HUMAN REPRODUCTION BIOLOGY 269

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HUMAN REPRODUCTIONBIOLOGY 269
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Congratulations! You have just given vaginal
birth to a healthy baby.She has been inspected
all parts are where they are supposed to be.
Plus, she is hungry! Your pituitary gland has
been producing a lot of the hormone
, which has caused your breasts to enlarge
and develop many glands to produce milk. Your
baby will naturally try to find your breast and
begin to suck on it.
This stimulates your pituitary gland to secrete
the hormone which
causes muscle cells in the ducts of the milk
glands to force the milk toward the nipple, where
it is expressed through 15-20 openings.
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First few days Milk is thick, high in fat,
protein, minerals, antibodies.Called colostrum

Later Also includes
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Your uterus continues to contract for a few days
to expel functional layer of endometrium.
Assisted when nursing stimulates oxytocin.These
contractions also cause your uterus to begin
returning to its normal, nonpregnant shape and
size will take a few weeksJoint between your
pubic bones tightens up again will take couple
of weeks.
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Baby, of course, started breathing as soon as she
was born.
With each breath, more microscopic air sacs
(alveoli) in her lungs open up Within few
minutes adequate to support her need for
oxygen.
Complete opening of all alveoli couple of days.
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Two openings in / near heart had allowed blood to
bypass lungs.These two openings now close, so
blood flows through lungs to pick up oxygen and
get rid of carbon dioxide. Will take couple
of days.
(Adjustments of the newborn)
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Right after birth Her temperature dropped by a
couple of degrees.Within few minutes able to
generate heat to regulate body temperature.
(Adjustments of the newborn)
Few days Stub of umbilical cord will dry up and
fall off, leaving the umbilicus (belly button)
as a scar.
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First 12 to 15 months called Infancy.Period of
rapid growth notably nervous, circulatory,
skeletal, muscle systems
Learning gross motor coordination Legs become
strong enough to bear weight walking begins to
develop Visual acuity develops Learns to
recognize patterns of vison, hearing Verbal
expression and comprehension increase rapidly
speech begins to develop Lungs heart strong
enough to support active movement
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Childhood end of infancy until puberty begins.
Less rapid growth Continued improvement in
function of most systems, particularly nervous
and muscular Significant increase in cognitive
function verbal expression and comprehension
fine motor skills
Interestingly very few other species have
extended childhoods Evolved to allow for this
cognitive development
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Pubescent period lasts through puberty.Caused
when pituitary begins secretion of follicle
stimulating hormone and luteinizing hormone.
Rapid skeletal and muscular growth again. Hips
and shoulders widen proportionately
more Ovaries, uterus, oviducts, vagina,
testicles, prostate, seminal vesicles begin adult
functions
Secondary sexual characteristics develop
Enlargement of clitoris/penis, labia/scrotum
Growth of pubic, anal, and axillary (armpit)
hair Specialized sweat glands begin
functioning Breasts develop in both girls
and boys (gynecomastia) Voice changes occur
Hair coursens over most of body
Cognitive function and verbal skills increase
quickly Emotional changes common.
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Typical sequence of events in puberty
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Average age of puberty has decreased in past
century
1900 14.2 years in girls 1920 13.8
years 1940 13.4 years 1960 12.8 years 1980
12.6 years 2000 12.2 years
Strangely Few people seems to be following this
type of information in boys, but it also appears
to be declining.
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Factors influencing decreasing age of puberty
a) Better general health and growth b)
Better nutrition More fat and protein in diet
c) Increase periods of light
Interestingly Body weight at beginning of
puberty has remained relatively constant in girls
at about 47 kg (104 pounds), assuming body fat of
at least 18. No such correlation between
weight and puberty appears to exist in boys.
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Adolescent period lasts three to four years after
puberty.
Bone and muscle mass continue to increase in both
sexes, but more pronounced in males. Fat
deposition continues to increase in both sexes,
but more pronounced in women. Mental maturity
increases emotions typically stabilize.
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Adult period very little growth or neural
development occur. Fat deposition continues in
both sexes.Reproduction and child-rearing
typically occur in this period.Decreased
function and diseases of many organs (e.g.
cancers, heart disease, respiratory disease)
common.Gradual loss of verbal skills, visual and
auditory acuity
Senescence (old age) involves deterioration and
lost of function of most organs. Bone and muscle
mass lost. Mental and verbal skills lost.
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