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INTERESTING ASPECTS
OFTHE
HUMAN LIFE CYCLE
With insemination, genes from both parents combine to form 23 pairs
of
chromosomes. These are DNA
fragments that have specific functions;
the
main units
of
the
hereditary
code.
10
days after insemination, the
embryo
is
embedded
into
the wall
of the
womb. The fetus
is
bathed
in
a
fluid called "amniotic
fluid".
All oxygen
and nutrition come from the maternal
blood.
As organs develop actively during
the first
few months, infections,
e.9., German measles
then may
result in an abnormal
fetus.
Even drinking
too
much may hurt! With
a
very
orderly
and programmed
cell
division and
differentiation,
various
tissues
and
organs are
ultimately formed
one by one.
The
newborn begins the first or "neonatal" period of life on earth
-
usually
10"/o
ol
body weight
is lost
during the first several days. From
1-3
years, there is
rapid
development
of
the central nervous system
and
teeth; 3-7
is
the "pre-school" stage, when the brain
rapidly
develops;7-12
is
the childhood stage,
fol-
lowed by
the teenage, when secondary sexual characteristics develop,
usually
the boys mature
later than
the
girls. The
adulthood
is, unfortunately,
fraught with
problems of aging, diseases and, finally, death, even
though the human
life
span
is
but
a
tiny fraction of human history. Nowadays, the average
life
span of human
beings is already much longer
than
before.
ln
this
Century,
the greatest challenge
of
medicine is
how
to
make
the
increasing number of elderly people not
only
live longer but also more healthy lives.
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