Chapter 2: BIOLOGICAL FOUNDATIONS:
The biological changes of puberty are a central part of development during adolescence in all
cultures (these changes also interact with cultural influences)
THE BIOLOGICAL REVOLUTION OF PUBERTY:
changes in physiology, anatomy, and physical functioning that develop a person into a mature
adult biologically/ prepares the body for sexual reproduction
The Endocrine System:
A network of glands in the body. Through hormones (chemicals), the glands coordinate their
functioning and affect the development and functioning of the body.
The Initiation of Puberty in the Hypothalamus:
-Hormonal changes of puberty begin in the hypothalamus.
The “master gland” - affects wide range of physiological/ psychological functions,
stimulates/ regulates production of hormones by other glands.
-Initiating puberty: hypothalamus increases the production of Gonadotropin-Releasing hormone
(GnRH) and releases it in pulses at intervals of about 2 hours.
-The increase occurs once a threshold level of body fat is reached
-Fat cells produce leptin (a protein) which signals the hypothalamus.
The Pituitary Gland and the Gonadotropins:
-Increase in GnRH affects the Pituitary, causing gonadotropins to be released
-Follicle-stimulating hormone (FSH)
-Luteinizing hormone (LH)
-Both stimulate the development of gametes and sex hormones in the ovaries/ testicles
The Gonads and the Sex Hormones:
-Gonads (sex glands): ovaries and testes
-In response to stimulation from FSH and LH releases by the pituitary gland, the gonads
increase their production of sex hormones
-2 classes of sex hormones:
-Androgens: sex hormones in males (primary/ secondary male characteristics)
-Testosterone: most important androgen in pubertal dev. for boys
-Estrogens: sex hormones in females (primary/ secondary female characteristics)
-Estradiol: most important estrogen in pubertal dev. for girls
-Estradiol and testosterone have stable levels in both boys and girls throughout childhood, until
-Mid-teens, estradiol production is about 8x as high in females (2x as high in males)
-Mid-teens, testosterone is about 20x as high (4x as high in females)
-Androgens are also produced by the adrenal glands -The pituitary increases production of the hormone Adrenocorticotropic hormone (ACTH)
at puberty, which causes the adrenal glands to increase androgen production
The Feedback Loop in the Endocrine System (Fig. 2.3 PG. 36):
-A system of hormones involving the hypothalamus, the pituitary gland, and the gonads (and
adrenal glands), that monitors and adjusts the levels of the sex hormones.
-The hypothalamus monitors the levels of the sex hormones in the bloodstream, and
when they reach an optimal level (set point), the hypothalamus reduces its production of GnRH.
-The pituitary responds to the reduction in GnRH by reducing its production of FSH, LH,
-The gonads and adrenal glands respond to lower levels of FSH and LH by reducing the
amount of sex hormones they produce.
-When puberty begins, the set points for androgens/ estrogens rise in the hypothalamus (set
point for androgens rising higher in males than females and vice versa)
-As puberty beings and the set points for the sex hormones rise in the hypothalamus, the
gonads can produce an increasing amount of sex hormones before the hypothalamus signals a
-in the course of puberty, it’s as if the thermostat rises to 80 and the heat of sex hormone
production rises accordingly
Physical Growth During Puberty:
-One of the earliest signs of puberty for both girls and boys is the adolescent growth spurt (rapid
increase in height).
-At peak height velocity (when the adolescent growth spurt is at its max), girls grow at about 3.5
inches per year, and boys grow at about 4.1 inches
-Girls typically reach the beginning of their growth spurt/ peak height velocity about 2 years
earlier than boys
-Girls also mature 2 years ahead of boys
-Earlier maturation of girls contributes to their smaller adult height (adolescent growth
spurt also marks the end of growth in height) - reach their final height earlier (15, compared to
17 for boys)
-Not all parts of the body grow at the same pace.
-A certain amount of asynchronicity in growth
-Extremities (feet/ hands/ head) are the first to hit the growth spurt, followed by the arms/
legs. The torso/ chest/ shoulders are the last parts to reach the growth spurt
-A spurt in muscle growth also occurs primarily because of the increase in testosterone
-Levels of body fat surge, but body fat increases more for girls than for boys
-Boys have a muscle-to-fat ratio of about 3:1
-Girls have a muscle-to-fat ration of about 5:4
-The heart becomes larger - boys’ hearts grow more than girls’ hearts and their heart rates fall
to a lower level (average girl’s heart rate is about 5 bpm faster than the average boy’s) -Vital capacity (the amount of air that can be exhales after a deep breath) increases more for
boys than girls.
-Exceeding a specific body mass index (BMI), which is a ratio of height to weight
-Across countries, rates of overweight and obesity are highest in the most affluent regions and
lowest in poorer regions
-About 14% of American adolescents ages 12-17 are classified as obese
-African Americans and Latinos obesity rates are 50% higher than the rates for Whites
-Obese adolescents have higher leptin levels, so it may be that increased obesity has
contributed to the earlier onset of puberty among African American/ Latino girls
Physical Functioning in Emerging Adulthood:
-Even after maximum height is attained, the bones continue to grow in density, and peak bone
mass is reached in the 20s.
-Measures of physical stamina (maximum oxygen uptake/ VO2 max - reflects the ability of the
body to take in oxygen and transport it to various organs) also peak in the early 20s
-Cardiac output (quantity of blood flow from the heart) peaks at age 25
-Reaction time is also faster in the early 20s
-Emerging adulthood is also the period with the least susceptibility to physical illness
-Automobile accidents are the leading cause of death among emerging adults
-Homicide is another common cause of death in developed countries during EA.
-Rates of contracting STIs are highest in the early 20s
Primary Sex Cha