Which system affects metabolism, growth, and reproduction through hormone secretion?

The endocrine system is the correct choice because it plays a crucial role in regulating various bodily functions through the secretion of hormones. Hormones are chemical messengers that travel through the bloodstream and target specific organs and tissues in order to maintain homeostasis, promote growth and development, and regulate metabolism.

For instance, the endocrine system includes glands such as the pituitary, thyroid, adrenal, and pancreas, each of which secretes hormones that influence different physiological processes. The thyroid gland, for example, releases thyroid hormones that regulate metabolism, while the pituitary gland produces growth hormone, which is essential for growth and development. Additionally, reproductive hormones secreted by the gonads (ovaries and testes) are vital for regulating reproductive processes.

In contrast, the anatomy pertains to the structure of the body, the skeletal system provides support and protection to organs and allows for movement, and the muscular system is responsible for facilitating movement and physical activity. While each of these systems plays an integral role in the body's overall function, it is the endocrine system that specifically affects metabolism, growth, and reproduction through its hormonal regulation.