bone

Dictionary: bone   (bōn)

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1. 1. The dense, semirigid, porous, calcified connective tissue forming the major portion of the skeleton of most vertebrates. It consists of a dense organic matrix and an inorganic, mineral component.
   2. Any of numerous anatomically distinct structures making up the skeleton of a vertebrate animal. There are more than 200 different bones in the human body.
   3. A piece of bone.
2. bones
   1. The skeleton.
   2. The body.
   3. Mortal remains.
3. An animal structure or material, such as ivory, resembling bone.
4. Something made of bone or of material resembling bone, especially:
   1. A piece of whalebone or similar material used as a corset stay.
   2. bones Informal. Dice.
5. bones The fundamental plan or design, as of the plot of a book.
6. 1. bones Flat clappers made of bone or wood originally used by the end man in a minstrel show.
   2. Bones (used with a sing. verb) The end man in a minstrel show.

1. To remove the bones from.
2. To stiffen (a piece of clothing) with stays, as of whalebone.

bone up

1. Informal. To study intensely, usually at the last minute: boned up for the final exam.

bone of contention

1. The subject of a dispute.

1. Grounds for a complaint or dispute.

[Middle English bon, from Old English bān.]

The hard connective tissue that, together with cartilage, forms the skeleton of humans and other vertebrates. It is made of calcium phosphate crystals arranged on a protein scaffold. Bone performs a variety of functions: it has a structural and mechanical role; it protects vital organs; it provides a site for the production of blood cells; it serves as a reserve of calcium. See also Connective tissue; Skeletal system.

There are two types of bone in the skeleton: the flat bones (for example, the bones of the skull and ribs) and the long bones (for example, the femur and the bones of the hand and feet). Both types are characterized by an outer layer of dense, compact bone, known as cortical bone, and an inner spongy bone material made up of thin trabeculae, known as cancellous bone. Cortical bone consists of layers of bone (lamellae) in an orderly concentric cylindrical arrangement around tiny Haversian canals. These interconnecting canals carry the blood vessels, lymph vessels, and nerves through the bone and communicate with the periosteum and the marrow cavity. The periosteum is a thin membrane covering the outer surface of bone and consisting of layers of cells that participate in the remodeling and repair of bone. The cancellous bone is in contact with the bone marrow, in which much of the production of blood cells takes place. The interface between the cancellous bone and the marrow is called the endosteum, and it is largely at this site that bone is removed in response to a need for increased calcium elsewhere in the body.

Bone is formed by the laying down of an osteoid matrix by osteoblasts, the bone-forming cells, and the mineralization of the osteoid by the development and deposition of crystals of calcium phosphate (in the form of hydroxyapatite) within it. It is the mineral, organized in a regular pattern on a collagen scaffold, that gives bone its stiffness. Osteoid contains largely fibers of type I collagen and lesser amounts of numerous noncollagenous proteins. Although the role of these proteins in bone is not well understood, it is thought that their particular combination in bone gives this tissue the unique ability to mineralize. It is clear that these proteins interact with each other and that collagen and several of the noncollagenous proteins can bind to specialized receptors on the surface of bone cells. This binding is important for the adhesion of the cells to the bone matrix, and also delivers behavioral signals to the cells. See also Apatite; Collagen.

The primary cell types in bone are those that result in its formation and maintenance (osteoblasts and osteocytes) and those that are responsible for its removal (osteoclasts). Osteoblasts form from the differentiation of multipotential stromal cells that reside in the periosteum and the bone marrow. Under the appropriate stimuli, these primitive stromal cells mature to bone-forming cells at targeted sites in the skeleton. Under different stimuli, they are also capable of developing into adipocytes (fat cells), muscle cells, and chondrocytes (cartilage cells). Osteocytes, which are osteoblasts that become incorporated within the bone tissue itself, are the most numerous cell type in bone. They reside in spaces (lacunae) within the mineralized bone, forming numerous extensions through tiny channels (cannaliculi) in the bone that connect with other osteocytes and with the cells on the endosteal surface. Osteocytes are therefore ideally placed to sense stresses and loads placed on the bone and to convey this information to the osteoblasts on the bone surface, thus enabling bone to adapt to altered mechanical loading by the formation of new bone. Osteocytes are also thought to be the cells that detect and direct the repair of microscopic damage that frequently occurs in the bone matrix due to wear and tear. Failure to repair the cracks and microfractures that occur in bone, or when this microdamage accumulates at a rate exceeding its repair, can cause the structural failure of the bone, such as in stress fractures. A large number of molecules that regulate the formation and function of osteoblastic cells have been identified. Circulating hormones, such as insulin, growth hormone, and insulinlike growth factors, combine with growth factors within the bone itself, such as transforming growth factor beta (TGFβ) and bone morphogenetic proteins (BMPs), to influence the differentiation of osteoblasts.

Osteoclasts are typically large, multinucleated cells, rich in the intracellular machinery required for bone resorption. This is accomplished when the cells form a tight sealing zone by attachment of the cell membrane against the bone matrix, creating a bone-resorbing compartment. Into this space, the cell secretes acid to dissolve the bone mineral, and enzymes to digest the collagen and other proteins in the bone matrix. The removal of bone by osteoclasts is necessary to enable the repair of microscopic damage and changes in bone shape during growth and tooth eruption. Osteoclast-mediated bone resorption is also the mechanism for releasing calcium stored in bone for the maintenance of calcium levels in the blood. Most agents that promote bone resorption act on osteoblastic cells, which in turn convey signals to osteoclast precursors to differentiate into mature osteoclasts. These agents include the active form of vitamin D, parathyroid hormone, interleukin-1, interleukin-6, and interleukin-11, and prostaglandins such as prostaglandin E₂. Differentiation to fully functional osteoclasts also requires close contact between osteoclast precursors and osteoblastic cells. This is due to a molecule called osteoclast differentiation factor (ODF) which is located on the surface of osteoblasts, binds to receptors on the surface of osteoclast precursor cells, and induces their progression to osteoclasts.

Flat bones and long bones are formed by different embryological means. Formation of flat bones occurs by intramembranous ossification, in which primitive mesenchymal cells differentiate directly into osteoblasts and produce bony trabeculae within a periosteal membrane. The initial nature of this bone is relatively disorganized and is termed woven bone. Later, this woven bone is remodeled and replaced by the much stronger mature lamella bone, consisting of layers of calcified matrix arranged in orderly fashion. Long bones are formed by intracartilaginous development in which the future bone begins as cartilage. The cartilage template is gradually replaced by bone in an orderly sequence of events starting at the center of the growing bone. Cartilage remains at the ends of long bones during growth, forming a structure at each end termed the growth plate. Cartilage cells (chondrocytes) that arise in the growth plates proliferate and add to the length of the bone. This occurs during a complex series of events, with expansion both away from and toward the center of the bone. When the bone achieves its final length in maturity, expansion from the growth plate ceases. Cartilage persists at the ends of the long bones in a specific form called articular cartilage, which provides the smooth bearing surfaces for the joints.

Bone is a dynamic tissue and is constantly being remodeled by the actions of osteoclasts and osteoblasts. After bone removal, the osteoclasts either move on to new resorption sites or die; this is followed by a reversal phase where osteoblasts are attracted to the resorption site. It is thought that growth factors that are sequestered in an inactive form in the bone matrix are released and activated by the osteoclast activity and that these in turn promote fresh osteoid production by the recruited osteoblasts. The new osteoid eventually calcifies, and in this way the bone is formed and replaced in layers (lamellae), which are the result of these repeated cycles. In growing bone, the activities of bone cells is skewed toward a net increase in bone. However, in healthy mature bone there is an equilibrium between bone resorption and bone formation. When the equilibrium between these two cell types breaks down, skeletal pathology results.

The most common bone disease is osteoporosis, in which there is a net loss of bone due to osteoclastic bone resorption that is not completely matched by new bone formation. The best-understood cause of osteoporosis is that which occurs in women due to the loss of circulating estrogen after menopause. Another cause of osteoporotic bone loss is seen in disuse osteoporosis. Just as bone can respond to increased loading with the production of additional bone, bone is also dependent on regular loading for its maintenance. Significant bone loss can occur during prolonged bed rest or, for example, in paraplegia and quadriplegia. Likewise, an unloading of the skeleton (due to a lack of gravitational pull) in space flight results in severe bone loss in astronauts unless the effects of gravity are simulated by special exercises and devices. See also Osteoporosis.

Many metabolic and genetic diseases can affect the amount and quality of bone. Metabolic diseases such as diabetes, kidney disease, oversecretion of parathyroid hormone by the parathyroid glands, anorexia nervosa, and vitamin D-dependent rickets may cause osteopenias (the reduction in bone volume and bone structural quality). Immunosuppressive therapy in organ transplant patients can lead to reduced bone mass, as can tumors of bone and other sites. Tumors can produce substances that cause the activation of osteoclastic bone resorption. In the genetically based disease osteogenesis imperfecta, mutations in the gene for type I collagen result in the production of reduced amounts of collagen or altered collagen molecules by osteoblasts. Other common diseases of the skeleton are diseases of the joints, such as rheumatoid arthritis and osteoarthritis. See also Arthritis; Calcium metabolism.

Fairly early in the evolution of multicellular organisms it became an advantage to have a hard body component which could provide protection for soft tissues and a firm base against which contractile elements such as muscle could perform precise movements like those involved in locomotion or grasping. The hard component was often formed from calcium carbonate, as found in shellfish, but other durable defences were provided by chitin (a complex carbohydrate), in crustaceans and insects, and even silica, in the glass sponges.

Man and most vertebrates are characterized by an internal rather than an external skeleton. With the exception of the young animal and the cartilaginous fishes, the hardness is provided by calcium phosphate, laid down as crystalline hydroxyapatite on a template of collagen (a fibrous protein), forming bone. The collagen confers some elasticity. In man, bone also acts as the major reservoir for several elements such as calcium, phosphorus, magnesium, zinc, and sodium. The storage and release of at least the first three of these into the extracellular space is modified by hormones such as parathyroid hormone, calcitonin, and 1, 25-dihydroxyvitamin D.

The longest bone is the femur (thigh bone), which accounts for a quarter of one's stature; the smallest bone is the stapes — one of the tiny ossicles in the middle ear which transmits the vibrations from the ear drum to the inner ear.

There are over 200 bones in the adult skeleton. They can be divided into two principal types: the long bones such as the femur, tibia, and humerus, which develop principally from within a cartilaginous framework, and the flat bones such as the skull, bones of the pelvis, and scapula, which develop within membranes of fibrous tissue.

Bone development and growth

X-rays can detect primary centres of bone formation (ossification) in the mid shaft of long bones from the end of the second month of intrauterine life. Secondary centres of ossification appear at the ends of these bones mostly at various times after birth and always earlier in females than males. Some secondary centres, however, such as in the lower end of the femur, occur before birth and this was used in the past as a indication of the maturity of a fetus; this had crucial forensic implications as it could determine whether or not a mother would be charged for concealing the birth of a viable infant.

Towards the ends of the long bones there are specialized discs of cartilage (epiphyseal plates) stretching across the entire bone. The cells in this area have a high rate of multiplication, and it is the major site of longitudinal growth in the juvenile bone. The rate of growth is greatest in infancy and around puberty, and growth ceases when the epiphyseal plate itself finally ossifies. It is over 200 years since the anatomist, John Hunter, showed that the mass and width of bone is increased by surface accretion from the periosteum — a tough fibrous layer covering the bone — rather than by internal expansion.

The ultimate bone length and mass is largely genetically determined and the average racial differences in bone mass exemplify this, with black people having a higher peak bone mass than white Caucasians and higher still than Asians. However this may be modified by general nutritional status — particularly calcium and protein intake — and by physical load bearing. There is evidence that the impact of such environmental influences may be greatest around the time of puberty, and unfortunately the lifestyle of the average teenager in present day Western society does not favour optimal bone development.

Premature arrest of growth at the epiphyseal plate will result in dwarfism. The cause may be genetic (as in achondroplasia), or environmental (as in severe illness or starvation).

Epiphyseal growth is most rapid at the wrists and shoulders in the upper limbs and at the knees in the lower limbs. The increased output of sex hormones at puberty provides a strong stimulus to accelerated bone growth for two or three years and then leads to epiphyseal closure — fusion with the shaft of the bone. Children with precocious puberty end up with stunted growth, whereas in eunuchs the epiphyses remain open and they become tall in their later teens. Pituitary growth hormone is the other hormone involved in bone growth.

All bone surfaces, with the exception of cartilaginous articular surfaces which form a joint with a neighbouring bone, are invested with the fibrous periosteum, which has osteogenic (bone-forming) potential. The flat bones ossify directly from such fibrous tissue rather than from intermediary cartilage. The skull is made up of several bones separated by very irregular interdigitating seams called sutures. This arrangement permits the necessary flexibility of the head during the birth process and after ossification is completed the sutures seal up progressively throughout adult life. Examination of the extent of suture union provides a means for assessing the age of an adult skeleton after death, whereas in a child this can be judged by which ossification centres are present and which epiphyses are fused.

Bone structure

About 80% of the skeleton consists of compact or ‘cortical’ bone which is extremely dense and resistant to trauma, and whose degree of hardness is exceeded in the body only by the enamel of the teeth. Such material forms the thick shafts of the long bones and the surface of all bones. It is perforated by microscopic channels; the Haversian canals (described by Havers, an English physician in the seventeenth century). Blood vessels pass through these canals, and bone cells are arranged concentrically around them. These cells, the osteocytes, have long extensions which pass down an interlocking network of canaliculi in the bone. This same network also allows nutrients, gases, and solutes to permeate the bone from the Haversian blood vessels.

The other 20% of bone forms a delicate, lacy honeycomb with a high surface-to-volume ratio. Cellular activity in this component (called trabecular or cancellous bone) is greater than in compact bone, and a variety of metabolic, hormonal, or physical stimuli on the cells renders it more labile. Trabecular bone is found principally in the bodies of the vertebrae, the ribs, the pelvis, and at the ends of the long bones. It contains the red bone marrow where the cellular components of the blood are manufactured. The remainder of the interior of bones — the medullary cavity — contains fat, and the proportion of fat to red marrow increases with age.

Metabolism and remodelling

Live adult bone is not a rigid inorganic framework. If it were, then like other crystalline structures it would be subject to frequent fatigue fractures as a result of the repetitive strains to which it is subjected. At millions of microscopic sites throughout the skeleton, bone is constantly being broken down and then remade in a cellular process first detailed in the mid twentieth century by an American orthopaedic surgeon, Harold Frost, and termed remodelling. At any site and in response to signals which are, as yet, poorly understood, the osteocytes permit access to the underlying bone by osteoclasts; these are specialized bone-resorbing cells derived from primitive cells in the marrow which also generate other types of phagocytes. These large, multinucleated cells dig small pits in the bone over a period of several days and are then replaced by bone-forming cells, the osteoblasts — which are derived from precursors of the fibrous-tissue-forming series. Osteoblasts synthesize fibres of the protein collagen and dispose them in a regular pattern determined in part by the direction of local strain forces. They also synthesize matrix mucopolysaccharide and direct the later mineralization of collagen with crystalline calcium phosphate. Active metabolites of vitamin D are required to allow adequate provision of both calcium and phosphate at those sites. The osteoblasts are ultimately trapped in the calcified matrix which they themselves have created, and become osteocytes. These cells appear to be able to communicate with each other throughout the bone; their elongated processes form close junctions with each other rather than being joined together.

Whatever the details, one end of a bone can interpret strain and chemical signals from the other. In healthy young adults the remodelling process is in balance, with as much new bone being synthesized as old bone removed. It also permits some adaptation of distribution of bone within a bone (or even within the skeleton) in response to changing physical or biochemical stimuli. Thus the disposition of bony trabeculae or cortical thickness is not haphazard but determined by mechanical and growth signals. Throughout the vertebrates there is a fairly constant ratio between the amount of bone required to cope with the largest forces normally encountered, and that required to deal with average gravitational demands. It is about three to one — for mice through to elephants.

Bone mass and ageing

A minimum regular stress is required simply to maintain your skeletal mass — you either use it or lose it — but the strains required to increase your bone mass significantly have to be substantially more than is customary for the individual concerned. Men have more bone than women at all ages because they are larger, but in both sexes bone mass (as measured conveniently by ‘dual energy X-ray densitometers’) increases into the third decade and plateaus from then till about the end of the fifth decade. It then declines, very slowly in men, but more rapidly in women for some years following the menopause. The average woman has lost around 20% of her peak bone mass by the time she is 70 years old (though estimates from different studies vary). This increases her risk of fractures and broken bones. The decline in bone mass in postmenopausal women can be reduced by taking oestrogen, and load-bearing exercise can increase bone mass to a modest extent in both men and women.

Any bone will fracture if it is subjected to sufficient force, but orthopaedic statistics reveal that over the past fifty years in the Western world there has been a striking rise in the incidence of certain fractures in older people, usually associated with only modest trauma. Fractures of the femoral neck (hip fracture), vertebral bodies (spine fracture), and wrist predominate, and appear to relate to populations having less bone at these sites. This condition, where reduced bone mass increases the liability to fracture, is called osteoporosis and represents one of our principal medical challenges today. In osteoporosis the remodelling process is not in equilibrium; less new bone is being formed than is being removed. It probably relates to several modern lifestyle changes affecting bone metabolism — notably diet and physical labour. The fact that Asian populations have smaller skeletons in any event and are adopting many of the same lifestyle features has led to predictions that hip fracture in that part of the world will become one of the greatest health care problems of the twenty-first century.

Several drugs are now available which have powerful actions on bone metabolism: examples are the bisphosphonates and the calcitonins, both of which inhibit bone resorption and can be used in the treatment of osteoporosis. The drug most commonly taken with such an effect is oestrogen, as hormone replacement therapy (HRT). It may also enhance bone formation.

The other common bone pathology is osteomalacia (called ‘rickets’ in children). In this disorder the bone is poorly mineralized, permitting softening and deformity such as bow legs. The usual cause is lack of vitamin D in the diet and/or lack of exposure to sunlight, and supplements of vitamin D are the appropriate treatment.

Ancient bones

Of all the body tissues, bone — apart from the teeth — is usually the only one to survive significantly beyond our mortal span. Ignoring palaeological niceties, some ‘human’ skeletons have been dated at around two million years old and provide us with much of the scanty evidence we have concerning the evolution of our species. Depending on the bones available, careful examination can allow reasonable inference concerning cranial development, height, and nutrition, in addition to the presence of diseases such as tuberculosis and leprosy and the medico-social practice of skull trepanning. The persistence of minute quantities of DNA within ancient bones may, by the application of sophisticated Polymerase Chain Reaction (PCR) augmentation and analysis, permit conclusions on the evolutionary/racial classification of some prehistoric skeletal remains. Look after your bones — they may tell your story long after you are gone!

— Iain Boyle

Bibliography

• Frost, H. M. (1964). Laws of bone structure. Thomas Springfield, Illinois

See also calcium; hormone replacement therapy; joints; parathyroid glands; skeleton.

Bones consist of an organic matrix composed of collagen and other proteins and crystalline mineral, mainly hydroxyapatite (calcium phosphate and calcium hydroxide), together with magnesium phosphate, fluorides, and sulphates. See also calcium.

Hard tissue consisting of a calcified matrix (mainly calcium phosphate) and fibres of protein. About 200 bones make up the human skeleton. It is living tissue with its own blood supply. Bones have a number of functions: they support and protect soft tissues; they act as levers for muscle movement; and the central cavities of long bones store minerals and produce blood cells.

The long bones and some flat bones contain a central cavity filled with a very active tissue called bone marrow. In adults, the marrow in certain bones (e.g. those of the sternum, ribs, and limbs) produce new red blood cells and destroy those which are defunct. Marrow is also an important source of white blood cells which play a vital role in the body's immunity against disease.

Bone elongation stops in adults, but bones may change their density and strength at any age (figure 18). Bones need to be mechanically stressed if they are to remain strong and healthy. They tend to become thicker and denser when exercise intensity increases, but they get less dense and weaker if a person becomes inactive. They also weaken if there is a deficiency of calcium or vitamin D in the diet, or if calcium absorption is impaired. See also osteoporosis.

Figure 18 Bone density decreases with age, increasing the risk of osteoporosis (brittle bone disease)

To remove the bones from meat, fish or fowl.

Idioms beginning with bone:
bone up

See also bare bones; chilled to the bone; cut to the bone; feel in one's bones; funny bone; make no bones about; pull a boner; roll the bones; skin and bones; work one's fingers to the bone.

1. the material of the skeletons of most vertebrate animals; the tissue composing bones. n 2. dense, hard, and slightly elastic connective tissue in which the fibers are impregnated with a form of calcium phosphate similar to hydroxyapatite. Bone tissue makes up the 206 bones of the human skeleton. n 3. any single element of the skeleton such as a rib or femur.

(click to enlarge)
Internal structure of a human long bone, with a magnified cross section of the interior. The … (credit: © Merriam-Webster Inc.)

Rigid connective tissue of vertebrates, consisting of cells embedded in a hard matrix. Bones serve as the body's supporting framework, provide muscle-attachment points for movement, protect the internal organs, house the blood-cell formation system (red bone marrow), and hold about 99% of the calcium vital to many body processes. Bone consists of a matrix of crystals of calcium, chiefly the phosphate and carbonate, embedded among collagen fibres, providing strength and elasticity, and bone cells (less than 5% of its volume). An external layer of compact bone surrounds a central area of spongy bone, except at the marrow cavity. Bone does not grow by cell division; instead, different types of bone cells generate bone matrix, break it down, and maintain it. Bone is remodeled by this process, which strengthens it in areas under greatest stress, permits healing of fractures, and helps regulate calcium levels in body fluid (see calcium deficiency). The process also causes underutilized bone, as in an immobilized limb, to atrophy. Bone disorders include rheumatoid arthritis, osteoarthritis, rickets, osteoporosis, and tumours. Bone can fracture suddenly or over time, as in stress fractures.

For more information on bone, visit Britannica.com.

A belief reported in England and Scotland from the mid-19th century onwards was that it is unwise to burn bones, usually with the reason that your own bones will ache if you do so, and a much earlier notion links burnt bones with toothache (Gospelles of Dystaues (1507), part 2, p. xiii, quoted in Opie and Tatem, 1989: 15). Aubrey (1686: 165) reported that women wear a tooth taken from a skull to prevent toothache, and that ‘cunning alewives putt the ashes of … bones in their Ale to make it intoxicating. Dr. Goddard bought bones of the Sextons to make his drops with. Some make a playster for the Gowte with the earth or musilage newly scraped from the shin-bone.’ Many other recorded cures mention the use of skulls.

See also BLADE-BONE, WISHBONE, SKULL, LUCKY BONE, CRAMP BONE.

Bibliography
The full bibliography list is available here.

• Opie and Tatem, 1989: 35

The hardest connective tissue in the body. Bone consists of hard calcified matrix (mainly calcium phosphate) and collagen fibres. Over 200 bones make up the human skeleton. Bone is living material and is very well vascularized (see Haversian system). Bones support and protect soft body parts; they act as levers for muscles during locomotion; they store calcium and fats; and they are involved in the production of blood cells. Bones fall into four main categories according to their size and shape (see flat bones, irregular bones, long bones, short bones). Bone may also be classified according to its density and porosity as either smooth, dense compact bone, or less dense, porous spongy bone.

The preparation of meat for human consumption by removing the bones from the carcass.

• hot b. — the boning process is carried out immediately, before the carcass has had time to cool and the meat to set.

Bones can obviously represent death, either literal or metaphorical. They can also symbolize a state of reduction or deprivation (as in being "stripped to the bare bones" and being left with a "skeleton crew"). Less ominously, bones may simply refer to the structure of something.

This article is about the skeletal organs. For the tissue, see Osseous tissue. For other uses, see Bone (disambiguation).

Drawing of a human femur.

Bones are rigid organs that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue. Because bones come in a variety of shapes and have a complex internal and external structure they are lightweight, yet strong and hard, in addition to fulfilling their many other functions. One of the types of tissue that makes up bone is the mineralized osseous tissue, also called bone tissue, that gives it rigidity and a honeycomb-like three-dimensional internal structure. Other types of tissue found in bones include marrow, endosteum and periosteum, nerves, blood vessels and cartilage. There are 206 bones in the adult human body^[1] and about 300 in an infant.^[2]

Functions Bones have ten main functions:

Mechanical

• Protection — Bones can serve to protect internal organs, such as the skull protecting the brain or the ribs protecting the heart and lungs.
• Shape — Bones provide a frame to keep the body supported.
• Movement — Bones, skeletal muscles, tendons, ligaments and joints function together to generate and transfer forces so that individual body parts or the whole body can be manipulated in three-dimensional space. The interaction between bone and muscle is studied in biomechanics.
• Sound transduction — Bones are important in the mechanical aspect of overshadowed hearing.

Synthetic

• Blood production — The marrow, located within the medullary cavity of long bones and interstices of cancellous bone, produces blood cells in a process called haematopoiesis.

Metabolic

• Mineral storage — Bones act as reserves of minerals important for the body, most notably calcium and phosphorus.
• Growth factor storage — Mineralized bone matrix stores important growth factors such as insulin-like growth factors, transforming growth factor, bone morphogenetic proteins and others.
• Fat Storage — The yellow bone marrow acts as a storage reserve of fatty acids
• Acid-base balance — Bone buffers the blood against excessive pH changes by absorbing or releasing alkaline salts.
• Detoxification — Bone tissues can also store heavy metals and other foreign elements, removing them from the blood and reducing their effects on other tissues. These can later be gradually released for excretion.^{[citation needed]}

Contents 1 Characteristics 2 Structure 2.1 Gross anatomy 2.2 Individual bone structure 2.2.1 Compact bone or (Cortical bone) 2.2.2 Trabecular bone 3 Cellular structure 4 Molecular structure 4.1 Matrix 4.1.1 Inorganic 4.1.2 Organic 4.2 Woven or lamellar 5 Types 6 Formation 6.1 Endochondral ossification 6.2 Bone marrow 7 Remodeling 7.1 Purpose 7.1.1 Calcium balance 7.1.2 Repair 8 Paracrine cell signalling 8.1 Osteoblast stimulation 8.2 Osteoclast inhibition 9 Disorders 9.1 Osteoporosis 9.2 Other 10 Osteology 11 Alternatives to bony endoskeletons 12 Exposed bone 13 Terminology 14 See also 15 Footnotes 16 References 17 External links

Characteristics

The primary tissue of bone, osseous tissue, is a relatively hard and lightweight composite material, formed mostly of calcium phosphate in the chemical arrangement termed calcium hydroxylapatite (this is the osseous tissue that gives bones their rigidity). It has relatively high compressive strength but poor tensile strength of 104-121 MPa, meaning it resists pushing forces well, but not pulling forces. While bone is essentially brittle, it does have a significant degree of elasticity, contributed chiefly by collagen. All bones consist of living and dead cells embedded in the mineralized organic matrix that makes up the osseous tissue.

Structure

Gross anatomy

See also: Human skeleton and List of bones of the human skeleton

v • d • e Bones (Axial skeleton, Appendicular skeleton) VERTEBRAL COLUMN vertebrae (cervical, thoracic, lumbar) · sacrum · coccyx THORAX sternum · rib cranial bones of SKULL occipital · parietal · frontal · temporal  · sphenoid · ethmoid facial bones of SKULL nasal · maxilla · lacrimal · zygomatic · palatine · inferior nasal conchae · vomer · mandible · THROAT: hyoid (greater cornu, lesser cornu, body) UPPER EXTREMITY SHOULDER GIRDLE:clavicle · scapula · ARM: humerus · ulna · radius- HAND:carpals (scaphoid · lunate bone · triquetral · pisiform · trapezium · trapezoid · capitate · hamate) · metacarpals · phalanges (prox, int, dist) LOWER EXTREMITY PELVIS:pelvis (ilium, ischium, pubis) · LEG: femur · patella · fibula · tibia · FOOT: tarsals (calcaneus, talus, navicular, cuneiform, cuboid ) · metatarsals · phalanges (prox, int, dist) MIDDLE EAR OSSICLES malleus · incus · stapes

v • d • e Bones of head and neck: the facial bones of the skull Maxilla Surfaces Anterior: fossae (Incisive fossa, Canine fossa) · Infraorbital foramen · Anterior nasal spine Infratemporal: Alveolar canals · Maxillary tuberosity Orbital: Infraorbital groove · Infraorbital canal Nasal: Pterygopalatine canal Processes Zygomatic process Frontal process (Agger nasi, Anterior lacrimal crest) Alveolar process Palatine process (Incisive foramen, Incisive canals, Foramina of Scarpa, Incisive bone, Anterior nasal spine) Other Body of maxilla · Maxillary sinus Zygomatic Orbital process (Zygomatico-orbital) · Temporal process (Zygomaticotemporal) · Lateral process (Zygomaticofacial) Palatine Fossae Pterygopalatine fossa · Pterygoid fossa Plates Horizontal plate (Posterior nasal spine) · Perpendicular plate (Pterygopalatine canal, Sphenopalatine foramen, Pyramidal process) Processes Orbital · Sphenoidal Mandible Body external surface (Symphysis menti, Mental protuberance, Mental foramen) · internal surface (Mental spine, Mylohyoid line, Sublingual fovea, Submandibular fovea) · Alveolar part of mandible Ramus Mylohyoid groove (Mandibular canal, Lingula) · Mandibular foramen · Angle Coronoid process · Mandibular notch · Condyloid process · Pterygoid fovea Minor/ nose Nasal bone: Internasal suture · Nasal foramina Inferior nasal concha: Ethmoidal process · Maxillary process Vomer: Wing Lacrimal: Posterior lacrimal crest · Lacrimal groove · Lacrimal hamulus

v • d • e Bones of head and neck: the cranium of the skull Occipital Squama external (Inion/External occipital protuberance, Nuchal lines) · planes (Occipital, Nuchal) · internal (Cruciform eminence, Internal occipital protuberance, Sagittal sulcus, Internal occipital crest) Lateral parts Condyle (Condyloid fossa, Condylar canal) · Hypoglossal canal · jugular (Jugular process, Jugular tubercle) Basilar part Pharyngeal tubercle Other Foramen magnum Parietal Parietal eminence · Temporal line · Parietal foramen Frontal Squama Frontal suture · Frontal eminence · external (Superciliary arches, Glabella) · foramina (Supraorbital, Cecum) · Zygomatic process · internal (Sagittal sulcus, Frontal crest) Orbital part Ethmoidal notch · Lacrimal fossa · Trochlear fovea · Frontal sinus · Frontonasal duct Temporal Squama Articular tubercle · Suprameatal triangle · Mandibular fossa · Petrotympanic fissure · Zygomatic process Mastoid part Mastoid foramen · Mastoid process (Mastoid cells) · Mastoid notch · Occipital groove · Sigmoid sulcus · Mastoid antrum (Entrance) Petrous part Carotid canal · Facial canal (Hiatus) · Internal auditory meatus · Aqueduct of cochlea · Stylomastoid foramen fossae (Subarcuate fossa, Jugular fossa) · canaliculi (Inferior tympanic, Mastoid) · Styloid process · Petrosquamous suture (note: ossicles in petrous part, but not part of temporal bone) Tympanic part Suprameatal spine Sphenoid Surfaces Superior surface: Sella turcica (Dorsum sellae, Tuberculum sellae, Hypophysial fossa, Posterior clinoid processes) · Ethmoidal spine · Chiasmatic groove · Middle clinoid process · Petrosal process · Clivus Lateral surface: Carotid groove · Sphenoidal lingula Anterior surface: Sphenoidal sinuses Great wings foramina (Rotundum, Ovale, Vesalii, Spinosum) · Spine · Infratemporal crest · Sulcus for auditory tube Small wings Superior orbital fissure · Anterior clinoid process · Optic canal Pterygoid processes fossae (Pterygoid, Scaphoid) · pterygoid plates (Lateral, Medial) · Pterygoid canal · Hamulus Other Body · Sphenoidal conchae Ethmoid Plates Cribriform plate (Crista galli, Olfactory foramina) · Perpendicular plate Surfaces Lateral surface Orbital lamina · Uncinate process Medial surface Superior nasal concha · Superior meatus · Middle nasal concha · Middle meatus Labyrinth Ethmoid sinus · ethmoidal foramina (Posterior, Anterior)

v • d • e Bones of head and neck: cranial sutures, fontanelles, and related regions Cranial sutures Cranial: frontoethmoidal – frontal or metopic (frontal/frontal) – coronal (frontal/parietal) – occipitomastoid (occipital/temporal) – lambdoid (parietal/temporal) – sagittal (parietal/parietal) – sphenoethmoidal – sphenofrontal – sphenoparietal – sphenosquamosal (sphenoid/temporal) – sphenopetrosal (sphenoid/temporal) – squamosal (temporal/parietal) – petrosquamous (temporal/temporal) Facial: palatomaxillary suture Cranial–facial: sphenozygomatic – zygomaticotemporal – zygomaticofrontal Fontanelles anterior – posterior – sphenoidal – mastoid Foramina of multiple bones inferior orbital fissure – foramen lacerum – jugular foramen – nasolacrimal canal Fossae anterior cranial fossa – middle cranial fossa – posterior cranial fossa – cranial cavity Other compound structures Cranial: asterion – pterion – calvaria – stephanion – bregma – lambda Facial: nasion Cranial–facial: dacryon – zygomatic arch – temporal fossa – infratemporal fossa – pterygomaxillary fissure – pterygopalatine fossa

v • d • e Bones of upper limbs Pectoral girdle, clavicle conoid tubercle – trapezoid line – costal tuberosity – subclavian groove Scapula fossae (subscapular, supraspinatous, infraspinatous) – suprascapular notch – glenoid cavity tubercles (infraglenoid, supraglenoid) – spine of scapula – acromion – coracoid process borders (superior, lateral/axillary, medial/vertebral) – angles (superior, inferior, lateral) Humerus upper extremity: necks (anatomical, surgical) – tubercles (greater, lesser) – intertubercular sulcus body: radial sulcus – deltoid tuberosity lower extremity: capitulum – trochlea – epicondyles (lateral, medial) – supracondylar ridges (lateral, medial) – fossae (radial, coronoid, olecranon) Forearm radius: upper extremity (head, tuberosity) – body – lower extremity (ulnar notch, styloid process) ulna: upper extremity (tuberosity, olecranon, coronoid process, radial notch, trochlear notch) – body – lower extremity (head, styloid process) Hand carpus: scaphoid – lunate – triquetral – pisiform – trapezium – trapezoid – capitate – hamate (hamulus) metacarpus: 1st metacarpal – 2nd – 3rd – 4th – 5th phalanges of the hand: proximal – intermediate – distal

v • d • e Bones of torso Sternum Suprasternal notch, Manubrium, Sternal angle, Body of sternum, Xiphisternal joint, Xiphoid process Rib specific ribs (1, 2, 9, 10, 11, 12, true – 1–7, false – 8–12, floating – 11–12) – parts (Angle, Tubercle, Costal groove, Neck, Head) Vertebra General structures body of vertebra, vertebral arch (pedicle, lamina, vertebral notch), foramina (vertebral, intervertebral), processes (transverse, articular/zygapophysis, spinous), spinal canal Cervical vertebrae C1 (anterior arch, posterior arch, lateral mass), C2 (dens), C3, C4, C5, C6, C7 anterior tubercle, posterior tubercle, foramen transversarium Thoracic vertebrae T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12 costal facets (superior, inferior, transverse) Lumbar vertebrae accessory process, mammillary process, L5 Sacrum pelvic surface (anterior sacral foramina), dorsal surface (posterior sacral foramina, median sacral crest, medial sacral crest, lateral sacral crest), lateral surface (sacral tuberosity), base, sacral hiatus – presacral space – sacral promontory – sacral canal  – ala of sacrum – sacrovertebral angle Coccyx

v • d • e Bones of lower limbs Femur upper extremity head (fovea) · neck · greater trochanter (trochanteric fossa) · lesser trochanter · intertrochanteric line · intertrochanteric crest body linea aspera · gluteal tuberosity / third trochanter · pectineal line lower extremity adductor tubercle · patellar surface · epicondyles (lateral, medial) · condyles (lateral, medial) · intercondylar fossa Crus Tibia upper extremity condyles (lateral, medial) · intercondylar eminence (lateral/medial intercondylar tubercle) · posterior/anterior intercondylar area body tuberosity · soleal line lower extremity medial malleolus · fibular notch Fibula head · body · lateral malleolus Other patella Foot Tarsus calcaneus (sustentaculum tali, trochlear process) · talus (body, neck, head) · navicular · cuboid · cuneiform (medial, intermediate, lateral) Metatarsus 1st metatarsal · 2nd · 3rd · 4th · 5th Other phalanges of the foot

v • d • e Bones of pelvis / pelvic cavity General sacrum · coccyx · hip bone Ilium body arcuate line wing gluteal lines (posterior, anterior, inferior) iliac spines (anterior superior, anterior inferior, posterior superior, posterior inferior) other: crest · tuberosity · fossa Ischium body ischial spine · lesser sciatic notch superior ramus tuberosity of the ischium inferior ramus no substructures Pubis body pubic crest superior ramus pubic tubercle · obturator crest inferior ramus pectineal line Compound acetabulum (acetabular notch) · iliopubic eminence / iliopectineal line · linea terminalis · ischiopubic ramus / pubic arch obturator foramen · greater sciatic foramen / greater sciatic notch · lesser sciatic foramen lesser pelvis (pelvic inlet, pelvic brim, pelvic outlet) · greater pelvis

Individual bone structure

A femur with a cortex of compact bone and medulla of trabecular bone

Bone is not a uniformly solid material, but rather has some spaces between its hard elements.

Compact bone or (Cortical bone)

The hard outer layer of bones is composed of compact bone tissue, so-called due to its minimal gaps and spaces. This tissue gives bones their smooth, white, and solid appearance, and accounts for 80% of the total bone mass of an adult skeleton. Compact bone may also be referred to as dense bone.

Trabecular bone

Filling the interior of the organ is the trabecular bone tissue (an open cell porous network also called cancellous or spongy bone), which is composed of a network of rod- and plate-like elements that make the overall organ lighter and allowing room for blood vessels and marrow. Trabecular bone accounts for the remaining 20% of total bone mass but has nearly ten times the surface area of compact bone.

Cellular structure

There are several types of cells constituting the bone;

• Osteoblasts are mononucleate bone-forming cells that descend from osteoprogenitor cells. They are located on the surface of osteoid seams and make a protein mixture known as osteoid, which mineralizes to become bone. Osteoid is primarily composed of Type I collagen. Osteoblasts also manufacture hormones, such as prostaglandins, to act on the bone itself. They robustly produce alkaline phosphatase, an enzyme that has a role in the mineralisation of bone, as well as many matrix proteins. Osteoblasts are the immature bone cells.

• Bone lining cells are essentially inactive osteoblasts. They cover all of the available bone surface and function as a barrier for certain ions.
• Osteocytes originate from osteoblasts that have migrated into and become trapped and surrounded by bone matrix that they themselves produce. The spaces they occupy are known as lacunae. Osteocytes have many processes that reach out to meet osteoblasts and other osteocytes probably for the purposes of communication. Their functions include to varying degrees: formation of bone, matrix maintenance and calcium homeostasis. They have also been shown to act as mechano-sensory receptors—regulating the bone's response to stress and mechanical load. They are mature bone cells.

• Osteoclasts are the cells responsible for bone resorption (remodeling of bone to reduce its volume). Osteoclasts are large, multinucleated cells located on bone surfaces in what are called Howship's lacunae or resorption pits. These lacunae, or resorption pits, are left behind after the breakdown of the bone surface. Because the osteoclasts are derived from a monocyte stem-cell lineage, they are equipped with phagocytic like mechanisms similar to circulating macrophages. Osteoclasts mature and/or migrate to discrete bone surfaces. Upon arrival, active enzymes, such as tartrate resistant acid phosphatase, are secreted against the mineral substrate.

Molecular structure

Matrix

The majority of bone is made of the bone matrix. It has inorganic and organic parts. Bone is formed by the hardening of this matrix entrapping the cells. When these cells become entrapped from osteoblasts they become osteocytes.

Inorganic

The inorganic is mainly crystalline mineral salts and calcium, which is present in the form of hydroxyapatite. The matrix is initially laid down as unmineralised osteoid (manufactured by osteoblasts). Mineralisation involves osteoblasts secreting vesicles containing alkaline phosphatase. This cleaves the phosphate groups and acts as the foci for calcium and phosphate deposition. The vesicles then rupture and act as a centre for crystals to grow on.

Organic

The organic part of matrix is mainly composed of Type I collagen. This is synthesised intracellularly as tropocollagen and then exported, forming fibrils. The organic part is also composed of various growth factors, the functions of which are not fully known. Factors present include glycosaminoglycans, osteocalcin, osteonectin, bone sialo protein, osteopontin and Cell Attachment Factor. One of the main things that distinguishes the matrix of a bone from that of another cell is that the matrix in bone is hard.

Woven or lamellar

Collagen fibres of woven bone

Bone is first deposited as woven bone, in a disorganized structure with a high proportion of osteocytes in young and in healing injuries. Woven bone is weaker, with a small number of randomly oriented collagen fibers, but forms quickly. It is replaced by lamellar bone, which is highly organized in concentric sheets with a low proportion of osteocytes. Lamellar bone is stronger and filled with many collagen fibers parallel to other fibers in the same layer (these parallel columns are called osteons). The fibers run in opposite directions in alternating layers, much like plywood, assisting in the bone's ability to resist torsion forces. After a fracture, woven bone forms initially and is gradually replaced by lamellar bone during a process known as "bony substitution."

Types

There are five types of bones in the human body: long, short, flat, irregular and sesamoid.

• Long bones are characterized by a shaft, the diaphysis, that is much greater in length than width. They are comprised mostly of compact bone and lesser amounts of marrow, which is located within the medullary cavity, and spongy bone. Most bones of the limbs, including those of the fingers and toes, are long bones. The exceptions are those of the wrist, ankle and kneecap.
• Short bones are roughly cube-shaped, and have only a thin layer of compact bone surrounding a spongy interior. The bones of the wrist and ankle are short bones, as are the sesamoid bones.
• Flat bones are thin and generally curved, with two parallel layers of compact bones sandwiching a layer of spongy bone. Most of the bones of the skull are flat bones, as is the sternum.
• Irregular bones do not fit into the above categories. They consist of thin layers of compact bone surrounding a spongy interior. As implied by the name, their shapes are irregular and complicated. The bones of the spine and hips are irregular bones.
• Sesamoid bones are bones embedded in tendons. Since they act to hold the tendon further away from the joint, the angle of the tendon is increased and thus the leverage of the muscle is increased. Examples of sesamoid bones are the patella and the pisiform.

Formation

The formation of bone during the fetal stage of development occurs by two processes: Intramembranous ossification and endochondral ossification.

Intramembranous ossification mainly occurs during formation of the flat bones of the skull; the bone is formed from mesenchyme tissue. The steps in intramembranous ossification are:

1. Development of ossification center
2. Calcification
3. Formation of trabeculae
4. Development of periosteum

Endochondral ossification

Endochondrial ossification

Endochondral ossification, on the other hand, occurs in long bones, such as limbs; the bone is formed from cartilage. The steps in endochondral ossification are:

1. Development of cartilage model
2. Growth of cartilage model
3. Development of the primary ossification center
4. Development of the secondary ossification center
5. Formation of articular cartilage and epiphyseal plate

Endochondral ossification begins with points in the cartilage called "primary ossification centers." They mostly appear during fetal development, though a few short bones begin their primary ossification after birth. They are responsible for the formation of the diaphyses of long bones, short bones and certain parts of irregular bones. Secondary ossification occurs after birth, and forms the epiphyses of long bones and the extremities of irregular and flat bones. The diaphysis and both epiphyses of a long bone are separated by a growing zone of cartilage (the epiphyseal plate). When the child reaches skeletal maturity (18 to 25 years of age), all of the cartilage is replaced by bone, fusing the diaphysis and both epiphyses together (epiphyseal closure).

Bone marrow

Bone marrow can be found in almost any bone that holds cancellous tissue. In newborns, all such bones are filled exclusively with red marrow , but as the child ages it is mostly replaced by yellow, or fatty marrow. In adults, red marrow is mostly found in the marrow bones of the femur, the ribs, the vertebrae and pelvic bones.

Remodeling

Remodeling or bone turnover is the process of resorption followed by replacement of bone with little change in shape and occurs throughout a person's life. Osteoblasts and osteoclasts, coupled together via paracrine cell signalling, are referred to as bone remodeling units.

Purpose

The purpose of remodeling is to regulate calcium homeostasis, repair micro-damaged bones (from everyday stress) but also to shape and sculpture the skeleton during growth.

Calcium balance

The process of bone resorption by the osteoclasts releases stored calcium into the systemic circulation and is an important process in regulating calcium balance. As bone formation actively fixes circulating calcium in its mineral form, removing it from the bloodstream, resorption actively unfixes it thereby increasing circulating calcium levels. These processes occur in tandem at site-specific locations.

Repair

Repeated stress, such as weight-bearing exercise or bone healing, results in the bone thickening at the points of maximum stress (Wolff's law). It has been hypothesized that this is a result of bone's piezoelectric properties, which cause bone to generate small electrical potentials under stress.^[3]

Paracrine cell signalling

The action of osteoblasts and osteoclasts are controlled by a number of chemical factors which either promote or inhibit the activity of the bone remodelling cells, controlling the rate at which bone is made, destroyed or changed in shape. The cells also use paracrine signalling to control the activity of each other.

Osteoblast stimulation

Osteoblasts can be stimulated to increase bone mass through increased secretion of osteoid and by inhibiting the ability of osteoclasts to break down osseous tissue.

Bone building through increased secretion of osteoid is stimulated by the secretion of growth hormone by the pituitary, thyroid hormone and the sex hormones (estrogens and androgens). These hormones also promote increased secretion of osteoprotegerin.^[4] Osteoblasts can also be induced to secrete a number of cytokines that promote reabsorbtion of bone by stimulating osteoclast activity and differentiation from progenitor cells. Vitamin D, parathyroid hormone and stimulation from osteocytes induce osteoblasts to increase secretion of RANK-ligand and interleukin 6, which cytokines then stimulate increased reabsorbtion of bone by osteoclasts. These same compounds also increase secretion of macrophage colony-stimulating factor by osteoblasts, which promotes the differentiation of progenitor cells into osteoclasts, and decrease secretion of osteoprotegerin.

Osteoclast inhibition

The rate at which osteoclasts resorb bone is inhibited by calcitonin and osteoprotegerin. Calcitonin is produced by parafollicular cells in the thyroid gland, and can bind to receptors on osteoclasts to directly inhibit osteoclast activity. Osteoprotegerin is secreted by osteoblasts and is able to bind RANK-L, inhibiting osteoclast stimulation.^[4]

Disorders

See also: List of skeletal disorders

There are many disorders of the skeleton. One of the more prominent is osteoporosis.

Osteoporosis

Main article: Osteoporosis

Osteoporosis is a disease of bone - leading to an increased risk of fracture. In osteoporosis, the bone mineral density (BMD) is reduced, bone microarchitecture is disrupted, and the amount and variety of non-collagenous proteins in bone is altered. Osteoporosis is defined by the World Health Organization (WHO) in women as a bone mineral density 2.5 standard deviations below peak bone mass (20-year-old sex-matched healthy person average) as measured by DXA; the term "established osteoporosis" includes the presence of a fragility fracture.^[5] Osteoporosis is most common in women after the menopause, when it is called postmenopausal osteoporosis, but may develop in men and premenopausal women in the presence of particular hormonal disorders and other chronic diseases or as a result of smoking and medications, specifically glucocorticoids, when the disease is called steroid- or glucocorticoid-induced osteoporosis (SIOP or GIOP).

Osteoporosis can be prevented with lifestyle advice and medication, and preventing falls in people with known or suspected osteoporosis is an established way to prevent fractures. Osteoporosis can be treated with bisphosphonates and various other medical treatments.

Other

Other disorders of bone include:

• Bone fracture
• Osteomyelitis
• Osteosarcoma
• Osteogenesis imperfecta
• Osteochondritis Dissecans
• Bone Metastases

Osteology

The study of bones and teeth is referred to as osteology. It is frequently used in anthropology, archeology and forensic science for a variety of tasks. This can include determining the nutritional, health, age or injury status of the individual the bones were taken from. Preparing fleshed bones for these types of studies can involve maceration - boiling fleshed bones to remove large particles, then hand-cleaning.

Typically anthropologists and archeologists study bone tools made by Homo sapiens and Homo neanderthalensis. Bones can serve a number of uses such as projectile points or artistic pigments, and can be made from endoskeletal or external bones such as antler or tusk.

Alternatives to bony endoskeletons

There are several evolutionary alternatives to mammilary bone; though they have some similar functions, they are not completely functionally analogous to bone.

• Exoskeletons offer support, protection and levers for movement similar to endoskeletal bone. Different types of exoskeletons include shells, carapaces (consisting of calcium compounds or silica) and chitinous exoskeletons.
• A true endoskeleton (that is, protective tissue derived from mesoderm) is also present in Echinoderms. Porifera (sponges) possess simple endoskeletons that consist of calcareous or siliceous spicules and a spongin fiber network.

Exposed bone

Bone penetrating the skin and being exposed to the outside can be both a natural process in some animals, and due to injury:

• A deer's antlers are composed of bone.^[6]
• Instead of teeth, the extinct predatory fish Dunkleosteus had sharp edges of hard exposed bone along its jaws.
• A compound fracture occurs when the edges of a broken bone puncture the skin.
• Though not strictly speaking exposed, a bird's beak is primarily bone covered in a layer of keratin over a vascular layer containing blood vessels and nerve endings.

Terminology

Several terms are used to refer to features and components of bones throughout the body:

Bone feature	Definition
articular process	A projection that contacts an adjacent bone.
articulation	The region where adjacent bones contact each other—a joint.
canal	A long, tunnel-like foramen, usually a passage for notable nerves or blood vessels.
condyle	A large, rounded articular process.
crest	A prominent ridge.
eminence	A relatively small projection or bump.
epicondyle	A projection near to a condyle but not part of the joint.
facet	A small, flattened articular surface.
foramen	An opening through a bone.
fossa	A broad, shallow depressed area.
fovea	A small pit on the head of a bone.
labyrinth	A cavity within a bone.
line	A long, thin projection, often with a rough surface. Also known as a ridge.
malleolus	One of two specific protuberances of bones in the ankle.
meatus	A short canal.
process	A relatively large projection or prominent bump.(gen.)
ramus	An arm-like branch off the body of a bone.
sinus	A cavity within a cranial bone.
spine	A relatively long, thin projection or bump.
suture	Articulation between cranial bones.
trochanter	One of two specific tuberosities located on the femur.
tubercle	A projection or bump with a roughened surface, generally smaller than a tuberosity.
tuberosity	A projection or bump with a roughened surface.

Several terms are used to refer to specific features of long bones:

Bone feature	Definition
diaphysis	The long, relatively straight main body of a long bone; region of primary ossification. Also known as the shaft.
epiphysis	The end regions of a long bone; regions of secondary ossification.
epiphyseal plate	Also known as the growth plate or physis. In a long bone it is a thin disc of hyaline cartilage that is positioned transversely between the epiphysis and metaphysis. In the long bones of humans, the epiphyseal plate disappears by twenty years of age.
head	The proximal articular end of the bone.
metaphysis	The region of a long bone lying between the epiphysis and diaphysis.
neck	The region of bone between the head and the shaft.

See also

Wikimedia Commons has media related to: Bones

• List of bones of the human skeleton
• Terms for anatomical location
• Orthopaedics
• Artificial bone

Footnotes

1. ^ Steele, D. Gentry; Claud A. Bramblett (1988). The Anatomy and Biology of the Human Skeleton. Texas A&M University Press. p. 4. 
2. ^ Schmiedeler, Edgar; Mary Rosa McDonough (1934). Parent and Child: An Introductory Study of Parent Education. D. Appleton-Century. p. 31. 
3. ^ Netter, p. 187-189, A scholarly review of the subject.
4. ^ ^{a b} Boulpaep, Emile L.; Boron, Walter F. (2005). Medical physiology: a cellular and molecular approach. Philadelphia: Saunders. pp. p.1089–1091. ISBN 1416023283. 
5. ^ WHO (1994). "Assessment of fracture risk and its application to screening for postmenopausal osteoporosis. Report of a WHO Study Group". World Health Organization technical report series 843: 1–129. PMID 7941614. 
6. ^ Hans J. Rolf; Alfred Enderle (1999). "Hard fallow deer antler: a living bone till antler casting?". The Anatomical Record 255 (1): 69–77. doi:10.1002/(SICI)1097-0185(19990501)255:1<69::AID-AR8>3.0.CO;2-R. PMID 10321994. http://www3.interscience.wiley.com/cgi-bin/fulltext/67500212/HTMLSTART. Retrieved on 2008-08-20. 

References

• Katja Hoehn; Marieb, Elaine Nicpon (2007). Human Anatomy & Physiology (7th Edition). San Francisco: Benjamin Cummings. ISBN 0805359095. 
• Netter, Frank H. (1987). Musculoskeletal system: anatomy, physiology, and metabolic disorders. New Jersey, Summit: Ciba-Geigy Corporation. ISBN 0914168886
• Bryan H. Derrickson; Tortora, Gerard J. (2005). Principles of anatomy and physiology. New York: Wiley. ISBN 0471689343. 

External links

• Review (including references) of piezoelectricity and bone remodelling
• A good basic overview of bone biology from the Science Creative Quarterly
• Bone Health at Got Bones?
• Osteopathic physicians

v • d • e Musculoskeletal system, connective tissue: bone and cartilage Cartilage perichondrium, fibrocartilage callus, metaphysis cells (chondroblast, chondrocyte) types (hyaline, elastic, fibrous) Bone Ossification intramembranous, endochondral Cycle osteoblast, osteoid, osteocyte, osteoclast Types cancellous, cortical Regions subchondral bone, epiphysis, epiphyseal plate/metaphysis, diaphysis Structure osteon / Haversian system, Haversian canals, Volkmann's canals, connective tissue (endosteum, periosteum), Sharpey's fibres, enthesis, lacunae, canaliculi, trabeculae, medullary cavity, bone marrow Shapes long, short, flat, irregular, sesamoid

v • d • e Bones (Axial skeleton, Appendicular skeleton) VERTEBRAL COLUMN vertebrae (cervical, thoracic, lumbar) · sacrum · coccyx THORAX sternum · rib cranial bones of SKULL occipital · parietal · frontal · temporal  · sphenoid · ethmoid facial bones of SKULL nasal · maxilla · lacrimal · zygomatic · palatine · inferior nasal conchae · vomer · mandible · THROAT: hyoid (greater cornu, lesser cornu, body) UPPER EXTREMITY SHOULDER GIRDLE:clavicle · scapula · ARM: humerus · ulna · radius- HAND:carpals (scaphoid · lunate bone · triquetral · pisiform · trapezium · trapezoid · capitate · hamate) · metacarpals · phalanges (prox, int, dist) LOWER EXTREMITY PELVIS:pelvis (ilium, ischium, pubis) · LEG: femur · patella · fibula · tibia · FOOT: tarsals (calcaneus, talus, navicular, cuneiform, cuboid ) · metatarsals · phalanges (prox, int, dist) MIDDLE EAR OSSICLES malleus · incus · stapes

v • d • e Bones of head and neck: the facial bones of the skull Maxilla Surfaces Anterior: fossae (Incisive fossa, Canine fossa) · Infraorbital foramen · Anterior nasal spine Infratemporal: Alveolar canals · Maxillary tuberosity Orbital: Infraorbital groove · Infraorbital canal Nasal: Pterygopalatine canal Processes Zygomatic process Frontal process (Agger nasi, Anterior lacrimal crest) Alveolar process Palatine process (Incisive foramen, Incisive canals, Foramina of Scarpa, Incisive bone, Anterior nasal spine) Other Body of maxilla · Maxillary sinus Zygomatic Orbital process (Zygomatico-orbital) · Temporal process (Zygomaticotemporal) · Lateral process (Zygomaticofacial) Palatine Fossae Pterygopalatine fossa · Pterygoid fossa Plates Horizontal plate (Posterior nasal spine) · Perpendicular plate (Pterygopalatine canal, Sphenopalatine foramen, Pyramidal process) Processes Orbital · Sphenoidal Mandible Body external surface (Symphysis menti, Mental protuberance, Mental foramen) · internal surface (Mental spine, Mylohyoid line, Sublingual fovea, Submandibular fovea) · Alveolar part of mandible Ramus Mylohyoid groove (Mandibular canal, Lingula) · Mandibular foramen · Angle Coronoid process · Mandibular notch · Condyloid process · Pterygoid fovea Minor/ nose Nasal bone: Internasal suture · Nasal foramina Inferior nasal concha: Ethmoidal process · Maxillary process Vomer: Wing Lacrimal: Posterior lacrimal crest · Lacrimal groove · Lacrimal hamulus

v • d • e Bones of head and neck: the cranium of the skull Occipital Squama external (Inion/External occipital protuberance, Nuchal lines) · planes (Occipital, Nuchal) · internal (Cruciform eminence, Internal occipital protuberance, Sagittal sulcus, Internal occipital crest) Lateral parts Condyle (Condyloid fossa, Condylar canal) · Hypoglossal canal · jugular (Jugular process, Jugular tubercle) Basilar part Pharyngeal tubercle Other Foramen magnum Parietal Parietal eminence · Temporal line · Parietal foramen Frontal Squama Frontal suture · Frontal eminence · external (Superciliary arches, Glabella) · foramina (Supraorbital, Cecum) · Zygomatic process · internal (Sagittal sulcus, Frontal crest) Orbital part Ethmoidal notch · Lacrimal fossa · Trochlear fovea · Frontal sinus · Frontonasal duct Temporal Squama Articular tubercle · Suprameatal triangle · Mandibular fossa · Petrotympanic fissure · Zygomatic process Mastoid part Mastoid foramen · Mastoid process (Mastoid cells) · Mastoid notch · Occipital groove · Sigmoid sulcus · Mastoid antrum (Entrance) Petrous part Carotid canal · Facial canal (Hiatus) · Internal auditory meatus · Aqueduct of cochlea · Stylomastoid foramen fossae (Subarcuate fossa, Jugular fossa) · canaliculi (Inferior tympanic, Mastoid) · Styloid process · Petrosquamous suture (note: ossicles in petrous part, but not part of temporal bone) Tympanic part Suprameatal spine Sphenoid Surfaces Superior surface: Sella turcica (Dorsum sellae, Tuberculum sellae, Hypophysial fossa, Posterior clinoid processes) · Ethmoidal spine · Chiasmatic groove · Middle clinoid process · Petrosal process · Clivus Lateral surface: Carotid groove · Sphenoidal lingula Anterior surface: Sphenoidal sinuses Great wings foramina (Rotundum, Ovale, Vesalii, Spinosum) · Spine · Infratemporal crest · Sulcus for auditory tube Small wings Superior orbital fissure · Anterior clinoid process · Optic canal Pterygoid processes fossae (Pterygoid, Scaphoid) · pterygoid plates (Lateral, Medial) · Pterygoid canal · Hamulus Other Body · Sphenoidal conchae Ethmoid Plates Cribriform plate (Crista galli, Olfactory foramina) · Perpendicular plate Surfaces Lateral surface Orbital lamina · Uncinate process Medial surface Superior nasal concha · Superior meatus · Middle nasal concha · Middle meatus Labyrinth Ethmoid sinus · ethmoidal foramina (Posterior, Anterior)

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Dansk (Danish)
n. - ben, knogle
v. tr. - udbene, afbene
v. intr. - boge den, studere hårdt, terpe

idioms:

• bone china    benporcelæn
• bone lazy    luddoven
• bone meal    benmel
• bone of contention    et stridens æble
• bone up on    terpe, studere intensivt, boge den
• have a bone to pick    have en høne at plukke
• make no bones about    ikke lægge skjul på noget, ikke stikke noget under stolen, være ligefrem

Nederlands (Dutch)
bot, been, graat, skelet, (mv) dobbelstenen, uitbenen, fileren, ontgraten, opstijven met bot, jatten, blokken (studie), zeer

Français (French)
n. - arête, ossements, os, restes, (Mus) castagnettes, dés (à jouer), os (substance), baleine (corset), en os
v. tr. - désosser, enlever les arêtes, piquer, voler, consolider (un corset)
v. intr. - désosser, enlever les arêtes

idioms:

• bone china    porcelaine
• bone lazy    fainéant
• bone meal    engrais
• bone of contention    pomme de discorde
• bone up on    bûcher
• have a bone to pick    choisir son os, avoir un compte à régler
• make no bones about    ne pas cacher que, ne pas hésiter à, aller carrément
• off the bone    poulet désossé
• on the bone    poulet à l'os
• to the bone    jusqu'à la m¯lle des os

Deutsch (German)
n. - Knochen, Gräte, Elfenbein
v. - ausbeinen, entgräten

idioms:

• bone china    Porzellan
• bone lazy    stinkfaul
• bone meal    Knochenmehl
• bone of contention    Zankapfel
• bone up on    etwas büffeln
• have a bone to pick    ein Hühnchen zu rupfen haben
• make no bones about    keinen Hehl machen aus
• off the bone    [Fleisch] ohne Knochen
• on the bone    [Fleisch] mit Knochen
• to the bone    bis aufs Minimum, völlig

Ελληνική (Greek)
n. - κόκαλο, οστό, (πληθ.) ζάρια
v. - ξεκοκαλίζω, ενισχύω με μπαλένες, (καθομ.) κλέβω, σελεμίζω

idioms:

• bone china    φωσφορική πορσελάνη
• bone lazy    τεμπελχανάς
• bone meal    οστεάλευρο
• bone of contention    μήλο της έριδος
• bone up on    σπαζοκεφαλιάζω με, μελετώ εντατικά
• close to the bone    σχεδόν προσβλητικός
• cut to the bone    περιορίζω στο ελάχιστο
• have a bone to pick    έχω προηγούμενα/παλιές διαφορές
• make no bones about    δε διστάζω να

Italiano (Italian)
disossare, osso

idioms:

• all skin and bone    pelle e ossa
• bone china    porcellana
• bone lazy    pigro
• bone meal    fertilizzante di ossa
• bone of contention    pomo della discordia
• bone up on    studiare intensamente
• close to the bone    molto vicino al vero
• have a bone to pick    avere una ragione per litigare
• in one's bones    nel proprio sangue
• make no bones about    non farsi scrupolo
• the bare bones    l'essenziale
• to the bone    fino all'osso
• work one's fingers to the bone    lavorare sodo

Português (Portuguese)
n. - osso (m)
v. - desossar, por barbatanas em

idioms:

• all skin and bone    muito magro
• bone china    porcelana (f) chinesa
• bone lazy    preguiçoso
• bone meal    adubo (m) de ossos
• bone of contention    pomo (m) da discórdia (gír.)
• bone up on    mergulhar no estudo (gír.)
• close to the bone    indecente
• cut to the bone    reduzir custos
• have a bone to pick    ter reclamação a fazer
• in one's bones    acreditar piamente
• make no bones about    não ter dúvidas
• the bare bones    essência (f) dos fatos
• to the bone    até os ossos (gír.)
• work one's fingers to the bone    morrer de trabalhar (gír.)

Русский (Russian)
отделять мясо от костей, кость

idioms:

• all skin and bone    кожа да кости
• bone china    английский фарфор
• bone lazy    ужасно ленивый
• bone meal    костная мука
• bone of contention    яблоко раздора
• bone up on    зубрить
• close to the bone    слишком близко (и может ранить)
• cut to the bone    снижать до минимума
• have a bone to pick    у (меня) с (ним) свои счеты
• in one's bones    предчувствие
• make no bones about    ничего не скрывать
• the bare bones    минимум
• to the bone    до минимума
• work one's fingers to the bone    много работать, пахать

Español (Spanish)
n. - hueso
v. tr. - deshuesar, quitar las espinas, quitar los huesos
v. intr. - deshuesar, quitar las espinas, quitar los huesos

idioms:

• bone china    porcelana blanca y translúcida
• bone lazy    perezoso
• bone meal    harina de huesos
• bone of contention    manzana de la discordia
• bone up on    estudiar duro, empollar
• have a bone to pick    tener que ajustar cuentas
• make no bones about    no andarse con rodeos
• off the bone    deshuesado
• on the bone    con hueso (carne)
• to the bone    hasta los huesos

Svenska (Swedish)
n. - ben
v. - bena, bena ur, knycka, sno

中文（简体）(Chinese (Simplified))
骨头, 骨制品, 骨, 剔去...的骨, 施骨肥于, 用鲸骨撑, 苦学, 考前临时抱佛脚

idioms:

• bone china    骨灰瓷
• bone lazy    懒骨头
• bone meal    骨粉
• bone of contention    争论的原因
• bone up on    熟习
• have a bone to pick    同某人有争论
• make no bones about    对...毫不犹豫

中文（繁體）(Chinese (Traditional))
n. - 骨頭, 骨製品, 骨
v. tr. - 剔去...的骨, 施骨肥於, 用鯨骨撐
v. intr. - 苦學, 考前臨時抱佛腳

idioms:

• bone china    骨灰瓷
• bone lazy    懶骨頭
• bone meal    骨粉
• bone of contention    爭論的原因
• bone up on    熟習
• have a bone to pick    同某人有爭論
• make no bones about    對...毫不猶豫

한국어 (Korean)
n. - 뼈, 시체, 몸
v. tr. - ~의 뼈를 바르다, ~을 고래 수염 따위로 빳빳하게 하다, ~에 골분 비료를 주다
v. intr. - 부지런히 공부하다

idioms:

• bone up on    열심히 공부하다, 열심히 준비하다
• have a bone to pick    따져야 할 일이 있다
• make no bones about    ~을 개의치 않다

日本語 (Japanese)
n. - 骨, 骨格, 死骸, 身体, 骨状のもの
v. - 骨を取る

idioms:

• bone china    ボーンチャイナ
• bone lazy    怠け者の
• bone meal    骨粉
• bone of contention    争いの種
• bone up on    詰め込む
• have a bone to pick    話を付けることがある
• in one's bones    予感する, 確信する
• make no bones about    平気でする
• pared to the bone    がりがりに痩せた
• to the bone    骨まで, 徹底的に

العربيه (Arabic)
‏(الاسم) عظم, عظمه (فعل) أزال العظام‏

עברית (Hebrew)
n. - ‮עצם, חומר העצמות, שנהב, קסטנייטות, קוביות, עצם עשוי עצם‬
v. tr. - ‮הוציא את העצמות מ-, גירם, גנב (מדוברת)‬
v. intr. - ‮עצם, חומר העצמות, שנהב, הוציא את העצמות מ-, גירם, קסטנייטות, קוביות, עבד קשה (מדוברת)‬

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