The Skeletal SystemThe average human adult skeleton has
206 bones joined to ligaments and tendons to form a protective and supportive framework for the attached muscles and the soft tissues which underlie it.
The skeleton has two main parts: the
axial skeleton and the
appendicular skeleton.The axial skeleton includes 80 bones and is made of bones of the skull, the chest, and the spine. The bones of the axial skeleton protect the body's vital organs, the brain, spinal cord, heart, and lungs.
The appendicular skeleton includes two limb girdles (the shoulders and pelvis) and their attached limb bones. 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 women's bones and the women's pelvic cavity (hip section )is wider to accommodate childbirth.
The skeleton plays an important part in movement by providing a series of independently movable levers, which the muscles can pull to move 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.