# Bone

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Rigid organs of the skeleton of vertebrates

"Bones" redirects here. For other uses, see [Bones (disambiguation)](/source/Bones_(disambiguation)) and [Bone (disambiguation)](/source/Bone_(disambiguation)).

Bone A bone dating from the Pleistocene Ice Age of an extinct species of an elephant, possibly a mammoth A scanning electronic micrograph of a Wistar rat's bone at 10,000× magnification Details Identifiers Latin os, ossis Greek ὀστέον (ostéon) MeSH D001842 TA98 A02.0.00.000 TA2 366, 377 TH H3.01.00.0.00001 FMA 5018 Anatomical terminology [edit on Wikidata]

A **bone** is a [rigid](/source/Stiffness) [organ](/source/Organ_(biology)) that constitutes part of the [skeleton](/source/Skeleton) in most [vertebrate](/source/Vertebrate) animals.[1] Bones protect the organs of the body, produce [red](/source/Red_blood_cell) and [white blood cells](/source/White_blood_cell), store [minerals](/source/Mineral_(nutrient)), help regulate acid-base homeostasis, provide structure and support for the body, and enable [mobility](/source/Animal_locomotion) and hearing. Bones come in a variety of shapes and sizes and have complex internal and external structures.[2]

**Bone tissue** (also known as osseous tissue or **bone** in the [uncountable](/source/Mass_noun)) is a form of [hard tissue](/source/Hard_tissue), specialised [connective tissue](/source/Connective_tissue) that is [mineralized](/source/Mineralized_tissues) and has an intercellular [honeycomb](/source/Honeycomb)-like [matrix](/source/Matrix_(biology)),[3] which helps to give the bone rigidity. Bone tissue is made up of different types of bone cells: [osteoblasts](/source/Osteoblast) and [osteocytes](/source/Osteocyte) (which form and [mineralise](/source/Mineralization_(biology)) bone), [osteoclasts](/source/Osteoclast) (which [resorb](/source/Bone_resorption) bone), and modified or flattened osteoblasts (lining cells that form a protective layer on the bone surface). The mineralised matrix of bone tissue has an [organic](/source/Organic_chemistry) component of mainly [ossein](/source/Ossein), a form of [collagen](/source/Collagen), and an inorganic component of [bone mineral](/source/Bone_mineral), made up of various salts. Bone tissue comprises **cortical bone** and **cancellous bone**, although bones may also contain other kinds of [tissue](/source/Tissue_(biology)) including [bone marrow](/source/Bone_marrow), [endosteum](/source/Endosteum), [periosteum](/source/Periosteum), [nerves](/source/Nerve), [blood vessels](/source/Blood_vessel), and [cartilage](/source/Cartilage).

In the [human body](/source/Human_body) at birth, approximately 300 bones are present. Many of these fuse together during development, leaving a total of 206 separate bones in the adult, not counting numerous small [sesamoid bones](/source/Sesamoid_bone).[4][5] The largest bone in the body is the [femur](/source/Femur) or thigh-bone, and the smallest is the *[stapes](/source/Stapes)* in the [middle ear](/source/Middle_ear).

The Ancient Greek word for bone is ὀστέον ("*osteon*"). In [anatomical terminology](/source/Anatomical_terminology), including in the *[Terminologia Anatomica](/source/Terminologia_Anatomica)*, the word for a bone is *[os](https://en.wiktionary.org/wiki/os#Noun)* (for example, *[os breve](/source/Short_bone)*, *[os longum](/source/Long_bone)*, *[os sesamoideum](/source/Sesamoid_bone)*). (This is not to be confused with the alternative medical use of *os* to mean *orifice*, from the Latin *[ōs](https://en.wiktionary.org/wiki/os#Etymology_2),* mouth.)

## Gross anatomy

Five types of bones are found in the human body: long, short, flat, irregular, and sesamoid.[6]

One way to classify bones is by their shape or appearance.

- [Long bones](/source/Long_bone) are characterized by a shaft, the [diaphysis](/source/Diaphysis), that is much longer than its width; and by an [epiphysis](/source/Epiphysis), a rounded head at each end of the shaft. They are made up mostly of [compact bone](/source/Cortical_bone), with lesser amounts of [marrow](/source/Bone_marrow), located within the [medullary cavity](/source/Medullary_cavity), and areas of spongy, cancellous bone at the ends of the bones.[7] - Most bones of the [limbs](/source/Limb_(anatomy)), including those of the [fingers](/source/Metacarpus) and [toes](/source/Metatarsus), are long bones. The exceptions are the eight [carpal bones](/source/Carpal_bones) of the [wrist](/source/Wrist), the seven articulating [tarsal bones](/source/Tarsal_bone) of the [ankle](/source/Tarsus_(skeleton)) and the sesamoid bone of the [kneecap](/source/Kneecap). Long bones such as the clavicle, that have a differently shaped shaft or ends are also called *modified long bones*.

- [Short bones](/source/Short_bone) are roughly [cube](/source/Cube)-shaped, and have only a thin layer of compact bone surrounding a spongy interior. Short bones provide stability and support as well as some limited motion.[8] - The bones of the wrist and ankle are short bones.

- [Flat bones](/source/Flat_bone) are thin and generally curved, with two parallel layers of compact bone sandwiching a layer of spongy bone. - Most of the bones of the [skull](/source/Skull) are flat bones, as is the [sternum](/source/Sternum).[9]

- [Sesamoid bones](/source/Sesamoid_bone) 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](/source/Patella) and the [pisiform](/source/Pisiform).[10]

- [Irregular bones](/source/Irregular_bone) 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. Often this irregular shape is due to their many centers of ossification or because they contain bony sinuses. - The bones of the [spine](/source/Vertebral_column), [pelvis](/source/Pelvis), and some bones of the skull are irregular bones. Examples include the [ethmoid](/source/Ethmoid) and [sphenoid](/source/Sphenoid_bone) bones.[11]

### Terminology

Main article: [Anatomical terms of bone](/source/Anatomical_terms_of_bone)

Structure of a long bone

Anatomists use a number of [anatomical terms](/source/Anatomical_terminology) to describe the appearance, shape and function of bones. Like other anatomical terms, many of these derive from [Latin](/source/Latin) and [Greek](/source/Greek_language). Some anatomists still use Latin to refer to bones. The term "osseous", and the prefix "osteo-", referring to things related to bone, are still used commonly today.

Some examples of terms used to describe bones include the term "foramen" to describe a hole through which something passes, and a "canal" or "meatus" to describe a tunnel-like structure. A protrusion from a bone can be called a number of terms, including a "condyle", "crest", "spine", "eminence", "tubercle" or "tuberosity", depending on the protrusion's shape and location. In general, [long bones](/source/Long_bone) are said to have a "head", "neck", and "body".

When two bones join, they are said to "articulate". If the two bones have a fibrous connection and are relatively immobile, then the joint is called a "suture".

### Functions

#### Mechanical

See also: [Skeleton](/source/Skeleton), [Human skeleton](/source/Human_skeleton), and [List of bones of the human skeleton](/source/List_of_bones_of_the_human_skeleton)

Bones serve a variety of mechanical functions. Together the bones in the body form the [skeleton](/source/Skeleton). They provide a frame to keep the body supported, and an attachment point for [skeletal muscles](/source/Skeletal_muscle), [tendons](/source/Tendon), [ligaments](/source/Ligament) and [joints](/source/Joint), which 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](/source/Biomechanics)).

Bones protect internal organs, such as the [skull](/source/Skull) protecting the [brain](/source/Brain) or the [ribs](/source/Ribs) protecting the [heart](/source/Heart) and [lungs](/source/Lungs). Because of the way that bone is formed, bone has a high [compressive strength](/source/Compressive_strength) of about 170 [MPa](/source/Pascal_(unit)) (1,700 [kgf/cm2](/source/Kilogram-force)),[12] poor [tensile strength](/source/Tensile_strength) of 104–121 MPa, and a very low [shear stress](/source/Shear_stress) strength (51.6 MPa).[13][14] This means that bone resists pushing (compressional) stress well, resist pulling (tensional) stress less well, but only poorly resists shear stress (such as due to torsional loads). While bone is essentially [brittle](/source/Brittleness), bone does have a significant degree of [elasticity](/source/Elasticity_(physics)), contributed chiefly by [collagen](/source/Collagen).

Mechanically, bones also have a special role in [hearing](/source/Hearing_(sense)). The [ossicles](/source/Ossicles) are three small bones in the [middle ear](/source/Middle_ear) which are involved in sound transduction.

#### Synthetic

The cancellous part of bones contain [bone marrow](/source/Bone_marrow). Bone marrow produces blood cells in a process called [hematopoiesis](/source/Hematopoiesis).[15] Blood cells that are created in bone marrow include [red blood cells](/source/Red_blood_cell), [platelets](/source/Platelet) and [white blood cells](/source/White_blood_cell).[16] Progenitor cells such as the [hematopoietic stem cell](/source/Hematopoietic_stem_cell) divide in a process called [mitosis](/source/Mitosis) to produce precursor cells. These include precursors which eventually give rise to [white blood cells](/source/White_blood_cells), and [erythroblasts](/source/Erythroblast) which give rise to red blood cells.[17] Unlike red and white blood cells, created by mitosis, platelets are shed from very large cells called [megakaryocytes](/source/Megakaryocyte).[18] This process of progressive differentiation occurs within the bone marrow. After the cells are matured, they enter the [circulation](/source/Circulatory_system).[19] Every day, over 2.5 billion red blood cells and platelets, and 50–100 billion [granulocytes](/source/Granulocyte) are produced in this way.[20]

As well as creating cells, bone marrow is also one of the major sites where defective or aged red blood cells are destroyed.[20]

#### Metabolic

- Mineral storage – bones act as reserves of minerals important for the body, most notably [calcium](/source/Calcium) and [phosphorus](/source/Phosphorus).[21][22][23]

Determined by the species, age, and the type of bone, bone cells make up to 15 percent of the bone. [Growth factor](/source/Growth_factor) storage—mineralized bone matrix stores important growth factors such as [insulin](/source/Insulin)-like growth factors, transforming growth factor, [bone morphogenetic proteins](/source/Bone_morphogenetic_protein) and others.[24]

- [Fat](/source/Fat) storage – [marrow adipose tissue](/source/Marrow_adipose_tissue) (MAT) acts as a storage reserve of [fatty acids](/source/Fatty_acid).[25]

- [Acid](/source/Acid)-[base](/source/Base_(chemistry)) balance – bone buffers the blood against excessive [pH](/source/PH) changes by absorbing or releasing [alkaline salts](/source/Alkali_salt).[26]

- Detoxification – bone tissues can also store [heavy metals](/source/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](/source/Excretion).[27]

- [Endocrine](/source/Endocrine_system) organ – bone controls [phosphate](/source/Phosphate) metabolism by releasing [fibroblast growth factor 23](/source/Fibroblast_growth_factor_23) (FGF-23), which acts on [kidneys](/source/Kidney) to reduce phosphate [reabsorption](/source/Reabsorption). Bone cells also release a hormone called [osteocalcin](/source/Osteocalcin), which contributes to the regulation of [blood sugar](/source/Blood_sugar) ([glucose](/source/Glucose)) and [fat deposition](/source/Adipose_tissue). Osteocalcin increases both the [insulin](/source/Insulin) secretion and sensitivity, in addition to boosting the number of [insulin-producing cells](/source/Beta_cell) and reducing stores of fat.[28]

- 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.[29]

Skeletal System of Human Body

## Tissue

Bone is not uniformly solid, but consists of a flexible [matrix](/source/Matrix_(biology)) (about 30%) and bound minerals (about 70%), which are intricately woven and continuously remodeled by a group of specialized bone cells. Their unique composition and design allows bones to be relatively [hard](/source/Rockwell_scale) and strong, while remaining lightweight. Bone matrix is 90 to 95% composed of elastic [collagen](/source/Collagen) fibers, also known as ossein,[30] and the remainder is [ground substance](/source/Ground_substance).[31] The elasticity of [collagen](/source/Collagen) improves fracture resistance.[12] The matrix is hardened by the binding of inorganic mineral salt, [calcium phosphate](/source/Calcium_phosphate), in a chemical arrangement known as [bone mineral](/source/Bone_mineral), a form of calcium [apatite](/source/Apatite).[32][33] It is the mineralisation that gives bones rigidity.

Within any single bone, the tissue is woven into two main patterns: cortical and cancellous bone, each with distinct appearances and characteristics. Bone is actively constructed and remodeled throughout life by specialized bone cells known as osteoblasts and osteoclasts.

### Cortex

Cross-section details of a long bone

The hard outer layer of bones is composed of **cortical bone**, which is also called **compact bone** as it is much denser than cancellous bone. It forms the hard exterior (cortex) of bones. The cortical bone gives bone its smooth, white, and solid appearance, and accounts for 80% of the total bone mass of an adult [human skeleton](/source/Human_skeleton).[34] It facilitates bone's main functions—to support the whole body, to protect organs, to provide [levers](/source/Lever) for movement, and to store and release chemical elements, mainly calcium. It consists of multiple microscopic columns, each called an [osteon](/source/Osteon) or Haversian system. Each column is multiple layers of [osteoblasts](/source/Osteoblast) and [osteocytes](/source/Osteocyte) around a central canal called the [osteonic canal](/source/Haversian_canal). [Volkmann's canals](/source/Volkmann's_canal) at right angles connect the osteons together. The columns are metabolically active, and as bone is reabsorbed and created the nature and location of the cells within the osteon will change. Cortical bone is covered by a [periosteum](/source/Periosteum) on its outer surface, and an [endosteum](/source/Endosteum) on its inner surface. The endosteum is the boundary between the cortical bone and the cancellous bone.[35] The primary anatomical and functional unit of cortical bone is the [osteon](/source/Osteon).

### Trabeculae

Further information: [Trabecula § Bone trabecula](/source/Trabecula#Bone_trabecula)

Micrograph of cancellous bone

**Cancellous bone**, **spongy bone**,[36][35] or **trabecular bone** is the internal tissue of the skeletal bone and is an open-cell [porous](/source/Porosity) network that follows the material properties of [biofoams](/source/Biofoams).[37][38] Cancellous bone has a higher [surface-area-to-volume ratio](/source/Surface-area-to-volume_ratio) than cortical bone and it is less [dense](/source/Dense). This makes it weaker and more flexible. The greater surface area also makes it suitable for metabolic activities such as the exchange of calcium ions. Cancellous bone is typically found at the ends of long bones, near joints, and in the interior of vertebrae. Cancellous bone is highly [vascular](/source/Blood_vessel) and often contains red [bone marrow](/source/Bone_marrow) where [hematopoiesis](/source/Hematopoiesis), the production of blood cells, occurs. The primary anatomical and functional unit of cancellous bone is the [trabecula](/source/Trabecula). The trabeculae are aligned towards the mechanical load distribution that a bone experiences within long bones such as the [femur](/source/Femur). As far as short bones are concerned, trabecular alignment has been studied in the [vertebral](/source/Vertebral) [pedicle](/source/Pedicle_of_vertebral_arch).[39] Thin formations of [osteoblasts](/source/Osteoblast) covered in endosteum create an irregular network of spaces,[40] known as trabeculae. Within these spaces are [bone marrow](/source/Bone_marrow) and [hematopoietic stem cells](/source/Hematopoietic_stem_cell) that give rise to [platelets](/source/Platelet), [red blood cells](/source/Red_blood_cell) and [white blood cells](/source/White_blood_cell).[40] Trabecular marrow is composed of a network of rod- and plate-like elements that make the overall organ lighter and allow 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.[41]

The words *cancellous* and *trabecular* refer to the tiny lattice-shaped units (trabeculae) that form the tissue. It was first illustrated accurately in the engravings of [Crisóstomo Martinez](/source/Cris%C3%B3stomo_Martinez).[42]

### Marrow

[Bone marrow](/source/Bone_marrow), also known as [myeloid tissue](/source/Myeloid_tissue) in red bone marrow, can be found in almost any bone that holds [cancellous tissue](/source/Cancellous_tissue). In [newborns](/source/Infant), all such bones are filled exclusively with red marrow or [hematopoietic](/source/Hematopoietic) marrow, but as the child ages the hematopoietic fraction decreases in quantity and the fatty/ yellow fraction called [marrow adipose tissue](/source/Marrow_adipose_tissue) (MAT) increases in quantity. In adults, red marrow is mostly found in the bone marrow of the femur, the ribs, the vertebrae and [pelvic bones](/source/Pelvic_bones).[43]

### Vascular supply

Bone receives about 10% of cardiac output.[44] Blood enters the [endosteum](/source/Endosteum), flows through the marrow, and exits through small vessels in the cortex.[44] In humans, [blood oxygen tension](/source/Blood_gas_tension#Oxygen_tension) in bone marrow is about 6.6%, compared to about 12% in arterial blood, and 5% in venous and capillary blood.[44]

## Histology and physiology

Bone cells

Bone is metabolically active tissue composed of several types of cells. These cells include [osteoblasts](/source/Osteoblast), which are involved in the creation and [mineralization](/source/Mineralized_tissue) of bone tissue, [osteocytes](/source/Osteocyte), and [osteoclasts](/source/Osteoclast), which are involved in the reabsorption of bone tissue. Osteoblasts and osteocytes are derived from [osteoprogenitor](/source/Osteoprogenitor) cells, but [osteoclasts](/source/Osteoclast) are derived from the same cells that differentiate to form [macrophages](/source/Macrophage) and [monocytes](/source/Monocyte).[45] Within the marrow of the bone there are also [hematopoietic stem cells](/source/Hematopoietic_stem_cell). These cells give rise to other cells, including [white blood cells](/source/White_blood_cell), [red blood cells](/source/Red_blood_cell), and [platelets](/source/Platelet).[20]

### Osteoblast

[Light micrograph](/source/Micrograph) of [decalcified](/source/Bone_decalcification) cancellous bone tissue displaying osteoblasts actively synthesizing osteoid, containing two osteocytes.

[Osteoblasts](/source/Osteoblast) are mononucleate bone-forming cells. They are located on the surface of osteon seams and make a [protein](/source/Protein) mixture known as [osteoid](/source/Osteoid), which mineralizes to become bone.[46] The osteoid seam is a narrow region of a newly formed organic matrix, not yet mineralized, located on the surface of a bone. Osteoid is primarily composed of Type I [collagen](/source/Collagen). Osteoblasts also manufacture [hormones](/source/Hormone), such as [prostaglandins](/source/Prostaglandin), to act on the bone itself. The osteoblast creates and repairs new bone by actually building around itself. First, the osteoblast puts up collagen fibers. These collagen fibers are used as a framework for the osteoblasts' work. The osteoblast then deposits calcium phosphate which is hardened by [hydroxide](/source/Hydroxide) and [bicarbonate](/source/Bicarbonate) ions. The brand-new bone created by the osteoblast is called [osteoid](/source/Osteoid).[47] Once the osteoblast is finished working it is actually trapped inside the bone once it hardens. When the osteoblast becomes trapped, it becomes known as an osteocyte. Other osteoblasts remain on the top of the new bone and are used to protect the underlying bone, these become known as bone lining cells.[48]

### Osteocyte

[Osteocytes](/source/Osteocyte) are cells of mesenchymal origin and originate from osteoblasts that have migrated into and become trapped and surrounded by a bone matrix that they themselves produced.[35] The spaces the cell body of osteocytes occupy within the mineralized collagen type I matrix are known as [lacunae](/source/Lacuna_(histology)), while the osteocyte cell processes occupy channels called canaliculi. The many processes of osteocytes reach out to meet osteoblasts, osteoclasts, bone lining cells, and other osteocytes probably for the purposes of communication.[49] Osteocytes remain in contact with other osteocytes in the bone through gap junctions—coupled cell processes which pass through the canalicular channels.

### Osteoclast

[Osteoclasts](/source/Osteoclast) are very large [multinucleate](/source/Multinucleate) cells that are responsible for the breakdown of bones by the process of [bone resorption](/source/Bone_resorption). New bone is then formed by the osteoblasts. Bone is constantly [remodeled](/source/Bone_remodeling) by the resorption of osteoclasts and created by osteoblasts.[45] Osteoclasts are large cells with multiple [nuclei](/source/Cell_nucleus) located on bone surfaces in what are called *Howship's lacunae* (or *resorption pits*). These lacunae are the result of surrounding bone tissue that has been reabsorbed.[50] Because the osteoclasts are derived from a [monocyte](/source/Monocyte) [stem-cell](/source/Stem_cell) lineage, they are equipped with [phagocytic](/source/Phagocytosis)-like mechanisms similar to circulating [macrophages](/source/Macrophage).[45] Osteoclasts mature and/or migrate to discrete bone surfaces. Upon arrival, active enzymes, such as [tartrate-resistant acid phosphatase](/source/Tartrate-resistant_acid_phosphatase), are [secreted](/source/Secretion) against the mineral substrate.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] The reabsorption of bone by osteoclasts also plays a role in [calcium](/source/Calcium) [homeostasis](/source/Homeostasis).[50]

### Composition

Main article: [Extracellular matrix](/source/Extracellular_matrix)

Bones consist of living cells (osteoblasts and osteocytes) embedded in a mineralized organic matrix. The primary inorganic component of human bone is [hydroxyapatite](/source/Hydroxyapatite), the dominant [bone mineral](/source/Bone_mineral), having the nominal composition of Ca10(PO4)6(OH)2.[51] The organic components of this matrix consist mainly of [type I collagen](/source/Collagen#Types)—"organic" referring to materials produced as a result of the human body—and inorganic components, which alongside the dominant [hydroxyapatite](/source/Hydroxyapatite) phase, include other compounds of [calcium](/source/Calcium) and [phosphate](/source/Phosphate) including salts. Approximately 30% of the acellular component of bone consists of organic matter, while roughly 70% by mass is attributed to the inorganic phase.[52] The [collagen](/source/Collagen) fibers give bone its [tensile strength](/source/Ultimate_tensile_strength), and the interspersed crystals of [hydroxyapatite](/source/Hydroxyapatite) give bone its [compressive strength](/source/Compressive_strength). These effects are [synergistic](/source/Synergy).[52] The exact composition of the matrix may be subject to change over time due to nutrition and [biomineralization](/source/Biomineralization), with the ratio of [calcium](/source/Calcium) to [phosphate](/source/Phosphate) varying between 1.3 and 2.0 (per weight), and trace minerals such as [magnesium](/source/Magnesium), [sodium](/source/Sodium), [potassium](/source/Potassium) and [carbonate](/source/Carbonate) also be found.[52]

Type I collagen composes 90–95% of the organic matrix, with the remainder of the matrix being a homogenous liquid called [ground substance](/source/Ground_substance) consisting of [proteoglycans](/source/Proteoglycan) such as [hyaluronic acid](/source/Hyaluronic_acid) and [chondroitin sulfate](/source/Chondroitin_sulfate),[52] as well as non-collagenous proteins such as [osteocalcin](/source/Osteocalcin), [osteopontin](/source/Osteopontin) or [bone sialoprotein](/source/Bone_sialoprotein). Collagen consists of strands of repeating units, which give bone tensile strength, and are arranged in an overlapping fashion that prevents shear stress. The function of ground substance is not fully known.[52] Two types of bone can be identified microscopically according to the arrangement of collagen: woven and lamellar.

- Woven bone (also known as *fibrous bone*), which is characterized by a haphazard organization of collagen fibers and is mechanically weak.[53]

- Lamellar bone, which has a regular parallel alignment of collagen into sheets ("lamellae") and is mechanically strong.[38][53]

[Transmission](/source/Transmission_electron_microscopy) [electron micrograph](/source/Electron_micrograph) of decalcified woven bone matrix displaying characteristic irregular orientation of collagen fibers

Woven bone is produced when osteoblasts produce osteoid rapidly, which occurs initially in all [fetal](/source/Fetus) bones, but is later replaced by more resilient lamellar bone. In adults, woven bone is created after [fractures](/source/Bone_fracture) or in [Paget's disease](/source/Paget's_disease_of_bone). Woven bone is weaker, with a smaller number of randomly oriented collagen fibers, but forms quickly; it is for this appearance of the fibrous matrix that the bone is termed *woven*. It is soon replaced by lamellar bone, which is highly organized in [concentric](/source/Concentric) sheets with a much lower proportion of osteocytes to surrounding tissue. Lamellar bone, which makes its first appearance in humans in the [fetus](/source/Fetus) during the third trimester,[54] is stronger and filled with many collagen fibers parallel to other fibers in the same layer (these parallel columns are called osteons). In [cross-section](/source/Cross_section_(geometry)), the fibers run in opposite directions in alternating layers, much like in [plywood](/source/Plywood), assisting in the bone's ability to resist [torsion](/source/Torsion_(mechanics)) forces. After a fracture, woven bone forms initially and is gradually replaced by lamellar bone during a process known as "bony substitution". Compared to woven bone, lamellar bone formation takes place more slowly. The orderly deposition of collagen fibers restricts the formation of osteoid to about 1 to 2 [μm](/source/Micrometre) per day. Lamellar bone also requires a relatively flat surface to lay the collagen fibers in parallel or concentric layers.[55]

#### Deposition

The extracellular matrix of bone is laid down by [osteoblasts](/source/Osteoblast), which secrete both collagen and ground substance. These cells synthesise collagen alpha polypeptide chains and then secrete collagen molecules. The collagen molecules associate with their neighbors and crosslink via lysyl oxidase to form collagen fibrils. At this stage, they are not yet mineralized, and this zone of unmineralized collagen fibrils is called "osteoid". Around and inside collagen fibrils calcium and phosphate eventually [precipitate](/source/Precipitation_(chemistry)) within days to weeks becoming then fully mineralized bone with an overall carbonate substituted hydroxyapatite inorganic phase.[56][52]

In order to mineralise the bone, the osteoblasts secrete alkaline phosphatase, some of which is carried by [vesicles](/source/Vesicle_(biology_and_chemistry)). This cleaves the inhibitory pyrophosphate and simultaneously generates free phosphate ions for mineralization, acting as the foci for calcium and phosphate deposition. Vesicles may initiate some of the early mineralization events by rupturing and acting as a centre for crystals to grow on. Bone mineral may be formed from globular and plate structures, and via initially amorphous phases.[57][58]

## Development

Endochondral ossification

Light micrograph of a section through a juvenile knee joint (rat) showing the cartilagineous growth plates

The formation of bone is called [ossification](/source/Ossification). During the [fetal stage of development](/source/Prenatal_development) this occurs by two processes: [intramembranous ossification](/source/Intramembranous_ossification) and [endochondral ossification](/source/Endochondral_ossification).[59] Intramembranous ossification involves the formation of bone from [connective tissue](/source/Connective_tissue) whereas endochondral ossification involves the formation of bone from [cartilage](/source/Cartilage).

**Intramembranous ossification** mainly occurs during formation of the flat bones of the [skull](/source/Skull) but also the mandible, maxilla, and clavicles; the bone is formed from connective tissue such as [mesenchyme](/source/Mesenchyme) tissue rather than from cartilage. The process includes: the development of the [ossification center](/source/Ossification_center), [calcification](/source/Calcification), trabeculae formation and the development of the periosteum.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

**Endochondral ossification** occurs in long bones and most other bones in the body; it involves the development of bone from cartilage. This process includes the development of a cartilage model, its growth and development, development of the primary and secondary [ossification centers](/source/Ossification_center), and the formation of articular cartilage and the [epiphyseal plates](/source/Epiphyseal_plate).[60]

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](/source/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](/source/Epiphysis) 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](/source/Epiphyseal_plate)). At 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).[61] In the upper limbs, only the diaphyses of the long bones and scapula are ossified. The epiphyses, carpal bones, coracoid process, medial border of the scapula, and acromion are still cartilaginous.[62]

The following steps are followed in the conversion of cartilage to bone:

1. Zone of reserve cartilage. This region, farthest from the marrow cavity, consists of typical hyaline cartilage that as yet shows no sign of transforming into bone.[63]

1. Zone of cell proliferation. A little closer to the marrow cavity, chondrocytes multiply and arrange themselves into longitudinal columns of flattened lacunae.[63]

1. Zone of cell hypertrophy. Next, the chondrocytes cease to divide and begin to hypertrophy (enlarge), much like they do in the primary ossification center of the fetus. The walls of the matrix between lacunae become very thin.[63]

1. Zone of calcification. Minerals are deposited in the matrix between the columns of lacunae and calcify the cartilage. These are not the permanent mineral deposits of bone, but only a temporary support for the cartilage that would otherwise soon be weakened by the breakdown of the enlarged lacunae.[63]

1. Zone of bone deposition. Within each column, the walls between the lacunae break down and the chondrocytes die. This converts each column into a longitudinal channel, which is immediately invaded by blood vessels and marrow from the marrow cavity. Osteoblasts line up along the walls of these channels and begin depositing concentric lamellae of matrix, while osteoclasts dissolve the temporarily calcified cartilage.[63]

Bone development in youth is extremely important in preventing future complications of the skeletal system. Regular exercise during childhood and adolescence can help improve bone architecture, making bones more resilient and less prone to fractures in adulthood. Physical activity, specifically resistance training, stimulates growth of bones by increasing both bone density and strength. Studies have shown a positive correlation between the adaptations of resistance training and bone density.[64] While nutritional and pharmacological approaches may also improve bone health, the strength and balance adaptations from resistance training are a substantial added benefit.[64] Weight-bearing exercise may assist in osteoblast (bone-forming cells) formation and help to increase bone mineral content. High-impact sports, which involve quick changes in direction, jumping, and running, are particularly effective with stimulating bone growth in the youth.[65] Sports such as soccer, basketball, and tennis have shown to have positive effects on bone mineral density as well as bone mineral content in teenagers.[65] Engaging in physical activity during childhood years, particularly in these high-impact osteogenic sports, can help to positively influence bone mineral density in adulthood.[66] Children and adolescents who participate in regular physical activity will place the groundwork for bone health later in life, reducing the risk of bone-related conditions such as osteoporosis.[66]

### Remodeling

Main article: [Bone remodeling](/source/Bone_remodeling)

Bone is constantly being created and replaced in a process known as [remodeling](/source/Bone_remodeling). This ongoing turnover of bone is a process of resorption followed by replacement of bone with little change in shape. This is accomplished through osteoblasts and osteoclasts. Cells are stimulated by a variety of [signals](/source/Paracrine), and together referred to as a remodeling unit. Approximately 10% of the skeletal mass of an adult is remodelled each year.[67] The purpose of remodeling is to regulate [calcium homeostasis](/source/Calcium_homeostasis), repair [microdamaged bones](/source/Microdamage_in_bone) from everyday stress, and to shape the skeleton during growth.[68] Repeated stress, such as weight-bearing [exercise](/source/Exercise) or bone healing, results in the bone thickening at the points of maximum stress ([Wolff's law](/source/Wolff's_law)). It has been hypothesized that this is a result of bone's [piezoelectric](/source/Piezoelectricity) properties, which cause bone to generate small electrical potentials under stress.[69]

The action of osteoblasts and osteoclasts are controlled by a number of chemical [enzymes](/source/Enzyme) that either promote or inhibit the activity of the bone remodeling cells, controlling the rate at which bone is made, destroyed, or changed in shape. The cells also use [paracrine signalling](/source/Paracrine_signalling) to control the activity of each other.[26][70] For example, the rate at which osteoclasts resorb bone is inhibited by [calcitonin](/source/Calcitonin) and [osteoprotegerin](/source/Osteoprotegerin). Calcitonin is produced by [parafollicular cells](/source/Parafollicular_cell) in the [thyroid gland](/source/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.[71]

Osteoblasts can also be stimulated to increase bone mass through increased secretion of [osteoid](/source/Osteoid) and by [inhibiting](/source/Enzyme_inhibitor) the ability of osteoclasts to break down [osseous tissue](/source/Osseous_tissue).[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] Increased secretion of osteoid is stimulated by the secretion of [growth hormone](/source/Growth_hormone) by the [pituitary](/source/Pituitary), [thyroid hormone](/source/Thyroid_hormone) and the sex hormones ([estrogens](/source/Estrogen) and [androgens](/source/Androgen)). These hormones also promote increased secretion of osteoprotegerin.[71] Osteoblasts can also be induced to secrete a number of [cytokines](/source/Cytokine) that promote reabsorption of bone by stimulating osteoclast activity and differentiation from progenitor cells. [Vitamin D](/source/Vitamin_D), [parathyroid hormone](/source/Parathyroid_hormone) and stimulation from osteocytes induce osteoblasts to increase secretion of RANK-[ligand](/source/Ligand) and [interleukin 6](/source/Interleukin_6), which cytokines then stimulate increased reabsorption of bone by osteoclasts. These same compounds also increase secretion of [macrophage colony-stimulating factor](/source/Macrophage_colony-stimulating_factor) by osteoblasts, which promotes the differentiation of progenitor cells into osteoclasts, and decrease secretion of osteoprotegerin.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

### Volume

Bone volume is determined by the rates of bone formation and bone resorption. Certain growth factors may work to locally alter bone formation by increasing osteoblast activity. Numerous bone-derived growth factors have been isolated and classified via bone cultures. These factors include insulin-like growth factors I and II, transforming growth factor-beta, fibroblast growth factor, platelet-derived growth factor, and bone morphogenetic proteins.[72] Evidence suggests that bone cells produce growth factors for extracellular storage in the bone matrix. The release of these growth factors from the bone matrix could cause the proliferation of osteoblast precursors. Essentially, bone growth factors may act as potential determinants of local bone formation.[72] Cancellous bone volume in postmenopausal osteoporosis may be determined by the relationship between the total bone forming surface and the percent of surface resorption.[73]

## Clinical significance

See also: [Bone disease](/source/Bone_disease)

A number of diseases can affect bone, including arthritis, fractures, infections, osteoporosis and tumors. Conditions relating to bone can be managed by a variety of doctors, including [rheumatologists](/source/Rheumatology) for joints, and [orthopedic](/source/Orthopedic) surgeons, who may conduct surgery to fix broken bones. Other doctors, such as [rehabilitation specialists](/source/Rehabilitation_medicine) may be involved in recovery, [radiologists](/source/Radiology) in interpreting the findings on imaging, and [pathologists](/source/Pathologist) in investigating the cause of the disease, and [family doctors](/source/Family_doctor) may play a role in preventing complications of bone disease such as osteoporosis.

When a doctor sees a patient, a history and exam will be taken. Bones are then often imaged, called [radiography](/source/Radiography). This might include [ultrasound](/source/Ultrasound) [X-ray](/source/X-ray), [CT scan](/source/CT_scan), [MRI scan](/source/MRI_scan) and other imaging such as a [Bone scan](/source/Bone_scan), which may be used to investigate cancer.[74] Other tests such as a blood test for autoimmune markers may be taken, or a [synovial fluid](/source/Synovial_fluid) aspirate may be taken.[74]

### Fractures

[Radiography](/source/Radiography) used to identify possible [bone fractures](/source/Bone_fracture) after a knee injury

Main article: [Bone fracture](/source/Bone_fracture)

In normal bone, [fractures](/source/Bone_fracture) occur when there is significant force applied or repetitive trauma over a long time. Fractures can also occur when a bone is weakened, such as with osteoporosis, or when there is a structural problem, such as when the bone remodels excessively (such as [Paget's disease](/source/Paget's_disease_of_bone)) or is the site of the growth of cancer.[75] Common fractures include [wrist fractures](/source/Wrist_fracture) and [hip fractures](/source/Hip_fracture), associated with [osteoporosis](/source/Osteoporosis), [vertebral fractures](/source/Vertebral_fracture) associated with high-energy trauma and cancer, and fractures of long-bones. Not all fractures are painful.[75] When serious, depending on the fractures type and location, complications may include [flail chest](/source/Flail_chest), [compartment syndromes](/source/Compartment_syndrome) or [fat embolism](/source/Fat_embolism). [Compound fractures](/source/Compound_fracture) involve the bone's penetration through the skin. Some [complex fractures](/source/Complex_fracture) can be treated by the use of [bone grafting](/source/Bone_grafting) procedures that replace missing bone portions.

Fractures and their underlying causes can be investigated by [X-rays](/source/X-ray), [CT scans](/source/CT_scans) and [MRIs](/source/MRI).[75] Fractures are described by their location and shape, and several classification systems exist, depending on the location of the fracture. A common long bone fracture in children is a [Salter–Harris fracture](/source/Salter%E2%80%93Harris_fracture).[76] When fractures are managed, pain relief is often given, and the fractured area is often immobilised. This is to promote [bone healing](/source/Bone_healing). In addition, surgical measures such as [internal fixation](/source/Internal_fixation) may be used. Because of the immobilisation, people with fractures are often advised to undergo [rehabilitation](/source/Physical_medicine_and_rehabilitation).[75]

### Tumors

Main article: [Bone tumor](/source/Bone_tumor)

Tumor that can affect bone in several ways. Examples of benign [bone tumors](/source/Bone_tumor) include [osteoma](/source/Osteoma), [osteoid osteoma](/source/Osteoid_osteoma), [osteochondroma](/source/Osteochondroma), [osteoblastoma](/source/Osteoblastoma), [enchondroma](/source/Enchondroma), [giant-cell tumor of bone](/source/Giant-cell_tumor_of_bone), and [aneurysmal bone cyst](/source/Aneurysmal_bone_cyst).[77]

### Cancer

Main article: [Bone metastases](/source/Bone_metastases)

[Cancer](/source/Cancer) can arise in bone tissue, and bones are also a common site for other cancers to spread ([metastasise](/source/Metastasise)) to.[78] Cancers that arise in bone are called "primary" cancers, although such cancers are rare.[78] Metastases within bone are "secondary" cancers, with the most common being [breast cancer](/source/Breast_cancer), [lung cancer](/source/Lung_cancer), [prostate cancer](/source/Prostate_cancer), [thyroid cancer](/source/Thyroid_cancer), and [kidney cancer](/source/Kidney_cancer).[78] Secondary cancers that affect bone can either destroy bone (called a "[lytic](/source/Lytic_cycle)" cancer) or create bone (a "[sclerotic](/source/Sclerosis_(medicine))" cancer). Cancers of the bone marrow inside the bone can also affect bone tissue, examples including [leukemia](/source/Leukemia) and [multiple myeloma](/source/Multiple_myeloma). Bone may also be affected by cancers in other parts of the body. Cancers in other parts of the body may release [parathyroid hormone](/source/Parathyroid_hormone) or [parathyroid hormone-related peptide](/source/Parathyroid_hormone-related_peptide). This increases bone reabsorption, and can lead to bone fractures.

Bone tissue that is destroyed or altered as a result of cancers is distorted, weakened, and more prone to fracture. This may lead to compression of the [spinal cord](/source/Spinal_cord), destruction of the marrow resulting in [bruising](/source/Bruising), [bleeding](/source/Bleeding) and [immunosuppression](/source/Immunosuppression), and is one cause of bone pain. If the cancer is metastatic, then there might be other symptoms depending on the site of the original cancer. Some bone cancers can also be felt.

Cancers of the bone are managed according to their type, their [stage](/source/Cancer_staging), prognosis, and what symptoms they cause. Many primary cancers of bone are treated with [radiotherapy](/source/Radiotherapy). Cancers of bone marrow may be treated with [chemotherapy](/source/Chemotherapy), and other forms of targeted therapy such as [immunotherapy](/source/Immunotherapy) may be used.[79] [Palliative care](/source/Palliative_care), which focuses on maximising a person's [quality of life](/source/Quality_of_life), may play a role in management, particularly if the likelihood of [survival within five years](/source/5-year_survival) is poor.

### Diabetes

[Type 1 diabetes](/source/Type_1_diabetes) is an autoimmune disease in which the body attacks the insulin-producing pancreas cells causing the body to not make enough insulin.[80] In contrast [type 2 diabetes](/source/Type_2_diabetes) in which the body creates enough Insulin, but becomes resistant to it over time.[80]

Children makeup approximately 85% of Type 1 Diabetes cases and in America there was an average 22% rise in cases[81] over the first 24 months of the COVID-19 Pandemic. With the increase of developing some form of diabetes across all ranges continually growing the health impacts on bone development and bone health in these populations are still being researched. Most evidence suggests that diabetes, either Type 1 and Type 2, inhibits osteoblastic activity[82] and causes both lower BMD and BMC in both adults and children. The weakening of these developmental aspects is thought to lead to an increased risk of developing many diseases such as osteoarthritis, osteoporosis, osteopenia and fractures.[83] Development of any of these diseases is thought to be correlated with a decrease in ability to perform in athletic environments and activities of daily living.

Focusing on therapies that target molecules like osteocalcin or AGEs could provide new ways to improve bone health and help manage the complications of diabetes more effectively.[84]

### Other painful conditions

- [Osteomyelitis](/source/Osteomyelitis) is inflammation of the bone or bone marrow due to bacterial infection.[85]

- [Osteomalacia](/source/Osteomalacia) is a painful softening of adult bone caused by severe vitamin D deficiency.[86]

- [Osteogenesis imperfecta](/source/Osteogenesis_imperfecta)[87]

- [Osteochondritis dissecans](/source/Osteochondritis_dissecans)[88]

- [Ankylosing spondylitis](/source/Ankylosing_spondylitis)[89]

- [Skeletal fluorosis](/source/Skeletal_fluorosis) is a bone disease caused by an excessive accumulation of [fluoride](/source/Fluoride) in the bones. In advanced cases, skeletal fluorosis damages bones and joints and is painful.[90]

### Osteoporosis

Main article: [Osteoporosis](/source/Osteoporosis)

Reduced bone mineral density in Osteoporosis (R), increasing the likelihood of fractures

Osteoporosis is a disease of bone where there is reduced [bone mineral density](/source/Bone_mineral_density), increasing the likelihood of [fractures](/source/Bone_fracture).[91] Osteoporosis is defined in women by the [World Health Organization](/source/World_Health_Organization) as a bone mineral density of 2.5 [standard deviations](/source/Standard_deviation) below peak bone mass, relative to the age and sex-matched average. This density is measured using [dual energy X-ray absorptiometry](/source/Dual_energy_X-ray_absorptiometry) (DEXA), with the term "established osteoporosis" including the presence of a [fragility fracture](/source/Fragility_fracture).[92] Osteoporosis is most common in women after [menopause](/source/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](/source/Chronic_(medicine)) diseases or as a result of [smoking](/source/Tobacco_smoking) and [medications](/source/Medications), specifically [glucocorticoids](/source/Glucocorticoid).[91] Osteoporosis usually has no symptoms until a fracture occurs.[91] For this reason, DEXA scans are often done in people with one or more risk factors, who have developed osteoporosis and are at risk of fracture.[91]

One of the most important risk factors for [osteoporosis](/source/Osteoporosis) is [advanced age](/source/Ageing). Accumulation of oxidative [DNA damage](/source/DNA_damage_(naturally_occurring)) in [osteoblastic](/source/Osteocyte) and [osteoclastic](/source/Osteoclast) cells appears to be a key factor in age-related osteoporosis.[93]

Osteoporosis treatment includes advice to stop smoking, decrease alcohol consumption, exercise regularly, and have a healthy diet. [Calcium](/source/Calcium) and [trace mineral](/source/Trace_mineral) supplements may also be advised, as may [Vitamin D](/source/Vitamin_D). When medication is used, it may include [bisphosphonates](/source/Bisphosphonate), [Strontium ranelate](/source/Strontium_ranelate), and [hormone replacement therapy](/source/Hormone_replacement_therapy).[94]

### Bone health

Main article: [Bone health](/source/Bone_health)

Without strong healthy bones, humans are more at risk for different chronic diseases and fractures, with day-to-day function being more difficult with poor bone health. It is estimated that diet and exercise during childhood can impact peak bone mass as an adult nearly 20–40%.[95] One study done on children with developmental coordination disorder found an increase in bone mass up to 4% and 5% in the cortical areas of the tibia alone from a 13-week training period.[96] Peak bone mass occurs between the second and third decade of most people's lives.[97] Studies have shown that increasing calcium stores in childhood via food intake result in significant improvements in bone-mass density and overall health, even into adulthood.[98][99][100]

## Osteology

Human femurs and humerus from Roman period, with evidence of healed [fractures](/source/Bone_fracture)

The study of bones and teeth is referred to as [osteology](/source/Osteology). It is frequently used in [anthropology](/source/Anthropology), [archeology](/source/Archeology) and [forensic science](/source/Forensics) for a variety of tasks. This can include determining the sex, health, age, ancestry or injury status of the individual the bones were taken from.[101] Preparing fleshed bones for these types of studies can involve the process of [maceration](/source/Maceration_(bone)).[102]

Anthropologists and archeologists also study [bone tools](/source/Bone_tool) made by *[Homo sapiens](/source/Homo_sapiens)* and *[Homo neanderthalensis](/source/Homo_neanderthalensis)*.[103]

## Other animals

Main articles: [Bird anatomy](/source/Bird_anatomy) and [Exoskeleton](/source/Exoskeleton)

[Skeletal fluorosis](/source/Skeletal_fluorosis) in a cow's leg, due to industrial contamination

Leg and pelvic girdle bones of bird

[Bird](/source/Bird) skeletons are very lightweight. Their bones are smaller and thinner than those of mammals, to aid flight. Among mammals, [bats](/source/Bat) come closest to birds in terms of bone density, suggesting that small dense bones are a flight adaptation. Many bird bones have little marrow due to them being hollow.[104] A bird's [beak](/source/Beak) is primarily made of bone as projections of the [mandibles](/source/Mandible) which are covered in [keratin](/source/Keratin).

Some bones, primarily formed separately in subcutaneous tissues, include headgears (such as bony core of horns, antlers, ossicones), osteoderm, and [os penis](/source/Os_penis)/[os clitoris](/source/Os_clitoris).[105] A [deer](/source/Deer)'s [antlers](/source/Antler) are composed of bone which is an unusual example of bone being outside the skin of the animal once the velvet is shed.[106]

The extinct predatory fish *[Dunkleosteus](/source/Dunkleosteus)* had sharp edges of hard exposed bone along its jaws.[107][108]

The proportion of cortical bone that is 80% in the human skeleton may be much lower in other animals, especially in [marine mammals](/source/Marine_mammal) and [marine turtles](/source/Marine_turtles), or in various [Mesozoic](/source/Mesozoic) [marine reptiles](/source/Marine_reptile), such as [ichthyosaurs](/source/Ichthyosauria),[109] among others.[110] This proportion can vary quickly in evolution; it often increases in early stages of returns to an aquatic lifestyle, as seen in early [whales](/source/Whale) and [pinnipeds](/source/Pinniped), among others. It subsequently decreases in pelagic taxa, which typically acquire spongy bone, but aquatic taxa that live in shallow water can retain very thick, [pachyostotic](/source/Pachyostosis),[111] [osteosclerotic](/source/Osteosclerosis), or pachyosteosclerotic[112] bones, especially if they move slowly, like [sea cows](/source/Sirenia). In some cases, even marine taxa that had acquired spongy bone can revert to thicker, compact bones if they become adapted to live in shallow water, or in [hypersaline](/source/Hypersaline_lake) (denser) water.[113][114][115]

Many animals, particularly [herbivores](/source/Herbivore), practice [osteophagy](/source/Osteophagy)—the eating of bones. This is presumably carried out in order to replenish lacking [phosphate](/source/Phosphate).

Many bone diseases that affect humans also affect other vertebrates—an example of one disorder is skeletal fluorosis.

## Society and culture

Bones of slaughtered [cattle](/source/Cattle) on a [farm](/source/Farm) in [Namibia](/source/Namibia)

Bones from slaughtered animals have a number of uses:

- In [prehistoric times](/source/Prehistoric_times), they have been used for making [bone tools](/source/Bone_tool).[116] They have further been used in [bone carving](/source/Bone_carving), already important in [prehistoric art](/source/Prehistoric_art), and also in [modern time](/source/Modern_time) as crafting materials for [buttons](/source/Button), [beads](/source/Bead), [handles](/source/Handle), [bobbins](/source/Bobbin), [calculation aids](/source/Napier's_bones), [head nuts](/source/Head_nut), [dice](/source/Dice), [poker chips](/source/Poker_chip), [pick-up sticks](/source/Pick-up_sticks), [arrows](/source/Arrow), [scrimshaw](/source/Scrimshaw), and ornaments.

- [Bone glue](/source/Bone_glue) can be made by prolonged boiling of ground or cracked bones, followed by filtering and evaporation to thicken the resulting fluid. Once historically important, bone glue and other animal glues today have only a few specialized uses, such as in [antiques restoration](/source/Antiques_restoration). Essentially the same process, with further refinement, thickening and drying, is used to make [gelatin](/source/Gelatin).

- [Broth](/source/Broth) is made by simmering several ingredients for a long time, traditionally including bones.

- [Bone char](/source/Bone_char), a porous, black, granular material primarily used for [filtration](/source/Filtration) and also as a black [pigment](/source/Pigment), is produced by [charring](/source/Charring) mammal bones.

- [Oracle bone script](/source/Oracle_bone_script) was a writing system used in [ancient China](/source/Ancient_China) based on inscriptions in bones. Its name originates from oracle bones, which were mainly ox clavicle. The Ancient Chinese (mainly in the [Shang dynasty](/source/Shang_dynasty)), would write their questions on the [oracle bone](/source/Oracle_bone), and burn the bone, and where the bone cracked would be the answer for the questions.

- The [wishbones](/source/Furcula) of fowl have been used for [divination](/source/Divination), and are still customarily used in a tradition to determine which one of two people pulling on either prong of the bone may make a wish.

To [point the bone](https://en.wiktionary.org/wiki/point_the_bone) at someone is considered bad luck in some cultures, such as [Australian aborigines](/source/Australian_aborigines), such as by the [Kurdaitcha](/source/Kurdaitcha#Bone_pointing).

Various cultures throughout history have adopted the custom of shaping an infant's head by the practice of [artificial cranial deformation](/source/Artificial_cranial_deformation). A widely practised custom in China was that of [foot binding](/source/Foot_binding) to limit the normal growth of the foot.

## Additional images

		- Cells in bone marrow

		- Scanning electron microscope of bone at 100× magnification

		- Structure detail of an animal bone

## See also

- [Artificial bone](/source/Artificial_bone)

- [Calcareous](/source/Calcareous)

- [Cuttlebone](/source/Cuttlebone)

- [Skeleton](/source/Skeleton)

- [Ossicle (echinoderm)](/source/Ossicle_(echinoderm))

- [Ossification § Evolution](/source/Ossification#Evolution)

## References

1. **[^](#cite_ref-BoneOrgan_1-0)** Lee C (January 2001). [*The Bone Organ System: Form and Function*](https://www.sciencedirect.com/science/article/pii/B9780124708624500027). Academic Press. pp. 3–20. [doi](/source/Doi_(identifier)):[10.1016/B978-012470862-4/50002-7](https://doi.org/10.1016%2FB978-012470862-4%2F50002-7). [ISBN](/source/ISBN_(identifier)) [978-0-12-470862-4](https://en.wikipedia.org/wiki/Special:BookSources/978-0-12-470862-4). Retrieved 30 January 2022 – via Science Direct.

1. **[^](#cite_ref-de_Buffrénil_2021_2-0)** de Buffrénil V, de Ricqlès AJ, Zylberberg L, Padian K, Laurin M, Quilhac A (2021). [*Vertebrate skeletal histology and paleohistology*](https://books.google.com/books?id=tJcwEAAAQBAJ&dq=Vertebrate+Skeletal+Histology+and+Paleohistology&pg=PT8) (First ed.). Boca Raton, FL: CRC Press. pp. xii + 825. [ISBN](/source/ISBN_(identifier)) [978-1-351-18957-6](https://en.wikipedia.org/wiki/Special:BookSources/978-1-351-18957-6).

1. **[^](#cite_ref-3)** Langley, Natalie, Tersigni-Terrant, Maria-Teresa, eds. (2017). *Forensic Anthropology: A Comprehensive Approach* (2nd ed.). CRC Press. p. 82. [ISBN](/source/ISBN_(identifier)) [978-1-315-30003-0](https://en.wikipedia.org/wiki/Special:BookSources/978-1-315-30003-0).

1. **[^](#cite_ref-4)** Steele DG, Bramblett CA (1988). [*The Anatomy and Biology of the Human Skeleton*](https://archive.org/details/anatomybiologyo00stee). Texas A&M University Press. p. [4](https://archive.org/details/anatomybiologyo00stee/page/4). [ISBN](/source/ISBN_(identifier)) [978-0-89096-300-5](https://en.wikipedia.org/wiki/Special:BookSources/978-0-89096-300-5).

1. **[^](#cite_ref-5)** *Mammal anatomy: an illustrated guide*. New York: Marshall Cavendish. 2010. p. 129. [ISBN](/source/ISBN_(identifier)) [978-0-7614-7882-9](https://en.wikipedia.org/wiki/Special:BookSources/978-0-7614-7882-9).

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1. **[^](#cite_ref-115)** Houssaye A (January 2022). ["Evolution: Back to heavy bones in salty seas"](https://hal.archives-ouvertes.fr/hal-03820094/file/Houssaye_et_al_Current_Biology.pdf) (PDF). *Current Biology*. **32** (1): R42–R44. [Bibcode](/source/Bibcode_(identifier)):[2022CBio...32..R42H](https://ui.adsabs.harvard.edu/abs/2022CBio...32..R42H). [doi](/source/Doi_(identifier)):[10.1016/j.cub.2021.11.049](https://doi.org/10.1016%2Fj.cub.2021.11.049). [PMID](/source/PMID_(identifier)) [35015995](https://pubmed.ncbi.nlm.nih.gov/35015995). [S2CID](/source/S2CID_(identifier)) [245879886](https://api.semanticscholar.org/CorpusID:245879886). [Archived](https://web.archive.org/web/20221123162936/https://hal.archives-ouvertes.fr/hal-03820094/file/Houssaye_et_al_Current_Biology.pdf) (PDF) from the original on 23 November 2022.

1. **[^](#cite_ref-116)** Laszlovszky J, Szabo P (January 2003). [*People and Nature in Historical Perspective*](https://books.google.com/books?id=ft2d-zrlLWcC&q=Bones+from+slaughtered+animals+have+a+number+of+uses.+In+prehistoric+times%2C+they+have+been+used+for+making+bone+tools&pg=PA142). Central European University Press. [ISBN](/source/ISBN_(identifier)) [978-963-9241-86-2](https://en.wikipedia.org/wiki/Special:BookSources/978-963-9241-86-2).

## Sources

- Davidson S (2010). Colledge NR, Walker BR, Ralston SH (eds.). *Davidson's Principles and Practice of Medicine*. Illustrated by Robert Britton (21st ed.). Edinburgh: Churchill Livingstone/Elsevier. [ISBN](/source/ISBN_(identifier)) [978-0-7020-3085-7](https://en.wikipedia.org/wiki/Special:BookSources/978-0-7020-3085-7).

- Hall AC, Guyton JE (2005). *Textbook of Medical Physiology* (11th ed.). Philadelphia: W.B. Saunders. [ISBN](/source/ISBN_(identifier)) [978-0-7216-0240-0](https://en.wikipedia.org/wiki/Special:BookSources/978-0-7216-0240-0).

- Young B, Lowe JS, Stevens A, Heath JW (2006). *Wheater's Functional Histology: a text and colour atlas* (5th ed.). London: Churchill Livingstone/Elsevier. [ISBN](/source/ISBN_(identifier)) [978-0-443-068-508](https://en.wikipedia.org/wiki/Special:BookSources/978-0-443-068-508).

## Further reading

- Derrickson BH, Tortora GJ (2005). *Principles of anatomy and physiology*. New York: Wiley. [ISBN](/source/ISBN_(identifier)) [978-0-471-68934-8](https://en.wikipedia.org/wiki/Special:BookSources/978-0-471-68934-8).

- Fauci AS, Braunwald E, Kasper DL, Hauser SL, Longo DL, Jameson JL, et al. (2008). *Harrison's principles of internal medicine* (17th ed.). New York: McGraw-Hill Medical. [ISBN](/source/ISBN_(identifier)) [978-0-07-147692-8](https://en.wikipedia.org/wiki/Special:BookSources/978-0-07-147692-8).

- Hoehn K, Marieb EN (2007). *Human Anatomy & Physiology* (7th ed.). San Francisco: Benjamin Cummings. [ISBN](/source/ISBN_(identifier)) [978-0-8053-5909-1](https://en.wikipedia.org/wiki/Special:BookSources/978-0-8053-5909-1).

- Kini U, Nandeesh BN (3 January 2013). ["Ch 2: Physiology of Bone Formation, Remodeling, and Metabolism"](https://web.archive.org/web/20201106152855/https://www.springer.com/cda/content/document/cda_downloaddocument/9783642023996-c1.pdf?SGWID=0-0-45-1356540-p173959977) (PDF). In Fogelman I, Gnanasegaran G, van der Wall H (eds.). *Radionuclide and hybrid bone imaging*. Berlin: Springer. pp. 29–57. [ISBN](/source/ISBN_(identifier)) [978-3-642-02399-6](https://en.wikipedia.org/wiki/Special:BookSources/978-3-642-02399-6). Archived from [the original](https://www.springer.com/cda/content/document/cda_downloaddocument/9783642023996-c1.pdf?SGWID=0-0-45-1356540-p173959977) (PDF) on 6 November 2020. Retrieved 28 August 2017.

## External links

Wikimedia Commons has media related to [Bones](https://commons.wikimedia.org/wiki/Category:Bones).

Wikiquote has quotations related to ***[Bone](https://en.wikiquote.org/wiki/Special:Search/Bone)***.

- [Educational resource materials (including animations) by the American Society for Bone and Mineral Research](https://web.archive.org/web/20170509104452/http://depts.washington.edu/bonebio/ASBMRed/ASBMRed.html)

- [Review (including references) of piezoelectricity and bone remodelling](http://silver.neep.wisc.edu/~lakes/BoneElectr.html)

- [A good basic overview of bone biology from the Science Creative Quarterly](http://www.scq.ubc.ca/?p=400)

- [Bone histology photomicrographs](http://www.histology-world.com/photoalbum/thumbnails.php?album=8) [Archived](https://web.archive.org/web/20200706203057/http://histology-world.com/photoalbum/thumbnails.php?album=8) 6 July 2020 at the [Wayback Machine](/source/Wayback_Machine)

v t e Bone and cartilage Cartilage perichondrium fibrocartilage callus metaphysis Cells chondroblast chondrocyte Types hyaline elastic fibrous Bone Ossification primary bone intramembranous endochondral Cells osteoblast osteocyte osteoclast Matrix bone mineral ossein osteoid Types cancellous cortical Regions subchondral bone epiphysis epiphyseal plate/epiphyseal line metaphysis diaphysis condyle epicondyle Structure osteon 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

Bones of the human skeleton v t e Bones in the human skeleton Axial skeleton Skull Neurocranium occipital parietal frontal temporal sphenoid ethmoid Face nasal maxilla lacrimal zygomatic palatine inferior nasal conchae vomer mandible hyoid Ear ossicles malleus incus stapes Thorax sternum rib cage rib Vertebral column vertebrae cervical thoracic lumbar sacrum coccyx Appendicular Shoulder clavicle scapula Arm humerus ulna radius Hand carpals (scaphoid, lunate bone, triquetral, pisiform, trapezium, trapezoid, capitate, hamate) metacarpals phalanges (prox, int, dist) Pelvis ilium ischium pubis Leg femur patella fibula tibia sesamoid bones Foot tarsals heelbone anklebone navicular cuneiform cuboid metatarsals phalanges proximal intermediate distal accessory accessory navicular v t e The facial skeleton of the skull Maxilla Surfaces Anterior: fossae (Incisive fossa, Canine fossa) Infraorbital foramen Orbital bones Anterior nasal spine Infratemporal: Alveolar canals Maxillary tuberosity Orbital: Infraorbital groove Infraorbital canal Nasal: Greater palatine 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 (Greater palatine canal, Sphenopalatine foramen) Hard palate Processes Pyramidal Orbital Sphenoidal Mandible Body external surface (Chin, Jaw, Mandibular prominence, Mandibular symphysis, Lingual foramen, Mental protuberance, Mental foramen, Mandibular incisive canal) internal surface (Mental spine, Mylohyoid line, Sublingual fovea, Submandibular fovea) Alveolar part Ramus Mylohyoid groove Mandibular canal Lingula Mandibular foramen Angle Coronoid process Mandibular notch Condyloid process Pterygoid fovea Nose Nasal bone Internasal suture Nasal foramina Inferior nasal concha Ethmoidal process Maxillary process Vomer Wing Other Lacrimal Posterior lacrimal crest Lacrimal groove Lacrimal hamulus Prognathism Retromolar space v t e Neurocranium of the skull Occipital Squamous part external Inion/External occipital protuberance Occipital bun External occipital crest Nuchal lines Suprainiac fossa planes Occipital Nuchal internal Cruciform eminence Internal occipital protuberance Internal occipital crest Groove for transverse sinus Lateral parts Condyle Condyloid fossa Condylar canal Hypoglossal canal jugular Jugular process Jugular tubercle Basilar part Pharyngeal tubercle Clivus Other Foramen magnum Basion Opisthion Parietal Parietal eminence Temporal line Parietal foramen Sagittal sulcus Sagittal keel Sagittal crest Frontal Squamous part Frontal suture Frontal eminence external Superciliary arches Glabella foramina Supraorbital foramen Brow ridge Foramen cecum Zygomatic process internal Sagittal sulcus Frontal crest Orbital part Ethmoidal notch Fossa for lacrimal gland Trochlear fovea Frontal sinus Frontonasal duct Temporal Squamous part 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 (Aditus) Petrous part Carotid canal Facial canal Hiatus Internal auditory meatus Cochlear aqueduct 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 of 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 Supreme nasal concha Superior nasal concha Superior meatus Middle nasal concha Middle meatus Labyrinth Ethmoid sinus ethmoidal foramina Posterior Anterior v t e Compound structures of skull Neurocranium Calvaria Diploë Asterion Pterion Stephanion Inion Bregma Lambda Fossae anterior middle posterior cranial cavity Base of skull Fontanelle anterior posterior sphenoidal mastoid Facial skeleton Nasion Gonion Both dacryon zygomatic arch temporal fossa infratemporal fossa pterygomaxillary fissure pterygopalatine fossa v t e Bones of the arm Shoulder girdle, clavicle conoid tubercle trapezoid line costal tuberosity subclavian groove Scapula fossae (subscapular, supraspinatous, infraspinatous) notches (suprascapular, great scapular) glenoid fossa tubercles (infraglenoid, supraglenoid) spine of scapula acromion coracoid process angles (superior, inferior, lateral) Humerus upper extremity: necks (anatomical, surgical) tubercles (greater, lesser) bicipital groove body: radial sulcus deltoid tuberosity lower extremity: capitulum trochlea epicondyles (lateral, medial) supracondylar ridges (lateral, medial) fossae (radial, coronoid, olecranon) Forearm Radius near elbow (head, tuberosity) near wrist (ulnar notch, styloid process, Lister's tubercle) Ulna near elbow (tuberosity, olecranon, coronoid process, radial notch, trochlear notch) near wrist (styloid process) Hand Carpal bones scaphoid lunate triquetral pisiform trapezium trapezoid capitate hamate hamulus Metacarpal bones 1st 2nd 3rd 4th 5th Phalanges proximal intermediate distal v t e Bones of the torso Vertebrae General structure Body Arch pedicle lamina notch Vertebral foramen Intervertebral foramen Processes transverse articular spinous Spinal canal Cervical vertebrae Uncinate process of vertebra Transverse foramen Anterior tubercle Carotid tubercle Posterior tubercle Atlas lateral mass anterior arch posterior arch Axis dens Vertebra prominens Thoracic vertebrae Costal facets superior inferior transverse Uncinate process of vertebra Lumbar vertebrae Processes accessory mammillary Sacrum Base sacral promontory Ala of sacrum Lateral surface sacral tuberosity Pelvic surface anterior sacral foramina Dorsal surface posterior sacral foramina Median sacral crest Medial sacral crest Lateral sacral crest Sacral canal sacral hiatus Coccyx none Thorax Rib cage Ribs true ribs false ribs floating ribs Parts angle tubercle costal groove neck head Sternum Suprasternal notch Manubrium Sternal angle Body of sternum Xiphisternal joint Xiphoid process Thoracic cage Superior thoracic aperture Intercostal space Costal margin Infrasternal angle v t e Bones of the human leg Femur upper extremity head fovea neck greater trochanter fossa lesser trochanter intertrochanteric line intertrochanteric crest quadrate tubercle shaft linea aspera upper medial: merges with intertrochanteric line upper intermediate: pectineal line upper lateral: gluteal tuberosity / third trochanter lower extremity adductor tubercle patellar surface epicondyles lateral medial condyles lateral medial intercondylar fossa Tibia upper extremity Gerdy's tubercle condyles lateral medial intercondylar area shaft tuberosity soleal line lower extremity medial malleolus Anterior colliculus Posterior colliculus fibular notch Fibula lateral malleolus Other patella apex Foot Tarsus calcaneus sustentaculum tali calcaneal tubercle talus navicular cuboid cuneiform medial intermediate lateral Metatarsals 1st 2nd 3rd 4th 5th Other Phalanges v t e Bones of the pelvis 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 tubercle 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 Foramina obturator foramen greater sciatic foramen / greater sciatic notch lesser sciatic foramen Landmarks pelvic inlet pelvic brim pelvic outlet

v t e Fractures and cartilage damage General Avulsion fracture Chalkstick fracture Greenstick fracture Open fracture Pathologic fracture Spiral fracture Head Basilar skull fracture Blowout fracture Mandibular fracture Nasal fracture Le Fort fracture of skull Zygomaticomaxillary complex fracture Zygoma fracture Spinal fracture Cervical fracture Burst fracture Chance fracture Clay-shoveler fracture Craniocervical instability Flexion teardrop fracture Hangman's fracture Holdsworth fracture Jefferson fracture Vertebral compression fracture Ribs Rib fracture Sternal fracture Shoulder fracture Clavicle Scapular Arm fracture Humerus fracture: Proximal Supracondylar Holstein–Lewis fracture Forearm fracture: Ulna fracture Monteggia fracture Hume fracture Radius fracture/Distal radius Galeazzi Colles' Chauffeur's Smith's Barton's Essex-Lopresti fracture Hand fracture Scaphoid Rolando Bennett's Boxer's Busch's Broken finger Pelvic fracture Duverney fracture Pipkin fracture Leg Tibia fracture: Bumper fracture Segond fracture Gosselin fracture Toddler's fracture Pilon fracture Plafond fracture Tillaux fracture Fibular fracture: Maisonneuve fracture Le Fort fracture of ankle Bosworth fracture Combined tibia and fibula fracture: Trimalleolar fracture Bimalleolar fracture Pott's fracture Crus fracture: Patella fracture Femoral fracture: Hip fracture Foot fracture Lisfranc Jones Cuneiform March Calcaneal Broken toe

Authority control databases International GND FAST National United States France BnF data Japan Czech Republic Spain Israel Other NARA Terminologia Anatomica

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Adapted from the Wikipedia article [Bone](https://en.wikipedia.org/wiki/Bone) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Bone?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.