Composed of the body’s

• Bones

• Ligaments ( bone -- bone )

• Tendons ( bone -- muscle )

• Cartilage

Infants have more than 300 bones at birth

• Bones fuse as babies develop

• 206 bones in the adult human body (can be less)

1. Structure and Support

Leg bones, pelvis, and vertebrae

Supports the body’s weight

2. Protection

Skull protects the brain

Ribs and sternum

(breastbone) protects the lungs and heart

Functions of the Skeletal System

3. Movement

4. Muscles attach to bones and use them as levers to move the body

5. Storage

   1. Calcium and Fat (Stored E)

6. Blood Cells Production :

   1. Bone marrow produces millions per second

Bone Classification

Each bone belongs to one of two major groups:

• Axial Skeleton

  • Skull, vertebral column, and rib cage

  • Involved in protection, support, and carrying other body parts

• Appendicular Skeleton

  • Bones of upper & lower limbs

  • Involved in locomotion

Types of Bones :

1. Long Bones

   1. Longer than they are wide

   2. All limb bones except the patella (kneecap) and the bones of the wrist + ankle

2. Short Bones

   1. Roughly cube shaped

   2. Bones of the wrists and ankle

3. Flat Bones

   1. Thin; flattened, and usually a bit curved

   2. Scapula (shoulder blade)

      Sternum (breast bone), ribs, and most bones of the skull

4. Irregular Bones

   1. Have weird shapes that fit none of the 3 previous classes

   2. Vertebrae, hip bones, 2 skull bones - mandible, and maxilla

Long Bone Structure:

• Periostern : Hard outer covering

• Epiphysis : Ends of the bones

• Diaphysis : The shaft of the bone

• Articular Cartilage : Cushions the ends of the bones and allows for smooth movement

• Epiphyseal Plate : Areas made of cartilage allowing for the growth of the bone growth plate

Collagen (protein) -- provides strength and resillience

Calcium -- provides hardness and resistance to crushing

Three Types of Bone Cells

1. Osteocytes --

   1. Mature bone cells suspended in matrix [ cytes = basic cells ]

2. Osteoblasts --

   1. Build new bone by adding Collagen and Calcium to matrix [ blasts = build ]

3. Osteoclasts --

   1. Breakdown matrix to replace stored Calcium; can also clean up unhealthy or unwanted bone

Yellow Marrow:

• Largely fat

• In emergencies -- massive blood loss -- convert to red bone marrow

Red Marrow

Medullary Canal

All bones consist of a dense, solid layer known as compact bone and an inner layer spongy bone