Diagram of a human skeleton
The human skeleton is made of individual or joined bones, supported and supplemented by a structure of ligaments, tendons, muscles, cartilage and other organs.
The skeleton is not unchanging; it changes composition over a lifespan. Early in gestation, a fetus has no hard skeleton — bones form gradually during nine months in the womb. At birth, all bones will have formed, but a newborn baby has more bones than an adult. On average, an adult human has 206 bones (according to Gray's Anatomy) in their skeleton (the number can vary slightly from individual to individual), but a baby is born with approximately 270. The difference comes from a number of small bones that fuse together during growth. These include the bones in the skull and the spine. The sacrum (the bone at the base of the spine) consists of six bones which are separated at birth but fuse together into a solid structure in later years.
Not all bones are interconnected directly. There are 6 bones (three on each side) in the middle ear that articulate only with themselves. Another bone, the hyoid bone in the neck, does not touch any other bones in the body but is rather supported by muscles.
The longest bone in the body is the femur and the smallest is the stapes bone in the middle ear.
Function
A prepared human skeleton, as often used in biology classrooms
The skeleton functions not only as the support for the body but also in haematopoiesis, the manufacture of blood cells that takes place in bone marrow (which is why bone marrow cancer is very often a terminal disease). It is also necessary for protection of vital organs and is needed by the muscles for movement. Not only does the skeleton serve to help manufacture blood cells, but it also serves as a mineral storage deposit in which nutrients can be stored and retrieved.
A prepared human skeleton, as often used in biology classrooms
Organization
One way to group the bones of the human skeleton is to divide them into two groups, namely the axial skeleton and the appendicular skeleton. The axial skeleton consists of bones in the midline and includes all the bones of the head and neck, the vertebrae, ribs and sternum. The appendicular skeleton consists of the clavicles, scapulae, bones of the upper limb, bones of the pelvis and bones of the lower limb.
The bones of the human skeleton are structurally and in many taxonomies organized as those of the:
Gender differences
- See also: sexual dimorphism
There are many differences between the male and female human skeletons. Men tend to have slightly thicker and longer limbs and digit bones while women tend to have larger pelvic bones in relation to body size. Women also tend to have narrower rib cages, smaller teeth, less angular mandibles, and less pronounced cranial features such as the brow ridges and occipital protuberance (the small bump in the cranium's posterior). Most striking is the difference in hip bones, owing to differences related to the process of reproduction, and very likely also to the biological process of sexual selection. There are also a number of smaller differences between human male and female skeletons.
There is an occasional misunderstanding that men have one less rib than women, stemming from the story in the book Genesis of the Bible that Eve was created from one of Adam's ribs, but both men and women have 12 pairs of ribs. Removed ribs can regenerate within 2-3 months of sectional surgery, as in the surgical procedure rib thoracoplasty.
Diseases
The skeleton can be affected by many diseases that compromise physical mobility and strength. Skeletal diseases range from minor to extremely debilitating. Bone cancer and bone tumors are extremely serious and are sometimes treated by radical surgery such as amputation of the affected limb. Various forms of arthritis attack the skeleton resulting in severe pain and debility. Osteoporosis can increase the likelihood of fractures and broken bones, especially among post-menopausal women and the elderly. Scoliosis is another, when the spine curves from side to side.
See also
External links
The content of this page is retrieved from http://en.wikipedia.org/wiki/Human_skeleton under GFDL
