Week 4 Conception and Prenatal Development Flashcards
When is the preembryonic peroid?
The first two weeks after conception
The fertilized ovum is considered a ____ after the 4th day and enters the ___
Zygote
uterus
When the zygote divides into 16 cells it is considered a ___
Morula
What stage comes after the morula? how is this formed?
the blastocyst. The outter cells of the morula secrete fluids that divide the morula into and inner and outer cell mass
How does the zygote maintain itself in the uterus
It moves to the uterus during the secretory phase of the mestral cycle
-it then releases hormones that signal pregnancy and the uterus stays in this phases allowing for more nutrients and blood flow
what hormone is released by the conceptus that causes the corpus luteum to persist?
human chorionic gonadotropin
hCG
Why is the site of implantation important?
Because it is where the placenta develops
Where does normal implantation occur?
the upper uterus
Why is the upper uterus the ideal place for implantation?
- Rich supply of blood
- Think lining
- limits blood loss after birth
Explain the mechanism of implantation
the conceptus produces corrosive enzymes that erode the decidua
-chorionic villi project into the surface of the decidua
How many days after fertilization does implantation fully occur?
10days
What is a common reason for women to think they are not pregnant during the time of their next mestral period after conception?
The implantation of the concepus may cause a small amount of spotting that can be confused with a normal menstral period
When does the embryonic period start/end?
Beginning of the third week through the eight wek after conception
What occurs duing the embryonic period?
Basic structures of all major body organs are completed and are in place
When is the fetus most vulnerable for teratogens? Why is this?
-The embryonic period
Because all the major body systems are developing at a rapid rate. If one system is affected by a teratogen than it can cascade and cause a multi system issue
Explain the direction of growth during the embryonic stage
- Cephalocaudal
- Central-to-peripheral
- simple to complex
- General to specific
An infant if considered full term __ weeks after conception and ___ weeks after last menstrual period
36-40
38-42
Most women miss their period after __ weeks
3
Describe the neural tube at 3 weeks?
Open at both ends
When does the primitive/tubular heart begin beating?
22-23 days
When does the neural tube close?
during the 4th week
What happens if the neural tube does not close?
defects such as anencephaly and spinal bifida results
The cranial end of the neural tube forms the ___ and the caudal end forms the ___
Brain
Spinal cord
When does the infant heart develop its 4 chambers and begin beating?
during the 4th week
