Early Embryo Development Flashcards
(100 cards)
1
Q
When is fertilisation age measured from?
A
From the time of fertilisation, assumed to be more than one day from the last ovulation
2
Q
What other name is fertilisation date known as?
A
Conceptualisation date
3
Q
How practical is fertilisation date?
A
Not very, its also difficult to know the time exactly so its not used very commonly
4
Q
When is gestational age measured from?
A
From the time of the beginning of the last period
5
Q
How is gestational age determined?
A
Fertilisation date + 14 days if known
Early obstetric ultrasound
6
Q
How practical is gestational date?
A
More practical, it is used often clinically
7
Q
What is carnegie age?
A
23 stages of embryo development based on embryo features not time
8
Q
What window does carnegie age cover?
A
0-60 days fertilisation age (in humans)
9
Q
What are the 3 major stages of time in embryo foetal development?
A
Embryogenic stage
Embryonic stage
Foetal stage
10
Q
How many days post fertilisation is the embryogenic stage?
A
14-16 days
11
Q
How many days post fertilisation is the embryonic stage?
A
16- 50 days
12
Q
How many days post fertilisation is the foetal stage?
A
50-270 days or 8-38 weeks
13
Q
What happens in the embryogenic stage?
A
Establishment of the early embryo from the fertilised oocyte
14
Q
What are the 2 populations of cells in the embryogenic stage and what do they do?
A
Pluripotent embryonic cells (contribute to fetus) Extraembryonic cells (contribute to the support structures eg placenta)
15
Q
What do pluripotent embryonic cells contribute to?
A
The foetus
16
Q
What so extraembryonic cells contribute to?
A
Support structures eg placenta
17
Q
What happens in the embryonic stage?
A
Establishment of the germ layers and differentiation of tissue types
Establishment of the body plan
18
Q
What is present when the foetal stage is reached?
A
Major organ systems
19
Q
What stages does the first trimester include?
A
Embryogenic and embryonic
20
Q
What stages does the second trimester include?
A
Foetal stage
21
Q
When does the transition from embryo to foetus occur?
A
At the end of the first trimester
22
Q
How many cells is an ovulate oocyte?
A
1
23
Q
How many cells is a zygote?
A
1
24
Q
How many cells is a cleavage stage embryo
A
2-8
25
How many cells is a morula?
16
26
How many cells is a blastocyst?
200-300
27
When is the zona pellucida present?
From ovulated oocyte until blastocyst
28
Does the embryo transcribe its own genes?
No, it is dependant on materal mRNAs and proteins to get through the first few divisions until it has 4/8 cells. Failure in the mother to synthesise and store these mRNAs during oogenesis can impair development of the embryo
29
What happens at the maternal to zygotic transition?
Transcription of embryonic genes begins due to zygotic genome activation
Increased protein synthesis
Organelles mature eg mitochondria, Golgi
30
At what cell stage does compaction occur?
When the zygote is around 8 cells
31
Describe the process of compaction
Outer cells become pressed against zona pellucida
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 polarized
32
What are the cell types in the blastocyst? Describe them
Inner cell mass are pluripotent embryonic cells that will contribute to the final organism
Trophoectoderm are extra-embryonic cells that contribute to the extraembryonic structures that support development
33
What is the zona pellucida?
Hard protein shell inhibiting polyspermy and protects early embryo
34
What is the blastoceal?
Fluid-filled cavity formed osmotically by trophoblast pumping Na+ ions into cavity and then water following osmotically
35
What is hatching?
Degredation and weakening of the zona pellucida to allow the blastocyst to escape it
36
Why is hatching required?
To allow the blastocyst to implant into the uterus
37
How is hatching achieved?
Enzymatic digestion of the zona pellucida and cellular contractions to allow the blastocyst to escape the seal
38
What does the morula split into? Describe what each component contributes to
Inner cell mass which contributes to embryonic cells
| Trophectoderm which contributes to extra embryonic cells
39
What is formed when trophoblast cells fuse
Syncitiotrophoblast
40
What ability does the syncitiotrophoblast have?
It can invade and destroy local maternal cells in the endometrium, the destruction of capillaries allows the embryo to be bathed in blood which is an important interface
41
What individual cells are a source of syncitiotrophoblast cells?
Cytotrophoblasts
42
What does the inner cell mass separate into and what are the roles of these cells?
Epiblast from which the foetal tissues will be derived
| Hypoblast which will form the yolk sac
43
What is the yolk sac needed for
Haematopoiesis and gut development
44
What does the trophoblast give rise to?
Cytotrophoblast
| Syncitiotrophoblast
45
When does bi laminar embryonic disc formation occur?
After day 12
46
What is the final stage before gastriculation?
Bi laminar embryonic disc formation
47
Where particularly do changes occur in bi laminar embryonic disc formation?
Epiblast and hypoblast
48
What are the 2 layers of a bi laminar embryonic disc made of?
Epiblast and hypoblast
49
What secretes hCG and when?
Syncitiotrophoblast after 12 days
50
What does the epiblast give rise to?
The epiblast and the amnion
51
What is the role of the amnion cells?
They contribute to the extra-embryonic membranes
52
Define gastrulation
The process by which the bilaminar embryonic disc undergoes reorganisation to form a trilaminar disc
53
When does gastrulation occur?
3rd week
54
Describe the primitive streak and what it defines
A thickened structure that forms along a midline of the epiblast near the caudal end of the bilaminar embryonic disc
Defines the cranial end (towards the head) and caudal end (towards the feet) as well as the left and right sides of the embryo
55
When does the primitive streak form?
15 days after fertilisation
56
What is the primitive pit?
An expansion at the cranial end to create a primitive node that contains a circular depression
57
What is formed by the continuation of the primitive pit?
Primitive groove
58
What is invagination in relation to gastrulation?
Cells detach from the epiblast and migrate into the groove into the internal part of the embryo
59
What cells form the endoderm?
The first cells to carry out invagination and invade the hypoblast
60
At what day has much of the hypoblast been invaded and replaced?
Day 16
61
What cells is the mesoderm formed by?
The remaining cells in the space between the ectoderm and definitive endoderm
62
What is the definitive endoderm?
Layer that the hypoblast cells are completely replaced by
63
What cells is the ectoderm formed by?
Remaining cells of the epiblast
64
What 3 layers are formed in gastrulation (from exterior to interior)?
Ectoderm
Mesoderm
Endoderm
65
When do epiblast cells stop migrating to the primitive streak?
After the mesoderm and ectoderm are formed
66
What does the epiblast give rise to?
Ectoderm
Mesoderm
Endoderm
67
What does the endoderm give rise to?
```
GI tract
Liver
Pancreas
Lung
Thyroid
```
68
What does the ectoderm give rise to?
CNS and neural crest
Skin epithelia
Tooth enamel
69
What does the mesoderm give rise to?
```
Blood (endothelial cells, RBCs, WBCs)
Muscle (smooth, skeletal and cardiac)
Gonads
Kidneys
Adrenal cortex
Bone
Cartilage
```
70
What day does notochord formation occur?
Day 13
71
What is the role of the notochord?
Acts as a key organizing center for neurulation and mesoderm development
72
What type of cells form notochord?
Cartilage like cells
73
What is neurulation?
Formation of the neural tube and CNS
74
Describe the process of neurulation briefly
Notochord signals direct the neural plate ectoderm to invaginate forming a neural groove
This creates two ridges
Neural folds move together over neural groove and ultimately fuse, forming a hollow tube
75
What is the key signalling structure in neurulation?
The notochord
76
Which end of the neural tube closes first?
The head end closes first then the tail end
77
What can happen once the ends of the neural tubes close
The brain structures can be formed
78
What are the main disorders that occur if the neural tubes don't close
Anencephaly
| Spina bifida
79
What is anencephaly?
A disorder that occurs when the neural tube doesn't close at the head end
80
What is spina bifida?
A disorder that occurs when the neural tube doesn't close at the tail end, it has varying severity
81
Where are neural crest derived from?
From the endoderm
82
What are some characteristics of neural crest cells?
They are plastic and migrate extensively during development
83
What are some defects that arise due to neural crest migration?
Pigmentation disorders, deafness, cardiac and facial defects and failure to innervate the gut
84
What do somites arise from and how?
From paired blocks of paraxial mesoderm flanking the neural tube and notochord
Blocks of paraxial mesoderm condense and bud off in somite pairs
85
At what end does somitogenesis occur?
Head end
86
In humans what rate does budding of somites occur?
1 pair every 90 mins
87
In humans how many pairs of somites are there?
44 pairs
88
What 2 types of tissue do somites form?
Sclerotome
| Dermomyotome
89
What does the sclerotome give rise to?
Vertebrae and rib cage
90
What does the dermomyotome split into?
Dermatome and myotome
91
What does the dermatome give rise to?
Dermis of the skin, some fat and connective tissues of neck and trunk
92
What does the myotome give rise to?
Muscles of the embryo
93
What 2 types of folding allow the formation of the primitive gut?
Ventral folding: where the head and tail ends curl together
| Lateral folding: where the two sides of the embryo roll
94
What are the 3 parts of the gut which develop from the primitive gut?
Foregut
Midgut
Hindgut
95
When is foetal heartbeat detectable?
Around 6 weeks
96
What does the heart arise from?
Tube of mesoderm
97
What gene is specific to the Y chromosome?
SRY gene
98
What does the SRY gene do?
Directs gonadal cells to become sertoli cells, triggering testis development, leydig cell formation and testosterone production
99
What does absence of the SRY gene do?
Leads to gonadal cells adopting a granulosa cell fate and ovary development
100
What reinforcing gene is needed for ovary development etc?
FOXL2
