Embryology Flashcards
The first stage in the development of a fetus
fertilisation the process by which the male sperm and female egg join together.
Approximately _______ hours after fertilizations, the fertilized oocyte (egg) splits into two cells of equal size; called _________.
thirty; blastomeres
After three more divisions, there are 16 cells. At this point, the group of cells is referred to as the ______.
morula
Within the first week, the cells of the morula reorganize to form a cavity, known as the ______.
blastocyst cavity (blastocoel).
the blastocyst is comprised of two different cell types:
Outer cell mass (trophoblast) Inner cell mass (embryoblast)
contacts with the endometrium of the uterus to facilitate implantation and the formation of the placenta
Outer cell mass (trophoblast)
responsible for the formation of the embryo itself
Inner cell mass (embryoblast)
The trophoblast divides into the _______ and ______
syncytiotrophoblast and cytotrophoblast.
The embryoblast divides into the ______ and ______.
epiblast and hypoblast , forming a two-layered structure; the bilaminar disk.
The amniotic cavity forms within
the epiblast
Initial Cellular Divisions
After the initial rounds of cellular divisions, the embryo must implant into the __________
endometrium of the uterus
During this process, the syncytiotrophoblast becomes continuous with the uterus – such that maternal blood vessels (known as sinusoids) invade the spaces within the syncytiotrophoblast (known as lacunae).
Implantation
In___________, implantation of the embryo occurs in the lower uterine segment (instead of in the normal position of the upper posterior uterine wall).
placenta praevia
A low-lying placenta is more susceptible to
haemorrhage
In the 3rd week of embryonic development, the cells of the bilaminar disk (epiblast and hypoblast) undergo a highly specialised process called
gastrulation
a process of cellular rearrangement which involves migration, invagination and differentiation of the epiblast.
Gastrulation
a groove in the midline of the epiblast which appears during the third week
The primitive streak
Within the primitive streak lies a ________ at the cranial end, and within that lies the ________ .
primitive node; primitive pit
Cells of the epiblast layer break off and migrate toward the __________
primitive pit
three germ cell layers:
Endoderm
Mesoderm
Ectoderm
formed by epiblast cells that migrate through the primitive pit and displace the hypoblast cells.
Endoderm
formed by epiblast cells that migrate through the primitive pit and lie between the epiblast layer and the newly created endoderm.
Mesoderm
formed by the epiblast cells that remain in position
Ectoderm
Formation of the three primary germ layers
Structures derived from the endoderm
- Epithelial lining of digestive and respiratory tracts
- Lining of urethra, bladder and reproductive System
- Liver and pancreas
Structures derived from the mesoderm
- Notochord
- Musculosketal system
- Muscular layer of stomach, intestine etc
- Circulatory system
Structures derived from the ectoderm
- Epidermis of skin
- Cornea and lens of eye
- Nervous system
