Disease: Puberty

    Puberty facts

    • Puberty is the period of sexual maturation and achievement of fertility.
    • The time when puberty begins varies greatly among individuals; however, puberty usually occurs in girls between the ages of 10 and 14 and between the ages of 12 and 16 in boys.
    • Both genetic and environmental factors are likely involved in the timing of puberty.
    • Body fat and/or body composition may play a role in regulating the onset of puberty.
    • Puberty is associated with the development of secondary sex characteristics and rapid growth.
    • Some medical conditions may worsen or first become apparent at puberty.
    • Precocious puberty is puberty that occurs earlier than usual. It is more common in girls than in boys.

    What is puberty?

    Puberty is the period during which growing boys or girls undergo 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 one possible mediator of the timing of puberty. In research 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, however, is likely only 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.

    Genetic factors are likely involved in the timing of puberty, and the timing of puberty has often been described to "run in families." Additionally, 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. Individuals who do not have a functioning copy of this gene are not able to enter puberty normally.

    What are the physical stages of puberty in girls and boys?

    The changes that happen during the process of puberty have a typical pattern in both boys and girls, with a generally predictable sequence of events. In most girls, the first sign of puberty is the beginning of breast development, which occurs at an average age of approximately 11 years. In girls, the growth of pubic hair typically begins next, followed by the growth of hair in the armpits. A minority of girls, however, begin to develop pubic hair prior to breast development. The onset of menstruation (having periods) usually happens later than the other physical changes and usually occurs around two and a half years after the onset of puberty.

    A regular pattern of ovulation, corresponding to achievement of fertility, usually develops rapidly once a girl begins having menstrual periods. However, girls who have a later onset of menstruation (after age 13) tend to have lower rates of regular ovulation in the years following the onset of menstruation. Studies have shown that one-half of adolescent girls who first begin to menstruate after age 13 will not ovulate regularly over the next four and a half years.

    In boys, an increase in the size of the testicles is the first change observed at the onset of puberty. Enlargement of the testicles begins at an approximate average age of 11 and a half years in boys and lasts for about six months. After enlargement of the testicles, the penis also increases in size. Enlargement of the testicles and penis almost always occurs before the development of pubic hair. The next stage is the growth of pubic hair and hair in the armpits. Next, the voice becomes deeper and muscles increase in size. The last step is usually the development of facial hair.

    Fertility is achieved in males near the onset of puberty, when a surge in testosterone triggers the production of sperm.

    The sequence of changes in puberty has been characterized by physicians and is referred to as sexual maturity rating (SMR) or Tanner stages, named after a physician who published a description of the sequence of physical changes in puberty in 1969. Tanner stages are determined by the development of the secondary sex characteristics and encompass changes in the size and appearance of the external genitalia, the development of pubic hair, and breast development in girls. Tanner stages allow doctors to classify the extent of development of sex characteristics into five distinct steps ranging from stage 1 (prepubertal) to stage 5 (mature adult type).

    What other changes in the body occur during puberty in boys and girls?

    The "growth spurt"

    A rapid increase in height, referred to as a growth spurt, usually accompanies puberty. This rapid increase in height typically lasts for two to three years. About 17%-18% of adult height is attained during puberty. Although the increase in height affects both the trunk and the limbs, growth in the limbs usually happens first. The growth spurt characteristically occurs earlier in girls than in boys, with girls having the growth spurt approximately two years prior to boys, on average. In girls, the growth spurt typically precedes the onset of menstruation by about six months.

    Bone growth and mineralization

    Puberty is accompanied by growth of bones and increases in bone density in both boys and girls. In girls, bone mineralization peaks around the time of the onset of menstrual periods, after the time of peak height velocity (growth spurt). Studies have shown that bone width increases first, followed by bone mineral content, and lastly by bone density. Because of the lag between bone growth and achievement of full bone density, adolescents may be at increased risk for fractures during this time.

    Weight changes

    Changes in weight and body composition occur in both boys and girls. Adolescent girls develop a greater proportion of body fat than boys, with redistribution of the fat toward the upper and lower portions of the body, leading to a curvier appearance. While boys also have an increase in the growth of body fat, their muscle growth is faster. By the end of puberty, boys have a muscle mass about one and a half times greater than that of comparably sized girls.

    Other changes

    Maturation of the cardiovascular systems and lungs results in an increased working capacity of these organs, associated with an overall increase in endurance and strength. These changes are more pronounced in boys than in girls.

    What are the medical concerns associated with normal puberty?

    While puberty is a normal condition and not an illness, many medical conditions and illnesses may first appear during puberty. Some conditions potentially associated with puberty include the following:

    • Acne: Acne is an inflammation of the sebaceous glands and hair follicles of the skin, which is most pronounced on the face but may occur on the neck, back, chest, or other areas. The hormonal changes in puberty lead to the development of acne in many adolescent boys and girls.
    • Gynecomastia: Gynecomastia is the term used to describe enlargement of the male breasts. The hormonal changes of puberty can cause a transient gynecomastia in normal boys that typically lasts for six to 18 months. Pubertal gynecomastia occurs at an average age of 13 in boys and affects up to one-half of normal adolescent boys.
    • Anemia: The normal pubertal progression in males is associated with increases in the ferritin (iron) and hemoglobin concentrations in the blood, but this increase is not observed in females. Adolescent girls tend to consume less iron-containing foods than boys, and this, combined with blood losses through menstrual bleeding, may place adolescent girls at risk for anemia.
    • Sexually transmitted diseases (STDs): If teens become sexually active at puberty, they are at risk for HIV and other sexually transmitted infections.
    • Scoliosis: Because of rapid growth during puberty, scoliosis (abnormal curvature of the spine) can be worsened or may first become apparent during puberty.
    • Vision changes: Nearsightedness (myopia) has a high incidence during puberty because of growth in the axial diameter of the eye.
    • Musculoskeletal injuries: Adolescents may be particularly prone to musculoskeletal injuries during the growth spurt and during growth of muscle mass. Since bone growth usually precedes full bone mineralization, adolescents are at risk for fractures. Also, since the growth in the limbs usually occurs prior to growth in the trunk, some joints may be left with a limited range of motion that increases the risk for sprains and strains.
    • Dysfunctional uterine bleeding: Girls who have recently begun menstruating may have irregular, prolonged, or heavy menstrual bleeding. Anovulation (not ovulating) is the most common reason for abnormal menstrual bleeding in adolescent girls.

    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 one possible mediator of the timing of puberty. In research 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, however, is likely only 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.

    Genetic factors are likely involved in the timing of puberty, and the timing of puberty has often been described to "run in families." Additionally, 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. Individuals who do not have a functioning copy of this gene are not able to enter puberty normally.

    What are the physical stages of puberty in girls and boys?

    The changes that happen during the process of puberty have a typical pattern in both boys and girls, with a generally predictable sequence of events. In most girls, the first sign of puberty is the beginning of breast development, which occurs at an average age of approximately 11 years. In girls, the growth of pubic hair typically begins next, followed by the growth of hair in the armpits. A minority of girls, however, begin to develop pubic hair prior to breast development. The onset of menstruation (having periods) usually happens later than the other physical changes and usually occurs around two and a half years after the onset of puberty.

    A regular pattern of ovulation, corresponding to achievement of fertility, usually develops rapidly once a girl begins having menstrual periods. However, girls who have a later onset of menstruation (after age 13) tend to have lower rates of regular ovulation in the years following the onset of menstruation. Studies have shown that one-half of adolescent girls who first begin to menstruate after age 13 will not ovulate regularly over the next four and a half years.

    In boys, an increase in the size of the testicles is the first change observed at the onset of puberty. Enlargement of the testicles begins at an approximate average age of 11 and a half years in boys and lasts for about six months. After enlargement of the testicles, the penis also increases in size. Enlargement of the testicles and penis almost always occurs before the development of pubic hair. The next stage is the growth of pubic hair and hair in the armpits. Next, the voice becomes deeper and muscles increase in size. The last step is usually the development of facial hair.

    Fertility is achieved in males near the onset of puberty, when a surge in testosterone triggers the production of sperm.

    The sequence of changes in puberty has been characterized by physicians and is referred to as sexual maturity rating (SMR) or Tanner stages, named after a physician who published a description of the sequence of physical changes in puberty in 1969. Tanner stages are determined by the development of the secondary sex characteristics and encompass changes in the size and appearance of the external genitalia, the development of pubic hair, and breast development in girls. Tanner stages allow doctors to classify the extent of development of sex characteristics into five distinct steps ranging from stage 1 (prepubertal) to stage 5 (mature adult type).

    What other changes in the body occur during puberty in boys and girls?

    The "growth spurt"

    A rapid increase in height, referred to as a growth spurt, usually accompanies puberty. This rapid increase in height typically lasts for two to three years. About 17%-18% of adult height is attained during puberty. Although the increase in height affects both the trunk and the limbs, growth in the limbs usually happens first. The growth spurt characteristically occurs earlier in girls than in boys, with girls having the growth spurt approximately two years prior to boys, on average. In girls, the growth spurt typically precedes the onset of menstruation by about six months.

    Bone growth and mineralization

    Puberty is accompanied by growth of bones and increases in bone density in both boys and girls. In girls, bone mineralization peaks around the time of the onset of menstrual periods, after the time of peak height velocity (growth spurt). Studies have shown that bone width increases first, followed by bone mineral content, and lastly by bone density. Because of the lag between bone growth and achievement of full bone density, adolescents may be at increased risk for fractures during this time.

    Weight changes

    Changes in weight and body composition occur in both boys and girls. Adolescent girls develop a greater proportion of body fat than boys, with redistribution of the fat toward the upper and lower portions of the body, leading to a curvier appearance. While boys also have an increase in the growth of body fat, their muscle growth is faster. By the end of puberty, boys have a muscle mass about one and a half times greater than that of comparably sized girls.

    Other changes

    Maturation of the cardiovascular systems and lungs results in an increased working capacity of these organs, associated with an overall increase in endurance and strength. These changes are more pronounced in boys than in girls.

    What are the medical concerns associated with normal puberty?

    While puberty is a normal condition and not an illness, many medical conditions and illnesses may first appear during puberty. Some conditions potentially associated with puberty include the following:

    • Acne: Acne is an inflammation of the sebaceous glands and hair follicles of the skin, which is most pronounced on the face but may occur on the neck, back, chest, or other areas. The hormonal changes in puberty lead to the development of acne in many adolescent boys and girls.
    • Gynecomastia: Gynecomastia is the term used to describe enlargement of the male breasts. The hormonal changes of puberty can cause a transient gynecomastia in normal boys that typically lasts for six to 18 months. Pubertal gynecomastia occurs at an average age of 13 in boys and affects up to one-half of normal adolescent boys.
    • Anemia: The normal pubertal progression in males is associated with increases in the ferritin (iron) and hemoglobin concentrations in the blood, but this increase is not observed in females. Adolescent girls tend to consume less iron-containing foods than boys, and this, combined with blood losses through menstrual bleeding, may place adolescent girls at risk for anemia.
    • Sexually transmitted diseases (STDs): If teens become sexually active at puberty, they are at risk for HIV and other sexually transmitted infections.
    • Scoliosis: Because of rapid growth during puberty, scoliosis (abnormal curvature of the spine) can be worsened or may first become apparent during puberty.
    • Vision changes: Nearsightedness (myopia) has a high incidence during puberty because of growth in the axial diameter of the eye.
    • Musculoskeletal injuries: Adolescents may be particularly prone to musculoskeletal injuries during the growth spurt and during growth of muscle mass. Since bone growth usually precedes full bone mineralization, adolescents are at risk for fractures. Also, since the growth in the limbs usually occurs prior to growth in the trunk, some joints may be left with a limited range of motion that increases the risk for sprains and strains.
    • Dysfunctional uterine bleeding: Girls who have recently begun menstruating may have irregular, prolonged, or heavy menstrual bleeding. Anovulation (not ovulating) is the most common reason for abnormal menstrual bleeding in adolescent girls.

    Source: http://www.rxlist.com

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