Human skeleton
From Free net encyclopedia
Image:Skelett-Mensch-drawing.jpg The human skeleton is made of individual or joined bones (such as the skull), 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, but 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. They leave pockets of cartilage to allow more growth. 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. Growing is usually completed between ages 12 and 14. This means that the bones have no pockets of cartilage left, so there is no material left to allow more growth.
Not all bones are interconnected directly. There are 6 bones (three on each side) in the middle ear that articulate only with each other. Another bone, the hyoid bone in the neck, does not touch any other bones in the body, and is supported by muscles.
The longest and heaviest bone in the body is the femur and the smallest is the stapes bone in the middle ear.
Contents |
Function
The most obvious function of bone is to support the body. It also the site of 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. Movement in vertebrates is dependent on the skeletal muscles, which are attached to the skeleton by tendons. Without the skeleton to give leverage, movement would be greatly restricted. Bone also serves as a mineral storage deposit in which nutrients can be stored and retrieved.
Organization
One way to group the bones of the human skeleton is to divide them into 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, the arm bones, the bones of the pelvis and the leg bones.
A more systematic division of the bones of the human skeleton divides them into the:
Gender differences
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 at the back of the skull). 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.
The book Genesis of the Bible tells that Eve was created from one of Adam's ribs. This leads some people to assume that men have one less rib than women, but is clearly incorrect; men and women both 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.
A fracture occurs when a bone is subjected to too much force. Fractures are divided into "simple" and "compound" fractures, a slightly confusing terminology: A "simple" fracture simply means that the broken bone has not broken through the skin, and does not imply a single break. A broken bone is called a "compound fracture" when it has broken through the skin, also not implying that the bone has broken in more than one place. Osteoporosis can increase the likelihood of fractures and broken bones, especially among post-menopausal women and the elderly.
Scoliosis is a condition where the spine is curved from side to side.
See also
External links
- Learning Zone: The human skeleton (from the Oxford University Museum of Natural History)
- A skeleton page for kids
- A detailed page on the skeleton by besthealth.com
| Human organ systems - edit |
|---|
| Cardiovascular system | Digestive system | Endocrine system | Immune system | Integumentary system | Lymphatic system | Muscular system | Nervous system | Skeletal system | Reproductive system | Respiratory system | Urinary system |
da:Menneskeskelet fr:Squelette humain fi:Luuranko he:שלד ko:인체골격 is:Mannbeinagrindin it:Scheletro (anatomia umana) pl:Układ kostny człowieka cs:Kostra (člověk)