Chapter 1 (blz. 13-33): biological transitions
A fundamental change that happens during adolescence concerns biological transitions. These
transitions have a huge impact on the psychological and social development of teenagers.
What is puberty?
The term puberty refers to the period during which an individual becomes capable of sexual
reproduction. It has four main physical manifestations:
1. A quick acceleration in growth (increases in height and weight)
2. The development of primary sex characteristics (gonads/sex glands, results in hormonal
changes)
3. The development of secondary sex characteristics (changes in genitals and breasts, growth of
pubic, facial and body hair)
4. Changes in the brain’s anatomy and activity as a result of hormonal influences
These changes are the result of developments in the endocrine and central nervous systems.
The endocrine system produces, circulates, and regulates levels of hormones. Important terms are:
- Hormones: highly specialized substances that are secreted by one or more endocrine glands
and enter the bloodstream.
- Glands: organs that stimulate certain parts of the body to respond in specific ways.
- Gonadotropin-releasing hormone (GnRH) neurons: specialized neurons that are activated by
certain pubertal hormones.
The endocrine system receives its instructions to increase or decrease circulating levels of certain
hormones from the central nervous system, mainly through the firing of GnRH neurons in the brain.
Hormonal levels are “set” at a certain point (set point), which may differ depending on the stage of
development. When a certain hormonal level in the body dips below the set point for that hormone,
secretion of the hormone increases; when the level reaches the set point, secretion temporarily
stops. This is an example of a feedback loop. That is a cycle through which two or
more bodily functions respond to and regulate each other.
Another feedback loop is known as the HPG axis. That is the neurophysiological
pathway that involves the hypothalamus, the pituitary gland, and the
gonads. Gonads are the glands that secrete sex hormones. The glands are the testes
in males and the ovaries in females. The sex hormones are androgens and estrogens.
The HPG axis is set to maintain certain levels of androgens and estrogens.
Adrenarche is the maturation of the adrenal glands that takes place during
adolescence. Development of body odor, signaling the beginning of sexual
maturation. Changes at puberty in the brain system that regulates the adrenal gland
are also important because this is the brain system that controls how we respond to stress. The
hormonal changes of puberty make us more responsive to stress (period of vulnerability to mental
disorders). This leads to excessive secretion of the stress hormone cortisol.
The onset of puberty is stimulated by an increase in kisspeptin, a brain chemical. A chemical called
Leptin stimulates kisspeptin and a chemical called melatonin suppresses kisspeptin. The more fat cells
you have and the more light to which you have been exposed in childhood, the earlier you are likely
to go through puberty.
Many changes in behavior during adolescence do occur because of changes in hormone levels at
puberty. Other changes in puberty are likely caused by an interaction between prenatal and pubertal
hormones.
,Somatic development/timing and tempo of puberty
The consequences of the hormonal changes of puberty on the body are remarkable. One of them is
the growth spurt. That is the dramatic increase in height and weight that occurs during puberty. The
peak height velocity is the time at which the adolescent is growing most rapidly. This is at the same
rate as a toddler. A process called epiphysis marks the conclusion of puberty because it is the closing
of the ends of the long bones which terminates growth in height.
The growth spurt in height is accompanied by an increase in weight, because of an increase in muscle
and fat. There are important sex differences in body composition. Muscle tissue grows faster in boys
than in girls. Body fat increases more for girls, which brings concerns about weight. Girls who mature
early begin dating early and are more susceptible to feelings of dissatisfaction over the body. Before
puberty, there is not much difference for the sexes and this explains why differences in strength and
athletic ability often appear for the first time during adolescence. However, sex differences in physical
ability are influenced by a variety of factors, of which hormonal differences are but one part of a
complex picture.
The development of the secondary sex characteristics is often divided into five stages and these
stages are also called the Tanner stages. Secondary sex characteristics are the manifestations of
sexual maturity at puberty (development of breasts, growth of facial and body hair, and voice
changes). Boys are generally fertile before they have developed an adult-like appearance. Girls
generally appear physically mature before they are fertile. Menarche is the beginning of menstruation
and is a relatively late development. Full reproductive function does not occur until numerous years
after menarche.
Variations in the age at which puberty begins and in the rate at which maturation occurs are so great
that it is misleading to talk about average ages. There is no relation between the age at which
puberty begins and the rate at which pubertal development proceeds. The onset of puberty for girls
is between 8 and 13, for boys between 9 and 14. The timing of puberty has a small effect on one’s
weight or height. There are ethnic differences in the timing and rate of pubertal maturation. Black
girls mature earlier than Latinx, who mature earlier than white.
When identical twins and individuals who are not genetically identical are compared with regards to
the timing and tempo of a person’s pubertal maturation results indicate that the timing and tempo
are largely inherited. The environment nonetheless plays an important role. The timing and tempo
are the product of an interaction between nature and nurture. The two most important
environmental factors are nutrition and health. Puberty occurs earlier among individuals who are
better nourished.
Some study results indicate that social factors in the home environment may influence the onset of
maturation. An explanation for this is that tension in the family may induce stress, which may affect
hormonal secretions in the adolescent. Pheromones: a class of chemicals secreted by animals that
stimulate certain behaviors in other members of the species >> may stimulate puberty because of the
presence of someone you are unrelated to (stepfather).
The secular trend is the tendency, over the past 200 years, for individuals to be larger in stature and
to reach puberty earlier, primarily because of improvements in health and nutrition.
The psychological and social impact of puberty
Adolescent’s behavior and psychological functioning can be affected by puberty in several ways:
- Behavior can be directly affected by the biological changes of puberty.
- The adolescent’s self-image can change because of the changes in puberty and this can affect
how the adolescent behaves.
, - Others may react differently to the teenager, because of the new appearance of the
adolescent caused by the biological changes. This, in turn, might provoke changes in the
behavior.
To study the psychological and social effects of puberty, researchers have generally taken two
approaches:
- Cross-sectional study: a study that compares two or more groups of individuals at one point
in time.
- Longitudinal study: a study that follows the same group of individuals over time.
Study results indicate that physical maturation affects the adolescent’s:
- Self-image: the impact is to a great extent shaped by the social context.
- Mood: there is little evidence that moodiness results exclusively from hormones. The moods
of adolescents fluctuate during the day more than the moods of adults. These shifts in mood
appear to have more to do with shifts in activities than with internal, biological changes.
- Relationship with parents: puberty appears to increase conflict and distance between parents
and children. There is a distancing effect in puberty, but this is less observed in ethnic
minority families.
Stress is a cause rather than a consequence of pubertal maturation, it can speed the process up. The
problematic outcomes associated with early maturation are also associated with exposure to stress.
Heightened susceptibility to stress can make plasticity (the capacity of the brain to change in
response to experience) go two ways, a stressful experience can cause harm, or it can improve mental
health through interventions
Adolescents seem to have a delayed phase preference. That is a pattern of sleep characterized by
later sleep and wake times, which usually emerge during puberty. It appears that it is driven by the
biological changes of puberty. The tendency to stay up late is due to the interaction of biology and
the environment, which provides reasons to stay up. The preferred bedtime gets later as individuals
move into adolescence, the amount of sleep needed remains around nine hours. Because school
starts early, and adolescents go to sleep late at night they can get sleep deprivation. Many negative
consequences of sleep deprivation are due to its adverse impact on self-control.
Most adolescents react positively to the biological changes associated with puberty, especially those
related to the development of secondary sex characteristics. Adolescents are very aware of whether
they are early or late relative to their classmates, and their feelings about themselves are influenced
by comparing.
Findings on the emotional effects of early maturation on boys are mixed. Still, research results do
indicate that early-maturing boys feel better about themselves and are more likely than their peers to
get involved in antisocial or deviant activities. An explanation might be that boys who look mature
physically are less closely supervised by adults. Another explanation might be that older-looking boys
develop friendships with older peers, who lead them into problematic activities. Late matures
develop better coping skills.
A lot of research findings show that early-maturing girls have more emotional difficulties than their
peers. These difficulties seem to arise from how looking different from their peers affects girls’
feelings about their appearance and social relationships with other adolescents. Early-maturing girls
are more popular but experience more emotional upset in social life.
, There are numerous theories explaining why early maturation is harder on girls than boys. The
- The ‘Maturational deviance’ hypothesis states that teenagers who stand far apart from their
peers may experience more psychological distress than adolescents who blend in more easily.
Early-maturing girls mature earlier than both boys and girls. This makes them stand out at a
time when they would rather not stand out.
- A second explanation focuses on ‘developmental readiness’. Younger adolescents might be
less ready to cope with the challenge of psychological adaptation necessary for puberty than
older adolescents.
- A third explanation focuses on the cultural desirability of different body types. Early maturers
experience weight gain at a time when most of their peers are still girlishly thin. For boys, this
is often the other way around, where society admires a tall and muscular man.
Early-maturing girls are also more likely to become involved in problem behavior. Just as with boys,
these girls are more likely to spend time unsupervised and hanging out with older peers. It is still
important to consider the role of context. The predisposition may be realized only in an environment
that permits the behavior and/or has many stressful life events.
