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!!!!! BRS YR2 !!!!! > Age + Dev - Early Fetal Development > Flashcards

Age + Dev - Early Fetal Development Flashcards

1
Q

What are the 3 ways in which embryo-fetal development can be measured?

A

→ fertilization age
→ gestational age
→ carnegie age

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2
Q

What is fertilization age?

A

measured from the time of fertilization (assumed to be +1 day from last ovulation)

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3
Q

Why is fertilization age not very useful?

A

difficult to know time of fertilization exactly unless it’s IVF

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4
Q

What is gestational age?

A

→ calculated by time from the beginning of the last menstrual period (lmp)
→ determined by fertilzation date (+14 days) if known, or early obstetric ultrasound + comparison to embryo size charts

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5
Q

What is the carnegie age?

A

→ based off of 23 stages of embryo development which are based on embryo features rather than time
→ allows comparison of development rates between species
→ covers window of 0-60 days of fertilzation age in humans

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6
Q

How is pregnancy split up into stages to measure embryo-fetal development?

A

→ embryogenic stage
→ embryonic stage
→ fetal stage

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7
Q

What is the embryogenic stage?

A

→ 14-16 days post-fertilisation establishing the early embryo from the fertilized oocyte
→ Determining two populations of cells:
- Pluripotent embryonic cells (contribute to fetus)
- Extraembryonic cells (contribute to the support structures eg placenta)

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8
Q

What is the embryonic stage?

A

→ 16-~50 days post fertilisation
→ Establishment of the germ layers and differentiation of tissue types
→ Establishment of the body plan

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9
Q

What is the fetal stage?

A

→ ~50 to 270 days post-fertilization or ~8 to ~38 weeks
→ Major organ systems now present
→ Migration of some organ systems to final location
→ Extensive growth and acquisition of fetal viability (survival outside the womb)

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10
Q

What stages of embryo-fetal development occur in the first trimester of pregnancy?

A

→ embryogenic stage

→ embryonic stage

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11
Q

What stages of embryo-fetal development occur in the 2nd + 3rd trimester of pregnancy?

A

fetal stage

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12
Q

What does the ovulated oocyte become after fertilisation?

A

zygote

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13
Q

How many cells in a zygote?

A

1 cell

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14
Q

What is the next stage of development for a zygote?

A

cleavage division into “cleavage stage embryos”

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15
Q

How many cells are there in cleavage stage embryos?

A

2-8 cells

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16
Q

What is the next stage of development for cleavage stage embryos?

A

morula

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17
Q

How many cells are there in morula?

A

16+ cells

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18
Q

What is the next stage of development for morula?

A

blastocyst

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19
Q

How many cells are there in blastocyst?

A

200 - 300 cells

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20
Q

Where do the first few days of life take place in the female gonads?

A

happens while egg migrates from ovaries through fallopian tubes to the uterus

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21
Q

What is the first major developmental transition in the first few stages of life?

A

maternal-to-zygotic transition

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22
Q

What is the maternal-to-zygotic transition?

A

→ embryo stops being dependent on maternal mRNAs + proteins to get through first divisions
→ transcription of embryonic genes occurs + zygotic genome activation
→ increased protein synthesis
→ organelle (mitochondria + golgi) maturation

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23
Q

How does zygote survive before zygotic genome activation?

A

Dependent on maternal mRNAs + proteins (that were synthesised + stored during oocyte development) to get through the first divisions

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24
Q

What happens when mRNA + proteins are not properly synthesised or stored or interpreted properly?

A

Can impair embryonic development

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25
Q

When does the maternal-zygotic transition occur in terms of cell stage and human development time?

A

→ 4-8 cell stage

→ 2 days post-fertilization

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26
Q

What is the process that forms the morula + blastocyst?

A

Compaction

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27
Q

How does compaction produce a compacted morula?

A

→ Outer cells become pressed against zona
→ Change from spherical to wedge-shaped.
→ Outer cells connect to each other through tight gap junctions and desmosomes
→ Forms barrier to diffusion between inner and outer embryo
→ Outer cells become polarised

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28
Q

What is the arrangement of the compacted morula?

A

2 distinct cell populations:
→ inner
→ outer

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29
Q

How does a morula formation change to form a blastocyst?

A

Inner cells + outer cells reorganise with the formation of the blastocoel cavity

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30
Q

What are the different parts of the blastocyst?

A

→ zona pellucida
→ trophectoderm
→ inner cell mass
→ blastocoel

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31
Q

What is the purpose of the zona pellucida for the blastocyst?

A

Hard protein shell inhibiting polyspermy and protects early embryo

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32
Q

What is the purpose of the trophectoderm for the blastocyst?

A

Extra-embryonic cells that contribute to the extraembryonic structures that support development

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33
Q

What is the purpose of the inner cell mass for the blastocyst?

A

Pluripotent embryonic cells that will contribute to the final organism

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34
Q

What is the purpose of the blastocoel for the blastocyst?

A

Fluid-filled cavity formed
osmotically by
trophoblast pumping
Na+ ions into cavity

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35
Q

How does that blastocyst implant in the uterus?

A

blastocyst must escape zona pellucida

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36
Q

How does that blastocyst escape the zona pellucida?

A

→ enzymatic digestion

→ cellular contractions

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37
Q

What are the separate embryonic cell lineages of the morula?

A

→ inner cell mass = embryonic

→ trophectoderm = extra-embryonic

38
Q

How many days does it approximately take for the blastocyst to develop from a fertilised ovum?

A

6 days

39
Q

How does the trophectoderm lineage separate during peri-implantation events?

A

→ syncitiotrophoblast

→ cytotrophoblast

40
Q

How does the inner cell mass lineage separate during peri-implantation events?

A

→ epiblast

→ hypoblast

41
Q

What are the syncitiotrophoblasts?

A

→ Trophoblast cells fuse to form the syncitiotrophoblast
→ Syncitiotrophoblast invasion into the uterine endometrium destroys local maternal cells in the endometrium
→ Creates interface between embryo and maternal blood supply
→ secretes beta hCG subunit

42
Q

What are the cytotrophoblasts?

A

→ remains around the blastocoel cavity, remaining individual to provide a source of syncitio-trophoblasts

43
Q

What are the epiblasts?

A

→ layer closest to the cytotrophoblasts

→ from which the fetal tissue will be derived

44
Q

What are the hypoblasts?

A

→ layer furthest from the cytotrophoblasts

→ will form the yolk sac (extra-embryonic structure)

45
Q

When do the peri-implantation events occur?

A

day 7-9 approximately

46
Q

What is the next step after the peri-implantation events? When does it occur?

A

→ bi-laminar embryonic disc formation

→ day 12+

47
Q

What is the process of the formation of the bi-laminar embryonic disc?

A

→ some of the epiblasts separate from the border of the cytotrophoblasts to create 2 cavities
→ new cavity closer to the uterus = amnion cavity
→ 2-layer embryonic membrane disc made up of epiblasts + hypoblasts separates the 2 cavities
→ allows the embryo to be ready for gastrulation

48
Q

What are the amnion cells? What are their purpose?

A

→ epiblast cells that line the amniotic cavity + cytotrophoblasts
→ amnion cells contribute to extra-embryonic membranes

49
Q

Why can a pregnancy be detected using a pregnancy test usually after the formation of the bi-laminar embryonic disc formation?

A

→ syncitiotrophoblasts secrete beta hCG subunit

→ can now be detected in blood + urine by pregnancy test

50
Q

What happens after the formation of the bi-laminar embryonic disc formation?

A

gastrulation

51
Q

What is the process of gastrulation?

A

→ thickened structure forms in the caudal end of the epiblasts of the amniotic cavity called the primitive streak
→ primitive streak contains the primitive node + pit = groove
→ epiblasts pass through the groove down into the hypoblast layer = INVAGINATION
→ first epiblasts to invade hypoblasts = new layer called definitive endoderm
layer
→ remaining epiblasts above this = ectoderm
→ cells remaining in space between endoderm and ectoderm = mesoderm

52
Q

At what point does gastrulation occur?

A

15 days +

53
Q

What are the 3 germ layers that form from the epiblast cells?

A

→ ectoderm
→ mesoderm
→ endoderm

54
Q

Why are the germ layers so important?

A

they’re precursor tissues to organs of fetus

55
Q

What tissues and organs develop from the endoderm?

A 
→ GI tract
→ liver
→ pancreas
→ lungs
→ thyroid
56
Q

What tissues and organs develop from the ectoderm?

A

→ CNS
→ neural crest
→ skin epithelia
→ tooth enamel

57
Q

What tissues and organs develop from the mesoderm?

A 
→ blood (endothelial cells, red + white blood cell)
→ muscle (smooth, skeletal, cardiac)
→ gonads
→ kidneys
→ adrenal cortex
→ bone
→ cartilage
58
Q

What is the purpose of the notochord?

A

acts as a key organising centre for neurulation + mesoderm development

59
Q

What is neurulation?

A

forming of the neural tube + CNS

60
Q

What is the process of neurulation?

A

→ Notochord signals direct the neural plate ectoderm to invaginate forming neural groove
→ Creates two ridges (neural folds) running along the cranio-caudal axis
→ Neural crest cells specified in neural folds
→ Neural folds move together over neural groove
→ Ultimately neural folds fuse, forming a hollow tube
→ Neural tube overlaid with epidermis (ectoderm)
→ Migration of the neural crest cells from folds

61
Q

When does the head of the neural tube close?

A

the head end closes at day 23 approximately

62
Q

When does the tail end of the neural tube close?

A

day 27

63
Q

What happens after the closure of the neural tube?

A

formation of the brain structures

64
Q

What can the failure of the neural tube closure cause?

A

developmental defects :
→ anencephaly
→ spina bifida

65
Q

What is anencephaly?

A

→ absence of most of the skull and brain
→ arises from failure to close at the head end
→ 1/10,000 births

66
Q

What is spina bifida?

A

→ open neural tube at birth, usually lower spine
→ due to failure to close tail end– varying severity
→ 0.4-5/1000 births

67
Q

What are the different neural crest cells?

A

→ cranial NC
→ cardiac NC
→ trunk NC
→ vagral + sacral

68
Q

What do the cranial neural crest cells develop into?

A 
→ cranial neurones
→ glia
→ lower jaw
→ middle ear bones (ossicles)
→ facial cartilage
69
Q

What do the cardiac neural crest cells develop into?

A

→ aortic arch
→ pulmonary artery septum
→ large artery walls
→ musculo-connective tissues

70
Q

What do the trunk neural crest cells develop into?

A 
→ dorsal root ganglia
→ sympathetic ganglia
→ adrenal medulla
→ aortic nerve clusters
→ melanocytes
71
Q

What do the vagral + sacral neural crest cells develop into?

A

→ parasympathetic ganglia

→ enteric nervous system ganglia

72
Q

What can defects of the neural crest migration or specification lead to?

A

→ pigmentation disorders
→ deafness
→ cardiac + facial defects
→ failure to innervate gut

73
Q

What is somitogenesis?

A

→ formation of somites

→ segmentation of body axis

74
Q

What are somites?

A

arise from paired blocks of paraxial mesoderm flanking the neural tube + notochord

75
Q

What is the process of somitogenesis?

A

→ Blocks of paraxial mesoderm condense and bud off in somite pairs
→ One of each pair either side of the neural tube.
→ Somitogenesis commences at the head end and progresses down the long axis of the embryo
→ Rate of ‘budding’ or appearance of somite pairs is species-specific, as is the number of pairs.

76
Q

What are the 2 types of embryonic tissue formed from somites?

A

→ dermomyotome

→ sclerotome

77
Q

What is sclerotome?

A

vertebrae + rib cartilage

78
Q

What does dermomyotome split into?

A

→ dermatome

→ myotome

79
Q

What is a dermatome?

A

gives rise to dermis of skin, some fat + connective tissue of neck + trunk

80
Q

What is a myotome?

A

forms muscles of the embryo

81
Q

When does the primitive gut form?

A

day 16 +

82
Q

What 2 processes form the primitive gut?

A

→ ventral folding : where the head + tail ends curl together

→ lateral folding : where the 2 sides of embryo roll

83
Q

How does the the primitive gut form?

A

ventral folding + lateral folding pinch off part of the yolk sac to form the primitive gut

84
Q

How can the primitive gut be split up?

A

→ foregut
→ midgut
→ hindgut

85
Q

What is a part of the foregut?

A 
→ oesophagus
→ stomach
→ upper duodenum
→ liver
→ gall bladder
→ pancreas
86
Q

What is a part of the midgut?

A 
→ lower duodenum
→ jejunum
→ ileum
→ ascending colon
→ 2/3 of transverse colon
87
Q

What is a part of the hindgut?

A

→ last third of transverse colon
→ descending colon
→ rectum
→ upper anal canal

88
Q

How is the heart derived?

A

→ begins as tube of mesoderm at day 19

→ beating + pumping blood commences around day 22

89
Q

From when is a fetal heart beat detectable?

A

approx. 6 weeks gestational age

90
Q

How are the lungs formed?

A

→ Arise from the lung bud, and endodermal structure adjacent to the foregut, in the 4th week of development
→ Lung bud splits into two at the end of the 4th week, and progressively branches through development

91
Q

How do the female gonads develop?

A

Forms from mesoderm as bipotential (i.e. not committed to testis or ovary) structures known as gonadal/genital ridges

absence of SRY leads to gonadal cells adopting a granulosa cell fate and ovary development, requires reinforcement by FOXL2

92
Q

How do the male gonads begin to develop?

A

Forms from mesoderm as bipotential (i.e. not committed to testis or ovary) structures known as gonadal/genital ridges

XY embryos: presence of SRY gene on Y chromosome directs gonadal cells to become Sertoli cells, triggering testis development, Leydig cell formation and testosterone production

!!!!! BRS YR2 !!!!! (72 decks)

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