Marsha Wood - Printmaking
The Skeletal System
The average human adult skeleton has 206 bones joined to ligaments and tendons. The skeletal system forms a protective and supportive framework for the attached muscles and soft tissues which underlie it. The skeleton has two main parts: the axial skeleton and the appendicular skeleton. The axial skeleton consists of the skull, the spine, the ribs and the sternum (breastbone) and includes 80 bones. The appendicular skeleton includes two limb girdles (the shoulders and pelvis) and their attached limb bones (arms and legs). This part of the skeletal system contains 126 bones, 64 in the shoulders and upper limbs and 62 in the pelvis and lower limbs. There are only minor differences between the skeletons of the male and the female: the men's bones tend to be larger and heavier than corresponding women’s bones and the women's pelvic cavity is wider to accommodate childbirth.
The skeleton plays an important part in movement by providing a series of independently movable levers, which allow the muscles to flex and extend different parts of the body. It also supports and protects the internal body organs. The skeleton is not just a movable frame, however; it is an efficient factory, which produces red blood cells from the bone marrow of certain bones and white cells from the marrow of other bones to destroy harmful bacteria. The bones are also a storehouse for minerals - calcium, for example - which can be supplied to other parts of the body. Babies are born with 270 soft bones - about 64 more than an adult; and many of these will fuse together by the age of twenty or twenty-five into the 206 hard, permanent bones of an adult skeleton.
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The Skeletal System The Muscular System The Nervous System The Digestive System The Respiratory System |
The Endocrine System The Lymphatic System The Urinary System The Reproductive System |
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