Bilaminar Disk
The Epiblast and hypoblast. Derived from the embryoblast. This will later become the trilaminar disk with the formation of the primitive streak.
Germ Layer
A layer from which other developed tissues originated from
Ectoderm
The outermost layer of cells giving rise to the epidermis and nerve tissue
Endoderm
The innermost layer of cells giving rise to the gut lining
Doral Surface
The outermost surface during early development
Ventral Surface
The innermost surface during early development
Mesoderm
The middle germ layer giving rise to muscle, bone and more
Primitive Streak definition + role
A narrow groove that develops on the dorsal surface of the Epiblast. It has an important role in the orientation of the embryo, determining the front and the back.
Gastrulation
The reorganisation of the germ layers into the ectoderm, mesoderm and endoderm and hence establishing the origin of all tissues.
Trilaminar disc
The three germ layers. Ectoderm, mesoderm and endoderm.
Name 3 ectodermal derivatives
Skin, Skin derivatives (hair, nails, leans and cornea of eye, mouth annd anus lining), brain and spinal cord, peripheral nerves, Retina and iris of eye (Outside and nervous system)
Name 3 mesodermal derivatives
Smooth, skeletal and cardiac muscle Connective tissue Bone Cartilage Blood and blood vessels Urinary system (Muscle, Skeletal and Urinirary system)
Name three endodermal derivatives
Lining of the digestive tract Glands associates with digestion (E.g. liver, pancreas) Other gut derivates (E.g. lungs) (Gut and lungs)
Why are weeks 3-8 the most perilous for a developing child?
Period of greatest change, when all major structures and systems are formed
Why is week three called “the week of threes”?
Three cavities (at end of week 2), amniotic, yolk and chorionic. Three “germ layers” - Mesoderm, ectoderm and endoderm
What are two ways via which cell rearrangement occurs?
Migration and invagination
What happens to the primitive streak as gastrulation proceeds?
It regresses
In which direction does development proceed?
Cranial/Rostral to caudal (Front of head to back of head)
What do Anterior and Posterior refer to in normal language?
Anterior -front
Posterior - Back
What do dorsal and ventral refer to in plan English?
Dorsal - Top Ventral - Bottom
What are the two processes shown here called?
Migration and invagination
Name layers A, B and C
A - Ectoderm B - Mesoderm C - Endoderm
What do cells on epiblast move towards?
The primitive streak
What do the ectoderm, mesoderm and endoderm form?
The trilaminar disc
