IMMS - Embryology Flashcards
What are the stages of the early zygote?
1 cell -> 2 cell -> 4 cell -> 8 cell -> 16 cell morula
Define ‘morula’
A solid ball of cells
Division of the morula causes a cavity at one end of the morula. It is now known as the ____?
Blastocyst
What is the cavity that has been created in the morula called?
Blastocoele
What is the blastocyst made up of?
Embryoblast and trophoblast
What does the embryoblast go on to form?
Embryo proper
What dopes the trophoblast go on to form?
Placenta
What is the embryoblast made up of?
Epiblast and hypoblast
What are the epiblast and hypoblast known as?
Bilaminar disc
What cells line the epiblast?
Columnar cells
What cells line the hypoblast?
Cuboidal cells
A new cavity called the ____ forms between the epiblast and trophoblast
Amniotic cavity
What cells migrate to line the amniotic cavity and what are they then known as?
Epiblasts migrate and are known as amnioblasts
What cells migrate to line the inner surface of the trophoblast (blastocoele), and what does this cavity become known as?
Hypoblast cells migrate. The cavity is then known as the primitive yolk sac
How does the embryo initially receive nutrition?
By diffusion from the fluid it is travelling in
Which part of the structure initially grows fastest?
The ‘placenta’
What layers does the trophoblast develop into?
Outer syncytiotrophoblast and inner inner cytotrophoblast
What are lacunae?
Spaces in the outer syncytiotrophoblast which form a lacunar network
How is the primitive utero-placental circulation set up?
The outer syncytiotrophoblast erodes maternal sinuses, allowing maternal blood to enter the lacunar network
What is the extraembryonic mesoderm?
A new layer of cells which develops between the cytotrophoblast and primitive yolk sac
What happens to the extraembryonic mesoderm?
Spaces begin forming in it until they fuse together to form a cavity called the extraembryonic coelem (or chorionic cavity)
What lines the extraembryonic coelem/chorionic cavity?
The chorionic plate
What happens at around day 13 when part of the yolk sac is pinched off?
The remnant is the secondary yolk sac. An exocolemic cyst is also formed which is eventually eliminated
The bilaminar disc also becomes joined to the ___ by the ___ which is the future ___
trophoblast, connecting stalk, umbilical cord
What is gastrulation?
The rearrangement of cells in the bilaminar disc to form the trilaminar disc
Briefly describe gastrulation
1) The primitive streak occurs along the caudal midline.
2) It expands towards the cranial end to form a primitive node with a circular depression called the primitive pit. The depression continues along the streak, forming the primitive groove.
3) Once the primitive streak is formed, cells of the epiblast migrate inwards, detach from the epiblast layer and slip into the gap between epiblast and hypoblast. The process is called invagination.
4) Invagination disrupts hypoblast cells until they are all replaced by a new layer called the endoderm.
5) Remaining cells of the epiblast are now the ectoderm, and some cells that remain in between epiblast and hypoblast layers form the mesoderm.
What does the endoderm go on to differentiate into?
A tube forms in the endoderm, then flattens into the notochordal plate, then folds back into the notochord.
What does the ectoderm go on to differentiate into?
Neuralation occurs. Tissue in the ectoderm thicken to form the neural plate, with two neural plate borders separating it from the ectoderm. The borders then fold towards each other, forming the neural crest. Eventually, they join and close to form the neural tube.
What does the mesoderm go on to differentiate into?
Paraxial mesoderm, intermediate mesoderm and lateral mesoderm.
What happens during the 4th week of development?
Embryonic folding in two planes - lateral and cephalic to caudal.
What is embryonic folding a result of?
Differing rates of growth within the embryo
What final structures does the ectoderm develop into?
Epidermis of skin, hair, nails, lens of eye, pituitary, mammary, sweat and sebaceous glands, CNS, PNS, enamel of teeth and sensory epithelia of nose, ear and eye
What final structures does the paraxial mesoderm develop into?
Somites:
- Myotome: Muscle tissue.
- Scleratome: Bone and cartilage.
- Desmotome: Dermis of skin
What final structures does the intermediate mesoderm develop into?
Urogenital system: kidneys, gonads, and their respective ducts
What final structures does the lateral mesoderm develop into?
Somatic (parietal) layer: Future body walls
Splanchnic (visceral): Circulatory system, connective tissue for glands, muscle, connective tissue and peritoneal components of gut wall
What final structures does the endoderm develop into?
Epithelial lining of GI, respiratory and urinary tract, parenchyma of thyroid gland, parathyroid gland, liver and pancreas, epithelial lining of tympanic cavity and auditory tube.
