Epiphyseal plate

The epiphyseal plate (or epiphysial plate, physis, or growth plate) is a hyaline cartilage plate in the metaphysis at each end of a long bone. It is the part of a long bone where new bone growth takes place; that is, the whole bone is alive, with maintenance remodeling throughout its existing bone tissue, but the growth plate is the place where the long bone grows longer (adds length). The epiphyseal plate (or epiphysial plate, physis, or growth plate) is a hyaline cartilage plate in the metaphysis at each end of a long bone. It is the part of a long bone where new bone growth takes place; that is, the whole bone is alive, with maintenance remodeling throughout its existing bone tissue, but the growth plate is the place where the long bone grows longer (adds length). The plate is not only found in children and adolescents; in adults, who have stopped growing, the plate is replaced by an epiphyseal line. This replacement is known as epiphyseal closure or growth plate fusion. Complete fusion happens between ages 12–16 for girls and 14-19 for boys. Endochondral ossification is responsible for the initial bone development from cartilage in utero and infants and the longitudinal growth of long bones in the epiphyseal plate. The plate's chondrocytes are under constant division by mitosis. These daughter cells stack facing the epiphysis while the older cells are pushed towards the diaphysis. As the older chondrocytes degenerate, osteoblasts ossify the remains to form new bone. In puberty increasing levels of estrogen, in both females and males, leads to increased apoptosis of chondrocytes in the epiphyseal plate. Depletion of chondrocytes due to apoptosis leads to less ossification and growth slows down and later stops when the entire cartilage have become replaced by bone, leaving only a thin epiphyseal scar which later disappears. The growth plate has a very specific morphology in having a zonal arrangement as follows: A mnemonic for remembering the names of the epiphyseal plate growth zones is 'Real People Have Career Options,' standing for: Resting zone, Proliferative zone, Hypertrophic cartilage zone, Calcified cartilage zone, Ossification zone. The growth plate is clinically relevant in that it is often the primary site for infection, metastasis, fractures and the effects of endocrine bone disorders. Defects in the development and continued division of epiphyseal plates can lead to growth disorders. The most common defect is achondroplasia, where there is a defect in cartilage formation. Achondroplasia is the most common cause of dwarfism. Salter–Harris fractures are fractures involving epiphyseal plates and hence tend to interfere with growth, height or physiologic functions. Osgood-Schlatter disease results from stress on the epiphyseal plate in the tibia, leading to excess bone growth and a painful lump at the knee. John Hunter studied growing chickens. He observed bones grew at the ends and thus demonstrated the existence of the epiphyseal plates. Hunter is considered the 'father of the growth plate.'