What is the primary function of melanin?

A. Thyroxine:Thyroxine (T4) influences metabolic rate and can affect bone turnover but is not the primary hormone that raises blood calcium by stimulating osteoclasts.
B. Calcitonin:Calcitonin lowers blood calcium by inhibiting osteoclast activity and promoting calcium deposition in bone.
C. Growth hormone:Growth hormone stimulates overall growth and has indirect effects on bone growth via IGF-1, but it is not the principal hormone that raises blood calcium via osteoclast stimulation.
D. Parathyroid hormone:Parathyroid hormone increases blood calcium concentration by stimulating osteoclast activity (indirectly via osteoblast signaling), increasing renal calcium reabsorption, and promoting activation of vitamin D.

A. Saddle joint: Saddle joints allow biaxial movement (e.g., thumb carpometacarpal joint) but do not permit movement in all directions.
B. Pivot joint: Pivot joints allow rotation around a single axis (e.g., atlantoaxial joint) and therefore do not provide multiaxial movement.
C. Hinge joint: Hinge joints permit movement primarily in one plane (flexion/extension) like the elbow and do not allow movement in all directions.
D. Ball-and-socket joint: Ball-and-socket joints (for example the shoulder and hip) permit multiaxial movement including flexion/extension, abduction/adduction, and rotation, allowing the greatest directional range.