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Skeletal System

Bones And Medicine

Even though bones are very strong, they may be broken, but fortunately, most fractures do heal. The healing process may be stymied if bones are not reset properly or if the injured person is the victim of malnutrition. Osteoprogenitor cells migrate to the site of the fracture and begin the process of making new bone (osteoblasts) and reabsorbing the injured bone (osteoclasts). With proper care, the fracture will fully heal, and in children, often without a trace.

Bones are affected by poor diet and are also subject to a number of diseases and disorders. Some examples include scurvy, rickets, osteoporosis, arthritis and bone tumors. Scurvy results from the lack of vitamin C. In infants, scurvy causes poor bone development. It also causes membranes surrounding the bone to bleed, forming clots which are eventually ossified, and thin bones which break easy. In addition, adults are affected by bleeding gums and loss of teeth. Before modern times, sailors were often the victims of scurvy, as they were at sea for long periods of time with limited food. Hence, they tried to keep a good supply of citrus fruits, such as oranges and limes, on board, as these fruits supply vitamin C.

Rickets is a children's disease resulting from a deficiency of vitamin D. This vitamin enables the body to absorb calcium and phosphorus, and without it, bones become soft and weak and actually bend, or bow out, under the body's weight. Vitamin D is found in milk, eggs and liver, and may also be produced by exposing the skin to sunlight. Pregnant women can also suffer from a vitamin D deficiency, osteomalacia, resulting in soft bones. The elderly, especially women who had several children in a row, sometimes suffer from osteoporosis, a condition in which a significant amount of calcium from bones is dissolved into the blood to maintain the body's calcium balance. Weak, brittle bones dotted with pits and pores are the result.

Another condition commonly afflicting the elderly is arthritis, an often painful inflammation of the joints. Arthritis is not, however, restricted to the elderly, as even young people may suffer from this condition. There are several types of arthritis, such as rheumatoid, rheumatic and degenerative. Arthritis basically involves the inflammation and deterioration of cartilage and bone at the joint surface. In some cases, bony protuberances around the rim of the joint may develop. Unfortunately, most people will probably develop arthritis if they live long enough. Degenerative arthritis is the type that commonly occurs with age. The knee, hip, shoulder and elbow are the major targets of degenerative arthritis. A number of different types of tumors, some harmless and others more serious, may also affect bones.

See also Orthopedics.


Resources

Books

Shipman, P., A. Walker, and D. Bichell. The Human Skeleton. Cambridge: Harvard University Press, 1985.

Steele, D.G., and C.A. Bramblett. The Anatomy and Biology of the Human Skeleton. College Station: A&M; University Press, 1988.


Periodicals

Bower, B. "Fossils Put a New Face on Lucy's Species." Science News 145 (2 April 1994): 212.

Fischman, J. "Putting a New Spin on the Birth of Human Birth." Science 264:1082-1083, 1994.

Miller, A. "Collagen: The Organic Matrix of Bone." Phil. Trans. Roy Soc. Lond. ser. B 304:455-477, 1984.

Snow, C.C., B.P. Gatliff, and K.R. McWilliams. "Reconstruction of Facial Features from the Skull: An Evaluation of its Usefulness in Forensic Anthropology." American Journal of Physical Anthropology (1970).

Stevenson, J. "The Strong-boned Weavers of Spitalfields." Discover (August, 1993).


Elaine L. Martin

KEY TERMS


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Bone

—Composed primarily of a non-living matrix of calcium salts and a living matrix of collagen fibers, bone is the major component that makes up the human skeleton. Bone produces blood cells and functions as a storage site for elements such as calcium and phosphorus.

Calcium

—An essential macro mineral necessary for bone formation and other metabolic functions.

Cartilage

—A type of connective tissue that takes three forms: elastic cartilage, fibrocartilage and hyaline cartilage. Hyaline cartilage forms the embryonic skeleton and lines the joints of bones.

Haversian system

—Tubular systems in compact bone with a central Haversian canal which houses blood and lymph vessels surrounded by circular layers of calcium salts and collagen, called lamellae, in which reside osteocytes.

Marrow

—A type of connective tissue which fills the spaces of most cancellous bone and which functions to produce blood cells and store fat.

Ossification

—The process of replacing connective tissue such as cartilage and mesenchyme with bone.

Osteoblast

—The bone cell which deposits calcium salts and collagen during bone growth, bone remodeling and bone repair.

Osteoclast

—The bone cell responsible for reabsorbing bone tissue in bone remodeling and repair.

Osteocyte

—Mature bone cell which functions mainly to regulate the levels of calcium and phosphate in the body.

Skeleton

—Consists of bones and cartilage which are linked together by ligaments. The skeleton protects vital organs of the body and enables body movement.

Synovial joint

—One of three types of joints in the skeleton and by far the most common. Synovial joints are lined with a membrane which secretes a lubricating fluid. Includes ball and socket, pivot, plane, hinge, saddle, condylar and ellipsoid joints.

Vertebrate

—Includes all animals with a vertebral column protecting the spinal cord such as humans, dogs, birds, lizards, and fish.

Additional topics

Science EncyclopediaScience & Philosophy: Semiotics to SmeltingSkeletal System - Structure, Axial Skeleton, Appendicular Skeleton, Types Of Bone, Bone Development And Growth, Bones And Medicine