large, always require surgical removal. Can contain derivatives of all 3 germ layers.

45
Q

What are intrinsic errors of morphogenesis?

A

results in failure of the embryo to develop due to problems within the embryo itself. abnormal genes or other internal process most often causes them.

46
Q

What are extrinsic errors of morphogenesis?

A

Due to external forces that impact normal development such as disruption and deformation

47
Q

What is agenesis?

A

an intrinsic error

missing organ causes by missing embryonic tissue (renal agencies)

48
Q

What is aplasia?

A

an intrinsic error

missing organ due to growth failure of embryonic tissue (thymic aplasia)

49
Q

What is hypoplasia?

A

an intrinsic error

incomplete organ development (microcephaly)

50
Q

What is malformation?

A

an intrinsic error

abnormal development of a structure (neural tube defects, cleft lip or palate, congenital heart defect)

51
Q

What are classified as intrinsic errors?

A

agenesis, aplasia, hypoplasia, and malformation

52
Q

What are classified as extrinsic errors?

A

disruption an deformation

53
Q

What is disruption?

A

extrinsic error
external force leads to normal tissue growth arrest (amniotic brand syndrome occurs when fibrous bands in the amniotic cavity constricts growth of limbs or digits)

54
Q

What is deformation?

A

extrinsic error
external force leads to abnormal growth bu too arrest, resulting in deformed or misshaped structures (Potter sequence or syndrome is when the fetus is exposed to decreased amniotic fluid so the face and limbs are deformed because of lack of cushioning)

55
Q

What are teratogens?

A

substances that can cause errors in morphogenesis

56
Q

How do teratogens function?

A

by many mechanisms most of which are not well understood, know mechanisms include disruption fo cell health, metabolism, cell growth or proliferation.

57
Q

When is the greatest risk of exposure to teratogens?

A

embryonic period (from fertilization to 8 weeks)

58
Q

What happens when exposed to teratogens during the first 2 weeks post fertilization?

A

spontaneous abortion or has not effect

59
Q

When is the period of maximum sensitivity to teratogens?

A

Weeks 3-8 post fertilization

60
Q

What can happen if exposed to teratogens after week 9 post fertilization?

A

can disrupt growth and function

61
Q

What are errors in morphogenesis also called?

A

birth defects, congenital anomalies or congenital differences

CM Week 2 (4 decks)

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