Summary of human biological and health changes from infancy to death

1. Human Biological
and Health Development
By Jason Arca, Anne Hobbs, Tara Polich, and Martha Rivera
Alliant International University, School Psychology MAE Program
PPS6009 Life Span Development

2. Body Growth in Infancy
● On average, North American newborns are 20 inches long and weigh
7 ½ pounds
● Most newborns lose between 5 and 7 percent of their body weight in
the first days
● As soon as they adjust to sucking, swallowing, and digesting, they
grow quickly
● By the time they have reached 4 months they often double their birth
weight
● Infants grow approximately ¾ inch per month during the first year
● Growth rate slows down a lot in the second year of life
● At age 2, infants weigh about 26 to 32 pounds
● A typical 2-year-old is 32 to 35 inches tall

3. Brain Changes in Infancy
● The EGG is used to measure brain development in infancy
● The newborn’s brain is about 25 percent of its adult weight
● At two, the brain is about 75 percent of its adult weight
● The myelin sheath and connections between dendrites are
two important developments during the first two years
● The areas of the brain do not mature consistently
● The motor control centers around brain develop at about 2
month of age
● At about one year, the brain allows speech to occur
● Brain activity may be depressed in children who grow up
in a deprived environment
● As the frontal lobe matures, infants are able to regulate
their physiological states (such as sleep)

4. Sleep in Infancy
● Newborns sleep an average of 12.8 hours per day
● The most common infant sleep-related problem reported by parents is nighttime waking
● REM sleep occurs for a much longer period in infancy than any other point in life
● Infants spend about half of their sleep time in REM sleep
● SIDS is the number one cause of infant death in the United States
● When infants are placed on their backs to sleep their risk of SIDS is reduced
● Prone sleeping, maternal smoking, and bed sharing place infants at the greatest risk of SIDS

5. Breast Vs. Bottle Feeding
● Most people believe that breastfeeding is better for a child’s health
● In 2008 over 75% of newborns were breast fed
● The American Academy of Pediatrics Section on Breastfeeding recommends
exclusive breastfeeding for the first six months and to continue as other foods
are introduced
Benefits of Breastfeeding for the Child
● Less gastrointestinal infections
● Less respiratory tract infections
● Protects against wheezing in babies
● Less likely to develop middle ear infections
● Lowers chances of being overweight or obese in childhood, adolescence, and
adulthood
● Less likely to develop type 1 diabetes in childhood and type 2 in adulthood
● Less likely to develop SIDS

6. Growth In Childhood
Early Childhood (Preschool)
● When children reach the preschool years, the percentage of increase in height and weight
decreases with each additional year (Santrock,2016).
● At this time, girls are smaller than boys and have more fatty tissue, while boys have more
muscle tissue.
● As their bodies start to lengthen, they begin to slim down and lose their “baby fat”.
● All children grow at different rates. Some children might be significantly taller than the
rest. This variation is a result of mostly heredity, but environmental experiences play a
role as well.
● A child’s ethnic group and diet are the two biggest contributors when it comes to height
and weight.
Middle and Late Childhood (Elementary School)
● During this time, children are growing at a slow, yet consistent rate (an average of 2-3
inches per year).
● The average 8 year old is about 4 feet 2 inches and weighs 56 pounds.
● Weight gain is a result of the increase in size of the skeletal system, muscular system, and
the bodies organs.
● At this age, a child experiences significant changes in proportions. Head circumference,
waist circumference, and leg length all start to decrease while they grow.

7. Children’s Health
● Although disease is not as big of a threat as it use to be, it is still very important
for parents to be sure that their children are getting the immunizations they
need.
● Parents can improve their child’s health by avoiding accidents.
● Accidents include: falls, poison, burns, car accidents, foreign objects,
suffocation, and choking.
● It is the job of the parents or caregiver to keep a close eye on the child at all
times. The caregiver should make sure a young child’s surroundings are clear
of objects that could lead to an accident. In addition, the caregiver must be sure
that a child is securely strapped in when riding in a motor vehicle.
● In addition, research has found that children are at risk for health problems
when they live in a home where a parent or guardian smokes.
● Caregivers should also limit their drinking, or avoid it all together while their
children are young.
● Unfortunately, roughly 11 million young children in the United States are
malnourished as a result of poverty (Santrock, 2016). This increases their risk
of contracting both major and minor diseases.
● Experts are trying their best to come up with ways to help improve the health of
children living in poverty.

8. Sleep During Childhood
● According to Dr. Carolyn Thiedke (2001), many children have difficulty sleeping.
● Odd sleeping behaviors are one of the most common reasons for doctor office visits.
● Dr. Thiedke (2001) states that there are studies that have shown that “night awakenings” are common throughout early
childhood. In fact, 1 in 3 children up until the age of 4 will continue to wake up multiple times during the night and cannot go
back to sleep without the help of a parent.
● One example of a sleeping disorder is night terrors. Night terrors are common in children ages 3 to 8. They are most likely
caused by stress and fatigue. The best way to avoid any further night terrors is to eliminate any stress from the child’s
environment, and to make sure they are getting plenty of rest.
● Another common unhealthy sleeping behavior is a child’s constant attempt at delaying sleep. These children are usually dealing
with major autonomy and separation problems. The best way for parents to deal with this is by ignoring the child’s demands. A
common demand is “one more story”. Giving the child objects like a blanket or a stuffed animal could also help the situation.

9. Adolescent Body Growth and Development
● Adolescence is characterized by a growth spurt and other pubertal changes
● Girls start their growth spurt younger than boys.
● Boys later surpass girls in height and weight, as they grow at a faster rate.
● Puberty is typified by physical and behavioral changes caused by increase
in release of hormones by endocrine glands:
○ Hypothalamus (eating and sexual behavior)
○ Pituitary gland (growth and regulates other glands.
○ Ovaries in girl (menstruation and ovulation, release of eggs from
ovaries)
○ Testes in boys (sperm production)
● These changes often lead to teens and young adults to be overly self-
consciousness of body image.
Mean/typical feature Girls Boys
Growth spurt begins 9 years 11 years
Peak of pubertal change 11 1/2 years 13 1/2 years
Height increase per year 3 1/2 inches 4 inches
Order of appearance of
pubertal changes
Enlargement of breasts
Appearance of publc hair
Appearance of armpit hair
Widening of hips
First menstruation
Ovulation
Increase size of penis & testes
Appearance of pubic hair
Voice change
First ejaculation
Appearance of armpit hair
Growth of facial hair
From Twardos, M. (2011) “Average Height of American
Boys and Girls in Feet vs. Age”. Retrived from
http://theinformationdiet.blogspot.com/2011/11/average-
height-of-american-boys-and.html
U.S. GROWTH CHART FROM 2000 CDC DATA
SUMMARY OF PUBERTAL CHANGES OF GIRLS VS. BOYS

10. Brain Development from
Adolescence to Young Adulthood
● Neurons are continually pruned, becoming more specialized
through skills being acquired.
● Four sections of the brain undergo changes:
○ Limbic system, attributed to emotions and reward-
seeking, completely develops by early adolescence.
○ Prefrontal cortex, responsible for reasoning and long-
term decision-making, fully matures at 18-25 years.
○ Corpus callosum, which connects the two hemispheres,
becomes thicker (Santrock, 2016, p. 98).
○ Cerebellum, which is involved coordination of different
intellectual processes (Spinks, 2002).
● Since the limbic system matures much earlier than the
prefrontal cortex or cerebellum, teens seek short-term
rewards without thinking of long term consequence, leading
to risky behavior.
Adult and teen brain, JDeCarli (2009). Pro Consumer Safety.
Developing prefrontal cortex JDeCarli (2009). Pro Consumer Safety.

11. Behaviors and Environment
● Teens circadian clock shifts forward, creating a tendency to stay up
later and wake up later (Spinks).
● Viewing electronic media late at night and caffeine use is attributed to
teens not getting adequate sleep during this critical phase of growth
(Santrok, p. 107).
● Giving in to peer pressure is common, due to immature development of
prefrontal cortex.
● Many aspects of health will be determined if adolescents engage in
risky behaviors, such as drug abuse, unprotected sex, and activities
that can injure.
● Body image issues can lead to depression and eating disorders.
● Emerging and young adults are more likely to suffer from chronic
illnesses due to poor health habits, and have more than double the
mortality rate of adolescents (Santrok, p. 120).
● One study shows illegal drug use becomes more and more common as
grade level increases from 8th to 12th grades (Santrok, p. 141). Anggara, E. (2010). [Image]. Retrieved from
https://upload.wikimedia.org/wikipedia/commons/th
umb/7/7a/Kissing_by_Teen_1.jpg

12. Middle Adulthood
Women and men at the age of 40 are now entering middle adulthood. Some of the
physical and health changes that middle age adults experience occur at an earlier age
for some and later for others. The way one lives their life and the genes they inherit will
also play a vital role on when and if any or all of these changes can occur. If someone
chooses to drink excessively, smoke regularly, not exercise, and deprive themselves of
sleep, then this can lead to poor health and impairs life satisfaction ( Blake, 2015,
Donatelle, 2013). An adult, who early on eats right, exercises, can handle stress well,
and makes sure to rest, will have a better life satisfaction later on.
At this stage in life adults may start to experience some
or most of the following issues:
● Changes in vision begin affecting the ability to focus on
close objects and objects in the distance
● Hair begins to thin out and can begin to grey
● Skin becomes drier, wrinkles, and age spots start to
appear
● Immune system is less effective
● Height loss and weight gain may occur
● Reproduction system is changing
● Hearing loss might begin
● Difficulty Sleeping

13. Women vs Men
● Menopause (menstrual periods end
and no longer fertile)
● Sex drive decreases
● Live an average of 80.8
years
● Higher chance of non-
fatal chronic condtions
● Higher chance of
hypertension &
visuals problems
● 80 % of osteoporosis
cases are women
● Testosterone production sperm
count declines gradually but
don’t lose fertility
● Erectile Dysfunction
● Sex drive decreases gradually
● Live an average of 75.7 years
● Higher chance of a fatal chronic
condition
● Higher chance of hearing
problems
● 20% of osteoporosis
cases are men

14. Late Adulthood to Death
Today, more and more individuals are living longer lives. There were 72,000
centenarians living in the U.S. at that time and the number is expected to increase
to 600,000 by 2050 (U.S. Census Bureau, 2011). 23% of women and 17% of men
aged 85 years or older have a chance of developing a neurological disorder like
Dementia. Dementia is a neurological disorder that can lead to adults not being
able to physically care for themselves and unable to recognize familiar things.
Alzheimer’s and Parkinson’s are just two types of dementia, that both can be
treated with drugs to subside their symptoms and slow down the disease, but
eventually those individuals will succumb to the disease. Cardiovascular disease
was once the number one cause of death amongst this age but cancer is now the
leading cause of death. 60% of US adults between the age of 65-74 die from
cancer or cardiovascular disease( Murphy,Xu & Kochanek, 2012)
Source:Hebert LE, Weuve J, Scherr PA, Evans DA. Alzheimer
disease in the United States (2010-2050) estimated using the
2010 Census. Neurology 2013;80(19):1778-83.
At this stage in life adults might experience some of the
following issues:
● Physical decline & less energy
● Decrease in muscle mass & reaction time is slower
● Immune system less effective
● The body & its organs are becoming less efficient

15. References
Hebert LE, Weuve J, Scherr PA, Evans DA. Alzheimer disease in the United States (2010-2050) estimated using the
2010 Census. Neurology 2013;80(19):1778-83.
Santrock, J.W. (2016). A Topical Approach to Life-span Development (8th ed). New York, NY: McGraw-Hill
Education.
Spinks, S. (Writer, Director). (2012, January 31). Inside the Teenage Brain. [Television series episode] In S. Spinks
(Producer), Frontline. Boston: PBS. Retrieved from https://www.pbs.org/wgbh/frontline/film/inside-the-teenage-
brain/.
Thiedke, C. C. (2001). Sleep Disorders and Sleep Problems in Childhood. American Family Physician, 63(2), 277-
285. Retrieved September 8, 2018, from https://www.aafp.org/afp/2001/0115/p277.html.