Mechanisms of Disease During Embryogenesis* Flashcards
(58 cards)
1
Q
What are the 2 main periods in human development?
A
- Embryonic period
- Fetal period
2
Q
What is the embryonic period?
A
- Period up to the end of week 8
- Most of the organogenesis occurs in these first 8 weeks
3
Q
What is the fetal period?
A
- The remaining time in utero following the embryonic period (up to week 8)
- Involves growth and modelling
4
Q
What can defects during embryogenesis result in?
A
Defects during embryogenesis result in congenital malformations
5
Q
What are the mechanisms of development an egg goes through to develop into an adult?
A
From egg → fertilization → cleavage → gastrulation → neurulation and somitogenesis → organogenesis → adult
6
Q
Where does fertilisation occur?
A
In the fallopian duct (ampullary region)
7
Q
What must happen before the development of the embryo proper?
A
- Conceptus must first implant, then generate the “germ” disc.
- This takes ~10 days.
8
Q
What is the 16-cell zygote known as?
A
Morula
9
Q
When does cleavage occur?
A
- `Cleavage occurs when zygote is moving from the site of fertilisation to the uterus
10
Q
What is compaction?
A
- Morphogenic process
- The trophoblast secretes fluid inside, forming a blastocoele that pushes the inner cell mass to one side
- Inner cell mass splits into the hypoblast and the epiblast
11
Q
In the morula, which cells are polar and what are their poles called?
A
- Trophoblast cells have an apical and a basolateral surface
- Inner cell mass are apolar
12
Q
How can you describe the cells inside the embryo following compaction?
A
- The cells inside the embryo are apolar
- All their sites are in contact with other sites; they don’t have any surface that is free
13
Q
Blastocoele?
A
Fluid filled space secreted by trophoblast
14
Q
Blastocyst?
A
Formed when trophoblast has secreted the blastocoele and pushed the inner cell mass to the side
15
Q
What does the inner cell mass split into?
A
Hypoblast and Epiblast
16
Q
Which part of the epiblast is touching the blastocoele?
A
Hypoblast
17
Q
What happens once the embryo is fully implanted?
A
Formation of the bilaminar germ disk
18
Q
What happens to the cells following compaction?
A
- The cells on the outside give rise to the TROPHECTODERM
- Cells on the inside give rise to the inner cell mass.
- The outside cells start pumping fluid to the inside of the embryo which leads to the formation of a fluid filled cavity inside the embryo called the BLASTOCOELE.
19
Q
Blastocyst?
A
- The Blastocoele pushes the inner cell mass towards one side and gives an asymmetry to the embryo.
- Embryo has divided into 32-64 cells, (usually day 4/5) and now called a BLASTOCYST
- The blastocyst by now has reached the uterus and is ready to implant in the uterine wall.
20
Q
At the uterus, what happens on day 6/7?
A
- The 2nd cell fate is established, inner cell mass cells give rise to 2 cell types:
- Hypoblast
- Epiblast
- After implantation, you can see the bilaminar germ disk, composed of epiblast and hypoblast.
- Epiblast cells arrange in a way that gives rise to the Amniotic Cavity
21
Q
Gastrulation?
A
- Gastrulation is the process where the bilaminar embryonic disc (consisting of the hypoblast and epiblast) undergoes reorganisation to form a trilaminar disc (3 primary germ layers)
- Leads to the formation of 3 layers of cells (from 2 layers).
22
Q
How are the different layers formed in gastrulation?
A
- Hypoblast (primitive endoderm) is displaced by involuting cells that become definitive Endoderm (the endoderm is responsible for the formation of the GI tract)
- The remaining cells of the epiblast are called the Ectoderm
- Cells that remain in the space between the definitive endoderm and definitive ectoderm form a layer called the Mesoderm.
23
Q
What is another name for the hypoblast?
A
Primitive endoderm
24
Q
During gastrulation what displaces the hypoblast>
A
Involuting cells that become the definitive endoderm and mesoderm
25
What happens following gastrulation?
ECTODERM, ENDODERM and MESODERM have all be formed
So now there are all 3 layers and ready for **NEURULATION**.
26
Define neuralation
The folding process in vertebrate embryos which includes the transformation of the neural plate into the neural tube.
27
What happens when the primitive streak reaches the other end of the epiblast?
it regresses
28
Where does the mesoderm form?
Between the epidermis and the hypoblast
29
What does the epiblast form?
Ectoderm
30
What is the notochord?
A rod of cells that secrete molecules extracellularly that instruct the exoderm on top of it to become neural tissue
31
How is the notochord formed?
Regression of the primitive streak
32
What forms the neural plate?
Notochord sections
33
How is the neural tube formed?
* Folding of the neural plate
* Closure starts at **edge between hindbrain and spinal cord,** then progresses anteriorly and posteriorly till the neural tube is fully closed.
34
Where is the neural tube found\>
Covered by the surface ectoderm, buried in the embryo
35
Where does formation of the neural tube start?
From the middle and moves out towards the edges?
36
What does the ectoderm form?
Specification of the CNS
37
What does the mesoderm organise into?
Blocks called somites
38
What are somites precursors to?
Muscles and bones etc
39
What does folding of the embryo form?
Umbilical cord
40
What happens simulatenously to neuralation and somitogenis?
* Formation of the gut
* Body folding
41
What is neurulation is concomitant with?
* Neurulation is concomitant with other form-shaping (morphogenetic) processes
* Particulatly gut formation and body folding (“silk purse” model) to develop from flat embryo to a folded embryo.
42
What is the 'cloth purse' model?
* Septum and heart move from margin to centre
* Yolk sac, allantois and stalk make umbilical cord
43
What delimits the gut tube?
Prochordal and cloacal plates delimit gut tube.
44
Folding occurs in what 2 planes?
Folding occurs in 2 planes, **horizontal and median plane**, result of differing rates of growth of embryonic structures.
* Folding in horizontal plane → **2 lateral body folds**
* Folding in median plane → **cranial and caudal folds**
* Folding takes place simultaneously.
45
What happens to folding during 4/5th weeks?
* Endoderm moves towards midline and fuses incorporating the dorsal part of the yolk sac creating **primitive gut tube** which differentiates into foregut, midgut, hindgut.
* Foregut (found at cranial end) is covered by **oropharyngeal membrane** which at 4 weeks ruptures to form the mouth.
* Connection to yolk sac narrows to a thin stalk called **Vitelline duct**.
46
What does folding result in?
Folding results in formation of umbilical cord and formation of the gut.
47
What happens during the 7th week?
cloacal membrane ruptures to form urogenital and anal opening.
48
What happens if something goes wrong in embryogenesis?
* If something goes wrong in first 8 weeks of embryogenesis, can result in severe malformations in organ systems.
* Defects in first 2 weeks leads to complete death of embryo.
* Later than 8 weeks, can have malformations that have deleterious effects in later life.
49
What are the desirable characteristics of a model organism?
We cannot study embryos in detail so use other animal models.
* Relevance/representative – learn things from an organism that help us understand human embryonic development.
* Accessibility/availability
* Experimental manipulation
* Genetics – genome is fully sequenced so we can manipulate it.
* Cost/space
50
What occurs in Organogenesis?
* Differentiation of somitic derivatives
* Development of sensory organs
* Limb formation
* Formation of face structures
* Formation of genital structures
51
Differentiation of somitic derivatives
bones, muscles, tendons
52
Development of sensory organs
ears, eyes, olfactory pits
53
Limb formation
* forelimbs first, hindlimbs next
* establishment of pattern in the limbs:
* proximodistal, anterior-posterior, dorsal-ventral
54
Classification of causes of disease(?)
* Single gene mutations
* Chromosomal anomalies
* Polygenic disorders
* Environmental factors
55
Single gene mutations
Refers to the cases when mutation in one particular gene will be enough to display a characteristic defect.
56
Chromosomal anomalies (give an example)
* In some cases, rather than single mutations, whole chromosomal rearrangements are responsible for a disease.
* The most obvious examples are chromosomal trisomies, such as trisomy of chromosome 21, leading to Down syndrome.
57
Polygenic disorders
Refers to cases where it is not just one gene affected, but several different genes simultaneously affected, what causes the disease.
58
Environmental factors
* Refers to the deleterious influence of the environment on a particular process.
* These can be very diverse:
* diet
* infection,
* toxic compounds.
