Which of the following is NOT a main function of the skeletal system?

The skeletal system has several critical functions that contribute to the overall functioning of the body. Protection of vital organs, such as the heart and lungs, is a primary role, as bones like the rib cage shield these organs from external injury. Providing structural support is another vital function; the skeleton forms the framework that maintains the body’s shape and supports posture. Additionally, the skeletal system is involved in the production of blood cells through a process called hematopoiesis, which occurs primarily in the bone marrow of certain bones.

The production of hormones, however, is not a main function of the skeletal system. While bones can release certain signaling molecules that may have hormone-like effects, the primary organs responsible for hormone production are glands such as the pituitary, thyroid, and adrenal glands. Therefore, this choice accurately identifies a function that the skeletal system does not perform in a primary capacity.