The skeletal system forms the rigid framework of the human body, providing structural support, protecting delicate internal organs, and anchoring skeletal muscles to enable movement. At birth, a human infant has over 270 bones, but many fuse during growth, leaving the adult human skeleton with 206 distinct bones. Beyond mechanical support, bones serve as vital metabolic reservoirs for minerals and house bone marrow, the primary site of hematopoiesis.
Bone tissue is a specialized connective tissue composed of both organic and inorganic components that give it a unique combination of flexibility and immense compressive strength.
Grossly, bones display two distinct types of tissue architecture: compact bone and spongy bone. Compact bone forms the dense, hard outer shell of bones, providing protection and strength. It is organized microscopically into structural units called osteons or Haversian systems, which contain central canals for blood vessels surrounded by concentric rings of matrix known as lamellae. Inside lies spongy bone (cancellous bone), composed of a honeycomb network of trabeculae filled with bone marrow. Trabeculae align precisely along lines of stress to maximize strength while keeping the skeleton lightweight.
Bones are categorized into five major structural shapes, each suited to specific anatomical locations and biomechanical demands:
The human skeleton is divided into two primary divisions. The axial skeleton forms the central vertical axis of the body, consisting of the skull, vertebral column, thoracic cage, and hyoid bone; its main role is protection of the brain, spinal cord, and vital thoracic organs. The appendicular skeleton includes the bones of the upper and lower limbs, as well as the pectoral and pelvic girdles that attach the limbs to the axial trunk, facilitating locomotion and interaction with the environment.
Beyond providing posture and structural shape, bones perform several critical homeostatic functions. They act as a massive mineral reservoir, storing 99% of the body's calcium and roughly 85% of its phosphorus, releasing these ions into the bloodstream whenever extracellular fluid levels fluctuate. Skeletal bones also play a protective role by encasing soft organs, such as the cranium protecting the brain. Furthermore, bones assist in acid-base balance by absorbing or releasing alkaline mineral salts, and they store energy reserves in yellow bone marrow as adipose tissue.
Bone formation, termed ossification, occurs through two distinct pathways during embryonic development: intramembranous ossification (forming flat cranial bones and clavicles) and endochondral ossification (forming most other bones from a hyaline cartilage model). Throughout life, bones undergo continuous remodeling, a lifelong process where old bone tissue is broken down by osteoclasts and replaced by osteoblasts. This dynamic cycle repairs microscopic cracks, reshapes bones in response to physical stress, and maintains serum calcium levels.
Nurses frequently care for patients experiencing skeletal pathologies that compromise mobility and safety. Osteoporosis is a prevalent metabolic bone disease characterized by porous, brittle bones due to an imbalance where bone resorption outpaces bone deposition, drastically increasing fracture risk. Fractures, bone infections like osteomyelitis, and congenital skeletal malformations also demand vigilant nursing care. Nurses play a crucial role in assessing fall risks, promoting adequate dietary calcium and vitamin D intake, and encouraging weight-bearing exercises to preserve bone mass.