Adolescence begins with the onset of puberty, a developmental period in which hormonal changes cause rapid physical alterations in the body, culminating in sexual maturity. Although the timing varies to some degree across cultures, the average age range for reaching puberty is between 9 and 14 years for girls and between 10 and 17 years for boys (Marshall & Tanner, 1986). This period of physical development of the adolescent age 9-13 is divided into two phases. 9
Figure \(\PageIndex{1}\): Puberty brings dramatic changes in the body, including the development of primary and secondary sex characteristics. (Image by the Open University of Hong Kong is licensed under CC BY-SA 4.0)
The first phase of puberty begins when the pituitary gland begins to stimulate the production of the male sex hormone testosterone in boys and the female sex hormones estrogen and progesterone in girls. The release of these sex hormones triggers the development of the primary sex characteristics, the sex organs concerned with reproduction. It also involves height increases from 20 to 25 percent. Puberty is second to the prenatal period in terms of rapid growth as the long bones stretch to their final, adult size. Girls grow 2–8 inches (5–20 centimeters) taller, while boys grow 4–12 inches (10–30 centimeters) taller.
Secondary sexual characteristics are visible physical changes not directly linked to reproduction but signal sexual maturity. The growth spurt for girls usually occurs earlier than that for boys, with some boys continuing to grow into their 20s. For males this includes broader shoulders, an enlarged Adam’s apple, and a lower voice as the larynx grows. Boys typically begin to grow facial hair between ages 14 and 16, which becomes coarser and darker, and hair growth occurs in the pubic area, under the arms, and on the face.
For females the enlargement of breasts is usually the first sign of puberty and, on average, occurs between ages 10 and 12 (Marshall & Tanner, 1986). Girl’s hips broaden and pubic and underarm hair develops and becomes darker and coarser. Both boys and girls experience a rapid growth spurt during this stage. Males and females may begin shaving during this time period as well as showing signs of acne on their faces and bodies.
Acne is an unpleasant consequence of the hormonal changes in puberty. Acne is defined as pimples on the skin due to overactive sebaceous (oil-producing) glands (Dolgin, 2011). These glands develop at a greater speed than the skin ducts that discharge the oil. Consequently, the ducts can become blocked with dead skin and acne will develop. According to the University of California at Los Angeles Medical Center (2000), approximately 85% of adolescents develop acne, and boys develop acne more than girls because of greater levels of testosterone in their systems (Dolgin, 2011). Hormones that are also responsible for sexual development can also wreak havoc on the teenage skin.12
A major milestone in puberty for girls is menarche, the first menstrual period, typically experienced at around 12 or 13 years of age (Anderson, Dannal, & Must, 2003). The age of menarche varies substantially and is determined by genetics, as well as by diet and lifestyle, since a certain amount of body fat is needed to attain menarche. Girls who are very slim, who engage in strenuous athletic activities, or who are malnourished may begin to menstruate later. Even after menstruation begins, girls whose level of body fat drops below the critical level may stop having their periods. The sequence of events for puberty is more predictable than the age at which they occur. Some girls may begin to grow pubic hair at age 10 but not attain menarche until age 15.13
Male Anatomy
Males have both internal and external genitalia that are responsible for procreation and sexual intercourse. Males produce their sperm on a cycle, and unlike the female's ovulation cycle, the male sperm production cycle is constantly producing millions of sperm daily. The male sex organs are the penis and the testicles, the latter of which produce semen and sperm. The semen and sperm, as a result of sexual intercourse, can fertilize an ovum in the female's body; the fertilized ovum (zygote) develops into a fetus, which is later born as a child.
Figure \(\PageIndex{3}\): (Image is in the public domain)
Female Anatomy
Female external genitalia is collectively known as the vulva, which includes the mons veneris, labia majora, labia minora, clitoris, vaginal opening, and urethral opening. Female internal reproductive organs consist of the vagina, uterus, fallopian tubes, and ovaries. The uterus hosts the developing fetus, produces vaginal and uterine secretions, and passes the male's sperm through to the fallopian tubes while the ovaries release the eggs. A female is born with all her eggs already produced. The vagina is attached to the uterus through the cervix, while the uterus is attached to the ovaries via the fallopian tubes. Females have a monthly reproductive cycle; at certain intervals the ovaries release an egg, which passes through the fallopian tube into the uterus. If, in this transit, it meets with sperm, the sperm might penetrate and merge with the egg, fertilizing it. If not fertilized, the egg and the tissue that was lining the uterus is flushed out of the system through menstruation (around every 28 days).
The age of puberty is getting younger for children throughout the world. A century ago the average age of a girl’s first period in the United States and Europe was 16, while today it is around 13. Because there is no clear marker of puberty for boys, it is harder to determine if boys are maturing earlier, too. In addition to better nutrition, less positive reasons associated with early puberty for girls include increased stress, obesity, and endocrine disrupting.
Because rates of physical development vary so widely among teenagers, puberty can be a source of pride or embarrassment. Girls and boys who develop more slowly than their peers may feel self-conscious about their lack of physical development; some research has found that negative feelings are particularly a problem for late maturing boys, who are at a higher risk for depression and conflict with parents (Graber et al., 1997) and more likely to be bullied (Pollack & Shuster, 2000). Additionally, problems are more likely to occur when the child is among the first in his or her peer group to develop. Because the preadolescent time is one of not wanting to appear different, early developing children stand out among their peer group and gravitate toward those who are older (Weir, 2016).
Early maturing boys tend to be physically stronger, taller, and more athletic than their later maturing peers; this can contribute to differences in popularity among peers, which can in turn influence the teenager’s confidence. Some studies show that boys who mature earlier tend to be more popular and independent but are also at a greater risk for substance abuse and early sexual activity (Flannery, Rowe, & Gulley, 1993; Kaltiala-Heino, Rimpela, Rissanen, & Rantanen, 2001).
Early maturing girls may face increased teasing and sexual harassment related to their developing bodies, which can contribute to self-consciousness and place them at a higher risk for anxiety, depression, substance abuse, and eating disorders (Ge, Conger, & Elder, 2001; Graber, Lewinsohn, Seeley, & Brooks-Gunn, 1997; Striegel-Moore & Cachelin, 1999).16
The Brain and Sex
The brain is the structure that translates the nerve impulses from the skin into pleasurable sensations. It controls nerves and muscles used during sexual behavior. The brain regulates the release of hormones, which are believed to be the physiological origin of sexual desire. The cerebral cortex, which is the outer layer of the brain that allows for thinking and reasoning, is believed to be the origin of sexual thoughts and fantasies. Beneath the cortex is the limbic system, which consists of the amygdala, hippocampus, cingulate gyrus, and septal area. These structures are where emotions and feelings are believed to originate, and are important for sexual behavior.
The hypothalamus is the most important part of the brain for sexual functioning. This is the small area at the base of the brain consisting of several groups of nerve-cell bodies that receives input from the limbic system. Studies with lab animals have shown that destruction of certain areas of the hypothalamus causes complete elimination of sexual behavior. One of the reasons for the importance of the hypothalamus is that it controls the pituitary gland, which secretes hormones that control the other glands of the body.
Figure \(\PageIndex{5}\): Hypothalamus controls the pituitary gland. (Image is in the public domain)
Hormones
Several important sexual hormones are secreted by the pituitary gland. Oxytocin, also known as the hormone of love, is released during sexual intercourse when an orgasm is achieved. Oxytocin is also released in females when they give birth or are breast-feeding; it is believed that oxytocin is involved with maintaining close relationships. Both prolactin and oxytocin stimulate milk production in females. Follicle-stimulating hormone (FSH) is responsible for ovulation in females by triggering egg maturity; it also stimulates sperm production in males. Luteinizing hormone (LH) triggers the release of a mature egg in females during the process of ovulation.
In males, testosterone appears to be a major contributing factor to sexual motivation. Vasopressin is involved in the male arousal phase, and the increase of vasopressin during erectile response may be directly associated with increased motivation to engage in sexual behavior.
The relationship between hormones and female sexual motivation is not as well understood, largely due to the overemphasis on male sexuality in Western research. Estrogen and progesterone typically regulate motivation to engage in sexual behavior for females, with estrogen increasing motivation and progesterone decreasing it. The levels of these hormones rise and fall throughout a woman's menstrual cycle. Research suggests that testosterone, oxytocin, and vasopressin are also implicated in female sexual motivation in similar ways as they are in males, but more research is needed to understand these relationships.
Figure \(\PageIndex{6}\): By the end of high school, more than half of boys and girls report engaging in sexual behaviors. (Image by Pedro Ribeiro Simoes is licensed under CC BY 2.0)
Sexuality will be discussed in Chapter 15, Adolescence Social Emotional Development. The following section will look at the reasons and the consequences of teenage pregnancy, forms of birth control, and sexually transmitted diseases.
Adolescent Pregnancy, Birth Control Methods, and Sexually Transmitted Infections
By the end of high school, more than half of boys and girls report having experienced sexual intercourse at least once, though it is hard to be certain of the proportion because of the sensitivity and privacy of the information. (Center for Disease Control, 2004; Rosenbaum, 2006).
Teen Pregnancy
Although adolescent pregnancy rates have declined since 1991, teenage birth rates in the United States are higher than most industrialized countries. In 2014, females aged 15–19 years experienced a birth rate of 24.2 per 1,000 women. This is a drop of 9% from 2013. Birth rates fell 11% for those aged 15–17 years and 7% for 18–19 year-olds. It appears that adolescents seem to be less sexually active than in previous years, and those who are sexually active seem to be using birth control (CDC, 2016).
Figure \(\PageIndex{7}\): Birth rates for American teenagers. (Image is in the public domain)Figure \(\PageIndex{8}\): Birth rates by state. (Image is in the public domain)
Risk Factors for Adolescent Pregnancy
Miller, Benson, and Galbraith (2001) found that parent/child closeness, parental supervision, and parents' values against teen intercourse (or unprotected intercourse) decreased the risk of adolescent pregnancy. In contrast, residing in disorganized/dangerous neighborhoods, living in a lower SES family, living with a single parent, having older sexually active siblings or pregnant/parenting teenage sisters, early puberty, and being a victim of sexual abuse place adolescents at an increased risk of adolescent pregnancy.
Consequences of Adolescent Pregnancy
After a child is born life can be difficult for a teenage mother. Only 40% of teenagers who have children before age 18 graduate from high school. Without a high school degree, her job prospects are limited and economic independence is difficult. Teen mothers are more likely to live in poverty and more than 75% of all unmarried teen mothers receive public assistance within 5 years of the birth of their first child. Approximately, 64% of children born to an unmarried teenage high-school dropout live in poverty. Further, a child born to a teenage mother is 50% more likely to repeat a grade in school and is more likely to perform poorly on standardized tests and drop out before finishing high school (March of Dimes, 2012).21
Figure \(\PageIndex{9}\): Effects and risks of teenage pregnancy. (Image by Ian Joslin is licensed under CC BY 4.0)
Sexually Transmitted Infections
Sexually transmitted infections (STIs), also referred to as sexually transmitted diseases (STDs) or venereal diseases (VDs), are illnesses that have a significant probability of transmission by means of sexual behavior, including vaginal intercourse, anal sex, and oral sex. It’s important to mention that some STIs can also be contracted by sharing intravenous drug needles with an infected person, through childbirth, or breastfeeding. Common STIs include:
chlamydia;
herpes (HSV-1 and HSV-2);
human papillomavirus (HPV);
gonorrhea;
syphilis;
trichomoniasis;
HIV (human immunodeficiency virus) and AIDS (acquired immunodeficiency syndrome).
According to the Centers for Disease Control and Prevention (CDC) (2014), there was an increase in the three most common types of STDs in 2014. Those most affected by STDS include younger, gay/bisexual males, and females. The most effective way to prevent transmission of STIs is to practice abstinence, (not participating in sexual intercourse), safe sex, and to avoid direct contact of skin or fluids which can lead to transfer with an infected partner. Proper use of safe-sex supplies (such as male condoms, female condoms, gloves, or dental dams) reduces contact and risk and can be effective in limiting exposure; however, some disease transmission may occur even with these barriers.23
Practicing safe sex is important to one’s physical health. In the following section we’ll look at elements of adolescent health, including sleep, diet, and exercise.
Contraceptive Methods and Protection from Sexually Transmitted Infection
There are many methods of contraception that sexually active adolescents can use to reduce the chances of pregnancy.
Table \(\PageIndex{1}\): Reversible Methods of Birth Control (Contraception by the CDC is in the public domain)
Method
Description
Failure Rate
Intrauterine Contraception (IUD)
An IUD is a small device that is shaped in the form of a “T” placed inside the uterus
0.1-0.8%
Implant
A single, thin rod that is inserted under the skin of a woman’s upper arm.
0.01%
Injection
Injections or shots of hormones to prevent pregnancy are given in the buttocks or arm every three months.
4%
Oral contraceptives
Also called “the pill,” contain the hormones to prevent pregnancy. A pill is taken at the same time each day.
7%
Patch
This skin patch is worn on the lower abdomen, buttocks, or upper body and releases hormones to prevent pregnancy into the bloodstream. A new patch once a week for three weeks and then left off for a week.
7%
Hormonal vaginal contraceptive ring
The ring is placed in the vagina and releases the hormones to prevent pregnancy. It is worn for three weeks. A week after it is removed a new ring is placed.
7%
Spermicide
These kill sperm and come in several forms—foam, gel, cream, film, suppository, or tablet. They are placed in the vagina before intercourse.
21%
Diaphragm or cervical cap
A cup that is placed inside the vagina to cover the cervix to block sperm. It is inserted with spermicide before sexual intercourse.
17%
Sponge
This contains spermicide and is placed in the vagina where it fits over the cervix.
14-27%
Male condom
Worn (single use) by the man over the penis to keep sperm from getting into a woman’s body.
13%
Female condom
Worn (single use) by the woman inside the vagina to keep sperm from getting into a woman’s body.
21%
Natural Family Planning
During a regular menstrual cycle, fertile days can be predicted. Sexual intercourse can be avoided on those days.
2-23%
Copper IUD
Can be inserted up to 5 days after sexual intercourse
<1%25
Emergency contraceptive pills
Can be taken up to 5 days after sexual intercourse and may be available over-the-counter.
1-10%26
In choosing a birth control method, dual protection from the simultaneous risk for HIV and other STIs also should be considered. Although hormonal contraceptives and IUDs are highly effective at preventing pregnancy, they do not protect against STIs, including HIV. Consistent and correct use of the male latex condom reduces the risk for HIV infection and other STIs, including chlamydial infection, gonococcal infection, and trichomoniasis.
Figure \(\PageIndex{10}\): There are many types of birth control methods. (Image by rexchimex is licensed under CC BY 4.0)
