Lecture 3 - Embryology Flashcards
Embryo
Beginning of 4th week to end of 8th week (2nd month)
Fetus
3rd month to birth
Ovulation
A secondary oocyte is released from the ovary and swept into the oviduct
Fertilisation
A single sperm penetrates the secondary oocyte. The sperm and egg nuclei will fuse, resulting in a fertilised egg/zygote.
Cleavage
Zygote undergoes rapid mitotic division as it moves along the oviduct towards to the uterus. (16 cells)
Morula
By day 4, successive division produces a cluster of 16 cells called Morula and enters cavity of uterus.
Blastocysts (overview)
Morula is filled with fluid and forms blastocyst. Zona pellucida degenerates and blastocyst hatches into uterine walls
Implantation
Blastocyst attached to uterine lining (endometrium) and begins to digest it’s way inwards.
What are the two types of cells in a blastocyst?
Blastocyst has two types of cells: outer epithelial layer (trophoblast) and inner cell mass
What does the trophoblast form?
It forms some extra embryonic structures (ex: parts of placenta)
What happens to the inner cell mass in the late blastocyst?
The inner cell mass start to differentiate into a bilaminar embryonic disc composed of two cell layers; hypoblast (primitive endoderm) and epiblast
Gastrula
After bilaminar disc has formed, cavity appears called the amniotic cavity (from epiblast). Cells of hypoblast migrates, forming the yolk sac.
Egg/Zygote
Fertilisation to end of 3rd week
How long does it take to form 1 somite pair?
40 minutes
Gastrulaton
The bilaminar embryonic disc differentiates to form 3 germ layers.
- a line thickens along the midline in the epiblast (at caudal end) of the disc (primitive streak -invagination)
Invagination
Cells of epiblast migrates inwards toward streak, detaches from epiblast and slips beneath it into interior of embryo.
- cells in interior become mesoderm, cells remaining from epiblast become ectoderm
Neurulation
Neural plate forms at cranial end (thickens) of embryo and grows from the cranial to caudal
- formation of notochord (derived from mesoderm)
Notochord
Somites form with the notochord
Neural tube
Neural plate forms a grove into the mesoderm to form a tube.
- formation of tube begins in middle and extend out in both cranial and caudal ends
- some cells from the neural fold detach to form new population of cells call neural crest
What does the neural crest become?
It forms the peripheral nervous system
Which planes does the trilaminar disc fold?
The horizontal and median plane
The folding in a horizontal plane for what type of body folds?
It forms 2 lateral body folds
How does the rotation of the cilia determine the left and right sides of the embryo?
The rotation of the cilia causes the flow of fluids to migrate to the left more than the right. The side with the larger amount of fluid becomes the left side of the embryo.
What does the folding in the median plane create?
The plane forms at the cranial and caudal ends. The folding causes the endoderm to move inwards to form the gut tube.
