Embrology 2 Flashcards
When is the embryonic development period?
Weeks 3-8 (inclusive) of a pregnancy
What are some key features of the embryonic period?
The period of greatest change
All major structures and systems formed
Greatest risk of major congenital malformation - due to environ exposure or drugs
How does drug therapy effect a growing baby through the difff stages of development?
In pre-embryonic stage- lethal effects- loose pregnancy
In embryonic stage- very sensitive-significant/catastrophic effect
In feral stage- less sensitive but can still cause damage
After embryonic period risk of a structure defect is lowered except for CNS which is still very sensitive to alcohol etc
What is the result of early embryonic development and what does this involve?
Result= foundations laid for development of body systems
Means sufficient cell number of the right type in the right place
List the key events/processes in early development. Why is each stage so key to the next?
Fertilisation & implantation Gastrulation Neurulation Segmentation Folding
All so key ad each step depends on the preceding step being completed successfully
What marks the start of gastrulation?
At the end of the 2nd week the epiblast is a uniform disk. After Gastrolation a new feature the “primitive streak” appears on the dorsal surface of the epiblast
What happens during gastrulation?
Cells in the epiblast layer divide and migrate upwards into the epiblast layer. The hypoblast is displaced and a 3rd layer is created.
What is the structure created after gastrulation?
A triluminar disc made up of an ectoderm (becomes outside of foetus), a mesoderm (is middle), and an endoderm (becomes inside of foetus).
All 3 are derived from the epiblast layer.
What does the ectoderm go on to become?
The organs and structures that maintain contact with the outside world
Eg nervous system, skins epidermis
What does the Mesoderm go on to form?
Supporting tissues
Eg muscle, cartilage, bone and vascular system (inc heart and vessels)
What does the endoderm go on to form?
The internal structures
Eg GI tract’s epithelial lining, respiratory tract and parenchyma of glands
What is situs inverses? What are the complications if any?
It’s when the viscera is a complete mirror image of what it should be.
Commonly results from immobile cilia spring embryogenesis
No usual associated morbidity
Problems arise if there is both normal and mirror-image present
How is left-right asymmetry achieved?
On the node of the streak there are cilated cells. The action of these results in left-ward flow of signalling molecules. This causes side-specific signalling to cascade.
IE on left hand side any signalling molecules arrive
Lack of signals on right side is a signal within itself
Summarise when, what, how and why for Gastrulation.
When-3rd wee of development (starts embryonic period)
What-bilaminar disk becomes trilaminar disk with 3 germ layers
How-primitive streak forms leading to migration & invagination of cells
Why-to ensure correct placement or precursor tissues to allow subsequent morph oh genesis to take place
What is a Notochord?
A solid rod of cells running in the midline with an key signaling role.
It directs conversion of overlying ectoderm to Neuroectoderm.
(Receptors for this on ectoderm only not endoderm)
