The Skeletal System
Five Major Functions1. Gives shape and support to body2. Protects your internal organs
1. Ex: ribs protect heart, skull protects brain
3. Major muscles are attached to bone and help them move
4. Blood cells formed in center of bones in soft tissue called red marrow
5. Major quantities of calcium and phosphorus compounds are stored
Bone structure
Bones can have different sizes, shapes,
Bone surface covered with periosteum Small blood vessels in periosteum
carry nutrients to bone Two different bone tissues
Compact bone Spongy bone
Compact Bone
Directly under periosteum Hard, strong layer that gives bones
strength Framework containing calcium
phosphate Living tissue of bone cells and
blood vessels that keeps bones from being too rigid, brittle, or easily broken
Spongy Bone
Located towards end of long bones Has many small, open spaces that
make bones lightweight Inside cavities and spaces in
spongy bones, substance called marrow Some marrow yellow and composed
of fat cells Red marrow produces red blood cells
Cartilage Smooth, slippery,
thick layer of tissue that covers the end of bones
No blood vessels or minerals
Flexible and important in joints because it acts as shock absorber
Makes movement easier by reducing friction
Bone Formation Before being born, baby skeleton made
of cartilage Bone cells called osteoblasts deposit
calcium and phosphorus in bones, making the tissue hard
At birth, we have >300 bones, but as we develop, bones fuse and only have 206
Bone tissue always being formed Osteoblasts build bone Osteoclast breaks down bone
Joints
Any place where two or more bones come together Bones kept far enough apart by
cartilage Classified as immovable or movable
Ligaments tough band of tissue that holds bones in place at joints
Immovable joints
Allows little or no movement Joints of skull and pelvis are
immovable
Movable Joints
All movement requires movable joints
Several types Pivot Ball and socket Hinge gliding
Pivot Joint
One bone rotates in a ring of another bone that does not move Ex: turning your head
Ball and Socket
Bone with rounded end that fits into a cuplike cavity on another bone Provides wider range of motion
Why your arms and legs can swing in almost any direction
Hinge
Back and forth movement like hinges on door Ex: elbows, knees, fingers
Gliding Joint
One part of a bone slides over another bone
Move in back and forth motion and are used most in body Ex: wrist, ankle
Joint Problems
Arthritis pain, stiffness, and swelling of joints
Osteoarthritis results when cartilage breaks down because of years of use
Rheumatoid arthritis ongoing condition in which the body’s immune system tries to destroy its own tissues
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