2 Embryology Flashcards
Pre-embryonic period
Weeks 1-2. Development through implantation.
Embryonic period
Weeks 3-8. Through embryonic development, neurulation, and organogenesis.
Fetal period
Week 9-38. Development post embryonic organization of body.
Zygote
Unified male and female gametes. Diploid.
Morula
16 cell mass post fertilization and cleavage.
Blastocyst
c. 100 cels. Divided into two structures, embryoblast and trophoblast.
Trophoblast
Outer cellular layer forming fetal half of placenta. Divides into two layers during the process of implantation, cytotrophoblast and syncytiotrophoblast, which help form the chorion.
Chorion
Cellular structure formed from the syncytiotrophoblast and cytotrophoblast which develops into the fetal half of placenta.
Cytotrophoblast
Derivative of trophoblast. Helps form the chorion which eventually becomes the placenta. Eventually forms inner layer of chorion, totally surrounding embryoblast and eventually epiblast/hypoblast.
Syncytiotrophoblast
Derivative of trophoblast which forms outer layer of chorion. Directly in contact with the uterine wall. Surrounds cytotrophoblast.
Inner cell mass
Embryoblast
What two layers does the embryoblast divide into?
Epiblast and hypoblast.
What does the epiblast become?
Embryo and amnion
What does hypoblast become?
Yolk sack
What are epiblast and hypoblast together called?
Bilaminar disk
On what side of the bilaminar disk and in what layer does the primitive streak form?
Dorsal side of epiblast. i.e. the side away from the hypoblast, towards antrum of uterus.
What happens at the primitive streak?
Gatrulation
What is Gastrulation?
Movement of cells from epiblast into space between epiblast and hypoblast, forming three primary germ layers.
Three primary germ layers from dorsal to ventral:
Ectoderm, mesoderm, endoderm.
What structures derive from the ectoderm?
Integumentary and nervous tissue
What structures derive from the mesoderm?
Everything not derived from ectoderm and endoderm, e.g. Heart, mucle, kidneys, reproductive organs, connective tissue
What structure induces neurulation and where does it form?
Notochord. In the mesoderm deep to and parallel with the primitive streak.
Where does the nueural tube form? What process forms it?
The neural tube forms superficial to and parallel with the primitive streak in the ectoderm, first as neural plate, then neural groove, then closing into neural tube. Induction.
What are the two types of folding that occur in embryonic development?
Transverse folding where sides parallel with the primitive streak curl ventrally enfolding the endoderm and creating a central canal. cephalocaudal folding where peak and tail of embryo curl toward each other.
How long is the embryo at week 8 and beginning of fetal period? What organ systems haven developed?
1 inch long. Most organ systems have developed.
What is the earliest babies can survive?
As early as 30 weeks without medical interventions. Early as 22 with medical tech.
What percentage of babies is born with a serious birth defect? Of these, what percentage of defects have a known cause?
3/100 or 3% of children. Only fifty percent have a known etiology.
What is a teratogen?
Anything that causes a birth defect.
What is the most common
Teratogen? What syndrome does it cause and what are its symptoms?
Alcohol. It causes fetal alcohol syndrome which is characterized by growth retardation, heart defects, microcephally, and is the leading cause of mental retardation.
What percentage of babies born to mothers taking accurate have birth defects?
25% physical defects. 50% are mentally disabled.
What does the epiblast form?
Amnion and embryo.
What does the hypoblast form?
Yolk sac
