**Core Concept:** Puberty is a critical period of development in humans, marked by the onset of secondary sexual characteristics and reproductive abilities. Hormones play a crucial role in this process, particularly sex hormones like estrogen, progesterone, and testosterone.

**Why the Correct Answer is Right:** Puberty is primarily regulated by the hypothalamic-pituitary-gonadal (HPG) axis, which is a complex interplay between the hypothalamus, pituitary gland, and gonads (testes or ovaries). During this process, gonadotropin-releasing hormone (GnRH) is secreted by the hypothalamus, which stimulates the anterior pituitary gland to secrete luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These hormones, in turn, stimulate the gonads (testes or ovaries) to produce sex hormones like testosterone (in males) and estrogen (in females), respectively.

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because estrogen is primarily produced in the ovaries during puberty in females, leading to menstruation and development of secondary sexual characteristics. Testosterone is the main sex hormone produced by the testes in males, which is responsible for the development of male secondary sexual characteristics.

B. This option is incorrect because progesterone is a hormone produced by the corpus luteum during the luteal phase of the menstrual cycle (in females) or by the testes in males. During puberty, the primary sex hormones are estrogen and testosterone, not progesterone.

C. This option is incorrect because cortisol is a hormone produced by the adrenal glands in response to stress or corticotrophin-releasing hormone (CRH) and adrenocorticotropic hormone (ACTH) from the pituitary gland. Cortisol is not directly involved in the onset of puberty.

D. This option is incorrect because thyroid hormones, including T3 and T4, are produced by the thyroid gland and regulate overall body growth and development. While thyroid hormones are crucial during growth and development, they are not directly involved in the onset of puberty.

**Clinical Pearls:**

Understanding the role of sex hormones in puberty is essential for medical students and physicians dealing with pediatric patients. A comprehensive understanding of the HPG (hypothalamus-pituitary-gonadal) axis and the development of secondary sexual characteristics is crucial for accurate diagnosis and management of pediatric patients.