Embryology 1 Flashcards
Describe the timeline for fetal development.
When a woman goes to her doctor thinking she’s pregnant and the tests reveal she is pregnant, the doctor should ask when her last menstrual period was. Fertilization is presumed to be 2 weeks after the date of her LMP. The expected gestation time is then 38 weeks from the time of fertilization.
What is happening in weeks 1 - 3 of fetal development?
- Fertilization
- Cleavage
- Blastocyst formation
- Implantation
- Gastrulation
- Neurulation
What is happening in weeks 3 - 8 of fetal development?
Organogenesis
What is happening in weeks 8 - 40 of fetal development?
Growth and maturation of organs
What is the fetus’s response to teratogens during weeks 1 - 3?
All or none phenomenon - exposure to teratogen either has no effect or results in embryonic death
What is the fetus’s response to teratogens during weeks 3 - 8?
Most vulnerable to teratogens during this time, more likely to result in death
What is a teratogen
Any substance, agent or process that interferes with normal prenatal development causing the formation of one or more developmental abnormalities in the fetus
What is the difference before embryonic age and gestational age?
Embryonic age refers to day 1 of fertilization (embryologists say pregnancy is only 38 weeks long as a consequence)
Gestational age refers to day 1 of LMP (OB/GYNs usually use this, thus they say pregnancy is 40 weeks long)
Gametogenesis is the _____ function of the gonads
Exocrine
Where do the male and female gametes fuse to form the zygote?
The ampulla of the fallopian tube
What does fertilization accomplish? (3)
- Restores diploid number of chromosomes
- Determines chromosomal sex
- Initiates cleavage of the zygote
What is cleavage?
A series of mitotic divisions that occurs as the zygote is propelled toward the uterine cavity
What is the morulla?
The 16-cell stage
When is the blastocyst formed?
Day 5
Describe the structure of the blastocyst.
There is a central hollow cavity and 2 layers of cells: trophoblasts on the exterior of the blastocyst and an inner cell mass called the embryoblast.
All fetal structures derive from the _______ layer of the blastocyst.
Embryoblast
The placenta and fetal membranes are derived from the ______ cell layer of the blastocyst.
Trophoblast
When does implantation occur?
Day 6
_____ cells drive implantation
Trophoblast
They invade the maternal endometrial epithelium
When is the bilaminar disc formed?
Day 9
What does the bilaminar disc consist of?
The epiblast and hypoblast
What structures does the epiblast form?
The embryonic germ layers
What structures does the hypoblast form?
The roof of the yolk sac
What is the first morphologic sign of gastrulation?
Formation of the primitive streak
Describe where the primitive streak occurs?
Caudally in the median plane of the dorsal aspect
Which structures arise from the primitive streak?
Primitive groove
Primitive node
Primitive pit
When does gastrulation occur?
week 3
Explain how the embryonic endoderm and the embryonic mesoderm form.
Mesenchyme cells from the deep surface of the primitive sreak migrate to form these germ layers
What is gastrulation?
The formation of 3 embryonic germ cell layers
