Skeletal Classification

There are 2 types of Osseous Tissue:

Compact Bone - is Dense & Looks Smooth & Homogeneous
Spongy Bone - Made up of small, needle like pieces & has open spaces.

There are 4 main categories which bones may be classified as:

1) LONG BONES - found in the arms and legs. These are usually longer than wide, have a Shaft with heads at both ends. Long bones are composed of various areas: Epiphysis- refers to the ends of the bone; Diaphysis refers to the Shaft region. In adults, the shaft is a Primary storage area for Fat Tissue; In Infants, the shaft is an area for Blood Cell Formation.

2) FLATBONES - skull, shoulder blades and sternum are ex. Thin, flattened & usually curved. Contains Compact & Spongy bone.

3) SHORT BONES - Bones of the ankles, wrist and toes. Made up of mostly spongy bone.

4) IRREGULAR BONES - Bones of the Ear and Spine. Bones which do not fit in any of the above categories.

OSSIFICATION

This is the process of Bone Formation. Most bones begin their development by using Hyaline Cartilage as their model. Then, bone forming cell, Osteoblasts, cover this shell/model. Then, over time, the cartilage is replaced by the actual bone which will form the adult skeleton.

By Adulthood, most of this Hyaline Cartilage has been replaced, except for:

· Articular Cartilage, which covers the ends of bones;
· Areas at the end of Long Bones, known as Epiphyseal Plates, which provide for lengthening of long bones during childhood;

Bone is a Dynamic & Active Tissue-constantly remodeling itself in response to:

· Calcium levels in the blood;
· Weight Bearing forces (stress) on the body.

When blood levels of Calcium drop too low, specialized bone cells, Osteoclasts, break down bone to release calcium into the blood. When blood levels of calcium are too high, calcium in then stored in bones.

Bone Remodeling - is important so that the skeleton can adapt and strengthen itself in areas where it is subjected to areas of stress. On the other hand, people who are bed ridden, and don't give their skeletal system enough activity, their bones tend to lose bone mass:

Osteoporosis - a condition that affects older women and is characterized by decrease in bone mass with decreased density and enlargement of bone spaces producing porosity and fragility.

Bone remodeling is also necessary when Breaks or Fractures occur: