Final answer:
The pituitary gland is the key physical component of puberty that regulates pubertal changes by signaling other glands to secrete hormones.
Step-by-step explanation:
The key physical component of puberty is the pituitary gland, which regulates pubertal changes by signaling other glands to secrete hormones. The hypothalamus in the brain releases gonadotropin-releasing hormone (GnRH), which stimulates the pituitary gland to secrete hormones that target the gonads (testes and ovaries). These hormones, such as follicle-stimulating hormone (FSH) and luteinizing hormone (LH), control the development and regulation of the reproductive system during puberty.