Muscle and Skeletal Systems: Skeletal System: Bone Structure

Macroscopically: bone = solid strucuture with canals inside where blood vessel runs, and holes where cells can reside, the whole thing surrounded by membrane that contains stem cells (osteoblasts) and osteoclasts.

Microscopically: bone = cell + extracellular matrix = arranged in cylinders called osteons, with blood vessel and nerve running through the middle of the cylinder.

Osteocytes

Calcium-protein matrix: the extracellular matrix of bone consists of calcium salts, collagen fibers, and ground substance (glue).

Lengthwise bone growth occurs at the ends of long bones at the knobs.

Osteoblasts' role in lengthwise bone growth is to add bone tissue at the bone ends.

Osteoclasts' role in bone growth is to remodel bone tissue by chipping away the knobs until it's the right size and shape.

Osteoblasts' role in diameter growth of bones is to add bone tissue to the outside of the bone.

Osteoclasts' role in diameter growth of bones is to remove some bone tissue from the inside of the bone (bones are hollow).

Without osteoclasts, diameter growth will result in bones that are too thick and too heavy. Even with osteoclasts, bones still grow thicker, just not unwieldly thick.

Osteoblasts = stem cells that give rise to osteocytes = builds bone.

Osteocytes = mature bones cells = reside in bone for housekeeping.

Osteoclasts = large cells that break down bone.