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Bone Development and Growth
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By the sixth or seventh week of embryonic life, the actual process of bone development, ossification osteogenesis , begins. There are two osteogenic pathways—intramembranous ossification and endochondral ossification—but in the end, mature bone is the same regardless of the pathway that produces it. During intramembranous ossification , compact and spongy bone develops directly from sheets of mesenchymal undifferentiated connective tissue. The flat bones of the face, most of the cranial bones, and the clavicles collarbones are formed via intramembranous ossification. The process begins when mesenchymal cells in the embryonic skeleton gather together and begin to differentiate into specialized cells Figure 6.
Mechanisms of bone development and repair
Tetrapod life on land was the result of a lengthy process, the final steps of which resulted in full independence of amniotic tetrapods from the aquatic environment. Developmental strategies, including growth rate and the attainment of sexual maturity, played a major role in this transition. Early amniotes, such as Ophiacodon , tended to reach sexual maturity in a year while most non-amniotic Paleozoic tetrapods including Devonian tetrapods and temnospondyls became adult after 3 to 11 years. This ontogenetic transition is accompanied by a drastic change in growth rate and bone microstructure suggesting faster growth dynamics in early amniotes than in Devonian tetrapods and temnospondyls. Was the acquisition of a faster development earlier sexual maturity and faster growth rate a drastic evolutionary event or an extended process over geological time?
The terms osteogenesis and ossification are often used synonymously to indicate the process of bone formation. Parts of the skeleton form during the first few weeks after conception. By the end of the eighth week after conception, the skeletal pattern is formed in cartilage and connective tissue membranes and ossification begins. Bone development continues throughout adulthood. Even after adult stature is attained, bone development continues for repair of fractures and for remodeling to meet changing lifestyles. Osteoblasts, osteocytes and osteoclasts are the three cell types involved in the development, growth and remodeling of bones.
Although bone initially forms during fetal development, it undergoes secondary ossification after birth and is remodeled throughout life. When a tooth is lost and not replaced, bone remodeling will fill in much of the socket. Although the remodeling will be obvious within a few weeks especially when smiling , the process will continue for some months. Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support and protect the various organs of the body, produce red and white blood cells, and store minerals.
Breeder age and bone development in broiler chicken embryos. Alfonso-Torres I ; L. Gargaglioni I ; J. Pizauro I ; D.
Стоящая перед ним задача была крайне деликатна и требовала массу времени - вписать скрытый черный ход в сложный алгоритм и добавить невидимый ключ в Интернете. Тайна имела первостепенное значение. Любое подозрение об изменении Цифровой крепости могло разрушить весь замысел коммандера.
Сьюзан стало дурно оттого, что она увидела. Танкадо прижал изуродованную руку к груди с выражением недоумения и ужаса на лице. - Вы можете заметить, - продолжал Смит, - что взгляд его устремлен. Он ни разу не посмотрел по сторонам. - Это так важно? - полувопросительно произнес Джабба.