ADOLESCENCE GROWTH AND DEVELOPMENT

 

Adolescence is the period of psychological and social transition between childhood and adulthood. Adolescence is the transitional stage of human development in which a juvenile matures into an adult. This transition involves biological, social, and psychological changes, though the biological ones are the easiest to measure objectively. The time is identified with dramatic changes in the body, along with developments in a person's psychology and academic career. In the onset of adolescence, children usually complete elementary school and enter secondary education, such as middle school or high school. A person between early childhood and the teenage years is sometimes referred to as a pre-teen or 'tween.

Physical maturation resulting from puberty leads to an interest in sexual activities, sometimes leading to teenage pregnancy. Since teens may not be emotionally or mentally mature enough or financially able to support children, sexual activity among adolescents is considered problematic.

Female

In females, puberty is caused by alterations in brain functions that result in increased secretion by the hypothalamus of gonadotropin-releasing hormone (GnRH). Increased levels of GnRH stimulate secretion of pituitary gonadatrophins FSH and LH which cause follicle development and estrogen secretion. Estrogen is responsible for accessory sex organs and secondary sex characteristics. Menarche, the first menstrual cycle, occurs at about 12.5 years of age as a result of the release of FSH.

Breast development

The first physical sign of puberty in girls is usually a firm, tender lump under the center of the areola(e) of one or both breasts, occurring on average at about 10.5 years. This is referred to as thelarche. By the widely used Tanner staging of puberty, this is stage 2 of breast development (stage 1 is a flat, prepubertal breast). Within 6-12 months, the swelling has clearly begun in both sides, softened, and can be felt and seen extending beyond the edges of the areolae. This is stage 3 of breast development. By another 12 months (stage 4), the breasts are approaching mature size and shape, with areolae and papillae forming a secondary mound. In most young women, this mound disappears into the contour of the mature breast (stage 5), although there is so much variation in sizes and shapes of adult breasts that distinguishing advanced stages is of little clinical value.

Pubic hair in girls

Pubic hair is often the second unequivocal change of puberty. It is referred to as pubarche and the pubic hairs are usually visible first along the labia. The first few hairs are described as Tanner stage 2. Stage 3 is usually reached within another 612 months, when the hairs are too numerous to count and appear on the mons as well. By stage 4, the pubic hairs densely fill the "pubic triangle." Stage 5 refers to spread of pubic hair to the thighs and sometimes as abdominal hair upward towards the umbilicus. In about 15% of girls, the earliest pubic hair appears before breast development begins.


Vagina, uterus, ovaries

The mucosal surface of the vagina also changes in response to increasing levels of estrogen, becoming thicker and a duller pink in color (in contrast to the brighter red of the prepubertal vaginal mucosa). Whitish secretions (physiologic leukorrhea) are a normal effect of estrogen as well. In the next 2 years following thelarche, the uterus and ovaries increase in size. The ovaries usually contain small cysts visible by ultrasound.

Menstruation and fertility

The first menstrual bleeding is referred to as menarche. The average age of menarche in American girls is about 12.7 years, usually about 2 years after thelarche. Menses (menstrual periods) are not always regular and monthly in the first 2 years after menarche. Ovulation is necessary for fertility, and may or may not accompany the earliest menses. By 2 years after menarche, most girls are ovulating at least several times a year. Over 90% of girls who experience menarche before age 13 years are experiencing very regular, predictable menses accompanied by ovulation within 2 years, and a higher proportion of those with later menarche may not establish regular ovulation for 4 years or more. However, initiation of ovulation after menarche is not inevitable, and a high proportion of girls with continued irregularity several years from menarche will continue to have prolonged irregularity and anovulation, and are at higher risk for reduced fertility.

Pelvic shape, fat distribution, and body composition

During this period, also in response to rising levels of estrogen, the lower half of the pelvis widens. This prepares the body for the time when she will give birth by enlarging the birth canal. Fat tissue increases to a greater percentage of the body composition than in males, especially in the typical female distribution of breasts, hips, and thighs. This produces the typical female body shape. Also, the fat goes to the buttocks of a girl, giving their buttocks more shape and curve.

Body and facial hair in girls

In the months and years following the appearance of pubic hair, other areas of skin which respond to androgens develop heavier hair (androgenic hair) in roughly the following sequence: underarm (axillary) hair, perianal hair, upper lip hair, sideburn (preauricular) hair, and periareolar hair. Arm and leg hair becomes heavier gradually over a period of 10 years or more. While the appearance of hair in some of these areas is not always wanted, particularly in Western culture, it rarely indicates a hormone imbalance unless it occurs elsewhere as well, such as under the chin and in the midline of the chest.

Height growth in girls

The estrogen-induced pubertal growth spurt in girls begins at the same time the earliest breast changes begin, or even a few months before, making it one of the earliest manifestations of puberty in girls. Growth of the legs and feet accelerates first, so that many girls have longer legs in proportion to their torso in the first year of puberty. The rate of growth tends to reach a peak velocity (as much as 7.5-10 cm or 3-4 inches per year) midway between thelarche and menarche and is already declining by the time menarche occurs. In the 2 years following menarche most girls grow about 5 cm (2 inches) before growth ceases at maximal adult height. This last growth primarily involves the spine rather than the limbs.

Body odor, skin changes, and acne

Rising levels of androgens can change the fatty acid composition of perspiration, resulting in a more "adult" body odor. This often precedes thelarche and pubarche by 1 or more years. Another androgen effect is increased secretion of oil (sebum) from the skin. This change increases the susceptibility to acne vulgaris, a characteristic affliction of puberty greatly variable in its severity.

Male

 

The onset of puberty for males is similar to that of females. GnRH secretion from the hypothalamus results in an increase in pituitary gonadatropins secretion of LH / ICSH and FSH. The pituitary gonadatropins stimulate the seminiferous tubules and testosterone secretion. Testosterone causes changes in the accessory reproductive organs, secondary sex characteristics and male sex drive.

Testicular size, function, and fertility

In boys, testicular enlargement is the first physical manifestation of puberty. It is termed gonadarche. The testes in prepubertal boys change little in size from about 1 year of age to the onset of puberty, averaging about 23 cc in volume and about 1.5-2 cm in length. Testicular size continues to increase throughout puberty, reaching maximal adult size about 6 years later. While 18-20 cc is reportedly an average adult size, there is wide variation in the normal population.

The testes have two primary functions: to produce hormones and to produce sperm. The Leydig cells produce testosterone (as described below), which in turn produces most of the changes of male puberty. However, most of the increasing bulk of testicular tissue is spermatogenic tissue (primarily Sertoli and interstitial cells). The development of sperm production and fertility in males is not as well documented. Sperm can be detected in the morning urine of most boys after the first year of pubertal changes (and occasionally earlier).

Genitalia

A boy's penis grows little from the fourth year of life until puberty. Average prepubertal penile length is 4 cm. The prepubertal genitalia are described as stage 1. Within months after growth of the testes begins, rising levels of testosterone promote growth of the penis and scrotum. This earliest discernible beginning of pubertal growth of the genitalia is referred to as stage 2. The penis continues to grow until about 21 years of age, reaching an average adult size of about 7-15.5 cm.

Although erections and orgasms occur in prepubertal boys, they become much more common during puberty, accompanied by a markedly increased libido. Ejaculation becomes possible early in puberty; prior to this boys may experience dry orgasms. Emission of seminal fluid may occur due to masturbation or spontaneously during sleep (commonly termed a wet dream, and more clinically called a nocturnal emission). The ability to ejaculate is a fairly early event in puberty compared to the other characteristics. However, in parallel to the irregularity of the first few periods of a girl, for the first one or two years after a boy's first ejaculation, his seminal fluid may contain few active sperm.


Pubic hair in boys

Pubic hair often appears on a boy shortly after the genitalia begin to grow. As in girls, the first appearance of pubic hair is termed pubarche and the pubic hairs are usually first visible at the dorsal (abdominal) base of the penis. The first few hairs are described as stage 2. Stage 3 is usually reached within another 612 months, when the hairs are too numerous to count. By stage 4, the pubic hairs densely fill the "pubic triangle." Stage 5 refers to spread of pubic hair to the thighs and upward towards the umbilicus as part of the developing abdominal hair.

Body and facial hair in boys

In the months and years following the appearance of pubic hair, other areas of skin which respond to androgens develop heavier hair (androgenic hair) in roughly the following sequence: underarm (axillary) hair, perianal hair, upper lip hair, sideburn (preauricular) hair, periareolar hair, and the rest of the beard area. Arm, leg, chest, abdominal, and back hair become heavier more gradually. There is a large range in amount of body hair among adult men, and significant differences in timing and quantity of hair growth among different ethnic groups.


Voice change

Under the influence of androgens, the voice box, or larynx, grows in both genders. This growth is far more prominent in boys, causing the male voice to drop, rather abruptly, about one octave, because the larger vocal folds have a lower fundamental frequency. Occasionally, this is accompanied by cracking and breaking sounds in the early stages. Most of the voice change happens during stage 4 of male puberty around the time of peak growth. However, it usually precedes the development of significant facial hair by several months to years.

Height growth in boys

Compared to girls' early growth spurt, growth accelerates more slowly in boys and lasts longer, resulting in a taller adult stature among males than females (on average about 10 cm or 4 inches). The difference is attributed to the much greater potency of estradiol compared to testosterone in promoting bone growth, maturation, and epiphyseal closure. In boys, growth begins to accelerate about 9 months after the first signs of testicular enlargement and the peak year of the growth spurt occurs about 2 years after the onset of puberty, reaching a peak velocity of about 8.512 cm or 3.55 inches per year. The feet and hands experience their growth spurt first, followed by the limbs, and finally ending in the trunk. Epiphyseal closure and adult height are reached more slowly, at an average age of about 17.5 years. As in girls, this last growth primarily involves the spine rather than the limbs.

Male musculature and body shape

By the end of puberty, adult men have heavier bones and nearly twice as much skeletal muscle. Some of the bone growth (e.g., shoulder width and jaw) is disproportionately greater, resulting in noticeably different male and female skeletal shapes. The average adult male has about 150% of the lean body mass of an average female, and about 50% of the body fat.

This muscle develops mainly during the later stages of puberty, and muscle growth can continue even after a male is biologically adult. The peak of the so-called "strength spurt," the rate of muscle growth, is attained about one year after a male experiences his peak growth rate.

Breast development in boys: pubertal gynecomastia

Estradiol is produced from testosterone in male puberty as well as female, and male breasts often respond to the rising estradiol levels. This is termed gynecomastia. In most boys, the breast development is minimal, similar to what would be termed a "breast bud" in a girl, but in many boys, breast growth is substantial. It usually occurs after puberty is underway, may increase for a year or two, and usually diminishes by the end of puberty. It is increased by extra adipose tissue if the boy is overweight.

Although this is a normal part of male puberty, breast development for some boys is as unwelcome as upper lip hair in girls. If the boy's distress becomes too substantial during development, breast tissue can be removed and corrected surgically.