Embryogenesis Flashcards
How do cells migrate?
Down concentration gradient of growth factors and cytokines
What are the three broad periods of gestation?
- Ovum
- Embryo
- Foetus
What are the key evens of the ovum period?
fertilisation to the end of the 1st week of gestation
- Transport of zygote from oviduct to uterus
- Multiple mitotic cell division
- Transformation from zygote to morula to blastocyst
- Hatching of blastocyst out of zona pellucida
What is the zona pellucida?
A thick membrane surrounding the blastocyst
What is the cluster of cells at the top of the blastocyst referred to?
Inner cell mass (ICM)
What are the key events which occur during the 2nd week (embryo stage)?
- Blastocyst elongation
- Appearance of germ layers
- Implantation
What are the three germ layers?
- Ectoderm
- Mesoderm
- Endoderm
What is the formation of the germ layers called?
Gastrulation
What are the key events which occur during the 3rd week (embryo stage)?
- Ebryonic body established (tail, head and limb buds)
2. Extra-embryonic membranes formed through folding (amnion, chorion, yolk sac and allantois)
At what stage of development do organs become functional?
Foetal
What does CRL stand for?
Crown to Rump Length (spine length)
What can be used to age embryos?
Somite number
What does cleavage refer to?
Mitotic division inside the zona pellucida
What are the four extra embryonic membranes?
- Amnion
- Yolk sac
- Chorion
- Allantois
What are the cells produced by cleavage called?
Smaller cells called blastomeres.
What governs the pattern of cleavage?
Size of yolk. Avians have large yolk and partial cleavage (meroblastic). Mammals have minimal yolk and total cleavage (holoblastic)
What is the solid cluster of cells caused by cleavage called?
Morula
What are the two changes which differentiate a morula from a blastocyst?
- Blastomeres loose shape, becoming tightly apposed (compaction)
- Blastomeres start secreting into the centre of the morula (blastocoel)
What is the layer of cells surrounding the blastocoel called?
Tropoblast layer
Where does the embryo start developing from?
ICM aka. embryonic disc
What are the forces resulting in hatching of the blastocyst from the zona pellucida?
(except for in rodents and horses)
- Accumulation of fluid
- Enzymes secreted by the trophoblast layer
- Blastocyst contration
What type of junctions are between cells in the ICM?
GAP junction for cellular communication
What type of junctions are between cells in the trophoblast?
Tight junctions for controlled diffusion
What does delamination refer to?
Movement of a cell layer away from the ICM
How is the hypoblast formed?
Delamination of cells from the ICM, forming a layer of cells inside the trophoblast
After delamination of the hypoblast, what is the remaining ICM called?
Epiblast
Where is the amniotic cavity formed?
In-between the trophoblast and epiblast layers
How is the endoderm layer formed?
First migrating cells of epiblast layer down the primitive streak, which then move laterally
How is the mesoderm layer formed?
Second migrating cells of epiblast layer down the primitive streak
How is the ectoderm layer formed?
The remaining cells left on the top of the epiblast layer
What defines the major body axis during embryogenesis?
Formation of the primitive streak
What tissues arise from the ectoderm?
- Epithelium of skin
- Nervous tissue
- Brain and spinal cord
- PNS
What tissues arise from the mesoderm?
- Connective tissue
- Muscle
- Epithelial lining of some organs (cardiovascular, reproductive and urinary systems)
What tissues arise from the endoderm?
- Gastro intestinal tract
- Epithelial linings of respiratory tract, bladder, middle ear and auditory tube
- Parenchymal cells of the liver, pancreas, thyroid and parathyroid
What is a notochord?
Rod shaped aggregate of cells located cranial to the primitive streak, marks future location of the spinal cord
What does the formation of the notochord induce?
Formation of head, nervous system development and somite formation
What extra-embryonic membrane is derived from the trophoblast and the mesoderm?
Chorion and amnion
What is the function of the chorion?
Mediates attachment to the uterus
What extra-embryonic membrane is derived from the endoderm?
Yolk sac
What is the function of the amnion?
Fluid filled sac that protects the embryo
What extra-embryonic membrane is derived form the primitive gut?
Allantois
What is the function of the allantois?
Fluid filled sac that collects waste from the embryo, eventually fuses with chorion to form allantochorionic membrane
What is neurolation?
The initial development of the gut, heart and formation of the nervous system
What are the structures arised from neurolation?
- Neural plate and neural
- Somites
- Neural tube
- Neural crest cells
What do neural crests form?
Peripheral nervous system
What does the neural tube form?
Central nervous system
What does the folding of the endoderm form?
Primitive gut tube
How are placodes formed?
Thickening of ectodermal cells
What do the placodes form?
- Nasal chambers
- Lens
- inner ear (otic)
How are pharyngeal arches formed?
Concurrent invagination of surface ectoderm (clefts) and endoderm (pouches)
What structures arise from paraxial mesoderm?
Somites
What structures arise from intermediate mesoderm?
Urinary and reproductive organs
What structures arise from lateral mesoderm?
Body cavities (pleural, pericardial and peritoneal)
What structures are derived form the somites?
- Dermis
- Axial skeleton
- Skeletal, cardiac and smooth muscle
What is the function of the yolk sac?
Contributes to primitive germ cells
Does cleavage of blastomeres increase the size of the morula?
There is no net increase in size. This is because they are constricted by the zona pellucida
