Weeks 2-8 Flashcards
What does the dorsal side of the body refer to?
The back.
What plane divides the body into right and left halves?
Median plane.
What is the function of the coronal plane?
It divides the body into anterior (ventral) and posterior (dorsal) parts.
When does the blastocyst embed into the uterine lining?
Begins at day 7.
Name the two layers of the trophoblast.
Cytotrophoblast (inner layer) and syncytiotrophoblast (outer layer).
What hormone does the syncytiotrophoblast produce?
Human chorionic gonadotrophin (hCG).
By which day is the blastocyst fully embedded in the endometrium?
By day 10.
What are primary chorionic villi?
Structures that develop on days 13–14 and are part of the placental tissues.
What marks the beginning of secondary chorionic villus development?
Mesodermal cells penetrate the core of primary villi at the start of week 3.
What are the two layers of the inner cell mass?
Hypoblast (adjacent to the blastocyst cavity) and epiblast (adjacent to the amniotic cavity).
What structure forms the floor of the amniotic cavity?
The epiblast.
What happens to the primary yolk sac during embryogenesis?
It decreases in size as the secondary yolk sac forms.
What is the role of the extraembryonic somatic mesoderm?
It lines the trophoblast and covers the amnion, forming the chorion.
When does gastrulation occur?
During the third week of development.
What germ layers are formed during gastrulation?
MEE
Mesoderm
Ectoderm
Endoderm
What does the ectoderm give rise to? REN
Retina
Epidermis
Nervous system
What does the mesoderm give rise to? CBSS
Connective tissues
Blood vessels
Smooth muscle
Skeletal structures.
What does the endoderm give rise to?
Epithelial linings of the respiratory and gastrointestinal tracts.
What is the primitive streak?
A narrow groove that appears on days 15–16, signaling the site of mesoderm formation.
What can a remnant of the primitive streak lead to?
Sacrococcygeal teratoma.
What is the notochord?
A structure that serves as the basis for the axial skeleton and induces the formation of the neural plate.
What happens to the notochordal canal during its development?
It fuses with the endoderm, allowing communication with the yolk sac.
What does the allantois become as the bladder enlarges?
The urachus.
What are the blood vessels of the allantois associated with?
Umbilical arteries and vein.
What is ectopic pregnancy?
Implantation of the blastocyst outside the uterine cavity, commonly in the fallopian tube.
What is the incidence of ectopic pregnancies?
Varies from 1:80 to 1:250 pregnancies.
What is the main cause of embryo loss during the first three weeks?
Abnormal conceptuses or chromosomal abnormalities.
What is embryonic folding?
A process where the flat embryonic disc transforms into a cylindrical embryo.
What is the significance of the prechordal plate?
It marks where the ectoderm and endoderm meet and contributes to head development.
What are Carnegie stages?
Stages of embryonic development based on clinical features rather than size or age.
At what stage does the notochordal process develop?
Stage 8, around days 19–21.
What is the function of the neural plate?
It gives rise to the brain and spinal cord.
What triggers the development of the neural plate?
Induction by the notochord.
What is the main role of the syncytiotrophoblast?
To erode maternal tissues for implantation and produce hCG.
When does the secondary yolk sac form?
After the primary yolk sac reduces in size.
What defines the boundaries of the embryonic disk?
The epiblast and hypoblast layers.
What are intravillous spaces?
Cavities in the chorion filled with maternal blood for nutrient exchange.
When does the embryo first establish a connection to the placenta?
By the end of the third week, with the formation of blood vessels in chorionic villi.
What are the main contributors to maternal-placental abnormalities?
Adhesions, scarring, or infections delaying zygote transport.
What determines the differentiation of the embryonic germ layers?
Continuous migration of cells from the primitive streak.
