Human Skeleton

The human skeletal system is composed of individual bones and cartilage that receive a supply of blood and are held together by fibrous connective tissue, ligamens, and tendons. The three main fuctions of the skeletal system are protection, motion, and support. The system protect the body by enclosing the vital organs, it permits locomotion by responding at certain joints to the contractile activities of skeletal muscles, and it supports the body by serving as a framework to which tendons and fascia are attached, enabling skeletal muscles as a depot for calcium, which is vital to proper functioning of cell membranes, and for phosporus, which is needed in intermediary metabolism. In addition, the skeletal system is important because bone produce blood cells.

A birth the human body has about 275 bones, but as the body develops many of these bones fuse together. In the adult human the skeleton consist of 206 name bearing bones and a variable number of largely unnamed sesamoid bones. Sesamoid bones develop in the capsules of certain joints or in tendons, which hold muscle to bone, where they provide special support or reduce friction. The best known sesamoids are the patella (kneecap) and pisiform (wrist bone).

Classification of Bones
Bones may be classified as long, short, flat, irregular, or sesamoid. The long bones of the limbs consist of a central shaft (diaphysis) between two ends (epiphyses) that form joints with one or more other bones. The short bones, in the wrists and ankles, have a spongy core within a shell of compact bone. The flat bones include the ribs and many skull bones. They consist of two plates of compact bone with a spongy layer between. All this remaining named bones are irregular bones, except the patella, pisiform, and some foot bones.


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