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Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
Puberty is the time at which growing boys or girls begin 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.
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.
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.
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