ANATOMY

Detailed explanation-1: -The presence of gravity helps the mineralization of the bone cells during bone remodeling. The absence of gravity will disrupt the process of bone remodeling, thus decreasing the bone mass.

Detailed explanation-2: -Bone loss occurs in the weightless environment of space because bones no longer have to support the body against gravity. On Earth, gravity applies a constant mechanical load to the skeletal system, that causes healthy bones to maintain a certain density so that they are able to support the body.

Detailed explanation-3: -The transforming growth factor (TGF)- signaling pathway is known to control bone remodeling and maintenance.

Detailed explanation-4: -Bone “Remodeling" Throughout a lifetime, bone makes new osteons-minute tubes containing blood vessels. Microscopic exams show these changes, which can indicate adult age to within 5 to 10 years. Younger adults have fewer and larger osteons.

Detailed explanation-5: -Gravitational and muscle forces act on the skeleton during physical activity, resulting in a complex combination of forces, strains and pressures. Bone cells in the skeleton adapt to these pressures by translating the mechanical forces into a complex chain of molecular events that allow bones to adapt and repair.