1. Skeletal system

2. Compare

3. At birth, humans have 270 bones in human body, but by adulthood, the number will be 206
The skeletal system has 4 main functions: support, movement, protection, production/storage
Support
Movement
Protection
Production/storage: produces red blood cells inside the bones; bones store fat and calcium

4. Structures of bones
A bone is living tissue that contains 2 main types of tissue: compact and spongy
Compact bone tissue: hard, outer portion of bone made of a dense web of fibers
Spongy bone tissue: inside tissue of the bone that looks like a sponge, due to the small holes; less dense than compact bone

5. Bone Marrow: soft tissue inside most bones; red and yellow bone marrow
Red bone marrow is where the red blood cells are made
Yellow bone marrow stores fat
Cartilage: the special tissue that is strong and flexible covering the end of your bones offering protection; prevents the bones from rubbing together and reduces friction
Periosteum: a membrane that surrounds the bone in areas that are not covered by cartilage; contains blood vessels/nerves; produces new bone tissue; nourishes bones and helps function, grow, and heal

7. joints The bones of the skeletal system do not function independently.
They function together at places called joints, where 2 or more bones meet and provide flexibility and mobility
The bones are connected to other bones by ligaments
The skeletal system has movable and immovable joints

8. Movable joints
A ball and socket joint allows bones to move/rotate in nearly all directions; some examples are hips and shoulders
A hinge joint will allow bones to move back and forth in a single direction, much like a door; examples are fingers, elbows, and knees
A pivot joint allows bones to simply rotate; the neck and lower arm from the elbow down are examples

9. Pivot Joint
Hinge Joint
Ball and Socket