A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and enable mobility. Bones come in a variety of shapes and sizes and have complex internal and external structures. They are lightweight yet strong and hard and serve multiple functions.
In biology, the extracellular matrix (ECM), is a network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide structural and biochemical support to surrounding cells. Because multicellularity evolved independently in different multicellular lineages, the composition of ECM varies between multicellular structures; however, cell adhesion, cell-to-cell communication and differentiation are common functions of the ECM.
Bone healing, or fracture healing, is a proliferative physiological process in which the body facilitates the repair of a bone fracture.
Parathyroid hormone (PTH), also called parathormone or parathyrin, is a peptide hormone secreted by the parathyroid glands that regulates the serum calcium concentration through its effects on bone, kidney, and intestine.
Osteoblasts are cells with a single nucleus that synthesize bone. However, in the process of bone formation, osteoblasts function in groups of connected cells. Individual cells cannot make bone. A group of organized osteoblasts together with the bone made by a unit of cells is usually called the osteon.
Parathyroid hormone-related protein (PTHrP) is a proteinaceous hormone and a member of the parathyroid hormone family secreted by mesenchymal stem cells. It is occasionally secreted by cancer cells. However, it also has normal functions in bone, teeth, vascular tissues and other tissues.
An osteoclast is a type of bone cell that breaks down bone tissue. This function is critical in the maintenance, repair, and remodeling of bones of the vertebral skeleton. The osteoclast disassembles and digests the composite of hydrated protein and mineral at a molecular level by secreting acid and a collagenase, a process known as bone resorption. This process also helps regulate the level of blood calcium.
Osteoprotegerin (OPG), also known as osteoclastogenesis inhibitory factor (OCIF) or tumour necrosis factor receptor superfamily member 11B (TNFRSF11B), is a cytokine receptor of the tumour necrosis factor (TNF) receptor superfamily encoded by the TNFRSF11B gene.
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. The adult human body has about 42 billion of them. Osteocytes do not divide and have an average half life of 25 years. They are derived from osteoprogenitor cells, some of which differentiate into active osteoblasts. Osteoblasts/osteocytes develop in mesenchyme.
Ossification in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in the formation of normal, healthy bone tissue: Intramembranous ossification is the direct laying down of bone into the primitive connective tissue (mesenchyme), while endochondral ossification involves cartilage as a precursor.
A biochemical cascade, also known as a signaling cascade or signaling pathway, is a series of chemical reactions that occur within a biological cell when initiated by a stimulus. This stimulus, known as a first messenger, acts on a receptor that is transduced to the cell interior through second messengers which amplify the signal and transfer it to effector molecules, causing the cell to respond to the initial stimulus. Most biochemical cascades are series of events, in which one event triggers the next, in a linear fashion. At each step of the signaling cascade, various controlling factors are involved to regulate cellular actions, in order to respond effectively to cues about their changing internal and external environments.
The dental follicle, also known as dental sac, is made up of mesenchymal cells and fibres surrounding the enamel organ and dental papilla of a developing tooth. It is a vascular fibrous sac containing the developing tooth and its odontogenic organ. The dental follicle (DF) differentiates into the periodontal ligament. In addition, it may be the precursor of other cells of the periodontium, including osteoblasts, cementoblasts and fibroblasts. They develop into the alveolar bone, the cementum with Sharpey's fibers and the periodontal ligament fibers respectively. Similar to dental papilla, the dental follicle provides nutrition to the enamel organ and dental papilla and also have an extremely rich blood supply.
Bone resorption is resorption of bone tissue, that is, the process by which osteoclasts break down the tissue in bones and release the minerals, resulting in a transfer of calcium from bone tissue to the blood.
Osteocalcin, also known as bone gamma-carboxyglutamic acid-containing protein (BGLAP), is a small (49-amino-acid) noncollagenous protein hormone found in bone and dentin, first identified as a calcium-binding protein.
Receptor activator of nuclear factor kappa-Β ligand (RANKL), also known as tumor necrosis factor ligand superfamily member 11 (TNFSF11), TNF-related activation-induced cytokine (TRANCE), osteoprotegerin ligand (OPGL), and osteoclast differentiation factor (ODF), is a protein that in humans is encoded by the TNFSF11 gene.
Osteoimmunology is a field that emerged about 40 years ago that studies the interface between the skeletal system and the immune system, comprising the "osteo-immune system". Osteoimmunology also studies the shared components and mechanisms between the two systems in vertebrates, including ligands, receptors, signaling molecules and transcription factors. Over the past decade, osteoimmunology has been investigated clinically for the treatment of bone metastases, rheumatoid arthritis (RA), osteoporosis, osteopetrosis, and periodontitis. Studies in osteoimmunology reveal relationships between molecular communication among blood cells and structural pathologies in the body.
An endocrine bone disease is a bone disease associated with a disorder of the endocrine system. An example is osteitis fibrosa cystica.
In bone physiology, the bone remodeling period describes the temporal duration of the basic multicellular unit (BMU) that is responsible for bone turnover. Historically, this was referred to as the sigma (σ) or sigma period, but the terminology is now outdated.
The human skeletal system is a complex organ in constant equilibrium with the rest of the body. In addition to support and structure of the body, bone is the major reservoir for many minerals and compounds essential for maintaining a healthy pH balance. The deterioration of the body with age renders the elderly particularly susceptible to and affected by poor bone health. Illnesses like osteoporosis, characterized by weakening of the bone's structural matrix, increases the risk of hip-fractures and other life-changing secondary symptoms. In 2010, over 258,000 people aged 65 and older were admitted to the hospital for hip fractures. Incidence of hip fractures is expected to rise by 12% in America, with a projected 289,000 admissions in the year 2030. Other sources estimate up to 1.5 million Americans will have an osteoporotic-related fracture each year. The cost of treating these people is also enormous, in 1991 Medicare spent an estimated $2.9 billion for treatment and out-patient care of hip fractures, this number can only be expected to rise.
A bone growth factor is a growth factor that stimulates the growth of bone tissue.
