Fifth metacarpal bone Fifth metacarpal bone The fifth metacarpal bone (metacarpal bone of the little finger or pinky finger) is the most medial and second-shortest of the metacarpal bones. It presents on its base one facet on its superior surface, which is concavo-convex and articulates with the hamate, and one on its radial side, which articulates with the fourth metacarpal. On its ulnar side is a prominent tubercle for the insertion of the tendon of the extensor carpi ulnaris muscle. The dorsal surface of the body is divided by an oblique ridge, which extends from near the ulnar side of the base to
Bone mineral of the hydroxyapatite. Bone mineral is dynamic in living animals; it is continually being resorbed and built anew in the bone remodeling process. In fact, the bones function as a bank or storehouse in which calcium can be continually withdrawn for use or deposited for storage, as dictated by homeostasis, which maintains the concentration of calcium ions in the blood serum within a particular range despite the variability of muscle tissue metabolism. Parathormone and calcitonin are the principal hormones with which the neuroendocrine system controls this ongoing process. The parathyroid and thyroid glands in the neck produce those hormones; thus,