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early fetal development Flashcards

1
Q

what are the 3 ways of measuring embryo fetal development

A

fertilisation age
gestational age
carnegie stage

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2
Q

what is the fertilisation age

A

measured from time of fertilisation - ammued 1 day after last ovulation
difficult to know time unless ivf

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3
Q

what is the gestational age

A

calculated from time of beginning of last menstrual period
determined by fertilisation date + 14 days if known
or can use early obstetric ultrasound and compare to embryo size charts

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4
Q

what is the carnegie age

A

the 23 stages of embryo development based on features than time
allows comparison of development rates between species
covers window of 0-60 days

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5
Q

what are the stages we can divide pregnancy into

A

embryogenic stage

embryonic stage

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6
Q

what is the embryogenic stage

A

14-16 days post fertilisation
establishing early embryo from fertilised oocyte
determining 2 types of cells:
pluripotent embryonic and extraembryonic cells

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7
Q

what is the embryonic stage

A

16 - 50 days post fertilisation
establishment of germ layers and differentiation of tissue types
establishment of body plan

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8
Q

what is the foetal stage

A

50-270 days post fertilisation
major organs present
migration of some organs to final location
extensive growth and acquisition of fetal viability - survival outside womb

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9
Q

what trimester do embryogenic and embryonic stages take place

A

1st trimester

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10
Q

when does fetal stage take place

A

2nd and 3rd trimester

8+ weeks

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11
Q

what is the zygote

A

single cell after fertilisation

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12
Q

what are the cleavage stage embryos

A

2-8 cell embryos

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13
Q

what is the morula

A

16 cells+

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14
Q

what is a blastocyst

A

200-300 cells

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15
Q

how does embryo get through first divisions

A

until 4-8 cell stage genes of embryo arent transcribed

embryo is dependent on maternal mRNAs and proteins which are stored during oocyte development

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16
Q

what happens during maternal to zygotic transition

A

transcription of embryonic genes
increased protein synthesis
maturation of organelles e.g mitochondria and golgi

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17
Q

what is compaction

A

formation of first 2 cell types
around 8 cell stage + outer cells become pressed against zona
change from spherical to wedge shaped

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18
Q

what properties do cells pushing on zona gain

A

outercells connect to each other through tight junctions and desmosomes
forms barrier to diffusion between inner and outer embryo
outer cells become polarised

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19
Q

what two cells does blastocyst formation establish

A

inner cell mass - pluripotent embryonic cells

outer cells - trophectoderm - extraembryonic cells that contribute to extraembryonic that support development

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20
Q

what is the zona pellucide

A

hard protein shell inhibiting polyspermy and protects early embryo

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21
Q

what is the blasctocoel

A

fluid filled cavity formed osmotically by trophoblasts pumping na+ ions into cavity

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22
Q

hatching

A

escape of blastocyst from zona pellicuda done throguh enzymatic digestions and cellular contractions
can then implant into endometrium

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23
Q

when does peri implantation take place

A

7-9 days approx

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24
Q

what happens during peri implantation

A

trophectoderm lineage separates further:

  • trophoblast cells fuse to form syncitiotrophoblasts which invade local maternal cells in endometrium
  • creates interface between embryo and maternal blood supply
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25
what are cytotrophoblasts
cells remain individual to provide source of syncitiotrophoblast cells
26
what does inner cell mass separate into
epiblast - from which fetal tissues will be derived | hypoblast - form the yolk sac(imp in haematopoeisis) - extraembryonic structure
27
when does bi laminar embryonic disc formation take place
day 12+ | = final stage before gastrulation
28
what happens during bilaminar embryonic disc stage
syncitiotrophoblast continue to expand into endometrium | some cells from epiblast become separated by formation of amniotic cavity
29
what is the amnion
cells that continue to contribute to extra embryonic membranes
30
what is two layered /bilaminar disc
epiblast and hypoblast
31
what does syncitiotrophoblasts secrete
human chorionic gonadotrophin ,hcg used for pregnancy testing
32
what is gastrulation
change from single layer of epiblast cells to complex structure containing multiple layers
33
what is the first step in gastrulation
around 15 days thickened structure forms along midline in epiblast near caudal end of bilaminar disc = primitive streak
34
what does the primitive streak define
major axis of embryo incl cranial and caudal ends and left and right side
35
what takes place at cranial end of embryonic disc
primitive streak expands to create primitive node | which contains circular depression - primitive pit
36
what is primitive groove
when depression continues along midline of epiblast towards caudal end of streak
37
what is invagination
cells of epiblast migrate towards streak, detach from epiblast and slip beneath it into interior of embryo
38
what do first cells to invaginate primitive groove do
invade the hypoblast and displace its cells
39
what is the definitive endoderm
hypoblasts are eventually replaced by new proximal layers
40
what is the ectoderm
remaining cells of epiblast | forms most exterior distal layer
41
what is the mesoderm
layer of cells invaginated between endoderm and ectoderm
42
once mesoderm and endoderm form
epiblast cells no longer migrate towards primitive streak
43
what does ectoderm do throughout gastrulation
continues to form from cranial to caudal end of embryo
44
what organs/tissues does endoderm give rise to
gi tract liver, pancreas lung thyroid
45
what organs/tissues does ectoderm give rise to
cns and neural crest skin epithelia tooth enamel
46
what tissues does mesoderm give rise to
blood, endothelial cell,rbcs,wbcs muscle gonads, kidneys and adrenal cortex bone,cartiliage
47
what is the first major event after gastrulation
formation of notochord | around day 13
48
what is the notochord
rod like tube structure formed of cartilage like cells | forms along embryo midline, under ectoderm
49
what is role of notochord
acts as key organising centre for neuralation and mesoderm development
50
what is the neural plate
thickened ectoderm | sits on top of embryo
51
what is neuralation
forming neural tube and cns
52
how does cns form
notochord signals to neural plate ectoderm to invaginate forming neural groove creates 2 ridges running along craniocaudal axis
53
what does formation of neural fold create
neural crest cells which migrate away and populate variety of diff tissues
54
what happens when neural folds move together
neural folds fuse forming hollow tube neural tube is overlaid with epidermis migration of neural crest cells
55
when does closure of head and tail end of neural tube form
head end - around 23 days tail end - around 27 days closure at head end precedes formation of brain structure
56
what is anencephaly
failure of closure at head end = absence of most of skull and brain
57
what is spina bifida
open neural tube at birth | usually lower soine defect
58
what do neural crest cells do
``` become: cranial nc - cranial neurones,glia,lower jaw, middle ear bones,facial cartiliage cardiac nc trunk nc vagral and sacral nc ```
59
what can defects in nc migration cause
birth defects e.g pigmentation disorders, deafness, cardiac and facial defects and failure to innervate gut
60
what is somitogenesis
formation of somites which arise from paired blocks of paraxial mesoderm flanking the neural tube and notochord
61
what occurs during somitogenesis
blocks of paraxial mesoderm condense and bud off in somite pairs one of each pair either side of neural tube
62
where does somitogenesis commence
at head end and progresses down the long axis of embryo | rate of budding or appearance of somite pairs is species specific as is number of pairs
63
what do somites initially form
2 types of embryonic videos: sclerotome dermomyotome
64
what is the sclerotome
vertebrae and rib cartilage
65
what is the dermomyotome
in turn subdivides to form dermatome and myotome
66
what is the dermatome
gives rise to dermis of skin, some fat and connective tissues of neck and trunk
67
what is the myotome
forms muscles of the embryo
68
where does primitive gut arise
2 types of folding: ventral folding - where head and tail ends curl together lateral folding - where two sides of embryo roll pinches off part of yolk sac
69
what is primitive gut is split into
foregut midgut hindgut
70
what does foregut develop into
eosophagus, stomach, upper duodenum, liver, gallbladder and pancreas
71
what does midgut develop into
lower duodenum and remainder of small intestine, ascending colon and first two thirds of transverse colon
72
what does hindgut develop into
last third of tranverse colon, descending colon, rectum and upper anal canal
73
where does heart form from and when
begin as tube of mesoderm around day 19, beating and pumping blood commences around day 22 fetal heartbeat detectable from approx 6 weeks gestational age
74
when does lung form and where from
arise from lung bud and endodermal structure adjacent to foregut in 4th week of development lung bud splits into 2 at end of 4th week and progressively branches
75
when does gonads form and where from
forms from mesoderm as bipotential ( not committed to testis/ovary) structures known as gonadalgenital 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 xx embryos - absence of sry leads to gonadal cells adopting granulosa cell fate and ovary development, requires reinforcement of foxl2

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