2008-09-08T21:44:00.000-07:00

The human skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors muscles, and protects organs such as the brain, lungs and heart.
The longest and heaviest bone in the body is the femur and the smallest is the stapes bone in the middle ear. In an adult, the skeleton comprises around 20% of the total body weight, and half of this weight is water.
Fused bones include those of the pelvis and the cranium. Not all bones are interconnected directly: There are six bones in the middle ear called the ossicles (three on each side) that articulate only with each other. The hyoid bone, which is located in the neck and serves as the point of attachment for the tongue, does not articulate with any other bones in the body, being supported by muscles and ligaments.

Support
The skeleton provides the framework which supports the body, and maintains its shape. The joints between bones permit movement, some allowing a wider range of movement than others, e.g. the ball and socket joint allows a greater range of movement than the pivot joint at the neck.

[edit] Movement
Movement in vertebrates is powered by skeletal muscles, which are attached to the skeleton by tendons. Without the skeleton to give leverage, movement would be greatly restricted. However, biologically speaking, the skeleton does not enable movement.

[edit] Protection
The skeleton protects many vital organs:
The skull protects the brain, the eyes, and the middle and inner ears.
The spine protects the spinal cord.
The rib cage, spine, and sternum protect the lungs, heart and major blood vessels.
The clavicle and scapula protect the shoulder.
The ilium and spine protect the digestive and urogenital systems and the hip.
The patella and the ulna protect the knee and the elbow respectively.
The carpals and tarsals protect the wrist and ankle respectively.

[edit] Blood cell production
The skeleton is the site of haematopoiesis, which takes place in red bone marrow.

[edit] Storage
Bone matrix can store calcium and is involved in calcium metabolism, and bone marrow can store iron in ferritin and is involved in iron metabolism.

[edit] Endocrine regulation
Bone cells release a hormone called osteocalcin, which controls the regulation of blood sugar (glucose) and fat deposition. Osteocalcin increases both the insulin secretion and sensitivity, in addition to boosting the number of insulin-producing cells and reducing stores of fat.[2]

[edit] Sex-based differences

An articulated human skeleton, as used in biology education
There are many differences between the male and female human skeletons. Most prominent is the difference in the pelvis, owing to characteristics required for the processes of childbirth. The shape of a female pelvis is flatter, more rounded and proportionally larger to allow the head of a fetus to pass. Men tend to have slightly thicker and longer limbs and digit bones (phalanges), while women tend to have narrower rib cages, smaller teeth, less angular mandibles, less pronounced cranial features such as the brow ridges and external occipital protuberance (the small bump at the back of the skull), and the carrying angle of the forearm is more pronounced in females. Females also tend to have more rounded shoulder blades.

[edit] Disorders
See also: List of skeletal disorders
There are many disorders of the skeleton. One of the more prominent is osteoporosis.

[edit] Osteoporosis
Main article: Osteoporosis
Osteoporosis is a disease of bone - leading to an increased risk of fracture. In osteoporosis, the bone mineral density (BMD) is reduced, bone microarchitecture is disrupted, and the amount and variety of non-collagenous proteins in bone is altered. Osteoporosis is defined by the World Health Organization (WHO) in women as a bone mineral density 2.5 standard deviations below peak bone mass (20-year-old sex-matched healthy person average) as measured by DXA; the term "established osteoporosis" includes the presence of a fragility fracture.[3] Osteoporosis is most common in women after the menopause, when it is called postmenopausal osteoporosis, but may develop in men and premenopausal women in the presence of particular hormonal disorders and other chronic diseases or as a result of smoking and medications, specifically glucocorticoids, when the disease is called steroid- or glucocorticoid-induced osteoporosis (SIOP or GIOP).
Osteoporosis can be prevented with lifestyle advice and medication, and preventing falls in people with known or suspected osteoporosis is an established way to prevent fractures.Osteoporosis can also be prevented with having a good source of calcium and Vitmin D. Osteoporosis can be treated with bisphosphonates and various other medical treatments.

HUMAN SKELETON