The Skeletal System!
5 basic functions of bones:

Support~ Bones provide the internal framework that supports the body. The bones of the legs work like pillars supporting the body trunk when we stand, and the rib cage supports the thoracic wall.

Protection~ Bones protect and cradle the body's soft organs. The fused bones of the skull act as a snug enclosure for the brain and the vertebrae surround the spinal cord.

Movement~ Skeletal muscles are attached to bones by tendons and practically use the bones as levers to move the body and its parts.

Storage~ The internal cavities of bones works as a storage facility for fat and minerals. These minerals mainly consist of calcium and phosphorous.

Blood cell formation~ Hematopoiesis occurs within the marrow cavities of certain bones.

Classification of Bones:

Long Bones~ These particular bones are usually longer than they are wide. As a rule they have a shaft with heads at both ends, and contain mostly compact bone.

Short Bones~ Generally Cube-shaped and are composed mostly of spongy bone. Wrist and ankle bones are short bones.

Flat Bones~ They are thin, flattened, and usually curved. They have two thin layers of compact bone sandwiching a layer of spongy bone.

Irregular Bones~ Any bones that do not fit in one of proceeding catagories.

Bone Formation/Growth:
Key Points~

~Bone and cartilage make up most of the structure of the skeletal system.

~Skeletons of embryos are mostly composed of hyaline cartilage, whereas young children only having a few cartilage remains in isolated areas because most of it has turned into bone.

~Most bones, with the exception of flat bones, use hyaline cartilage as their 'model' structure. Flat bones form on fibrous membranes.

~Bone formation (Ossification) involves two main phases: First off, the hyaline cartilage becomes covered with bone matrix by forming osteoblasts. Soon, the enclosed hyaline cartilage model is digested away which opens up a medullary cavity within the new bone.

~When bones become fully grown, the epiphyseal line is formed. This line is a remnant of the epiphyseal plate, and appears when long bones are completely grown.

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