Bone Structure and Function Bone growth starts from the fetal period to adulthood and consists of the growth of bone tissue primary to secondary. Primary Bone Tissue, also called Immature Bone orWoven Bone,first formed during embryonic development. This tissue growth is temporary until it is replaced by secondary bone tissue in adulthood, except near the skull sutures and tendon insertions. Primary bone is also formed after a fracture occurs and during the healing process. The mineral content in primary bone is less than secondary bone and consists mostly of osteocyte cells. Secondary Bone Tissue, also called Mature Bone or Lamellar Bone, is generally found in adults. Collagen fibers in secondary bone are arranged in layers called lamellae which are arranged concentrically around vascular canals containing blood vessels, nerves and loose connective tissue. The primary bone structure forms a picture like an "onion slice" called the Haversian System or Osteon. System Histogenesis or Bone Formation: Bone formation from the fetal period occurs through two processes, namely: a.Intramembranous ossification: almost occurs in all flat bones and the mineralization process occurs directly in the matrix secreted by osteoblasts (bone-forming cells) b.Endochondral ossification: deposit of matrix (calcium) on the previous cartilage matrix. This process is also called the Calcification process. Long bone growth: - Epiphysis, enlarges due to radial growth of cartilage, followed by endochondral ossification. - Diaphysis, lengthens mainly due to the osteogenic activity of the epiphyseal plate and widens due to the addition of bone by the outer periosteum. At the same time the bone is resorbed or absorbed from the inner surface so that the diameter of the medullary cavity becomes larger. - When the epiphyseal plate cartilage stops growing, it will be replaced by bone tissue through the process of ossification. Epiphyseal closure progresses chronologically in each bone and is completed by the age of 20 years. Once the epiphysis closes, lengthwise growth is no longer possible but widening growth is still possible. Bones are composed of two components, namely: 1.Non-cellular, consisting of: a. Organic Matrix: collagen and proteoglycans b. Minerals: Calcium and Phosphate, forming crystalline salts Ca10(PO4)6(h(OydHro)x2y)awpahtitceh; are buried in the matrix and function to compact bones 2.Bone cells, consisting of: a. Osteoblasts, Located in a row on the surface of bone tissue and in the active state, it has a cuboidal - cylindrical shape, functions to synthesize organic components of the bone matrix, namely type I collagen, proteoglycans and glycoproteins. Osteoblasts have cytoplasmic projections (canaliculi) that communicate with other cells. b. Osteocytes, The cells are shaped like walnuts, located in lacunae between the lamellae. It is an osteoblast embedded in the matrix that actively maintains the bone matrix. Has cytoplasmic extensions that communicate with other cells through tight junctions . c. Osteoclasts, Multinucleated motile cells (5-50 pieces) of various shapes and sizes, originate from the combination of several monocytes so that they are part of the mononuclear phagocyte system. The surface of active osteoclasts folds facing the bone matrix to carry out the resorption process by secreting acid, collagenase and proteolytic enzymes until enzymatic indentations are formed which are called Hoship lacunae. d. Lining Cells It is a passive osteoblastresting cells of osteoblasts), are flat and line the surface of bone tissue. Functions as a protector on the bone surface and as a reserve for osteoblasts Bone Remodeling pairing process (coupling mechanism) between the dismantling of bone (resorption) by osteoclasts and the formation of new bone (formation) by osteoblasts. It not only occurs in growing bones but also occurs throughout human life at a slower rate with increasing age. Fracture repair (broken bones): During the repair process, blood clots, cells and damaged bone matrix will be cleaned by macrophages. The periosteum and endosteum around the fracture area respond with a violent proliferation of osteoprogenitor cells that form cellular tissue around and between the fracture tips. Then young bone will form through the process of endochondral and intramembranous ossification, so that irregular plates are formed which are called callus.