Top Questions

What is bone made of?

The two principal components of bone are collagen and calcium phosphate, which distinguish it from other hard tissues such as chitin, enamel, and shell.

What are the major functions of bone tissue?

Bone tissue makes up the individual bones of the skeletons of vertebrates. The other roles of bone include structural support for the mechanical action of soft tissues, protection of soft organs and tissues, provision of a protective site for specialized tissues such as the blood-forming system (bone marrow), and a mineral reservoir.

Do bones contain calcium?

Bone contains 99 percent of the calcium in the body and can behave as an adequate buffer for maintaining a constant level of freely moving calcium in soft tissues, extracellular fluid, and blood.

Why is calcium important for bone health?

The mechanical strength of bone is proportional to its mineral content. The Food and Nutrition Board of the U.S. National Academy of Sciences has recommended 1,0001,300 mg of calcium daily for adults and 7001,300 mg for children.

How does vitamin D deficiency affect bones in humans?

A deficiency in vitamin D results in poor mineralization of the bones of the skeleton, causing rickets in children and osteomalacia in adults.

Summary

bone, rigid body tissue consisting of cells embedded in an abundant hard intercellular material. The two principal components of this material, collagen and calcium phosphate, distinguish bone from such other hard tissues as chitin, enamel, and shell. Bone tissue makes up the individual bones of the human skeletal system and the skeletons of other vertebrates.

The functions of bone include (1) structural support for the mechanical action of soft tissues, such as the contraction of muscles and the expansion of lungs, (2) protection of soft organs and tissues, as by the skull, (3) provision of a protective site for specialized tissues such as the blood-forming system (bone marrow), and (4) a mineral reservoir, whereby the endocrine system regulates the level of calcium and phosphate in the circulating body fluids.

Bone is found only in vertebrates, and, among modern vertebrates, it is found only in bony fish and higher classes. Although ancestors of the cyclostomes and elasmobranchs had armoured headcases, which served largely a protective function and appear to have been true bone, modern cyclostomes have only an endoskeleton, or inner skeleton, of noncalcified cartilage and elasmobranchs a skeleton of calcified cartilage. Although a rigid endoskeleton performs obvious body supportive functions for land-living vertebrates, it is doubtful that bone offered any such mechanical advantage to the teleost (bony fish) in which it first appeared, for in a supporting aquatic environment great structural rigidity is not essential for maintaining body configuration. The sharks and rays are superb examples of mechanical engineering efficiency, and their perseverance from the Devonian Period attests to the suitability of their nonbony endoskeleton.

In modern vertebrates, true bone is found only in animals capable of controlling the osmotic and ionic composition of their internal fluid environment. Marine invertebrates exhibit interstitial fluid compositions essentially the same as that of the surrounding seawater. Early signs of regulability are seen in cyclostomes and elasmobranchs, but only at or above the level of true bone fishes does the composition of the internal body fluids become constant. The mechanisms involved in this regulation are numerous and complex and include both the kidney and the gills. Fresh and marine waters provide abundant calcium but only traces of phosphate; because relatively high levels of phosphate are characteristic of the body fluids of higher vertebrates, it seems likely that a large, readily available internal phosphate reservoir would confer significant independence of external environment on bony vertebrates. With the emergence of terrestrial forms, the availability of calcium regulation became equally significant. Along with the kidney and the various component glands of the endocrine system, bone has contributed to development of internal fluid homeostasisthe maintenance of a constant chemical composition. This was a necessary step for the emergence of terrestrial vertebrates. Furthermore, out of the buoyancy of water, structural rigidity of bone afforded mechanical advantages that are the most obvious features of the modern vertebrate skeleton.

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Bone | Definition, Anatomy, & Composition | Britannica