Integration of information- embryology Flashcards
What forms when the blastocyst implants?
Syncytiotrophoblast
What does the embryo consist of?
A bilaminar disc (epiblast and hypoblast)
- it’s a circular disc
In terms of embryonic development, what has developed by day 15/16?
Formulation of a trilaminar disc via gastrulation- it is now elongated in the anterior/posterior direction
Buccopharyngeal membrane begins to develop
Towards the tail of the embryo, there is a primitive streak which is a cleft between the cells in the epiblast layer
What is the result of gastrulation?
3-layered embryo which gives rise to three germ types- mesoderm, ectoderm and endoderm
What moves through the primitive streak?
Cells from the epiblast- they move through the primitive streak into a gap that’s opened up between the epiblast and hypoblast
What happens when cells from epiblast move through primitive streak?
They undergo differentiation to form mesoderm cells
There are multiple layers of cells moving, implying there’s proliferation in the epiblast before they move into the streak.
What does ectoderm give rise to?
Skin and CNS
What does the mesoderm give rise to?
Skeleton, muscle, kidney, heart and blood
What does the endoderm give rise to?
Gut, liver and lungs
How has the embryonic disc grown by day 21?
The embryo has elongated a lot and there is differentiation of the mesodermal cells between the primitive node and the buccopharyngeal membrane to form the notochord
What does the notochord go on to develop in simple organism and also most vertebrates?
In simplest organisms, the notochord is the CNS but in most other vertebrates, the notochord directs the formation of the CNS
When does formation of CNS begin?
Around day 17
What does the ectoderm undergo differentiation to form?
Neural cells
What does the neural plate do after it has expanded?
It begins to fold at around day 21- there is a cleft in the middle of the neural plate which occurs above the notochord
What effect does the notochord have on near cells?
It stops the change of cells- they stop proliferating/differentiating- To hold base of the to-be-neural tube in place
What is cell activity like in the neural folds?
There’s movement and differentiation of cells which are becoming prominent over next few days
When do neural folds stop expanding?
When they meet each other to form the tube above the notochord- this becomes the CNS
Around day 19, what is the mesoderm doing?
The mesoderm is continuing to proliferate rapidly while neural folds are developing as it will form the major components of the body (trunk, muscles, bones etc)
How does the amnion change?
The amnion initially lies mainly over the embryo but around day 19, the amnion seems to have a more rounded structure surrounding the embryo at the top
By day 21, most of the embryo is within the amniotic cavity
How do the changes in the amnion occur?
The amnion moves down and around the embryo and the embryo also moves upwards
What is the yolk sac connected to?
Digestive system as it provides nutrients
How important is the yolk sac in humans?
Not vital as it’s not only source of nutrients
What happens at day 28, in terms of amniotic cavity?
It completely surrounds the embryo
What happens to the yolk sac at day 28?
It doesn’t get cut off but it is believed that the amnion fuses around the yolk sac
What is found where the amnion fuses around the yolk sac?
It leaves a defect and this is the same place where the umbilical cord os found
In terms of neurulation, what happens around day 22?
From the middle of the embryo, the neural tube begins to zip up- ~day 23, there is still an anterior and posterior neuropore but these close over next week.
What develops at this stage near the anterior neuropore?
Brain development
What can be seen in the neural tube when it has zipped up?
The pericardial bulge- the heart develops here
What happens to the embryo around day 25-28?
It begins to curve in a head to tail direction
What begins to develop around the base of the mesoderm at around day 25?
Kidney and reproductive system
What begins to develop around the top of the mesoderm at around day 25?
The heart
What stage of development is the embryo at by day 28?
The curve is clear cut
There’s a heart bulge, the lens of the eyes are beginning to develop, the otic placode where the ears will develop; the pharyngeal arches are developing where the vasculature begins, the limb ridges are also visible. Clearly visible tail
Where does the angiogenic cell cluster which gives rise to vasculature begin?
Slightly outside the embryo
What brings the angiogenic cell cluster into the body cavity of the embryo?
Folding of the head
What does the folding of the tail bring into the body cavity?
The cloacal membrane which gives rise to kidneys and reproductive system- connecting stalk and yolk sac enter the body cavity at the same site
Where are the primitive blood vessels which give rise to endocardial tubes located?
On the side of the embryo
What controls development?
All the processes are controlled by signals from genes- complex gene interactions occur throughout development to form a foetus
What are the Hox genes involved in?
Establishing: - A-P axis - Differences in vertebrae - CNS divisions - Pattern the limbs It is involved in patterning (how cells relate to one another)
Why is a women’s diet important in development?
One of the signals that controls the activation of Hox genes is retinoic acid, a derivative of vitamin A- so without vitamin A, Hox genes may not function properly
When do the forelimb and hindlimb buds appear?
Forelimb ~day27/28
Hindlimb ~day 29
Describe hand development
Day 32- Flipper-like upper limb buds develop
Day 35- hand plate forms
Day 44- Digits begin to appear in the hand plate
Day 45- Upper limbs bend at the elbow and the fingers are short and webbed
Day 55- Fingers and toes are distinct and separated
When does apoptosis occur in limb development?
When the webbing between the fingers disappears
What are the two main genes that regulate limb development?
Fibroblast-like growth factor-8- Growth factor produced at the end of the developing limb
Sonic hedgehog- Determines the overall structure of the limb that is developing
What effect did thalidomide have on limb development?
Variably affected both sets of limbs but mainly upper limbs
Which gender were affected more by thalidomide?
Boys
What effect does fgf-10 have normally?
It normally has an effect in developing vasculature to the developing limb to provide nutrition
How does thalidomide have an effect on limb development?
The active form hinders blood vessel development- there’s a varying degree of cell death and limb development is prevented. Upper limbs are more susceptible to damage
What does long term and short term exposure to thalidomide lead to?
Long exposure- widespread cell death and all signalling/cells lost
Short exposure- Uniform cell death and only partial loss of signalling
When was thalidomide usually taken?
Around 8 weeks PF when morning sickness was worst- this is a vital stage of limb development
What is thalidomide commonly used to treat nowadays?
Leprosy especially in developing countries
What is achondroplasia?
Form of dwarfism where long bones don’t develop properly
What causes achondroplasia?
Loss of function mutation in fibroblast growth factor receptor 3 which is usually involved in development and particularly elongation of bones
