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Calcium is the most abundant mineral in the human body. [3] The average adult body contains in total approximately 1 kg, 99% in the skeleton in the form of calcium phosphate salts. [ 3 ] The extracellular fluid (ECF) contains approximately 22 mmol, of which about 9 mmol is in the plasma . [ 4 ]
The number of bones in the human skeletal system is a controversial topic. Humans are born with over 300 bones; however, many bones fuse together between birth and maturity. As a result, an average adult skeleton consists of 206 bones. The number of bones varies according to the method used to derive the count.
The human body is in a constant state of bone remodeling. [4] Bone remodeling is a process which maintains bone strength and ion homeostasis by replacing discrete parts of old bone with newly synthesized packets of proteinaceous matrix. [5] Bone is resorbed by osteoclasts, and is deposited by osteoblasts in a process called ossification. [6]
Bone tissue is removed by osteoclasts, and then new bone tissue is formed by osteoblasts. Both processes utilize cytokine (TGF-β, IGF) signalling.In osteology, bone remodeling or bone metabolism is a lifelong process where mature bone tissue is removed from the skeleton (a process called bone resorption) and new bone tissue is formed (a process called ossification or new bone formation).
It is an effective anabolic (promoting bone formation) agent [42] used in the treatment of some forms of osteoporosis. [41] [43] Teriparatide is a recombinant human parathyroid hormone analog (PTH 1-34). [41] It has an identical sequence to the 34 N-terminal amino acids of the 84-amino acid human parathyroid hormone. [41]
An osteoclast is a large multinucleated cell and human osteoclasts on bone typically have four nuclei [5] and are 150–200 μm in diameter. When osteoclast-inducing cytokines are used to convert macrophages to osteoclasts, very large cells that may reach 100 μm in diameter occur.
In the human body at birth, approximately 300 bones are present. Many of these fuse together during development, leaving a total of 206 separate bones in the adult, not counting numerous small sesamoid bones. [3] [4] The largest bone in the body is the femur or thigh-bone, and the smallest is the stapes in the middle ear.
An osteocyte, an oblate shaped type of bone cell with dendritic processes, is the most commonly found cell in mature bone. It can live as long as the organism itself. [1] The adult human body has about 42 billion of them. [2]