Bone:Classification and Structure

Structure:

The bones are classified into two divisions:

• Axial Skeleton {This includes the skull, vertebral column (spine), and the rib cage.}
• Appendicular Skeleton {bone of upper limbs, lower limbs, and the girdles

The 5 major shapes of bones:

• Long Bones-

• Structure

• shaft with two ends
• bone collar surrounding a hollow medullary cavity (area in the middle that holds the yellow bone marrow: fat)
• Diaphysis
• forms the long axis of the bone
• thick collar of compact bone that surrounds the medullary cavity.
• Epiphysis
• has spongy bone on the inside
• outside is covered by compact bone
• proximal is for the end closer to the center of the body
• distal is for the end that is farther away from the center of the body.
• end is covered with thin layer of articular cartilage.
1. This cartilage cushions the end during the joint movement & absorbs stress.
2. made of hyaline cartilage.
• Epiphyseal Line
• it is a remnant (leftover) of the epiphyseal plate (a disc of hyaline cartilage that grows during childhood to lengthen the bone).
• Periosteum
• glistening membrane that covers the entire external surface.
• Outer Layer- made of dense connective tissue (connective layer)
• Inner Layer- osteogenic (bone creating) layer and consists of osteoblasts (bone-forming cells) and osteoclasts (bone-destroying cells)
• has many nerve fibers and blood vessels which enter via a nutrient foramen.
• Secured to the underlying bone by Sharpy's Fibers ( collagen fibers that extend from the fibrous layer to the bone matrix)
• Periosteum provides anchoring points for tendons and ligaments, at these points the Sharpy's fibers are very dense.
• Endosteum
• internal surface of the bone lined with connective tissue membrane
• covers trabeculae of spongy bone in marrow cavities and lines canals that pass through compact bones.
• Osteoblast and osteoclasts are both located here.
• Ex. (femur, tibia, & phalanges)

• Short Bones-

• somewhat cube shaped
• Ex. (carpals & tarsals)

• Flat Bones-

• thin, flattened
• Ex. (ribs, skull)

• Irregular Bones-

• have complicated shapes
• "odd men out"
• Ex. (vertebrae)

• Sesamoid Bones-

• special type of short bone in the tendon
• vary in size and number in different people
• Some of these change the direction of a pull of a tendon (something connecting a muscle to a bone)
• The function of others is not know
• Ex. (patella)

Compact Bone and Spongy Bone:

Compact Bone-

• This external layer of the bone is very thick and looks smooth. 

Spongy Bone

• This part of the bone contains many holes and contains small flat pieces called trabeculae.
• These spaces within the between the trabeculae are filled with marrow (both red and yellow) in living bones.

Function:

There are 5 major functions of bones and these include:

1. Support the body and cradle the organs
2. Protect vital organs
3. Allow movement
4. Store Minerals (we like us some calcium and phosphate!)
5. Hematopoiesis (it is the formation of red blood cells)