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Summary Chapter 11 Themes and Variations
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detailed notes of chapter 11 in textbook, as well as important lecture notes.
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Human Development11.2 Progress Before Birth: Prenatal Development
11.2.1 The Course of Prenatal Development
The prenatal or antenatal period of gestation refers to foetal development over
the period of pregnancy from conception to parturition (birth).
1 spermatozoa bonds with matured egg a zygote forms, initiating the beginning
of the life cycle.
Development that occurs during prenatal stage is extremely rapid. From a
single cell -> complex biological being in 9 months. Prenatal period is divided
into 3 stages:
1. The Germinal stage (0-2 weeks)
2. The embryonic stage (week 2-8)
3. The foetal stage (week 8- birth)
The germinal stage
First two weeks of gestation, starts with conception and end with implantation
on the uterine wall.
Many zygotes are rejected at implantation. 1 in 5 pregnancies end before a
woman is aware that conception occurred.
Cell partition initiates during the first 24 to 36 hours after conception. The
cells are all similar until 4 days after implantation; they resemble a hollow
sphere with two outer layers = blastocyst
The external cells design constructions to maintain the emerging organism,
and the internal coat forms the embryo itself.
Day 6/7, the blastocyst comes into connection with the uterine wall and by
day 12 it is completely buried in the uterine tissue = implantation
The external cells insert in the uterine wall.
Several of the cells of the blastocyst’s wall merge with uterine coating cells to
construct placenta- permits oxygen, nutrients and other elements to travel
between the mother’s and the baby’s blood. Placenta imports the mother’s and
baby’s blood alongside one another, without permitting them to mix.
, Cluster of cells that attaches the embryo to the placenta becomes the umbilical
cord.
Alternative cells shape the yolk sac, a formation that will manufacture blood
cells until the embryo’s blood-cell producing organs are configured.
Still more growth to become the amnion - fluid filled pouch in which the infant
will drift until birth.
By day 12 the cells that will turn out to be the embryo’s anatomy are in
position.
The Embryonic Stage
The embryonic stage commences when implantation has been achieved, about
the end of the 2nd week of pregnancy. Continues for 6 weeks, until the end of
week 8.
The embryo’s cells start to concentrate to shape the basics of all the body’s
organs.
Week 3: the cells of the nervous system (neurons) shape a construction = neural
tube, from which the brain and spinal cord will grow.
A primordial heart and the precursor of the kidneys also evolve in week 3, along
with three pouches that develop into the digestive system.
,Week 4: the end of the neural tube proliferates to form the brain. Spots that will
grow to be the eyes emerge and the heart begins to throb. The spinal column
and ribs grow, as bone and muscle cells shifts into place. Face starts to obtain
from and the endocrine system begins to grow.
Week 5: the embryo is about 6 mm. Arms and legs grow quickly. Its eyes
contain corneas and lenses, and its lungs are starting to enlarge.
Week 6: embryo’s brain begins to create electrical activity and it moves in
reaction to stimulation. Genitalia also enlarge.
Week 7: embryos begin to move instinctively. Have observable skeletons and
fully developed limbs. Bones are starting to become firm and muscles are
growing. The eyelids close shut to guard the evolving eyes, and the ears are
entirely shaped.
Week 8: the liver and the spleen begin to work so that the embryo can create
and filter its own blood cells. Its heart is well developed, and links between the
brain and the rest of the body are well established. Digestive and urinary
systems are also performing.
Organogenesis- organ growth, is complete by the end of week 8.
, The Foetal Stage
The foetal stage is the closing phase that lasts about seven months, starting
from end of week 8 and progressing until delivery.
The foetus grows in weight from approx. 113g to 3/3.5 kg and its length
expands from 25mm to about 500mm.
Foetal period includes the procedure of cultivating and finishing all the
primitive organ systems.
Capability to live outside the uterus = viability. Occurs at the end of week 24.
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