Growth and Development 2
Terms in this set (49)
"the progressive development of a living being or part of an organism from its earliest stage to maturity, including the attendant increases in size". - British Medical Dictionary (1961)
• Growth involves a series of changes not just the addition of material to achieve an increase in size. These changes involve a differentiation of the various parts of the body to perform distinct functions.
Nature of Growth
• Not all parts of the human body grow at the same rate, nor do they all stop growing simultaneously.
• The body does not retain the same proportions throughout growth and the relative weights of given tissues and organs do not remain constant.
For example, the brain at birth is about 24% of its adult weight, whereas the neonatal body is only about 6% of its adult weight..
Stages of postnatal growth
extends from birth to the end of four weeks.
extends from the end of the neonatal period at four weeks until two years of age. Infancy is characterized by tremendous growth, increased coordination, and mental development.
the period of growth and development extending
from infancy (2 years) to adolescence, at which time puberty begins
- The chronological duration of childhood varies because puberty begins at different ages for different people.
- Childhood years are a period of relatively steady growth until preadolescence when there is a growth spurt.
the period of growth and development between
childhood and adulthood. It begins around the age of nine in girls and the age of eleven years in boys. The end of adolescence is approximately 17-18 years, but it is not clearly delineated.
- In Latin, adolescere meaning "to grow up"
the period of life beyond adolescence. An adult has reached maximum physical stature as determined by genetic, nutritional, and environmental factors.
• Height vs. time
• measurements taken at intervals are plotted against time to produce a graph of progress.
• Change in Height / year vs. time
• increments in growth are plotted against time to show the variation in the rate of growth with time.
Data for Growth Curves collected in two ways
- Longitudinal data
- Cross-sectional data
growth curve is derived from a single
individual or from repeated measurements on the same group of individuals over a period of many years.
measurements are made of several children in each age group, and these are then combined to form a cross-sectional picture of the various age groups in the community at the time of the investigation.
From birth to maturity, the most important difference between boys and girls is in the:
Rate of maturity
Girls grow up faster than boys
- Girls reach 50 percent of their adult height at an earlier age (1.75 vs. 2.0 years), enter puberty earlier, and cease growing earlier
- Half way through the fetal period, the skeleton is already three weeks more advanced in girls;
- at birth, the difference is four to six weeks of maturation;
- at puberty, the difference is two years.
Before the adolescent growth spurt, there is little difference between the average height of boys and girls
• Because the spurt begins earlier in girls, there is an age (approximately 9-10 years) at which girls become taller and heavier than boys of the same age. This balance is redressed by age 14.
• The mean growth takeoff age (ie,the onset of growth
acceleration) in children in North America growing at an average rate is approximately
• 9 ± 1 year in girls
• 11 ± 1.5 years in boys
• The age at growth takeoff correlates highly with pubertal stage.
• During the spurt,
• boys gain about 20 cm. in height
• while girls gain about 16 cm. in height.
• mostly growth of the trunk
•Peak height velocity in boys ~ 13.5 years
•Peak height velocity in girls ~ 11.5 years
The standard deviation for age at peak height velocity is slightly less than one year.
peak height velocity
Since the peak height velocity may occur as much as two years earlier or later than the average within each sex, a six year difference in the event between an early maturing girl and a late maturing boy is quite possible.
- PHV in Girls 11.5 ± 2 yrs
• Earliest 9.5 yrs; Latest 13.5 yrs
- PHV in Boys 13.5 ± 2 yrs
• Earliest 11.5 yrs; Latest 15.5 yrs
• The peak height velocity is often highest in early-maturing children and lowest in late-maturing children.
• The conclusion of the growth spurt is followed by a rapid slowing of growth.
• In USA cross-sectional studies, boys with a mean takeoff age of 11 years reached their final heights by 17-18 years of age, and girls with a mean takeoff age of 9 years reached their final heights by 14-15 years of age.
• However, there is a wide variation around these means
- plus or minus two years.
Why are men in Canada 13cm taller than women?
• Canadian - Men 176 cm (5' 9.5") - Women 163 cm ( 5' 4 .5")
• Boys end up being taller than girls because they have two more years of growth before the growth spurt.
• During these two extra years of prepubertal growth in boys, the legs are growing relatively faster than the trunk.
- Thus the average male has relatively longer legs than the average female.
• Peak growth rate also a bit higher on average
Growth in weight
• Weight of ovum (0.005 mg) -> birth - 3 X 109 fold increase
• Birth (~7.5 lb.) ---> maturity (20 years) - 20 fold increase
• Birth ---> 2 years - 4 fold increase
• then steady increase of 2 - 3 kg/yr until growth spurt.
• During the growth spurt, boys may add 20 kg. to their
weight, and girls 16 kg.
• The peak velocity for the spurt in weight lags behind the peak velocity for height by about 3 months - child shoots up and fills out later.
a condition of the bones where they become
thin and brittle due to decreased mineral content, which makes them susceptible to fracture.
For all bone sites in both boys and girls, peak velocity in bone mineral content occurs approximately:
one year after peak height velocity.
• This suggests that there could be a transient period of relatively long bone weakening during the adolescent growth spurt, resulting in an increased fracture risk following peak height
Need for nutrients
• The need for calcium during peak linear growth is
• An adequate level of Vitamin D in the body is also important
- effects of sunshine and diet.
• Vitamin D deficiency is not uncommon among children and adolescents in Canada, particularly during the dark seasons of the year.
bone mineral laid down during the four
• As much bone mineral will be laid down during the four adolescent years surrounding peak height velocity as most people lose mineralization during all of adult life.
• Peak bone mineral density of the lumbar spine and hip is achieved in the early to late twenties
bone mineral density decreases at Menopause
Changes in Body Proportions and
• The relationship between one part and another of the growing body is not a consistent one, but changes with age.
Shape of the Infant
• Large head - ratio of head height to total height equals 1:4 in the infant, 1:7.5 in the adult.
• Lower limbs are much less well developed at birth than upper limbs - ratio of leg length to total height equals 1:3 in infant, 1:2 in adult.
Changes in Shape With Growth
• At all ages the dimensions of the head are in advance of those of the trunk, and at all ages more peripheral parts of the limbs are in advance of the more central parts -
foot --> calf--> thigh.
• In the later stages of the adolescent spurt, there is laterality of growth rather than linearity.
• The bones of the face grow faster than those of the cranial vault - "at adolescence the face emerges from underneath the
Puberty - refers to the period at which the
• testes, prostate gland, and seminal vesicles
• the breasts, uterus and vagina, suddenly enlarge.
• This is the time of greatest sex differentiation since the early intrauterine months - sexual dimorphism
Puberty male vs female
• There are changes in reproductive organs and secondary sex characteristics, in body size and shape, and in relative proportions of muscle, fat, and bone.
• Recent studies have demonstrated a progressive decrease in the age of onset of puberty in children around the world.
• A research study reported in the April 1997 issue of "Pediatrics" indicated that girls in the United States mature sexually earlier than previously expected.
• The study of 17,077 girls indicated that puberty begins on average at age 9 or 10.
• For many girls, however, puberty starts much earlier. A very small percentage of girls begin to develop breasts and pubic hair by age 3.
refers to the onset of menstruation. It occurs relatively late in puberty.
• The average age of occurrence in North America is 12.2-13 years
- There is a standard deviation of plus or minus one year.
• The 95 percent range is 11.0 - 15.0 years.
height velocity is falling
• The development of mature ova follows menarche by as much as two years;
• puberty is not complete in females until sexual maturity has been attained.
Indices of Maturity
• It is important to be able to assess how far a individual child has progressed towards maturity.
• The chronological age of a child is an unreliable guide since children mature at very different rates and measurements of height and weight are only partially useful.
A. Radiological (Skeletal) Age
B. Dental Age
C. Growth Curves
D. Sexual Age
E. Neural Age
Radiological (Skeletal) Age
• During growth, every bone goes through a series of changes which can be recorded radiographically.
• The times of appearance of primary and secondary centers of ossification can be observed and the progressive enlargement of the ossified portion of an epiphysis can be followed in detail.
The radiological examination
allows one to determine how far the skeleton of a child has progressed toward the adult condition.
• The wrist and hand are most commonly used for this purpose because, in this region, there is a large number of centers of ossification.
• At every chronological age up to full maturity, the radiological age of girls is in advance of that of boys by a factor of about 20 percent or more.
• The deciduous dentition erupts from six months to two years of age and can be used during that period.
• The permanent dentition provides a measure from six to 13 years of age.
• However, skeletal maturity and dental maturity are not closely related in the individual.
• The timing of the peak height velocity and the peak weight velocity are useful maturity indicators
• The secondary sex characteristics can be used as a method of rating maturational development. Ratings can be made of stages in pubic hair development, stages in breast development, and stages of genital development.
• These indicators have limited applicability over the growth span, in contrast to skeletal maturation, which can be monitored from infancy into young adulthood.
• The "Tanner" stages of sexual maturity are used as the universal standard for classifying sexual maturity
• The age at which menarche occurs is an important indicator of maturation status in females.
• Menarche is more closely related to radiological age(12 - 14.5) than to chronological age (10 - 16 ).
• In spite of the large size of the central nervous system at birth, much of it is incompletely functional and requires considerable time to develop to the stage at which it can be fully utilized.
• Girls are ahead of boys throughout the phase of motor and sensory development -
• on the average, girls learn to
- walk earlier
- control their bladders earlier
- are ahead in the use and understanding of speech.
- They are also first in the development of skills which need fine movements and coordination, such as tying shoes.
Early and Late Maturing Children
• There is good evidence that, in European and North American school systems, children who are physically advanced towards maturity score, on average, slightly higher on most tests of mental ability than children of the same age who are less
• It is very likely that mental and psychological development are much more closely related with radiological age than with chronological age.
Boys with muscle dominant physiques, tend to mature earlier than others and have an early adolescent growth spurt.
• Late maturing boys are greatly handicapped in competition with early maturing boys.
• Late maturing boys may be deselected from age class sports early
• Early maturing boys may develop
unrealistic expectations and have difficulty adjusting to their loss of sports advantage when their late maturing peers catch up.
Five types of skeletal development have been recognized: (early and late maturing children)
(1) Average maturation and adult height
(2) Early maturation - tall in childhood but not as adults
(3) Early maturation and genetically tall
(4) Late maturation - small in childhood, average as adults
(5) Late maturation and genetically short
Fundamental Movement Skills Development
• Fundamental movements to more specialized and complex skills foundational in play, dance and sport
• vital for PE teachers helping children develop motor skills
• foundations for the drills and exercises prescribed for muscular strength training
• "Physical literacy is the motivation, confidence, physical competence, knowledge and understanding to value and take responsibility for engagement in physical activities for life."
- Whitehead, 2014
• Ideally developed in childhood, continued through life
- "children who develop early motor competencies are more physically active during childhood" (Lopes et al., 2001)
- "active children and youth are more likely to stay active into adulthood "(Telama et al., 2001).
- "top athletes are likely to have participated in more sports earlier, and specialized later "(Bridge & Toms, 2013).
Functional Health: Quality of Life
• As individuals age, they experience more declines in functional health, which reduces quality of life.
- Declines in functional health are associated with increased health care costs and a reduction in economic productivity
• Increasing functional health (durability) will increase the capacity of individuals to avoid poor health and recover more quickly (resilience)
Factors Influencing Growth and
A. Genetic Control
C. Secular Trends
D. Season and Climate
E. Differences between Races
• Both genetic and environmental factors influence growth, and the progress of any given child is the result of a complex interaction of many different factors.
• Studies of twins have shown that body shape and size, deposition of fat, and patterns of growth are all more closely related to nature (genetics) than to nurture (environment).
• Heredity affects not only the end result of growth, but also the rate of progress toward it.
• Malnutrition delays growth. Children subjected to an episode of acute starvation recover more or less completely provided that the adverse conditions are not too severe and do not last
• Adult size is affected by a less severe level of under-nutrition than adult body proportion (ie) leg length versus trunk length, etc.
• Between 1880 and 1950, the average height of American and West European children between the ages of five and seven years increased by more than 1 cm / decade for a total of more than 10 cm.
• Children are now growing faster and stopping growing earlier.
• There has been an upward trend in adult height of one centimeter per decade since 1880.
• In Western European countries, the average age of menarche decreased from 16 years in 1880 to 13 years in 1960.
• The causes of these trends are probably multiple - better nutrition, lessening of disease, some degree of dominance of height genes?
• During the past 20 years, these trends in industrialized countries towards increased height, etc. have been gradually stopping.
Season and Climate
• Studies done on West European children indicate that season of the year may exert a considerable influence on velocity of growth.
• The children grew faster in height in spring and summer than in autumn and winter.
• Weight gain was faster in the autumn than in the spring.
Differences Between Races
• Populations differ slightly in their average
- Adult size
- Tempo of growth
- Body Proportions (limb vs torso length, shoulder to hip width )
• Tempo of growth - Asiatic and African children are slightly ahead, on average, of European children in skeletal age, dental maturity and age of menarche.
• A research study involving 4,131 American boys, reported in the November 2012 issue of "Pediatrics", indicated that the average
African American boy is one year ahead in pubertal development compared to the average Caucasian boy.
• This knowledge may be important to consider when monitoring a child for developmental disorders.