Embryology Flashcards
Define Embryology
Study of the origin and development of an organism
How long is the “fetal” age?
38 weeks
How long is the “gestational” age?
40 weeks
How long and what defines the “embryonic” period?
First 8 weeks
All major organs formed
How long and what defines the “fetal” period?
Remaining 30 weeks
Organs grow larger and increase in complexity
Define Ovulation
Egg released into the peritoneal cavity
Define Fertilization
Occurs as egg travels down the fallopian tube
Define Zygote
The cell that forms when the ova and sperm fuse
Define Cell Division
Begins immediately as the zygote travels down the fallopian tube and into the uterus
What occurs during the first week after conception?
Zygote divides repeatedly
Daughter cells = blastomeres
Morula
Blastocyst
Define Morula
Solid cluster of 12-16 blastomeres at about 72 hours
When occurs on day 4 post conception?
Morula enters uterus and takes up fluid becoming a blastocyst
Types of Cells in the Blastocyst Stage
Inner cell mass
Trophoblast
Define Inner Cell Mass
Forms the embryo
Define Trophoblast
Layers of cells surrounding the cavity which helps form the placenta
What occurs on day 6 post conception?
Implantation of the zygote
What occurs during implantation?
Tropholast erodes uterine wall
Three Primary Germ Layers
Ectoderm
Endoderm
Mesoderm
The ectoderm and endoderm form what?
Sheets of epithelial tissue
The mesoderm forms what?
Mesenchyme tissue
Define Gastrulation
Invagination of epiblast cells
When does the endoderm form?
Days 14-15
When does the mesoderm form?
Day 16
What occurs during days 16-18?
Epiblast cells invaginate
Migrate anteriorly with endoderm cells
Rod defining body axis formed
Notochord is future site of vertebral column