Introduction To Embryology Flashcards
What is embryology?
The study of the development of embryos
Fertilisation is…
The fusion of the ovum and sperm.
What is formed initially after fertilisation?
Firstly a morula is formed which is free in the uterus.
Then a blastocyst forms. The inner cell mast of this becomes the embryo and the trophoblast becomes the placenta.
At about day 8 the embryo…
The trophoblast grows into uterus and forms the placenta.
The ectoderm forms and so does the endoderm
What day does the embryo become implanted?
About day 9
What is the bilaminar disc?
The inner cell mast forms two layers the ectoderm and the endoderm.
Cells from the base of the primitive streak break off and migrate to ie between layers of the endo and ectodermderm.
This new layer is called the mesoderm and by day 17 it has almost fully separated the two layers.
Now known as the trilaminar disc.
What is the primitive streak?
Folding that occurs along the caudal midline of the bilaminar disc
What does the ectoderm form?
Epidemics of skin, CNS, PNS, Pituitary gland, enamel of teeth, lens of the eye and pats of the inner ear.
What does the endoderm go and form?
Epithelial lining of the G-I tract, respiratory tract and urinary bladder.
Liver, pancreas
Epithelial lining of the tympanic cavity and auditory tube.
What does the endoderm form?
All of the musculoskeletal system Deep layers of the skin Abdominal and chest wall lining Urogenital system Bone Cartilage
What is the notochord?
A tube develops from the primitive streak and extends towards the cranial end.
Fuses with the endoderm t become a groove that folds and become a tube again = notochord.
It is responsible for the developments of the midline - it does this by releasing chemicals
Overview of the development of the ectoderm:
- Neural plate forms from the ectoderm separated by neural plate border
- plate bends forming a neural crest with the two ectoderm layers coming together
- These layers join and the neural tube disconnects. The Neural crest will go on to from PNS
- The mesoderm layer will now develop around the neural tube and the endoderm starts to from the skin.
What happens if the fusion of the ectoderm does not fully take place
The child will be born with spinal bifida
What do somites become in an embryo
They become the myotomes — muscle
Differentiation of the mesoderm:
Into intermediate mesoderm
Forms urogential system
Lateral mesoderm
Outer layer is known as parietal layer mesoderm and it covers the inside of the chest and abdominal walls
Second type is the visceral layer and it covers the organs in the thorax and abdomen
Paraxial mesoderm
Forms the somites, which form myotome, sclerotome, dermatome
