Puberty's Physical Changes
Puberty is the period of several years in which rapid physical growth and psychological changes occur, culminating in sexual maturity. The onset of puberty is at age 10 or 11 for girls, and age 11 or 12 for boys. Every person's individual timetable for puberty is influenced primarily by heredity, although environmental factors, such as diet and exercise, also exert some influence. These factors can also contribute to precocious or delayed puberty.
Some of the most significant parts of pubertal development involve distinctive physiological changes in an individual's height, weight, body composition, and circulatory and respiratory systems. These changes are largely influenced by hormonal activity. Hormones play an organizational role, priming the body to behave in a certain way once puberty begins, and an activational role, triggering certain behavioral and physical changes.
Puberty occurs through a long process, and begins with a surge in hormone production, which in turn causes a number of physical changes. It is the stage in life in which a child develops secondary sex characteristics (such as a deeper voice in boys; and development of breasts, and more curved and prominent hips in girls), as his or her hormonal balance shifts strongly towards an adult state. This is triggered by the pituitary gland, which secretes a surge of hormonal agents into the blood stream, initiating a chain reaction. The male and female gonads are subsequently activated, which puts them into a state of rapid growth and development. The testes primarily release testosterone, and the ovaries release estrogen. The production of these hormones increases gradually until sexual maturation is met.
Facial hair in males appears around age 14. Around age 13, a male usually has his first ejaculation. Early maturing boys are usually taller and stronger than their friends. Similarly, females usually begin menstruation around the age of 12 or 13. This variance can be influenced by heredity, as well as diet and lifestyle. A girl must have a certain proportion of body fat to attain menstruation. Girls with higher fat content often begin menstruation earlier, whereas malnourished girls or those under high physical demands begin menstruation later.
Girls usually complete puberty by ages 15 to 17, and boys usually complete puberty by ages 16 to 17. Girls attain reproductive maturity about four years after the first physical changes of puberty appear (Figure 1). Boys, however, accelerate more slowly but continue to grow for about six years after the first visible pubertal changes.
The adolescent growth spurt is a rapid increase in an individual's height and weight during puberty resulting from the simultaneous release of growth hormones, thyroid hormones, and androgens. Males experience their growth spurt about two years later than females. In addition to changes in height, adolescents also experience a significant increase in weight. The weight gained during adolescence constitutes nearly half of one's adult body weight. Teenage and early adult males may continue to gain natural muscle growth even after puberty.
The accelerated growth in different body parts happens at different times, but for all adolescents it has a fairly regular sequence. The first places to grow are the extremities (head, hands, and feet), followed by the arms and legs, then the torso and shoulders. This non-uniform growth is one reason why an adolescent body may seem out of proportion. During puberty, bones become harder and more brittle. At the conclusion of puberty, the ends of the long bones close during the process called epiphysis.
Before puberty, there are nearly no sexual differences in fat and muscle distribution. During puberty, boys grow muscle much faster than girls, and girls experience a higher increase in body fat. The ratio between muscle and fat in post-pubertal boys is around three to one, while for girls it is about five to four. An adolescent's heart and lungs increase in both size and capacity during puberty. These changes lead to increased strength and tolerance for exercise.
Primary sex characteristics are those directly related to the sex organs. In males, the first stages of puberty involve growth of the testes and scrotum, followed by growth of the penis. Simultaneously, the seminal vesicles, prostate, and bulbourethral gland enlarge and develop. In females, growth of the uterus, vagina, and other aspects of the reproductive system occur. Unlike males, females usually appear physically mature before they are capable of becoming pregnant.
Changes in secondary sex characteristics include every change that is not directly related to sexual reproduction. In males, this includes pubic, facial, and body hair, deepening of the voice, roughening of the skin, and increased development of sweat glands. In females, these include elevation of the breasts, widening of the hips, development of pubic and underarm hair, widening of the areolae, and elevation of the nipples.