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Abstract and Introduction
Abstract
Puberty is a complex developmental process culminating in sexual maturity. This transitional period begins in late childhood and is characterized by maturation of the hypothalamic-pituitary-gonadal axis, the appearance of secondary sexual characteristics, acceleration of growth, and, ultimately, the capacity for fertility. Significant endocrinologic changes accompany these developmental events. Disorders of pubertal development may occur at any of the steps of the maturational process leading to either precocious or delayed puberty. A thorough understanding of the normal pubertal process is important to the accurate diagnosis and treatment of pubertal disorders.
Introduction
The age at which the somatic change of puberty begins is variable. In the United States and most industrialized countries, pubertal changes usually begin between 8 and 13 years of age in girls and between 9 and 14 years of age in boys. This variability in the time of onset is due to a variety of genetic and environmental influences. Approximately 5% of a given population will have the onset of puberty at an age outside of this range and will be considered to have either precocious or delayed puberty.
In girls, the first somatic change that usually occurs is the beginning of breast development (thelarche), although in a minority of instances pubic hair growth (pubarche) is the initial event. Fig. 1 outlines the mean age of pubertal milestones in girls. Thelarche and pubarche occur at mean ages of 10.9 and 11.2 years, respectively. Although the process of pubertal development is in fact a continuum, for descriptive purposes it is usually recorded in terms of a series of distinct stages, the five stages of breast and pubic hair development outlined by Marshall and Tanner being the most commonly employed scheme ( Table 1 ). In parallel with the somatic changes of puberty, the resultant increase in follicle-stimulating hormone (FSH), luteinizing hormone (LH), and gonadotropin-releasing hormone (GnRH) causes ovarian stimulation. This, along with endogenous estrogen, allows fat accumulation to thicken the mons pubis and labia majora; the clitoris enlarges, the hymen thickens, and the vaginal orifice enlarges. The perineal tissue is smoother and more elastic, and the vaginal tissue becomes thicker, keratinized (evidenced clinically by lightening of the color of the mucosa, from a deep red to a pale pink), and more rugated. The volume of the ovaries and the size of the uterus enlarges as well. Adrenal production of dehydroepiandrosterone sulfate occurs and is involved in pubic hair growth. After a variable period, averaging about 2 years from the onset of breast development, most of the processes of pubertal maturation are complete and menarche (the first menstrual period) occurs. Average age of menarche in the United States is 12.8 years, but as the timing of these events are variable it may occur as late as 14.5 years in normal girls. Further, it is during this period that the most rapid increases in bone mineralization occur.
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Mean age of onset of pubertal milestones in girls (numbers 2,3,4, and so on denote Tanner stage).
As in girls, puberty in boys is often described as a series of five distinct stages, based on testicular size, penile development, and distribution and character of pubic hair. In boys, the first physical evidence of puberty is an increase in testicular size. Measurement of the testes (length and width) or estimation of testicular volume using a Prader orchidiometer allows for early detection of pubertal onset. Testicular volume of 4.0 mL (or length of 2.5 cm), representing the onset of puberty, is noted at an average age of ~11.5 years. Testicular enlargement is followed by scrotal thinning, development of pubic hair, and penile enlargement. Adult testicular volumes and penile dimensions are generally achieved by ~16 years of age; however, there is quite marked individual variation, and young men complete their sexual maturation anywhere between the ages of 14 and 18 years.
In addition to the appearance and development of secondary sexual characteristics in both boys and girls, puberty represents a period during which marked changes in body size and composition occur. Prior to the onset of puberty, the bodies of boys and girls are comprised of similar proportions of adipose tissue and muscle. By the end of puberty, boys have a higher percentage of muscle and a lower percentage of fat relative to girls.
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