The human long bones are subject to multiple changes in utero based on a cascade of pathways and cellular signaling mechanisms. In endochondral ossification, cartilage is gradually replaced by bone, beginning with diaphyseal ossification at 8 weeks of gestation. The epiphyses located at both ends between the joint and the primary physis (growth plate) are initially cartilaginous and later develop secondary ossification. The primary physis is responsible for longitudinal growth, and the newest bone forms the metaphysis. The secondary physis provides spherical growth of the epiphyseal ossification center. The diaphyseal diameter enlarges by means of bone deposition from the surrounding periosteum, and the diameter of the physis increases because of bone deposition from the perichondrium. In addition, the ossified components undergo bone marrow transformation. Any disturbances of epimetaphyseal development may result in various skeletal abnormalities. Skeletal patterning begins in the embryo, it is during fetal development that bone formation and mineralization accelerate. The formation of cartilage from stem cells during development is a complex process, which is regulated by both local growth factors and biomechanical cues, and results in the differentiation of chondrocytes into a range of subtypes in specific regions of the tissue. In fetal development cartilage also acts as a precursor scaffold for many bones, and mineralization of this cartilaginous bone precursor occurs through the process of endochondral ossification. In the endochondral formation of bones during fetal development the interplay between cell signalling, growth factors, and biomechanics regulates the formation of load bearing bone, in addition to the joint capsule containing articular cartilage and synovium, generating complex, functional joints from a single precursor anlagen. During embryonic development most of the skeleton begins as a cartilaginous scaffold that is progressively resorbed and replaced by bone. Endochondral bone development continues until the growth plates fuse during puberty. Growth and mineralization of the skeleton are dependent upon the adequate delivery of mineral. During fetal development, the placenta actively transports calcium, magnesium and phosphorus from the maternal circulation. In this talk, the timeline of fetal bone development and regulation will be summarized.
Disclosure: The author declared no competing interests.
27 - 30 Jun 2015