Chapter 17 Vian Middle School Mrs. Trotter

Internal & External Structures Protect Your Body  Bones  skin

Skeletal System  There are 206 bones of the human body  Give shape  Protect your internal organs  Are attached to major muscles  House blood cells  Store calcium & phosphorus

Periosteum  A tough, tight-fitting membrance on the living surface of a bone  Cells involved in growth and repair of bone are found here  Small blood vessels in the periosteum carry nutrients into the bone

Compact Bone  Found under the periosteum  Gives bones strength  A very hard, strong layer  Bone cells & blood vessels are found here  Keeps the bone from being too rigid, brittle, or easily broken

Spongy Bone  Located near the ends of long bones  Has many small open spaces that make the bones lightweight  In the center of these bones we call these openings cavities  Inside the cavities is marrow

Marrow  Some marrow is yellow and is composed of fat cells  Red marrow produces red blood cells at an incredible rate of 2 million to 3 million cells per second

Cartliage  The ends of bones are covered with a smooth, slippery, thick layer of tissue  It is flexible and important to joints because it acts as a shock absorber  It reduces friction for easier movement  It gets damaged from years of use and can cause a lot of pain

 Months before you were born, your entire body was made out of cartilage  Gradually the cartiliage was broken down and became bone

Osteoblasts  Bone forming cells  Deposit the minerals calcium & phosphorus  They make the bone tissue hard

Joints  Make motion possible  Anywhere two or more bones join is a joint  These joints are protected by a thin layer of cartilage

At birth  Your bone was made up of over 300 bones  As you grew and developed- these bones fused together to 206 bones  Healthy bone is always being formed and reformed

Osteoclasts  They help to break down the bone  The break down calcium and phosphorus into the bloodstream  These elements are necessary to keep your body working properly – including the moving of your muscles

Ligaments  The bones are held in place at these joints by tough bands of tissue called ligaments  Many joints have more than one ligament to help move the particular joint