PSYC 100 Study Guide - Ovulation, Menarche, Trophoblast

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10 Apr 2013
Week Three: Lifespan Development
Is there prenatal psychology?
Before the Sphinx
Germinal Period
The 8-10 days after the sperm and egg unite, before the developing cells attach to the uterine wall
Sperm and ova are specialized type of reproductive cell called a gamete, and both are haploid
(contain only one set of chromosomes / half the genetic complement required for life)
The result of the merging male and female gametes is the zygote, which contains a full genetic
load (half from each gamete), making is a diploid
The zygotic cell divides multiple times during the germinal period, through a process called
cleavage (forming blastomeres) which begins 24 hours after conception, and creates a spherical
mass of cells called a morula (solid mass of blastomeres)
Identical twins are formed when the morula spits into two parts and each part fully develops
into a fully formed infant they are identical because they share the same DNA
Every cell in your body (except for gametes) has identical DNA, however they all act differently
Epigenetic modification means that some genes are turned on and others are turned off, leading
to differential expression of proteins and eventually different cellular properties and functions
Stem cell: an undifferentiated cell that has not yet undergone any epigenetic modification can
divide and produce any one of a variety of differentiated cells
Embryonic Period
Begins after implantation in the uterine wall and lasts about 8 weeks
When the morula makes it down the fallopian tube into the uterus, it begins to fill with liquid
Here the cells begin to differentiate, forming two layers:
o Inner Cell Mass: mass of cells inside morula that will eventually form the embryo
o Trophoblast: outer layer protecting the inner cell mass and transmitting nutrients to it
eventually develops into the extra embryonic tissues, including the placenta
This differentiation signals means the organism has gone from morula to blastocyst
Trophoblast layer soon transforms into two parts:
o The Amniotic Sac, which is filled with liquid and provides a constant environment
o The Placenta, which attaches the sac with the umbilical cord; this provides a filter and
protective barrier for the embryo, preventing the blood of the mother and organism
from mixing, while transferring nutrients and waste between the two
The embryo separates into three layers:
o Endoderm: innermost layer later develops into digestive system, urinary tract, lungs
o Mesoderm: middle layer develops into muscle, bone, and the circulatory system
o Ectoderm: out layer develops into skin, hair teeth, and central nervous system
Ectoderm folds in on itself creating a small tube inside the embryo called the neural tube, which
begins to develop into the brain and spinal cord through neurulation
Neurogenesis: growth of new neurons cells grow inside neural tube beginning at 6-7 weeks
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