Puberty
Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR
What is puberty?
Puberty is the time at which a growing boy or girl begins the process of
sexual maturation. Puberty involves a series of physical stages or steps that
lead to the achievement of fertility and the development of the so-called
secondary sex characteristics, the physical features associated with adult males
and females (such as the growth of pubic hair). While puberty involves a series
of biological, or physical, transformations, the process can also have an effect
on the psychosocial and emotional development of the adolescent.
When does puberty occur?
The onset of puberty varies among individuals. Puberty usually occurs in
girls between the ages of 10 and 14, while in boys it generally occurs later,
between the ages of 12 and 16. In some African American girls, puberty begins
earlier, at about age 9, meaning that puberty occurs from ages 9 to 14.
Adolescent girls reach puberty today at earlier ages than were ever recorded
previously. Nutritional and other environmental influences may be responsible
for this change. For example, the average age of the onset of menstrual
periods in girls was 15 in 1900. By the 1990s, this average had dropped to 12 and a half years of age.
What determines when puberty begins?
The timing of the onset of puberty is not completely understood and is likely
determined by a number of factors. One theory proposes that reaching a critical
weight or body composition may play a role in the onset of puberty. It has been
proposed that the increase in childhood obesity may be related to the overall
earlier onset of puberty in the general population in recent years.
Leptin, a hormone produced by fat cells (adipocytes) in the body, has been
suggested as a possible mediator of the timing of puberty. In studies, animals
deficient in leptin did not undergo puberty, but puberty began when leptin was
administered to the animals. Further, girls with higher concentrations of the
hormone leptin are known to have an increased percentage of body fat and an
earlier onset of puberty than girls with lower levels of leptin. The
concentration of leptin in the blood is known to increase just before puberty in
both boys and girls.
Leptin likely is one of multiple influences on the hypothalamus, an area of
the brain that releases a hormone known as gonadotropin-releasing hormone
(GnRH), which in turn signals the pituitary gland to release leutinizing
hormone (LH) and follicle-stimulating hormone (FSH). LH and FSH secretion by the
pituitary is responsible for sexual development.
A gene has been identified that appears to be critical for the normal
development of puberty. The gene, known as GPR54, encodes a protein that appears
to have an effect on the secretion of GnRH by the hypothalamus.
Next: What are the physical changes of puberty? »
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