Embryology Flashcards
From when till when is the pregnancy considered an embryo?
Week 3 - week 8
From what point is the pregnancy classified as a foetus?
Week 9 and onwards
Name the process that happens during the embryonic period.
Organogenesis
What is the definition of embryology?
The study of initial development of an embryo
All organ systems are developed (rudimentary forms) by what week?
Week 8
What period follows the embryonic period?
The foetal period
After fertilisation of the egg cell what can we call the new cell?
A zygote
What is the name given to the division of the early embryo?
Cleavage
After three days of cleavage of the zygote what is the embryo now referred to as?
A morula
By day four what is the embryo referred to as?
A blastocoele has developed and the embryo is now seen as a blastocyst
At day five what is the name given to the embryo?
An embryoblast
Which cells will form the placenta?
Trophoblast cells
They are the outer ring of cells
Where does gastrulation occur?
The germinal disc
What is gastrulation?
The generation of three germ layers which derive all embryonic structures.
What happens during days 6/7?
Hatching occurs from the zona pellucida
What happens during days 8/9?
Blastocyst implantation
How is the amniotic cavity and yolk sac formed?
Hypoblast and epiblast cells divide, growing two lumens
What is the bilaminar germinal disc?
The interface of two cell types
It becomes the foetus
In what direction does gastrulation occur?
Along the primitive streak in a caudal to cranial orientation
What are the three germ layers?
Ectoderm (epiblast)
Mesoderm
Endoderm (hypoblast)
Is the yolk sac in mammals important?
It serves some function but is not as important in mammals as it is for species who lay eggs whose offspring do not have a placenta attached to the mother
What is the ectoderm responsible for forming?
Epidermis of the skin
Nervous system
Sensory receptors of epidermis
Epithelial lining of mouth and anus
What structures is the mesoderm responsible for forming?
The notochord
Skeletal muscle
Muscular layer of the stomach and intestines
Circulatory and lymphatic systems
Reproductive systems
Dermis if skin
What structures is the endoderm responsible for forming?
Epithelial lining of the digestive tract and the respiratory system
Lining of the urethra, urinary and reproductive systems
Liver
Pancreas
Thyroid and parathyroid glands
Why is the notochord important?
In vertebrates it’s transient and organises surrounding tissues and provides structural support.
What did the notochord regulate?
Left/ right asymmetry
Arterial/ venous identity in major vessels
Aids in specification of forming somites
Describe how the neural tube is formed.
The notochord will influence the tissue above it to develop into the neural tube, the tube is pinched off and is a true tube now, while the mesoderm not influenced by the notochord will develop into skin.
How are the neural groove and neural folds formed?
Uneven proliferation
What are neuro pores? Where are they?
The openings of the neural tube, there are cranial and caudal neuro pores which are the last areas of the neural tube to close.
What is a morphogen and what does it do?
It is a growth factor and it influences cells to change their activity,
It can be very potent, depending on its concentration gradient (if low if can influence one way, if high it may influence a different way)
How do different morphogen interact with each other?
They can influence the cells differently to how would have done separately
They not act complimentary, they may compete or cancel each other out
What is cell competence?
Whether the cell can react properly to the signal and influence being expressed on it
What is Sonic Hedgehog factor?
It is a very powerful morphogen released by the notochord to induce the neural plate
Changes ectodermal tissue into neural tissues
What other morphogen work with SHH?
Chordin and noggin
These are expressed in the node at the cranial end of the primitive streak
What does it mean to set the midline of the embryo?
Morphogens are key for this as they help to determine dorsal/ ventral and left/ right axes bit of which are required for future brain segmentation
What are neural crest cells?
These are neural tissue cells that can migrate from the CNS to the rest of the embryo which can give rise to the adrenal medulla and melanocytes
Defect can occur due to lack of migration or folding of crest cells
Where are neural crest cells found?
They detach from the neural folds and sit dorsal to the roof plate of the neural tube
