The rest undergo apoptosis cell suicide and disintegrate. Move your mouse over the photomicrograph to see labels. Bone cell origins This diagram summarizes the origins and fates of the bone cells. Mesenchymal refers to cells which were deep within the embryo during early development; some of them remain in the bone marrow but do not form blood cells.
The hematopoietic cells form the liquid part of the bone marrow, and some of them circulate with the blood. Local regulators Bone cells produce molecules usually proteins that communicate with other cells. Osteoprogenitor cells are the 'stem' cells of bone, and are the source of new osteoblasts.
Osteoblasts , lining the surface of bone, secrete collagen and the organic matrix of bone osteoid , which becomes calcified soon after it has been deposited. As they become trapped in the organic matrix, they become osteocytes. Osteocytes maintain bone tissue. Fine processes from these cells ramify through bone, and form gap junctions with other osteocytes. Osteocytes sit in the calcified matrix, in small spaces called lacunae lacuna - singular.
Long processes from the osteocyte lie in small channels called canaliculi small canals. These are channels for the transport for nutrients and waste. The osteocyte processes contact other ostocytes, forming gap junctions, so that they can communicate with each other.
Osteocytes communicate with the Haversian canal through cytoplasmic extensions that run through canaliculi, small interconnecting canals.
The layers of a long bone, beginning at the external surface, are therefore:. Bone development begins with the replacement of collagenous mesenchymal tissue by bone. This results in the formation of woven bone, a primitive form of bone with randomly organized collagen fibers that is further remodeled into mature lamellar bone, which possesses regular parallel rings of collagen.
Lamellar bone is then constantly remodeled by osteoclasts and osteoblasts. There are two different methods by which bone is produced from mesenchymal tissue:. In adults, after growth has ceased, bone is formed by the osteoblasts only where it was previously resorbed by the osteoclasts. This follows a specific sequence of events, and takes about three months in total to complete:. Answer: Haversian canals are central channels in bone that contain nerves, vessels, and lymphatics.
They all run parallel to each other but are connected perpendicularly by Volkmann's canals. Canaliculi are tiny extensions of the osteocytes through the bone matrix.
They allow these isolated cells to communicate with one another. Answer: Endochondral ossification involves the conversion of cartilage to bone. This occurs in most long bones of the body. Intramembranous ossification does not involve a cartilage precursor. It takes place in the bones of the skull. Answer: Activation, resorption, reversal, formation. See pre-lab for more details. Slides Please select whether to view the slides in study mode or quiz mode.
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