Skeletal System

The Skeletal System

1. Serves as an attachment for muscles (tendons=muscle to bone, ligament=bone to bone), as support for the body, and as protection for vital organs

2. Bones also store certain minerals (calcium and phosphorus) and contain special cells that form red and white blood cells

3. The human body contains 206 bones. Humans are born with around 270, but some fuse together as you grow.

Osseous Tissue Composition

1. Collagen - protein that is the major organic constituent of bone

2. Organic matrix - composite of collagenous fibers and ground substance that adds to overall strengthen of bones and gives some degree of resiliency to the bone

3. Inorganic salts - calcium phosphate (hydroxyapatite), Vitamin D is essential for absorption, and magnesium and sodium are also found in bone

Cells of Osseous Tissue

1. Osteoblasts - bone building and bone repairing cells in periosteum

2. Osteocytes - mature bone cells within the bone matrix

3. Osteoclasts - bone destroying, bone absorbing cells; causes reabsorption of bone

Periosteum

1. Dense, fibrous membrane covering the surface of the bone (except in joints)

2. Contains blood vessels and nerve fibers (can sense pain when damage is done)

3. Serves as a protective layer and is essential for bone cell survival and bone formation

Compact Bone

1. Dense and stress bearing bone

2. Haversian Systems - fundamental functional unit of compact bone, forming osteons

3. Lamellae - concentric cylinder shaped calcified structure (layers)

4. Lacunae - small spaces containing tissue fluid and osteocytes

5. Osteocytes - facilitate exchange of nutrients, waste, and calcium between blood and bone

6. Canaliculi - canals connecting the lacunae together and to the Haversian canal which carries nutrients and wastes to and form the osteocytes

Cancellous Bone

1. Light and spongy

2. Also known as trabecular bone; it is highly vascularized and contains red marrow

3. Found at the ends of long bones, ribs, sternum, hips, vertebrae, and cranium

4. No Haversian canals - nutrients delivered and waste removed by diffusion through tiny canaliculi

5. Web-like arrangement (arranged along lines of stress) enhancing the bone’s strength

6. Trabeculae - needle-like rods acting as support structures in spongy bone