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The percentage of dead osteocytes in bone increases with age from less than 1% at birth to 75% after age 80. [23] Osteocyte apoptosis is thought to be related to decreased mechanotransduction, which possibly leads to the development of osteoporosis. [24] Apoptotic osteocytes release apoptotic bodies expressing RANKL to recruit osteoclasts. [12]
Diagram of a typical long bone showing both cortical (compact) and cancellous (spongy) bone. Haversian canals [i] (sometimes canals of Havers, osteonic canals or central canals) are a series of microscopic tubes in the outermost region of bone called cortical bone. They allow blood vessels and nerves to travel through them to supply the osteocytes.
Osteocytes do not entirely fill up the canaliculi. The remaining space is known as the periosteocytic space, which is filled with periosteocytic fluid. This fluid contains substances too large to be transported through the gap junctions that connect the osteocytes. In cartilage, the lacunae and hence, the chondrocytes, are isolated from each ...
Diagram of a typical long bone showing both compact (cortical) and cancellous (spongy) bone. Osteons on cross-section of a bone. In osteology, the osteon or haversian system (/ h ə ˈ v ɜːr. ʒ ən /; named for Clopton Havers) is the fundamental functional unit of much compact bone.
Micrograph of cancellous bone. Cancellous bone or spongy bone, [12] [11] also known as trabecular bone, is the internal tissue of the skeletal bone and is an open cell porous network that follows the material properties of biofoams. [13] [14] Cancellous bone has a higher surface-area-to-volume ratio than cortical bone and it is less dense. This ...
Feedback from physical activity maintains bone mass, while feedback from osteocytes limits the size of the bone-forming unit. [33] [34] [35] An important additional mechanism is secretion by osteocytes, buried in the matrix, of sclerostin, a protein that inhibits a pathway that maintains osteoblast activity. Thus, when the osteon reaches a ...
As calcium binds to the osteoid, the matrix hardens, and the osteoblasts become entrapped, transforming into osteocytes. As osteoblasts continue to secrete osteoid, it surrounds blood vessels, leading to the formation of trabecular (cancellous or spongy) bone. These blood vessels will eventually develop into red bone marrow.
The first case of spongy degeneration of the CNS was reported in 1928 by Globus and Strauss, [42] who designated the case as Schilder's disease, a term for diffuse myelinoclastic sclerosis. [43] [44] [45] In 1931, Canavan reported a case where the megalencephaly of brain degeneration is different from that caused by a tumour. [46]