Bones change from birth to adulthood through a combination of bone formation, growth, and remodeling that progressively increases size, strength, and density while changing shape and structure to meet mechanical demands. Key stages and processes
- Embryonic development:
- Ossification begins early in gestation. Bones form from cartilage (endochondral ossification) and from fibrous membranes (intramembranous ossification). This sets up the skeleton’s basic shape and future growth potential.
- Postnatal growth and long bone lengthening:
- Growth plates (epiphyseal plates) at the ends of long bones drive longitudinal growth during childhood and adolescence. New bone tissue is laid down in the metaphysis as cartilage is progressively replaced by bone, allowing bones to lengthen until the plates close.
- Modeling and growth in childhood and adolescence:
- During childhood, bones grow by modeling: bone resorption and formation occur at different surfaces, enabling length increase and later thickening. Puberty accelerates growth due to sex hormones, enhancing periosteal (outer surface) formation and endosteal (inner surface) remodeling.
- Closure of growth plates and attainment of adult height:
- Growth plates progressively ossify and fuse, typically completing growth in the late teens to early twenties; once the epiphyseal plates close, bones stop increasing in length.
- Thickening and remodeling in adulthood:
- Even after length growth ends, bones can widen (appositional growth) and remodel in response to mechanical stress and metabolic needs. Osteoblasts add new bone on the outer surface while osteoclasts resorb on the inner surface, balancing strength and weight. This remodeling continues throughout life.
- Pediatric vs adult bone characteristics:
- Children’s bones are more flexible and have higher cartilage content, which contributes to a lower fracture risk from bending but higher plasticity; adults’ bones are denser but less forgiving to bending. Hormonal influences (growth hormone, sex steroids) regulate the timing and rate of these changes.
Putting it together
- At birth, the skeleton contains more cartilage and more unfused growth centers; as growth progresses, long bones lengthen at the growth plates while outer bone circumference increases through periosteal apposition.
- By early adulthood, growth plates have closed, bones have reached their final length, and remodeling maintains bone health and adapts to activity and loading demands.
If you’d like, I can tailor this overview to a particular bone (e.g., femur, tibia, or skull) or explain how certain conditions (like osteoporosis or growth plate injuries) affect these processes.
