How are children different than adults
The
most obvious difference between an adult and a child is their
size: most children weigh less than adults. Infants and children
have a greater body surface area to body weight ratio than adults.
This ratio is more than two times greater in an infant than
in an adult.1 This difference is important when evaluating the
safety of chemicals that can be absorbed through the skin. As
a result, products and chemicals considered safe for an adult
could be harmful for a child: the same exposure by an adult
would be significantly higher for a child.
Secondly, less than 50% of the US population is male. If the
standard of safety is based on a healthy adult male, it fails
to consider the impact on women. Many of the chemicals used
today may affect men and women and boys and girls differently.
There are entire groups of chemicals that behave like human
hormones once they enter the body.
Other critical differences between an adult and a typical child
include:
• Children have a significantly higher number of ways to be
exposed to chemicals. A fetus in its mother’s womb is exposed
to anything to which the mother is exposed, which is why expectant
mothers have to be careful about the products they use and the
foods they eat. After birth, nursing infants can be exposed
through their mother’s breast milk.
• As toddlers, children put anything they can into their mouths.
They also play close to the ground where they are more likely
to be exposed to various chemicals and chemical residues in
the form of dust and dirt. Heavier gases accumulate lower to
ground and chemicals applied to lawns and floors are closer
to a child.
Other critical differences between an
adult and a typical child include:
• Children’s rapidly developing bodies are more susceptible
to chemicals from the time of conception through their early
twenties. As the brain develops, for example, billions of brain
cells are busy arranging and rearranging themselves in precise
positions. Anything that interferes with that process may have
long-lasting impacts.
• Children generally have longer to live than adults so any
exposure to dangerous substances has a longer time to accumulate
and cause health problems.
• Children drink more water, eat more food, and breathe more
air pound-for-pound than adults.
• Children in the first six months of life drink seven times
as much for their size than adults. Children between the ages
of one and five eat three-to-four times as much on a bodyweight
basis than the average adult. An infant inhales twice as much
air for its size than a typical adult.
• Children are less able to remove harmful substances from their
bodies than adults because their organs and immune systems are
not fully developed. If an organ is damaged during development
the damage may be permanent.
“Many
organ systems in young children – the nervous system in particular,
but also the lungs, the immune system, and the reproductive
organs – undergo extensive growth and development throughout
pregnancy and in the first months and years of extra-uterine
life. During this period, structures are developed and vital
connections established. These systems are not well adapted
to repair any damage that may be caused by environmental toxicants.
Thus, if cells in the developing brain, immune system, or reproductive
organs are destroyed by neurotoxicants, or if development is
diverted by endocrine disruptors, there is high risk that the
resulting dysfunction will be permanent and irreversible. Depending
on the organ damaged, the consequences can include loss of intelligence,
immune dysfunction, or reproductive impairment.”2
1 Prioritization
of Toxic Air Contaminants Under Children’s Env. Health Protection
Act: California Environmental Protection Agency.
2 Landrigan PJ,
JE Carlson, CF Bearer, JS Cranmer, RD Bullard, RA Etzel, J Groopken,
JA McLachlan, FP Perera, JR Reigart, L Robison, L Schell, WA
Suk. Children’s health and the environment: A new agenda for
prevention research. Environmental Health Perspectives 106,
Supplement 3, June 1998
Contrary to previous widely
held beliefs, the human brain is not fully developed at birth.
In fact, a newborn's brain is about 25% of its approximate
adult weight. After birth, it grows dramatically by producing
billions of cells and hundreds of trillions of connections
between these cells. These cells form a complex control centre
for sensing the world and enabling the baby not only to see,
hear, move, taste and touch but also to think, feel, and behave
in particular ways.
Babies are born without the
ability to control their head and neck muscles. Muscles begin
to develop during the first year of life and the child learns
how to coordinate muscle movement.
Muscle development enables
the child to learn to roll, sit up and eventually walk. During
this stage the child is close to the ground and more susceptible
than an adult to hazards at ground level: toxins, pesticides,
dirt and other foreign substances.
Eyesight develops during the
first year of life and by four months the child’s sight should
be able to see as well as an adult.
In the first year of life the
child does not comprehend right and wrong. The ability to
understand direction improves as the child gets closer to
the age of four; however, during this stage, the child is
incapable of ascertaining situations that may place them in
harm and are incapable to protect themselves.
Reading skills develop at this
stage and children are not capable to understand warning labels
or safety measures created for adults. Keep all chemicals
out of reach of children at all times.
Organs are still growing and
developing. Many organs will continue to grow throughout adolescence.
This makes these organs susceptible to toxic exposure and
can retard the growth of these organs.
Proper nutrition is essential
for a child’s growth. A poor diet can affect how much a child
weighs and how the child grows. The developing child is vulnerable
to toxic exposure and environmental contaminates. Benchmarks
for safety regarding environmental hazards do not exist and
the level of safety currently used in by the US EPA is for
a 170 pound healthy adult. Children should avoid areas where
there is smoking, drugs, and areas that may expose the child
to higher levels of toxins. At this stage the child is unable
to determine right from wrong and is unable to take care of
itself.
For more information of
developmental milestones:
http://www.aap.org/healthtopics/stages.cfm
Resources:
-
"MedlinePlus Medical Encyclopedia"
-
Moore,
Keith L. The Developing Human: 3rd Edition. W.B.
Saunders Company, Philadelphia PA
-
Wilcox
AJ, Baird DD, Weinberg CR. Time of implantation of the conceptus
and loss of pregnancy. 1999 N Engl J Med. 340(23):1796-9.
PMID 10362823
-
Ljunger,
E, Cnattingius, S, Lundin, C, & Annerén, G. 2005 Chromosomal
anomalies in first-trimester miscarriages. Acta Obstetricia
et Gynecologica Scandinavica 84(11):1103-1107.
PMID 10362823
-
Gray’s Anatomy:
http://education.yahoo.com/reference/gray/
-
Developmental stages of a fetus:
www.en.wikipedia.org/wiki/Fetus
Organs are
still growing and developing. Many organs will continue
to grow throughout adolescence. This makes these organs
susceptible to toxic exposure and can retard the growth of
these organs.
Sexual identity and the maturation
of sexual organs occur with the offset of puberty. This
results in physiological and psychological changes.
Experimentation also occurs
in this stage and can expose the child to toxic substances
from alcohol, tobacco or drugs.
Proper
nutrition is essential for a child’s growth. A poor
diet can affect how much a child weighs and how the child
grows. The developing child is vulnerable to toxic exposure
and environmental contaminates. Benchmarks for safety
regarding environmental hazards do not exist and the level
of safety currently used in by the US EPA is for a 170 pound
healthy adult. Children should avoid areas where there
is smoking, drugs, and areas that may expose the child to
higher levels of toxins. At this stage the child
is unable to determine right from wrong and is unable to take
care of itself.
For
more information of developmental milestones:
http://www.aap.org/healthtopics/stages.cfm
Resources:
-
"MedlinePlus Medical Encyclopedia"
-
Moore,
Keith L. The Developing Human: 3rd Edition. W.B.
Saunders Company, Philadelphia PA
-
Wilcox
AJ, Baird DD, Weinberg CR. Time of implantation of the conceptus
and loss of pregnancy. 1999 N Engl J Med. 340(23):1796-9.
PMID 10362823
-
Ljunger,
E, Cnattingius, S, Lundin, C, & Annerén, G. 2005 Chromosomal
anomalies in first-trimester miscarriages. Acta Obstetricia
et Gynecologica Scandinavica 84(11):1103-1107.
PMID 10362823
-
Gray’s Anatomy:
http://education.yahoo.com/reference/gray/
-
Developmental stages of a fetus:
www.en.wikipedia.org/wiki/Fetus
Embryonic
Period
Toxic
exposures often cause major congenital malformations
Week
1-4 After conception, the embryo will begin to "search"
for a place to attach to the woman's uterus. When it finds
one and plants itself there, the connections between the mother
and the embryo will begin to form, including the umbilical
cord
Week
5-8 Chemicals produced by the embryo stop the mother's menstrual
cycle. The brain begins to develop, and the heart will begin
to beat. Stubs begin to be visible where arms and legs will
grow later. All the main organs begin to grow. The embryo's
blood type becomes apparent. Embryo is capable of motion,
and the eyes begin to form. Most organs have developed or
have begun developing. At the end of the 8th week, the embryonic
stage is over, and the fetal stage begins
In
humans, a fetus develops from the end of the 8th week of pregnancy,
when the major structures and organ systems have formed, until
birth.
There
is much natural variation in the growth of the fetus. Approximately
52% of the variation in birth weight can be accounted for
by genetic factors, whereas 48% can be accounted for by environmental
factors. Ultimately, the offspring should be able to live
up to its term growth potential. Factors affecting fetal growth
can be maternal, placental, or fetal.
Fetal
Period
During
the fetal period, toxic exposures often cause physiological
abnormalities or minor congenital malformation
The
circulatory system of a fetus
The
circulatory system of a human fetus works differently from
that of born humans, mainly because the lungs are not in use:
the fetus obtains oxygen and nutrients from the mother through
the placenta and the umbilical cord.
Blood
from the placenta is carried by the umbilical vein. About
half of this enters the ductus venosus and is carried
to the inferior vena cava, while the other half enters the
liver proper from the inferior border of the liver. The branch
of the umbilical vein that supplies the right lobe of the
liver first joins with the portal vein. The blood then moves
to the right atrium of the heart. In the fetus, there is an
opening between the right and left atrium (the foramen
ovale), and most of the blood flows from the right into
the left atrium, then into the left ventricle from where it
is pumped through the aorta into the body. Some of the blood
moves from the aorta through the internal iliac arteries to
the umbilical arteries, and re-enters the placenta, where
carbon dioxide and other waste products from the fetus are
taken up and enter the mother's circulation.
Some
of the blood from the right atrium does not enter the left
atrium, but enters the right ventricle and is pumped into
the pulmonary artery. In the fetus, there is a special connection
between the pulmonary artery and the aorta, called the ductus
arteriosus, which directs most of this blood away from
the lungs (which aren't being used for respiration at this
point as the fetus is suspended in amniotic fluid).
Remnants
of the fetal circulation can be found in adults.
In
addition to differences in circulation, the developing fetus
also employs a different type of oxygen transport molecule
than adults (adults use adult hemoglobin). Fetal hemoglobin
enhances the fetus' ability to draw oxygen from the placenta.
Its association curve to oxygen is shifted to the right, meaning
that it will take up oxygen at a lower concentration than
adult hemoglobin will. This enables fetal hemoglobin to absorb
oxygen from adult hemoglobin in the placenta, which has a
lower pressure of oxygen than at the lungs.
A human being's
heart is about the size of that human being's fist. As the
body develops, the heart grows at the same rate as the fist.
So an infant's heart and fist are about the same size at birth.
In the womb, however, that similarity was not always true.
During the first few weeks after conception, the fetal heart
occupies most of the fetus' mid-section. The heart size to
body size ratio is nine times greater in the fetus than in
the infant. During those first few weeks, the fetal heart
lies high in the chest. Soon, it moves down to occupy its
position in the chest cavity.
Proper
nutrition is essential for a baby's growth in the uterus and
beyond. A poor diet during pregnancy can affect how much a
newborn weighs and how the infant grows. The developing
fetus is vulnerable to toxic exposure and environmental contaminates.
Benchmarks for safety regarding environmental hazards do not
exist and the level of safety currently used in by the US
EPA is for a 170 pound healthy adult. Mothers should
avoid smoking, areas where there is smoking, consumption of
alcohol, drugs, and areas that may expose the mother to higher
levels of toxins.
Resources:
-
"MedlinePlus Medical Encyclopedia"
-
Moore,
Keith L. The Developing Human: 3rd Edition. W.B.
Saunders Company, Philadelphia PA
-
Wilcox
AJ, Baird DD, Weinberg CR. Time of implantation of the conceptus
and loss of pregnancy. 1999 N Engl J Med. 340(23):1796-9.
PMID 10362823
-
Ljunger,
E, Cnattingius, S, Lundin, C, & Annerén, G. 2005 Chromosomal
anomalies in first-trimester miscarriages. Acta Obstetricia
et Gynecologica Scandinavica 84(11):1103-1107.
PMID 10362823
-
Gray’s Anatomy:
http://education.yahoo.com/reference/gray/
-
Developmental stages of a fetus:
www.en.wikipedia.org/wiki/Fetus
