Bones are the hardest and most dense tissues in the human body. They support and protect our organs, anchor our muscles, and allow us to move. Our skeleton is made up of 206 bones. We are born with about 300 bones, but many fuse together as we grow. The average adult has about 200 bones.
The study of bones is called osteology. Bones can be classified by their shape: long bones, short bones, flatbones, sesamoid bones, and irregular bones. Long bones include the femur (thighbone), tibia (shinbone), humerus (upper arm bone), radius (forearm bone), ulna (inner forearm bone), metacarpals (hand bones), and phalanges (fingerbones). Short bones include the carpals (wristbones) and tarsals (anklebones). Flatbones include the sternum (breastbone), ribs, scapulae(shoulder blades),and hipbones. Sesamoid bones are small roundish Bones that form near joints; an example is the patella or kneecap. Irregular shaped Bones include vertebrae(backbones) , facial Bones , sacrum(tailbone) , coccyx(tailbone) .
The function of a bone depends on its location in the body. For example, long leg Bones bear much of our weight so they must be strong yet lightweight; facial Bones must provide rigidity while allowing for mobility; some Bones act as levers to help us move; others store minerals such as calcium phosphate .
Bone tissue is constantly being remodeled throughout life in a process known as remodeling or turnover . When we are young , more Bone tissue is produced than removed ; this makes our skeletons grow larger . As we age , more Bone tissue is lost than gained ; this makes our skeletons smaller and lighter . However , even in old age there is a balance between bone resorption and deposition so that our skeleton remains strong enough to support our bodies .
There are two types of cells involved in bone remodeling : osteoblasts and osteoclasts . Osteoblasts are responsible for Bone formation ; they secrete enzymes that promote cell division and Matrix synthesis . Osteoblasts become trapped in the matrix they secrete , where they mature into osteocytes . Osteocytes maintain communication with other osteocytes through tiny channels called canaliculi .Osteoclasts break down Bone tissue ; they secrete acids that dissolve mineral crystals and enzymes that degrade proteins . The end product of all this activity is newBone tissue identical to the original .
There are four main types of fracture: simple , compound , comminuted , pathologic A simple fracture occurs when there is a single break in the bone with no damage to surrounding tissues; examples include fractures of the wrist or ankle A compound fracture occurs when there is a break in both the bone AND surrounding tissues such as skin In a comminuted fracture there are multiple breaks in both cortical AND cancellous layers of bone A pathologic fracture occurs when weakenedBone collapses due to disease such as cancer Most fractures heal without complications but sometimes infection or malunion can occur Infection may delay healing or cause permanent damage if not treated early Malunion occurs when fractured pieces heal incorrectly which may lead to deformity