Transcript Unit 2 PHYSICAL GROWTH, MATURATION, and AGING 2

PHYSICAL GROWTH,
MATURATION, and AGING
(Changing Individual
Constraints Across the Life
Span)
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PRENATAL DEVELOPMENT
External factors can positively or
negatively affect growth and maturation.
Both genetic and external factors influence
normal embryonic and fetal growth.
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EMBRYONIC DEVELOPMENT
1 to 8 weeks
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Formation of Sex Cells
The genetic information that determines hair and eye
colour, height potential, skeletal structure etc is
contained in genes.
The genes are located on chromosones.
Humans have 23 pairs of chromosones in all their cells,
except for the sex cells when they are formed.
The sex cells are specialised cells formed by meiosis
(reduction division).
That is each sex cell divides into two “daughter” sex
cells.
Only one chromosone from each of the 23 pairs migrate
to each daughter cell.
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Which one of the pair each daughter cell
receives is a matter of chance.
When an ovum and spermatozoan unite in
fertilisation each donates the “chance” set of 23
chromosones, reestablishing the total of 46
chromosones (23 pairs).
Each human chromosone has 30 000 or more
pairs of genes – that helps bring variety and
that’s why each human being is unique.
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CELL GROWTH AND
DIFFERENTIATION
The genes also direct the continuous
development of the embryo in a precise and
predictable pattern.
The fertilised egg or zygote divides into two
cells, four, eight and so on, by mitotic cell
division.
As the cells continue to increase they also
differentiate to form specific tissues and organs.
This process occurs in a predictable time line.
The limbs are roughly formed and the heart beat
begins at 4 weeks.
Eyes , ears, nose, mouth, fingers and toes are
formed at approximately 8 weeks.
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FETAL DEVELOPMENT
9 to 38 weeks
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The Fetal Stage
From 8 weeks to birth there is further
growth and cell differentiation of the fetus.
Growth of organs and tissue happens in
two ways:
 1) Hyperplasia – increase in the absolute
number of cells.
 2) Hypertrophy – increase in the relative
size of an individual cell.
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It also happens in two directions:
 1) Cephalocaudal which is the direction of
growth beginning at the head and
extending towards the lower body.
 2) Proximodistall which is the direction of
growth proceeding from the body toward
extrimities.
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FETAL NOURISHMENT
•The fetus is nourished by the
diffusion of oxygen and nutrients
between fetal blood and maternal
blood in the placenta.
•Poor nourishment due to eg. poor
socio-economic status of the woman
may lead to low birth weight in
infant(s) - risk of disease, infection,
and death in the weeks after birth.
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ABNORMAL PRENATAL
DEVELOPMENT
Abnormal development may arise from
either genetic or external factors.
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Genetic Causes of Abnormal
Prenatal Development
Dominant disorders result when one parent passes on
defective gene.
Recessive disorders occur when a defective gene comes
from both parent.
Genetic abnormalities can result from a mutation – the
alteration or defection of a gene during formation of the
egg or sperm cell.
Both new mutations and inherited disorders can result in
single or multiple malformations of an organ, limb or
body region.
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external Causes of Abnormal
Prenatal Development
Too little or too much of the necessary
vitamins, nutrients and hormones can
have an adverse effect on the fetus.
Some of these substances can also act as
malformation- agents or teratogens.
A teratogen is any drug or chemical agent
that causes abnormal development in a
fetus upon exposure.
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Examples of Teratogens
Include:
Nutritional deficiencies;
Hypervitaminosis; eg excess vitamin D.
Drugs; eg.
Cocaine;
Alcohol
Infections;
Human Immunodeficiency Virus (HIV) – heights,
weights, and head circumference below third percentile,
head and facial abnormalities, cardiac defects, impaired
growth, develop mental problems, cataracts, deafness.
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Overall Growth
The growth pattern is predictable and
consistent but not linear.
Height and weight are characterised by:
 rapid growth after birth
 gradual but steady growth during childhood
 rapid growth during early adolescence
 then levelling off.
Thus the growth curves are roughly Sshaped – sigmoid curve.
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Gender
Gender differences are minimal in early
childhood.
Boys then are slightly taller and heavier.
Throughout childhood, girls mature at a faster
rate than boys.
At a given age (childhood) girls as a group are
biologically more mature than boys.
On average girls begin their adolescent growth
spurt at 9 and boys at 11 years.
It is the “Age at takeoff” the age at which the rate
of growth begins to increase.
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Height
On average girls reach peak height velocity during
the adolescent growth spurt at 11.5 to 12 years
Boys reach peak height velocity at 13.5 to 14 years
Boys velocity is faster than that of girls( 9cm/year).
Growth in height tapers off at approximately 14
years for girls & 17 years for boys.
Notable increase in height ending around 16 years
for girls & 18 years for boys.
Males have 2 more years of growth than females
amounting to 10 to 13cm of height.
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Weight
Rapid increase in infancy.
Moderate in childhood.
Spurt in early adolescence.
Then steady increase that tapers off at the
end of the growth period.
Weight is susceptible to external factors.
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Weight
Variations in the amount of muscle with exercise
and fat tissue with diet and exercise.
Disease can also influence body weight.
Peak weight velocity during the adolescent
growth spurt follows peak height velocity.
By 2.5 to 5.0 months in boys and 3.5 to 10.5
months in girls.
Thus individuals grow “up” 1st and then filling
“out”
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Relative Growth
Each part of the growing individual has its own
precise and orderly growth rate.
The head is one-fourth of the total height at birth
but one-eighth of adult height.
The legs are about three-eighths of the height at
birth but almost half of adult height.
The legs grow faster than the trunk and head in
infancy and childhood.
They undergo a growth spurt early in adolescence.
Growth in height results mostly from an increase in
trunk length during late adolescence and early
childhood.
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Relative Growth
In girls, shoulder and hip growth increase
at about the same rate.
Their shoulder to hip ratio is fairly stable.
Boys undergo a substantial increase in
shoulder growth during their growth spurt.
So boys’ ratio changes as they move into
adolescence.
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Physiological Maturation
Tissues of the growing body can advance without
necessarily increasing in size.
Physiological maturation is the developmental process
leading to a state of full function.
Two children of the same age can be dramatically
different in maturation status i.e. early and late maturer.
It is difficult to assume maturity from age alone, size
alone or even age and size together.
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Physiological Maturation
A child may be small and of slight build but may actually be
relatively mature for his or her chronological (linear) age.
Appearance of secondary sex characteristics during
adolescent growth spurt is a function of maturation.
Individuals who are more mature are likely to be stronger
and more coordinated than those who are less mature even
at the same chronological age.
Educators must consider maturation status in designing
activities and setting performance goals.
It is tempting to assume movement performance potential
from size alone or age alone, but in fact maturation status is
a powerful predictor of performance potential.
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MATURATION: INTERRELATIONSHIP WITH MOTOR
PERFORMANCE
Early maturation, with its associated size and
strength advantages, establishes an asset
positively associated with success in several
sports.
However, as adolescence approaches its
termination, the maturity status of the youngsters
is of less significance as the catch-up of latematuring boys reduces the size differences so
apparent in early adolescence. (1984, p. 56)
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external Influence on Postnatal
Growth
During periods of rapid growth, just after birth
and in early adolescence, growth is sensitive to
alteration by environmental factors.
There is “Catch-up growth” which is relatively
rapid physical growth of the body to recover
some or all of the slow growth during a period of
negative external influence once the negative
influence is removed.
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Assessment of Physiological
Maturation
Dental eruption – restricted to 6 months to
3 years and 6 to 13 years (permanent
teeth).
The appearance of secondary sex
characteristics.
Skeletal maturation – comparing an X-ray
of skeletal maturation to a set of
standards.
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Bones of the skeleton change in size and shape. These
changes can be seen by x-ray. The "bone age" of a child
is the average age at which children reach this stage of
bone maturation. A child's current height and bone age
can be used to predict adult height.
At birth, only the metaphyses of the "long bones" are
present.
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The metaphysis is the wide portion of a long bone
(femurs, tibias, fibulas humeri, radii, ulnas and
phalanges of the fingers and toes) and between
the epiphysis and the narrow diaphysis.[1] It is
considered a part of the growth plate, the part of the
bone that grows during childhood and as it grows, it
ossifies near the diaphysis and the epiphyses.
During childhood, the growth plate contains the
connecting cartilage enabling the bone to grow; at
adulthood (between the ages of 18 to 25 years), the
components of the growth plate stop growing altogether
and completely ossify into solid bone.
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DEVELOPMENT OF PUBIC HAIR
Males
Stage 1. There is no pubic hair.
Stage 2. There is a thin growth of long, slightly
pigmented, downy hair, straight or only slightly curled,
primarily at the base of the penis.
Stage 3. The hair is considerably darker, rougher, and
more curled. The hair spreads thinly over the intersection
of the pubes.
Stage 4. The hair, now adult in type, covers a smaller
area than in the adult. The hair is adult in quantity and
type.
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DEVELOPMENT OF PUBIC HAIR
Females
Stage1. There is no pubic hair.
Stage 2. There is thin growth of long, lightly pigmented,
downy hair, straight or only slightly curled, primarily
along the labia.
Stage 3. The hair is considerably darker, rougher, and
more curled. The hair spreads sparsely over the
intersection of the pubes.
Stage 4. The hair, now adult in type, covers a smaller
area than in the adult. The hair in adult is in quantity.
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Adulthood and Aging
Growth ends in the late teens or early
twenties.
Measures of body size can change in
adulthood mostly due to external factors.
Also the aging of tissues.
Lack of weight bearing exercise and
calcium in the diet could contribute to
osteoporosis and resulting decrease in
height.
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