Gray's illustration of a human femur, a typically recognized bone.

Bone, also called osseous tissue, (Latin: "os") is a type of hard endoskeletal connective tissue found in many vertebrate animals. Bones support body structures, protect internal organs, and (in conjunction with muscles) facilitate movement; are also involved with cell formation, calcium metabolism, and mineral storage. The bones of an animal are, collectively, known as the skeleton. Bone has a different composition than cartilage, and both are derived from mesoderm. In common parlance, cartilage can also be called "bone", certainly when referring to animals that only have cartilage as hard connective tissue, such as cartilaginous fish (Chondrichthyes) like sharks. True bone is present in bony fish (Osteichthyes) and all tetrapods. Image File history File links File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Henry Grays Anatomy of the Human Body, commonly known as Grays Anatomy, is an anatomy textbook widely regarded as a classic work on human anatomy. ... Anterior view of the femur The femur or thigh bone is the longest (length), largest (volume) and strongest (mechanical ability to resist deformity) bone of the human body. ... The Rockwell scale characterises the indentation hardness of materials through the depth of penetration of an indenter, loaded on a material sample and compared to the penetration in some reference material. ... An endoskeleton is an internal support structure of an animal. ... Connective tissue is any type of biological tissue with an extensive extracellular matrix and often serves to support, bind together, and protect organs. ... Groups Conodonta Hyperoartia Petromyzontidae (lampreys) Pteraspidomorphi (early jawless fish) Thelodonti Anaspida Cephalaspidomorphi (early jawless fish) Galeaspida Pituriaspida Osteostraci Gnathostomata (jawed vertebrates) Placodermi Chondrichthyes (cartilaginous fish) Acanthodii Osteichthyes (bony fish) Actinopterygii (ray-finned fish) Sarcopterygii (lobe-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Tetrapoda Amphibia Amniota Sauropsida/(Reptiles) Aves (Birds) Synapsida Mammalia... Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria (coral, jellyfish, anenomes) Placozoa (trichoplax) Subregnum Bilateria (bilateral symmetry) Acoelomorpha (basal) Orthonectida (flatworms, echinoderms, etc. ... In biology, an organ (Latin: organum, instrument, tool) is a group of tissues, which perform a specific function or group of functions. ... A top-down view of skeletal muscle Muscle is a contractile form of tissue. ... Look up movement in Wiktionary, the free dictionary The term Movement has a variety of different meanings related to motion: Physical movement between points in space (A to B). The amount of movement is called distance. ... Cells in culture, stained for keratin The cell is the structural and functional unit of all living organisms. ... Calcium metabolism or calcium homeostasis is the mechanism by which the body maintains adequate calcium levels. ... Minerals are natural compounds formed through geological processes. ... In biology, the skeleton or skeletal system is the biological system providing support in living organisms. ... Cartilage is a type of dense connective tissue. ... The mesoderm is one of the three germ layers in the early developing embryo, the other two layers being the ectoderm and the endoderm. ... Orders see text The Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nostrils, scales, two-chambered hearts, and skeletons made of cartilage. ... Orders Hexanchiformes Squaliformes Pristiophoriformes Squatiniformes Heterodontiformes Orectolobiformes Carcharhiniformes Lamniformes Sharks are a group (superorder Selachimorpha) of fish, with a full cartilaginous skeleton, a streamlined body plan, with normally 5, but up to 7 (depending on species) gill slits along the side of, or beginning slightly behind, the head (in some... Orders See under classes: Actinopterygii and Sarcopterygii Class Osteichthyes are the bony fish, a group paraphyletic to the land vertebrates, which are sometimes included. ... Groups Elginerpetontidae Acanthostegidae Ichthyostegidae Whatcheeriidae Crassigyrinidae Baphetidae Colosteidae Batrachomorpha/Amphibia Lepospondyli Reptiliomorpha Amniota Sauropsida/Reptilia Aves (Birds) Synapsida Mammalia A tetrapod (Greek tetrapoda, four-legged) is a vertebrate animal having four feet, legs or leglike appendages. ...

There are several evolutionary alternatives to bone. These evolutionary solutions are not completely functionally analogous to bone. A phylogenetic tree of all living things, based on rRNA gene data, showing the separation of the three domains, bacteria, archaea, and eukaryotes, as described initially by Carl Woese. ...

• Exoskeletal protection is offered by shells, carapaces (consisting of calcium compounds or silica) and chitinous exoskelotons.
• 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.

Bones and skeletons are studied in osteology. Bones can be prepared for study by several methods, such as maceration. Maceration is done by boiling fleshed bone with dish detergent and a little bleach until all large particles are off. The bones are then cleaned by hand, usually with a toothbrush and a degreaser. An exoskeleton, in contrast to an endoskeleton, is an external anatomical feature that supports and protects an animals body. ... Various seashells The hard, rigid outer calcium carbonate covering of certain animals is called a shell. ... The term carapace refers to a dorsal section of an exoskeleton or shell, in a number of animal groups. ... Calcium plays a vital role in the anatomy, physiology and biochemistry of organisms and of the cell, particularly in signal transduction pathways. ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... Structure of chitin molecule In biology, chitin (pronounced keye-tin) is one of the main components in the cell walls of fungi, the exoskeletons of insects and other arthropods, and in some other animals. ... An endoskeleton is an internal support structure of an animal. ... Classes Asteroidea Concentricycloidea Crinoidea Echinoidea Holothuroidea Ophiuroidea Echinoderms (Echinodermata) is a phylum of marine animals found in the ocean at all depths. ... The sponge, in the phylum Porifera, is a very primitive and specialized animal. ... Spicules are skeletal structures that appear in some types of sponges. ... Osteology is the scientific study of bones. ... Maceration is a bone preparation technique whereby parts of a vertebrate corpse are left to rot inside a closed container at near-constant temperature, to get a clean skeleton. ...

Functions

Long bones can be connected to muscles via tendons. Bones connect at joints by ligaments. The interaction between bone and muscle is studied in biomechanics. A tendon or sinew is a tough band of fibrous connective tissue that connects muscle to bone. ... This article is about a joint in zootomical anatomy. ... A ligament is a short band of tough fibrous connective tissue composed mainly of long, stringy collagen fibres. ... Biomechanics is the research and analysis of the mechanics of living organisms, pioneered by Professor Yuan-Cheng Fung. ...

Post-mortem functions

Cut and polished bone from a variety of animals is sometimes used as material for jewelry and other crafts. Ground cattle bone is sometimes used as fertilizer. In the Stone Age bone was used to manufacture art, weapons, needles, etc. Jewelry (the American spelling; spelled jewellery in Commonwealth English) consists of ornamental devices worn by persons, typically made with gems and precious metals. ... Stone Age fishing hook. ... // Pre-historic art of Europe Palaeolithic Venus of Willendorf The earliest known European art is from the upper palaeolithic period and includes both cave painting, such as the famous paintings at Lascaux, and portable art, such as animal carvings and so-called Venus figurines like the Venus of Willendorf. ...

Structure

Bone is a relatively hard and lightweight composite material, formed mostly of calcium phosphate in the chemical arrangement termed calcium hydroxyapatite. It has relatively high compressive strength but poor tensile strength. While bone is essentially brittle, it does have a degree of significant elasticity contributed by its organic components (chiefly collagen). Bone has an internal mesh-like structure, the density of which may vary at different points. Image File history File links Illu_compact_spongy_bone. ... Image File history File links Illu_long_bone. ... Composite materials (or composites for short) are engineering materials made from two or more components. ... Calcium phosphate is the name given to a family of minerals containing calcium ions (Ca2+) together with orthophosphates (PO43-), metaphosphates or pyrophosphates (P2O74-) and occasionally hydrogen or hydroxide ions. ... Compressive strength is the capacity of a material to withstand axially directed pushing forces. ... The tensile strength of a material is the maximum amount of tensile stress that it can be subjected to before it fails. Modes of failure typically vary with the type of material being stressed. ... Elasticity has meanings in two different fields: In physics and mechanical engineering, the theory of elasticity describes how a solid object moves and deforms in response to external stress. ... Collagen triple helix. ... A mesh is similar to fabric or a web in that it has many connected or weaved pieces. ... Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ... The word point can refer to: a location in physical space a unit of angular measurement; see navigation point is a typographic unit of measure in typography equal inch or sometimes approximated as inch; on computer displays it should be equal to point in typography if the correct display resolution...

Bone can be either compact or cancellous (spongy). Cortical (outer layer) bone is compact; the two terms are often used interchangeably. Cortical bone makes up a large portion of skeletal mass; but, because of its density, it has a low surface area. Cancellous bone is trabecular (honeycomb structure), it has a relatively high surface area, but forms a smaller portion of the skeleton.

Bone can also be either woven or lamellar. Woven bone is put down rapidly during growth or repair. It is so called because its fibres are aligned at random, and as a result has low strength. In contrast lamellar bone has parallel fibres and is much stronger. Woven bone is often replaced by lamellar bone as growth continues.

Long bones are tubular in structure (e.g. the tibia). The central shaft of a long bone is called the diaphysis, and has a hollow middle—the medullar cavity filled with bone marrow. Surrounding the medullar cavity is a thin layer of cancellous bone that also contains marrow. The extremities of the bone are called the epiphyses and are mostly cancellous bone covered by a relatively thin cortical of compact bone. In children, the bones are filled with red marrow, which is gradually replaced with yellow marrow as the child ages. Figure 1 : Upper surface of right tibia. ... The diaphysis is the main or mid section (shaft) of a long bone. ...

Short bones (e.g. finger bones) have a similar structure to long bones, except that they have no medullar cavity.

Flat bones (e.g. the skull and ribs) consist of two layers of compact bone with a zone of cancellous bone sandwiched between them.

Irregular bones are bones which do not conform to any of the previous forms (e.g. vertebrae).

All bones consist of living cells embedded in a mineralised organic matrix that makes up the main bone material.

Cells

Bone Heads include osteoblasts, so called Bone Lining Cells, osteocytes and osteoclasts. Osteoblasts are typically viewed as bone forming cells. They are located near to the surface of bone and their functions are to make osteoid and manufacture hormones such as prostaglandin which act on bone itself. Osteoblasts are mononucleate. Active osteoblasts are situated on the surface of osteoid seams and communicate with each other via gap-junctions. They contain alkaline phosphatase—a chemical which has a role in the mineralisation of bone. An osteoblast (from the Greek words for bone and to build) is a mononucleate cell which produces a protein that produces osteoid. ... An osteocyte, a star-shaped cell, is the most abundant cell found in bone. ... An osteoclast is a multinucleated cell that degrades and reabsorbs bone. ... Osteoid is a protein mixture which is secreted by osteoblasts. ... A hormone (from Greek horman - to set in motion) is a chemical messenger from one cell (or group of cells) to another. ... A prostaglandin is any member of a group of lipid compounds that are derived from fatty acids and have important functions in the animal body. ...

Bone Lining Cells (BLCs) share a common lineage with osteogenesis (bone forming) cells. They function as a barrier for certain ions, induced osteogenetic cells. They are flattened, mononucleate cells which line bone.

However, osteocytes do originate from osteoblasts which have migrated into and become trapped and surrounded by bone matrix which they themselves produce. The space which they occupy is known as a lacuna. Osteocytes have many processes which reach out to meet osteoblasts probably for the purposes of communication. Their functions include to varying degrees: formation of bone, matrix maintenance and calcium homeostasis. They possibly act as mechano-sensory receptors—regulating the bones' response to stress.

If osteoblasts can be described as bone forming cells, the osteoclasts can be described as bone destroying cells. Osteoclasts are large, multinucleated cells located on bone surfaces in what are called Howship's lacunae. These lacunae, or resorption pits, are left behind after the breakdown of bone and often present as scalloped surfaces. Because the osteoclasts are derived from a monocyte stem-cell lineage, they are equipped with engulfment strategies similar to circulating macrophages. Osteoclasts mature and/or migrate to discrete bone surfaces. Upon arrival active enzymes, such as acid phosphatase, are secreted against the mineral substrate. This process, called bone resorption, allows stored calcium to be released into systemic circulation and is an important process in regulating calcium balance. As bone formation actively fixes circulating calcium in its mineral form, resorption actively unfixes it thereby increasing circulating calcium levels. These processes occur in tandem at site-specific locations and are known as bone turnover, or remodeling. Osteoblasts and osteoclasts, coupled together via paracrine cell signalling, are referred to as bone remodeling units. The iteration of remodeling events at the cellular level is influential on shaping and sculpting the skeleton both during growth as well as after. An osteoblast (from the Greek words for bone and to build) is a mononucleate cell which produces a protein that produces osteoid. ... Macrophages (Greek: big eaters) are cells found in tissues that are responsible for phagocytosis of pathogens, dead cells and cellular debris. ... This page is a candidate to be copied to Wiktionary. ...

Matrix

The matrix comprises the other major constituent of bone. It has inorganic and organic parts. The inorganic is mainly crystalline mineral salts and calcium, which is present in the form of hydroxyapatite. The matrix is initially laid down as unmineralized osteoid (manufactured by osteoblasts). Mineralisation involves osteoblasts secreting vesicles containing alkaline phosphatase. This cleaves 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. In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ...

The organic part of matrix is mainly Type I collagen. This is made intracellularly as tropocollagen and then exported. It then associates into fibrils. Also making up the organic part of matrix include various growth factors, the functions of which are not fully known. Other factors present include GAGs, osteocalcin, osteonectin, bone sialo protein and Cell Attachment Factor. Collagen triple helix. ... Fibril is a fine fiber approximately 1 nm in diameter. ... Glycosaminoglycans (GAGs) are long unbranched polysaccharides, made up of repeating disaccharides that may be sulphated (e. ... Bone sialo protein is also known as BSP, it is one of the proteins for gene expression of bone Categories: Biology stubs ...

Formation

The formation of bone occurs by two methods: intramembranous and endochondral ossification. Intramembranous ossification mainly occurs during formation of the flat bones of the skull; the bone is formed from mesenchyme tissue. Endochondral ossification occurs in long bones, such as limbs; the bone is formed from cartilage. Image File history File links Illu_bone_growth. ... Osteoblasts and osteoclasts on trabecula of lower jaw of calf embryo. ... Section of fetal bone of cat. ... A hippopotamuss skull A skull, or cranium, is a bony structure of Craniates which serves as the general framework for a head. ... Mesenchyme (also known as embryonic connective tissue) is the mass of tissue that develops mainly from the mesoderm (the middle layer of the trilaminar germ disc) of an embryo. ... Cartilage is a type of dense connective tissue. ...

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 diaphyses and the epiphyses of long bones remain separated by a growing zone of cartilage (the metaphysis) until the child reaches skeletal maturity (18 to 25 years of age), whereupon the cartilage ossifies, fusing the two together (epiphyseal closure). The metaphysis is the body of cartilage that separates the epiphyses and the diaphysis of long bones during growth. ...

Marrow can be found in most any bone that holds cancellous tissue. In newborns, all such bones are filled exclusively with red marrow (or hemopoietic marrow), but as the child ages it is mostly replaced by yellow marrow (or fatty marrow). In adults, red marrow is mostly found in the flat bones of the skull, the ribs, the vertebrae and pelvic bones. Bone marrow is the tissue comprising the center of large bones. ... Sketch of bone marrow and its cells Pluripotential hemopoietic stem cells or pluripotential hematopoietic stem cells (PHSCs) are stem cells found in the bone marrow. ... Bone marrow is the tissue comprising the center of large bones. ... Fat is one of the three main classes of food and, at approximately 38 kJ (9 kilocalories) per gram, as compared to sugar with 17 kJ (4 kcal) per gram or ethanol with 29 kJ (7 kcal) per gram, the most concentrated form of metabolic energy available to humans. ... Bone marrow is the tissue comprising the center of large bones. ...

Remodeling is the process of resorption followed by replacement of bone with little change in shape and occurs throughout a person's life. Its purpose is the release of calcium and the repair of micro-damaged bones (from everyday stress). Repeated stress results in the bone thickening at the points of maximum stress. It has been hypothesized that this is a result of bone's piezoelectric properties, which cause bone to generate small electrical potentials under stress. Piezoelectricity is the ability of certain crystals to generate a voltage in response to applied mechanical stress. ...

Bone pathologies

One of the most common bone illnesses is a bone fracture. Bones heal by natural processes, but untended and unsupported can lead to misgrown bone. A fractured bone in a living person is typically treated by restoring the fractured pieces of bone to their natural positions (if necessary), and maintaining those positions while the bone heals. ... When a bone breaks the most important thing is the state of the periosteum, the membrane covering the bone. ...

Other illnesses are for example osteoporosis and bone cancer (osteosarcoma). The joints can be affected by arthritis. Osteoporosis is a disease of bone in which bone mineral density (BMD) is reduced and bone microarchitecture is disrupted. ... When normal cells are damaged beyond repair, they are eliminated by apoptosis. ... Osteosarcoma is a common primary bone cancer. ... Arthritis (from Greek arthro-, joint + -itis, inflammation) is a group of conditions that affect the health of the bone joints in the body. ...

Terminology

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

There are also names for specific parts of long bones. This article is about a joint in zootomical anatomy. ... Anterior view of the femur The femur or thigh bone is the longest (length), largest (volume) and strongest (mechanical ability to resist deformity) bone of the human body. ... The bones in the foot In anatomy, the ankle, or ancle (a word common, in various forms, to Teutonic languages, probably connected in origin with the Latin angulus, or Greek αγκυλος, bent), is the part of the lower limb that is located between the foot and the leg, and is actually...

diaphysis, shaft	The long, relatively straight main body of the bone; region of primary ossification.
epiphyses	The end regions of the bone; regions of secondary ossification.
epiphyseal plate	The thin sheet of bone marking the fusion of epiphyses to the diaphysis (adults only).
head	The proximal articular end of the bone.
neck	The region of bone between the head and the shaft.

See also

• List of bones of the human skeleton
• Terms for anatomical location

A typical adult human skeleton consists of the following 206 bones. ... In zootomy, several terms are used to describe the location of organs and other structures in the body of bilateral animals. ...

External links

• Review (including references) of piezoelectricity and bone remodelling