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Organ system histology
Bones are composed primarily of an extracellular calcified material called the bone matrix or collagen matrix.
Osteoblasts are found mostly along the surface of bones, but also within the bone matrix itself.
They’re responsible for both synthesizing and mediating the mineralization of the bone matrix.
Osteoclasts are large multinucleated cells that are responsible for removing calcified bone matrix and allow for the constant turnover and remodelling of bones.
Morphologically, there are two main types of bone.
The compact or cortical bone is the dense portion that’s found closer to the surface of bones.
In this electron microscopy or EM image of the tibia, the compact bone is also blue, and the more central trabecular bone is yellow. Microscopically, both compact and trabecular bones will be organized or arranged in two forms.
Layered or lamellar bone has a bone matrix that’s arranged in sheets.
This form of bone is found mostly within developing and growing bones, as well as bones that have healed after being fractured.
Alright, let’s compare sections of a long bone and a flat bone.
Bone is a connective tissue that consists of an organic matrix (containing collagen and proteoglycans) and inorganic minerals (primarily hydroxyapatite). The organic matrix provides the tensile strength, and the inorganic minerals provide the compressive strength. Bone also contains three major types of cells, which are osteocytes, osteoblasts, and osteoclasts. Bone undergoes continuous remodeling throughout life. Osteoblasts produce a new bone matrix, which is mineralized by osteocytes. Osteoclasts resorb old bone matrix. This process of remodeling ensures that bones are constantly adapting to changes in mechanical loading.
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