Biological Development in Adolescence
UNIT OBJECTIVES
Understand the relation of puberty to adolescence.
Define hormones.
Delineate differences between primary and secondary sexual characteristics.
Identify the Tanner stages.
Be able to explain the differences between precocious and delayed puberty.
Define teratogens.
HORMONES
One of the defining aspects of adolescence is puberty. This is the series of hormonal changes that actually begin to occur for many people in late childhood. The process involves biological, physical, and hormonal changes that will affect a person for life. Most researchers believe that adolescence is not synonymous with puberty but that the two overlap. Puberty is triggered by hormones. Hormones are chemicals made by the body. They send messages to various other parts of the body outside the nervous system. They help regulate many of the body’s processes.
The hormones that trigger puberty are released in the brain to other parts of the body. The hypothalamus, located deep in the brain, begins this process. This is largely under genetic control and does not occur consciously. These hormones activate another brain area called the pituitary glands. The pituitary glands are a small area in the brain the size of a pea. Here the hormones release gonadotropin, which in turn releases sex hormones from the gonads or sex glands.
Testosterone plays a critical role in developing male reproductive tissues such as the testes. It also promotes body hair and muscle and bone mass in both males and females. These are called secondary sexual characteristics. Biological females also have testosterone though not in the concentration that males typically have.
Estrogen is the primary female sex hormone. It is involved in the development and regulation of the female reproductive system and female secondary sex characteristics. While estrogen is present in both males and females, it is usually present at higher levels in females of reproductive age. Estrogen regulates the menstrual cycle. It also causes the development of secondary characteristics such as breasts. Males also have some estrogen, which may be necessary for a healthy libido and sperm development.
Adrenarche is the earliest stage of puberty. It actually occurs as young as ages six and eight. During this period, the adrenal glands secret androgen, causing increased body hair and body odor. Eventually, the skin will become oilier, leading to the likelihood of the development of acne. Acne is often a cause of concern. Usually, though, acne responds well to several home remedies or over-the-counter treatments. However, for a small group of teens, acne can be a severe condition. Adolescents who have problems with acne should consult a health care professional since treatments are available.
Gonadarche begins later, typically between ages 8 and 10 or 11. It includes menarche in females, the first menstrual period, which starts later. For males, this biological process is mirrored in spermache, the first ejaculation of semen. This typically occurs later than gonadarche.
Genes play a necessary process not only at the beginning of puberty but also in its ongoing timing. Some people seemed “timed” to experience puberty earlier or all at once. Some experience it much later. Some experience it more spread out. There are many individual differences.
PHYSICAL CHANGES
The primary sex characteristics of females involve the growth of the vagina, uterus, and other reproductive system aspects. Generally, a female is not fully or consistently fertile until several years after menarche since regular ovulation occurs about two years later. Adolescents should realize that this should not be used as birth control because it is not necessarily reliable.
Secondary sexual characteristics are those associated with sex hormones that cause physical changes. These are triggered by testosterone released from the pituitary glands for males, which releases other hormones. For girls, the trigger is estrogen, although other hormones are also involved.
During puberty, both girls and boys typically develop deeper voices. The voices of boys are generally deeper than girls because of a more significant Adam’s apple. In addition, girls develop more prominent breasts and curved hips.
For males, facial hair generally occurs first on the upper lips between 14-17. It then spreads to form a mustache and then over the cheeks. It may be completely present in late adolescence but may not appear until much later. Some men do not have much or any facial hair, which is dependent on genetics.
Secondary sexual development Puberty brings dramatic changes in the body, including primary and secondary sex characteristics. Hong Kong Open University CC
The Tanner Stages
The Tanner stages or system is a well-known method to describe normal sexual development in males and females. Named after a British pediatrician James Tanner who invented it, the Tanner stages are physical development stages in children, adolescents, and adults. The stages define measurements of development based on observable primary and secondary sex characteristics. Due to natural variation, individuals pass through the Tanner stages at different rates.
Pubic hair (both male and female)
Tanner I no pubic hair at all [typically age ten and under]
Tanner II small amount of long, downy hair with slight pigmentation at the base of the penis and scrotum (males) on the labia majora (females)
Tanner III hair becomes coarser and curlier and begins to extend laterally.
Tanner IV adult-like hair quality, extending across pubis but sparing medial thighs.
Tanner V hair extends to the medial surface of the thighs [14+]
Genitals (male)
Tanner I Prepubertal (testicular volume less than 1.5 ml; small penis of 3 cm or more minor) [typically age nine and under)
Tanner II Testicular volume between 1.6 and 6 ml; skin on scrotum thins, reddens and enlarges; penis length unchanged.
Tanner III Testicular volume between 6 and 12 ml; scrotum enlarges further; penis begins to lengthen to about 6 cm.
Tanner IV Testicular volume between 12 and 20 ml; scrotum enlarges further and darkens; penis increases in length to 10 cm and circumference.
Tanner V Testicular volume greater than 20 ml; adult scrotum and penis of 15 cm in length [14+]
Breasts (female)
Tanner I No glandular tissue; areola follows the skin contours of the chest (prepubertal) [typically age ten and under]
Tanner II Breast bud forms, with a small area of surrounding glandular tissue; the areola begins to widen.
Tanner III’s Breasts become more elevated.
Tanner IV Increased breast size and elevation. Areola and papilla form a secondary mound projecting from the surrounding breast’s contour.
Tanner V Breast reaches final adult size; the areola returns to the surrounding breast’s contour, projecting the central papilla.
Maturation and Growth
Before puberty, there are almost no sex differences in fat and muscle distribution between males and females. Their appearances are similar. However, during puberty, boys grow muscles much faster. Girls add fat much quicker than boys.
During adolescence, both weight and height increase substantially for both girls and boys. Adolescent growth spurts are a well-known phenomenon. They typically occur first for females. Usually, people gain 15%-25% of their height. Typically, growth spurts stop by 18-21 for boys and 17 -18 for girls. For a few years, girls are taller than boys but generally, by age 14, boys overtake girls.
During adolescence, girls may gain as much as 18 pounds a year on average. Girls generally put on about 52 pounds. Boys may gain 20 pounds per year, also putting on 52 lbs. These are averages, and there is a wide range of variations.
The height and timing of growth are primarily determined by genetic makeup. Weight is both genetic and is also influenced by the composition of diet and exercise.
Males tend to develop increased strength and a larger capacity for more strenuous exercise. This is probably because, on average, they have slightly larger heart and lung capacities that begin with puberty. Also, in our society, males have more opportunities to engage in heavy and exhausting exercise, so social influences should not be discounted. Blood pressure also increases in males. Recently, there has been an increase in teenage hypertension (high blood pressure). This has occurred in males and females. This was rare in previous generations and is likely due to dietary factors.
Data for individuals who identify as transgender are not known. Such research has not been conducted until recently or not at all.
Muscle growth also occurs in response to sex hormones, particularly testosterone. Bone growth occurs, and the gaps between bones fuse so that bones cannot grow any longer. This results in bones becoming more complete but also more brittle. This happens at the end of puberty when development is completed.
Adding testosterone or anabolic steroids that mimic testosterone for bulking up or adding strength is always a poor choice. This is exceptionally true during the teen years since they may easily interfere with puberty and suppress normal development.
Obesity can affect health and can cause early puberty. Image by the 59th Medical Wing is in the public domain.
PRECOCIOUS AND DELAYED PUBERTY
In our society, there has been a tendency for increasing earlier puberty, especially with females. Evidence suggests that dietary factors play a part in timing, with obesity related to early puberty. Some research suggests that the rising tide of obesity maybe delay the onset of puberty in boys. While more girls are increasingly entering puberty at younger ages, other research indicates that some boys may be starting later.
Precocious puberty occurs when puberty is two or more years earlier than usual for people’s peers. Medical factors can cause precocious puberty. It can also be related to the environment. People with questions should discuss concerns with a pediatrician or health provider.
The causes of early puberty are often unclear. As discussed above, girls who have a high-fat diet and are not physically active or obese are more likely to physically mature earlier.
Girls who grow up in homes where the father is absent or abusive may reach puberty earlier. One hypothesized reason is that the stress hormone cortisol influences other hormones. Cortisol is released when we feel stressed. Excessive cortisol may start a reaction that causes an early timing of puberty (Allen & Leary, 2010).
Early or precocious puberty is associated with a variety of behavioral problems, particularly in girls. However, the direction of causality is not clear. Researchers are presently investigating this topic.
Early puberty may also be associated with a higher risk for sexual abuse. However, research has had a hard time parceling out other relevant factors, such as poverty.
Early puberty clearly does put girls at high risk for bullying, teasing, and mental health problems. In addition, it places adolescents at higher risk for being of shorter height than adults. Early puberty additionally puts girls at a “far greater” risk for breast cancer later in life.
There is some evidence that boys who grow up without a father in the home may have disrupted puberty. However, the effects vary and may be highly individualistic. In some cases, this may result in early puberty and delayed puberty.
For boys, early puberty and physical maturation have been associated with various symptoms, including anxiety, depressions, impulsivity, substance abuse, and school withdrawal. Though boys face fewer problems from early puberty, early puberty is not always beneficial. For example, early sexual maturation in boys can increase aggressiveness. Because they appear older than their peers, boys may face increased social pressure to conform to adult norms. As a result, society may view them as more emotionally advanced. However, their intellectual and social development may not coincide with their appearances. Studies have also shown early maturing boys are more likely to be sexually active. In addition, they may be more impulsive.
The maturation compression hypothesis states that people who experience rapid and early maturation do not have the time to become accustomed to puberty’s biological changes. Hence those who experience early puberty are at high risk for a variety of problems.
Very little is known about early puberty and people who identify as transgender. This is an area where behavioral scientists have now begun substantial work.
Nutrients, particularly sugar and micronutrients such as vitamins and minerals, may also be essential for the timing of puberty. The American diet of high fat and carbohydrates, with processed food and sugar, is associated with early puberty and many other health problems. Many dietary experts now believe that processed foods and refined sugars should be consumed in moderation throughout the lifespan, including the teen years. Fresher, more natural foods are generally better for health for many reasons. Unfortunately, for many poor or needy people who lack access to quality food, consistent availability of fresh food items may be hard to secure. This may be one reason obesity and adolescent diabetes, discussed further in Unit 8, are much higher in more impoverished communities, rural communities, and communities of color.
Delayed puberty occurs when a person has incomplete development of sexual characteristics past the onset of puberty. In the United States, girls are defined as having delayed puberty if they lack breast development by age 13 or have not started menstruating by age 16.
Boys have delayed puberty if they lack enlargement of the testicles by age 14. Delayed puberty affects about 2% of adolescents.
Puberty can be delayed for several years and still be considered normal. Delay of puberty may also happen because of malnutrition, diseases, drug abuse, problems with sex hormones, or the reproductive system’s failure to develop.
Physically active girls may experience late puberty. Girls who mature later have, on average, more successful adjustments than many of their peers. Studies suggest that many late-maturing boys show more depression and anxiety than peers but may do better than many of their peers academically.
Vignette 5.1 Olivia: DELAYED PUBERTY
‘I had delayed puberty,” said Olivia, who is now 23. “It is not something I would wish on anyone.”
Olivia was an exceptional athlete. She was a highly competitive swimmer who had a very low body fat content. She was also a distance runner and excelled in other sports.
“I’m sure that put me at risk,” she noted. “I ate normally. That is important because my various doctors thought I might have an eating disorder. But that wasn’t the case at all. It’s just that my hormones thought I was too skinny, I guess.
“Also, there were probably some genetic factors with me. My sister, my mother, my aunt, they all had late puberties. My mother, who was, sorry mom, a pretty big lady in high school, didn’t get her first period until 16.”
“I was 17 and had, well, no chest. I was tall and lanky. So you can imagine the stares I got or thought I got. That made me feel depressed like I did not belong. I didn’t feel good about myself.
“My doctors really weren’t sure what to do. I remember having lots of blood tests, especially in tenth grade. It was a scary time. I even talked with a counselor.”
“Eventually, I was treated with hormones to start puberty. I was almost 18. That was a major decision, scary, for sure, but I am glad we did it. My family helped, but they left it to me. The counselor was helpful, too, not really in making a decision but in helping me know how to decide things if that makes sense.
“I am fine now. I now have normal periods like other girls. I feel like I have a normal shape. I’m still thin and wiry, but that’s me. I still run competitively. I don’t swim for a team, but I don’t have time because I’m in school.
“But the good news is that my doctor says there is no long-term damage to my body. Everything seems normal.”
HORMONAL DISRUPTION
Disruptions to hormones can affect puberty. They are suspected to be related to many causes. For example, some common environmental toxins may have substantial effects on hormones associated with puberty.
The plastic BPH (Bisphenol A), which at one time was very common in households, has recently been restricted because it is suspected of inhibiting or slowing down puberty. Nevertheless, BPH was until recently widely found in food containers and even in infant bottles.
Other chemicals that mimic estrogens, known as xenoestrogens, are a possible cause of early puberty in girls. These chemicals are released in a variety of ways and maybe in our food chain.
A teratogen is a chemical substance that is known to cause fetal problems. Usually, the dose is important because most dangerous materials only become toxic at certain strengths. Maternal (mother) or paternal (father) exposure to teratogens may have a long-term influence that becomes known only at puberty or later.
An example is DES (Diethylstilbestrol). This is a synthetic form of the female hormone estrogen. It was prescribed to pregnant women between 1940 and 1971 primarily to prevent miscarriages. The drug worked very well to reduce miscarriages. However, research has shown that it is causing various rare cancers in adolescents and even in older women.
Heavy nicotine exposure or exposure to other types of smoke may inhibit puberty. This occurs when adolescents themselves smoke but may also be observed in households with substantial secondhand smoking. Vaping and nicotine chewing may also have this effect, although current research is in progress. Alcohol consumed in beverages causes an increase in female hormones. In animal models, this delays puberty. In humans, it has been found to delay puberty in males. However, experimental evidence is lacking since it would be unethical to try such experiments with people.
The active ingredients in marijuana have been associated with increased disruptive hormones to puberty in laboratory animals. Data is not clear regarding humans, but research is suggestive that similar effects are likely to occur. Although the hormonal effects are complex, marijuana appears to increase female hormones in males. Heavy male marijuana users have reported accounts of gynecomastia or breast growth. This argues against the use of this drug at least until the end of adolescence or later. This statement should not be viewed as an endorsement of marijuana use for young adults.
Psychological or social stress may also affect puberty, depending on its severity and timing. Stress hormones appear to block other hormones in the body. This would typically delay puberty, although, in some situations, highly stressed children enter puberty earlier than expected. Further research is needed to clarify what types of stressors are likely to affect children and at what points in their life cycles(Hyman, Gold, & Sinha, 2010)/
Vignette 5.2 Patricia: A Lifelong Exposure to Terotogens
Patricia is a middle-aged woman. Her mother was one of the last group of pregnant women to receive the drug DES, which was prescribed to prevent miscarriages.
In middle and high school, Patricia struggled with a variety of serious gynecological problems. These included a precancerous condition. However, with frequent medical treatment, her problems seemed to subside, at least for a while.
Eventually, Patricia got married and planned to start a family. Unfortunately, it was extremely difficult for her to get pregnant. Once pregnant, she had a series of miscarriages. Eventually, she had a healthy daughter carried to term after a high-risk pregnancy, resulting in Patricia being hospitalized twice.
For a few years, her medical condition seemed better. She had a second child. Both children, girls, were normal and without medical problems.
However, Patricia is still worried. She must receive intensive medical screenings on a routine basis. She is aware that she is at higher risk for breast cancer and possibly other cancers.
Finally, she is concerned that both of her daughters may have problems related to her exposure to this hormone during her mother’s pregnancy. Current research has attempted to answer this concern but is not conclusive. However, her husband, their daughters, and her fear that these problems may not show up until much later.
END OF PUBERTY
The end of puberty is signaled by a chain of hormones and feedback processes that inhibits the young adult’s growth and end rapid development. Although the timing differs for most people, growth spurts are almost always over by the end of high school. However, some secondary sex characteristics can continue to develop into the early and even middle 20s. These include the thickening of beards or the darkening of bodily hair.
Although physical development ends during the teenage years, research now shows that cognitive development continues until the mid-twenties. Attention, concentration, motivation, and reasoning skills increase. Impulsivity and ability to resist temptation decreases. Together these are what is known as the Executive Function skills referred to in Unit 3. Although memory is probably as sharp as it will be by the early 20s, the capacity to make decisions and learn from the experience seems to actually grow throughout life.
What is remarkable about the process of adolescence is that despite its complexity and diversity, most people will arrive at the same endpoint. Despite the incredible complexity of hormonal timing and variations among people, the results have been the same throughout history.
CRITICAL THINKING
Do you think that the Covid-19 pandemic will have an effect on the timing and development of puberty? Why or why not?
What problems do you think that people who do not identify as male or female have during the transition of puberty face?
What are some critical questions regarding puberty that are still unclear?
Why is it impossible to do random assignment research regarding puberty experiments?
What are the ethical problems regarding puberty research and transgender people?