(11) EMBRYOLOGY SESSION 2 - WEEK 3 Flashcards
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)
What is B?
Amniotic Cavity
What is C?
Yolk sac
What is D?
Connecting stalk
What is E?
Chorionic Cavity
What is A?
Embryo, made up of epiblast and hypoblast
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 is A?
Primitive node, located at cranial end of streak
What is B?
Primitive pit, located at center of node
What is C?
Primitive streak
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
What do the two holes left in the mesoderm later form?
Future mouth and future anus
What does the fate of invaginating epiblast cells depend on?
Where in the primitive streak or node they invaginate in the formation of the mesoderm.
What is the black dot in the center of the diagram, and what do it drive the formation of?
The notochord, drives the formation of the nervous system
What is the notochord also the basis for?
The axial skeleton
How is the notochord formed?
Prenotochordal cells of epiblast migrate through cranial part of primitive pit
What happens to notochord in adults?
It regresses
What does the primitive streak define in development?
What is “front” and what is “back”
Name A, B, C and D
A - Superior
B - Inferior
C - Posterior
D - Anterior
What ensures correct orientation of embryo?
Molecular signals emanating from the primitive node
Which way does development occur?
Head to tail
When is gastrulation complete in the caudal region?
Week 4
