11.2 Early Foetal Development Flashcards
(120 cards)
1
Q
What does the endoderm develop into?
A
GI tract, liver, pancreas, lung, thyroid
2
Q
What does the embryogenic stage involve?
A
- establishing the early embryo from the fertilised oocyte
- determination of of two populations of cells: pluripotent embryonic cells (contribute to the foetus), extraembryonic cells (contribute to the support structures e.g. placenta)
3
Q
How is fertilsation (conceptual) age measured?
A
measured from the time of fertilisation (assumed to be +1 day from last ovulation)
4
Q
Why can fertilsation age be difficult to measure?
A
Difficult to know time of fertilisation exactly because could happen days after intercourse, unless IVF where fertilisation occurs in a dish
5
Q
How is gestational age measured?
A
calculated from time of the beginning of the last menstrual period (LMP)
Determined by fertilsation date (+14 days), if known, or early obstetric ultrasound and comparison to embryo size charts
6
Q
What is carnige staging?
A
Method of tracking embryoloical development.
Allows comparison of developmental rates between species.
Covers the window of 0-60 days fertilisation age in human.
7
Q
How is carnigie staging measured?
A
23 stages of embryo development based on embryological features not time
8
Q
What are 3 ways of measuring embryo-foetal development?
A
fertilisation age
gestational age
carnigie stage (only until 60 days fertilisation age)
9
Q
What are the three stages of of embryo-foetal development?
A
- Embryogenic Stage
- Embryonic Stage
- Foetal Stage
10
Q
When does the embryogenic stage occur?
A
14-16 days post fertilisation
11
Q
When does the embryonic stage occur?
A
16-50 days post fertilisation
12
Q
When does the foetal stage occur?
A
50-270 days post fertilisation ( 8 -38 weeks or 10-40 weeks gestational age)
13
Q
In which trimester does the embryogenic stage occur?
A
first
14
Q
In which trimester does the embryonic stage occur?
A
first
15
Q
In which trimester does the foetal stage occur?
A
second and third trimester
16
Q
What does the embryonic stage involve?
A
- establishment of the germ layers and differentiation of tissue types
- establishment of the body plan
17
Q
What does the foetal stage involve?
A
- major organ systems now present (although not all organs will be in the position they will be in at birth)
- migration of some organ systems to final location
- extensive growth and acquisition of foetal viability (survival outside the womb)
18
Q
What is the difference between an oocyte and a zygote?
A
Both one cell
Oocyte - unfertilised egg
Zygote - fertilised cell
19
Q
What are the 2-8 cell embryos known as and why?
A
cleavage stage embryos
mitotic divisions the cells undergo to go from zygote to 8 cell embryo are known as cleavage divisions
20
Q
What is the 16+ cell embryo known as ?
A
Morula
21
Q
What proceeds the morula and how many cells is it roughly?
A
blastocyst
200-300 cells
22
Q
Where does the development of the zygote into the blastocyst occur?
A
along the fallopian tube and into the uterus where it implants
23
Q
When does the maternal to zygotic transition occur?
A
4-8 cell stage
24
Q
What happens in the maternal to zygotic transition? (3)
A
- transcription of embryonic genes (zygotic genome activation)
- increased protein synthesis
- organelle maturation (mitochondria, golgi)
25
When does compaction occur?
Around 8 cell stage or later
26
What occurs during compaction?
Outer cells become pressed against zona, and change from spherical to wedge shaped.
Outer cells connect to each other through tight gap junction and desmosomes
Forms barrier to diffusion between inner and outer embryo.
Outer becomes polarised with distinct apical and basal polarity
27
What are the two distinct cell types in embryo after compaction?
inner and outer
28
What's the difference in embryological structure between the morula and the blastocyst?
Outer cells remain the same (tight ring around internal edge of zona) forming shell.
Inner cells reorganise into clump at one end of the blastocyst, forming blastocoel cavity.
29
What is the embryo contained in throughout zygote to blastocyst stages?
Zona pellucida
30
What is the zona pellucida and what does it do?
hard protein shell
| inhibits polyspermy and protects early embryo
31
What does the inner cell mass of the blastocyst give rise to?
Pluripotent embryonic cells that will contribute to the final organism
32
What is the outer ring of cells (which develops during the morula phase) known as in the blastocyst?
trophectoderm
33
How is the trophoectoderm formed?
Compaction
34
What does the trophectoderm give rise to?
extra-embryonic cells that contribute to the extraembryonic structures that support development
35
How is the blastocoel formed?
Formed osmotically
Trophoblasts (trophectoderm cells) pump Na+ ions into cavity
Water then follows osmotically to create fluid filled cavity
36
When is does hatching occur?
Day 5-6
37
Why does hatching occur?
After blastocyst stage, developmental potential becomes limited as contained within zona. The blastocyst must also hatch to implant in the uterine wall
38
Why does hatching occur?
After blastocyst stage, developmental potential becomes limited as contained within zona. The blastocyst must also hatch to implant in the uterine wall
39
What is hatching?
Escape of the blastocyst from the zona pellucida
40
How does hatching occur?
```
enzymatic digestion (blastocyst secrete enzymes)
cellular contraction
```
41
What two types of cells do the trophectoderm cells develop into?
Syncitiotrophoblasts
| Cytotrophoblast
42
What in the function of the syncitiotrophoblasts?
Invade maternal endometrium and destroys local cells (including capillaries, which allow the syncitiotrophoblasts to be bathed in maternal blood)
Creates interface between embryo and maternal blood supply
43
What are the function of cytotrophoblasts?
Remain individual so they can continue to divide to provide cells for the syncytiotrophoblasts
44
What two components does the inner cell mass develop into?
epiblast
| hypoblast
45
What is the epiblast?
cells from which the foetal tissues will be derived
46
What is the hypoblast?
cells which will form the yolk sac (extraembryonic structure)
47
Where does the hypoblast lie?
cytotrophoblasts
epiblast
hypoblast
blastocoel
48
What important development occurs in the embryo around day 12?
bi-laminar embryonic disc formation
49
Why is the bi laminar (two-layer) embryonic disc important?
because it is the final stage before gastrulation
50
What does the bilaminar embryonic disc consist of?
epiblasts (on top)
| hypoblasts
51
What happens during the bi-laminar disc formation?
Epiblast cells separate into two layers and a new cavity is formed - the amniotic cavity.
52
What is the name of the epiblast cells above the amniotic cavity?
amnion cells
53
What two structures is the bi laminar embryonic disc in between?
amniotic cavity
bi-laminar embryonic disk
blastocoel
54
What do the amnion cells give rise to?
extra-embryonic membranes
55
What does the syncitiotrophoblast secrete?
hCG (beta hCG subunit in blood and urine is how pregnancy detected)
56
the genes of the embryo are not transcribed until..
the maternal to zygotic transition
57
How does the embryo get through the first divisions (day 0-4)?
Embryo is dependent on maternal mRNAs and proteins to get through the first divisions.
58
Where does the mRNA and proteins required for the first divisions from?
mRNA and proteins are synthesised and stored during oocyte development (pre-ovulation).
failure to synthesise, store or interpret these mRNAs and proteins during oogenesis can impair embryonic development.
59
What are the three germ layers?
endoderm
ectoderm
mesoderm
60
When does the primitive streak form?
Day 15
61
What does the formation of the primitive streak define?
The major body axis of the embryo
62
What is the primitive streak
A thickened structure along the midline of the epiblast near the caudal end of the bilaminar disc.
63
What does the endoderm develop into?
```
GI tract
liver
pancreas
lung
thryoid
```
64
What is gastrulation?
The process whereby the bilaminar embryonic disc undergoes reorganisation to form a trilaminar disc
65
What does the ectoderm develop into?
CNS and neural crest
Skin epithelial
Tooth enamel
66
What does the mesoderm develop into?
blood (endothelial cells, RBC, WBC)
muscle (smooth, skeletal, cardiac)
gonads, kidneys, adrenal cortex
bone, cartilage
67
When does notochord formation occur?
day ~13+
68
What is the notochord?
rod like tube structure formed of cartilage-like cells
69
Where does the notochord form?
forms along the embryo midline, under the ectoctoderm
| forms from the primitive streak and grows toward the head end of the embryo
70
How does the notochord organise the development of the neural system?
Through control of the neural plate (area of thickened ectoderm)
71
What is the role of the notochord?
acts as a key organising centre for development
| releases signals for neurulation (CNS formation) and mesoderm development
72
When does the neural tube close at the head end?
d23
73
When does the neural tube close at the tail end?
d27
74
What does closure of the neural tube at the head end precede?
formation of brain structures
75
What are 2 developmental defects that result from failure of neural tube closure?
anencephaly
| spina bifida
76
What is anencephaly?
absence of most of the skull and brain;
| arises from failure to close at the head end
77
What is spina bifida?
open neural tube at birth, usually lower spine due to failure to close tail end;
varying severity
78
How can we classify neural crest cells?
According to where the end up in the embryo
79
What is somitogenesis?
formation of somites
80
What are somites?
somites arise from paired blocks of paraxial mesoderm flanking the neural tube and notochord which bud off
81
Where does somitogenesis begin?
At the head end of the embryo and progresses down the long axis of the embryo
82
What two types of embryonic tissue are somites made of?
sclerotome
| dermomyotome
83
What is scerotome?
vertebrae and rib cartilage
84
What does dermomyotome sub divide into?
Dermatome: gives rise to dermis of skin, some fat, connective tissues of neck and trunk
Myotome: forms the muscles of the embryo
85
When does formation of the gut tube occur?
day 16
86
The primitive gut arises from what two types of folding in the embryo?
ventral folding
| lateral folding
87
What is ventral folding?
where the head and tail ends curl together
88
What is lateral folding?
where the two sides of the embryo roll
89
How does the primitive gut arise?
two types of folding occur in the embryo, pinching off the yolk sac and this forms the primitive gut
90
What three structures does the primitive gut develop into?
foregut
midgut
hindgut
91
What does the foregut develop into?
```
oesauphagus
stomach
upper duodenum
liver
gallbladder
```
92
What does the midgut develop into?
lower duodenum
remainder of small intestine (ilium, jejunum)
ascending and transverse colon
93
What does the hindgut develop into?
last third of transverse colon
descending colon
rectum and upper anal canal
94
How do the lungs develop?
In the 4th week
- arises from the lung bud, and endoderm structure adjacent to the foregut
- lung bud splits in two
- -> then progressively branches through development
95
How does the heart develop?
Day 19: begins as tube of mesoderm
Day 22: beating and pumping blood
4 weeks: fetal heartbeat detectable (6 weeks gestational age)
96
How do gonads develop?
forms from mesoderm as bipotential (i.e. not committed to testis or ovaries) structures known as gonadal ridges
97
How do gonads develop in 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
98
How do gonads develop in XX embryos?
absence of SRY leads to gonadal cells adopting a granulosa cell fate and ovary development, requires reinforcement by FOXL2
99
What are the two ends of the embryo?
```
Cranial end
Caudal end (tail)
```
100
At the cranial end of the embryonic disk, the primitive streak expands to create a...
primitive node (which contains primitive pit)
101
The primitive node and primitive pit form the ...
primitive groove
102
Cells migrate inwards towards the primitive groove and slip beneath it in a process known as...
invagination
103
Hypoblast cells are displaced by cells invaginating and a new proximal cell layer is formed called the..
Definitive endoderm
104
After invagination what are the remaining epiblast cells called?
Ectoderm (most exterior, distal layer)
105
Some of the invaginated epiblast cells remain in the space between the ectoderm and definitive endoderm, what happens to this layer?
These cells form a germ layer, the mesoderm
106
What do the first cells to invaginate through the primitive groove form?
the definitive endoderm
107
What do cells that invaginate but don't form the definitive endoderm become?
Cells that remain in the space become the mesoderm
108
The formation of the primitive streak defines which axis of the embryonic disc?
head-tail
AND
left-right
109
What are the two functions of the notochord?
Form neural groove --> notochord signals direct the neural plate ectoderm to invaginate
Creates two ridges (neural folds) running along crainio-caudal axis
110
What cells form in the neural crest?
neural crest cells
111
How does the neural tube form?
neural folds move together over neural groove and fuse
112
What control the process of neural tube formation?
notochord
113
What are some features of neural crest cells?
endoderm derived
| plastic and migrate extensively during developement
114
What are 4 types of neural crest cells:
cranial
cardiac
trunk
vagral & sacral
115
What do cranial neural crest cells form? (5)
```
cranial neurones
glia
lower jaw
middle ear bones
facial cartilage
```
116
What do cardiac neural crest cells form?
aortic arch
pulmonary artery septum
large artery walls
117
What do trunk neural crest cells form? (5)
```
dorsal root ganglia
sympathetic ganglia
adrenal medulla
aortic nerve clusters
melanocytes
```
118
What do vagral and sacral neural crest cells form?
parasympathetic ganglia
| enteric nervous system ganglia
119
What do defects of neural crest migration/specification lead to?
```
birth defects
including:
- pigmentations disorders
- deafness
- cardiac and facial defects
- failure to innervate the gut
```
120
What is unique about the rate of budding off of somite pairs?
species specific as is number of pairs
| human: 90 mins/pair, 44 pairs
