PSYC 100 Lecture Notes - Lecture 3: Amniotic Sac, Programmed Cell Death, Prenatal Development

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Published on 22 Apr 2013
Week 3: Development
Periods of Prenatal Development
Conception begins when sperm enters egg , matching chromosomes become one cell
Till two weeks, it is known as the zygote when it is implanted into the uterine wall, where
rapid cell division occurs
From the 3rd to 8th week, major development occurs when it is known as the embryo, where
the major organ systems are built as well as cell differentiation and many other bodily
9th week to birth, it is known as the fetus where there is continued development and rapid
growth of the body
Developmental Processes
Cell division begins to divide in first 12 hours at an exponential rate
Cell migration occurs during the embryonic period
Cell differentiation initially all the cells are stem cells but undergo differentiation, there
are 350 types of cells and their location ultimately determines their type
Programmed cell death also happens which is called apoptosis
Eg. Our webbed fingers, tail
Hormonal Effects all foetuses can go either way
Period of the Zygote
Blastocyst, a hollow sphere with inner cell mass-less than 1mm in diameter
Identical twins are the cause of the splitting of the inner cell mass
Implantation end of first week occurs for about a week
Period of the Embryo
Early development is mostly rapid
All development proceeds in a cephalocaudal and proximodistal manner (head to tail and
inside to outside respectively)
Ectoderm outer most layer, nervous system, nails, teeth, inner ear, eye lens and epidermis
Mesoderm muscles, bones, circulatory system, skin
Endoderm digestive system, lungs, urinary tract and glands
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U shaped groove forms down center of top layer-neural tube where one end will swell to
become brain and spinal cord
Placenta blood doesn’t mix with mothers but allows nutrients to go in
Amniotic sac protects and provides a constant temperature and allows exercise for the baby
Fetus at 16 Weeks
Mom begins to feel babies first kicks
Beginning of period of lower body growth
Fetus at 20 weeks
More head down position, goes upside down
Should turn by 22nd week
Less movement, cramped
Putting on weight
Facial expressions begin to occur, and will shield eyes from fetoscope
May be able to survive at 20-22 weeks with lots of intervention
Lungs aren’t developed, no fat on body etc
Fetus at 28 weeks
Age of viability where brains and lungs are developed enough to survive without major
medical intervention
Eyes open and move, auditory system is functional
In the last 3 months of pre-natal development, the fetus triples in weight in the form of fat
under the skin
Fetal Behaviour
Normal formation of organs and muscles depends on the baby being able to move even
such as hiccups
By the age of 12 weeks the developing organism has all the newborn’s movements
Chest movements similar to breathing though its not constant, but can’t really breathe as it
is in fluid
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