

Long, narrow, and mountainous submarine lineation that generally separates ocean-floor ridges differing in depth by as much as 1 mi (1.6 km). The largest fracture zones, in the eastern Pacific, are more than 1,000 mi (1,600 km) long and 60–125 mi (100–200 km) wide. Numerous shorter fracture zones in the Atlantic are associated with the Mid-Atlantic Ridge.

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Break in a bone, caused by stress. It causes pain, tenderness, and inability to use the part with the fracture. The site appears deformed, swollen, and discoloured, and the bone moves in abnormal ways. It must be protected from weight bearing and movement between the broken ends while it heals, producing puttylike new tissue that hardens to join the broken pieces together. Complications include failure to heal, healing in the wrong position, and loss of function despite good healing. Fractures in joints present a particularly serious problem, often requiring surgery. Seealso osteoporosis.

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or myeloid tissue

Soft, gelatinous tissue that fills bone cavities. Red bone marrow contains stem cells, progenitor cells, percursor cells, and functional blood cells (see reticuloendothelial system). Lymphocytes mature in the lymphoid organs (see lymphoid tissue). All other blood-cell formation occurs in red marrow, which also takes part in destruction of old erythrocytes (red blood cells). Yellow bone marrow mainly stores fats. Because the leukocytes (white blood cells) produced in bone marrow are involved in immune defenses, marrow transplants can treat some types of immunodeficiency. Radiation and some anticancer drugs can damage marrow and impair immunity. Bone-marrow examination helps diagnose diseases related to blood and blood-forming organs.

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Wedgwood bone china plate, Staffordshire, 1815–20; in the Victoria and Albert Museum, London.

Hard-paste porcelain containing bone ash. It was developed by Josiah Spode (1754–1827) in England circa 1800. The addition of bone ash to china stone and china clay (i.e., hard china) made bone china easier to manufacture; it is stronger, does not chip easily, and has an ivory-white colour that lends itself to decoration. Other factories (Minton, Derby, Worcester, Wedgwood, Rockingham) adopted the formula in the early 19th century. Bone china remains popular for tableware in Britain and the U.S. Seealso stoneware.

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

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or osteitis deformans

Chronic bone disease of middle age. Named for James Paget, it is characterized by excessive bone destruction alternating with disordered bone construction (with dense, brittle bones and deformity that can compress internal structures). The long bones, vertebrae, pelvis, and skull are most often affected, more often in men. The risk of cancer, usually osteosarcoma, is high. Increased blood supply to the area of bone destruction may lead to heart or circulatory problems. Calcitonin (which regulates bone growth) and bisphosphonates (which block excessive bone breakdown) are drugs of treatment.

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Bones have ten main functions:





Gross anatomy

Individual bones


Compact bone or (Cortical bone)


Trabecular bone


Cellular structure

There are several types of cells constituting the bone;


Molecular structure







Woven or lamellar


Five types of bones






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

Endochondral ossification


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


Bone marrow






Calcium balance




Paracrine cell signalling


Osteoblast stimulation



Osteoclast inhibition







Other disorders of bone include:




Alternatives to bony endoskeletons


Exposed bone


  • A deer's antlers are composed of bone.


Bone feature Definition
articular process A projection that contacts an adjacent bone.
condyle A large, rounded articular process.
crest A prominent ridge.
eminence A relatively small projection or bump.
facet A small, flattened articular surface.
foramen An opening through a bone.
fossa A broad, shallow depressed area.
fovea A small pit on the head of a bone.
labyrinth A cavity within a bone.
malleolus One of two specific protuberances of bones in the ankle.
meatus A short canal.
sinus A cavity within a cranial bone.
spine A relatively long, thin projection or bump.
suture Articulation between cranial bones.
trochanter One of two specific tuberosities located on the femur.
tuberosity A projection or bump with a roughened surface.


Bone feature Definition
head The proximal articular end of the bone.
neck The region of bone between the head and the shaft.

See also



External links

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