Embryology Lecture 2 - Early Embryonic Development 2 Flashcards
What constituates the Bilaminar disk?
What is it derived from?
What will it later become?
The Epiblast and Hypoblast.
Derived from the embryoblast.
This will later become the trilaminar disk.
What is a germ layer?
A layer from which other developed tissues will arise
What is the ectoderm?
Where is it located?
The outermost layer of cells on the dorsal face of the trilaminar disk
What tissues are derived from the Ectoderm?
Skin
Skin derivatives (hair, nails, lens and cornea, mouth and anal lining)
Brain and spinal cord
Peripheral nerves
Retina and Iris
What is the Mesoderm?
Where is it located?
The middle layer of cells in the trilaminar disk
What tissues are derived from the Mesoderm?
Smooth, skeletal and cardiac muscle
Connective tissue
Bone
Cartilage
Vasculature and Heart
Blood
Urinary system
What is the Endoderm?
Where is it located?
Innermost layer of cell on the ventral face of the trilaminar disk
What tissues are derived from the Endoderm?
Lining of the GI tract
Glands associated with the GI tract (E.g. Liver, pancreas)
Other gut derivatives (E.g. Lungs)
What is the primitive streak?
Why is it important?
A narrow groove that develops on the dorsal surface of the epiblast.
Has an important role in the orientation of the embryo (determining the front and back)
What is the trilaminar disk?
The three germ layers, ectoderm, mesoderm and endoderm
Give a very brief description of the embryonic period of development (3-8 weeks)
Period of greatest change
All major structures and systems formed
Most perilous for the developing child
What 3 cavities are established around the embryo at the start of week 3 of development?
Amniotic cavity immediately dorsal
Yolk sac immediately ventral
Chorionic cavity surrounding
What is gastrulation?
What does it achieve?
The process establishing the three germ layers
Trilaminar disk is formed and axes observed in an adult are set
What three axes are set by the process of gastrulation?
Rostral/Caudal
Dorsal/ventral
Medial/Lateral
How does gastrulation start?
With the appearance of the primitive streak, node and pit
After the appearance of the primitive streak, what are the two processes that constitute gastrulation?
Migration
Invagination
When and where does the primitive streak form?
Describe the appearance of the primitive streak and associated structures
In the third week of development the primitive streak appears on the dorsal surface of the epiblast
The streak is a narrow groove with bulging edges
Primitive node located at the cranial end of the streak
Primitive pit located at the centre of the node
What happens to the primitive streak after it has formed?
It regresses (disappears)
In which direction does development of the trilaminar disk occur?
Cranial/rostral to caudal
Describe the migration and invagination processes
Cells on the epiblast migrate towards the primitive streak
They then invaginate into the epiblast and displace the hypoblast, this creates the 3 layers of the trilaminar disk
As more cell migrate through the streak they spreak laterally and cephalad (cranially/rostrally)
Mesoderm spreads out between the ectoderm and the endoderm like a sandwich filling leaving two gaps/holes
Cephalad gap corresponds to the mouth
Caudal gap corresponds to the anus
What is the significance of the site of any particular epiblast cell’s invagination?
Fate of the invaginating epiblast depends on location of invagination
What is the significance of the notochord?
Notochord defines the phylum ‘Chordata’
It’s the basis for the axial skeleton/axial skeleton forms around it
It drives the formation of the nervous system (neurulation)
Has an important signalling role
Describe the formation and location of the notochord
Prenotochordal cells of the epiblast migrate through the cranial part of the primitive pit
Forms a solid rod of cells running in the midline of the mesoderm along the same axis as the primitive streak
After the notochord has performed its function, what happens to it?
It regresses (disappears)
Vestigial remnants in an adult is the nucleus pulposus if the intervertebral disks
