Skeletal System

1. 206 bones in the body

2. Functions:

   1. providing support & shape to the body

   2. protecting vital organs

   3. providing points of attachment for muscles

   4. manufacturing blood cells

   5. storing calcium & mineral salts

3. Bones are levers - move when force is applied

   1. Internal forces: muscles

   2. External forces: gravity, load, or application of force

4. Wolff's law: states that bone density increases for areas on which increased forces are imposed and decreases for areas on which forces are decreased  

5. Axial & Appendicular Skeletons

1. • Axial skeleton: forms the central part of the body

     • 80 bones

     • Incl: head, neck, thorax, & vertebral column

   • Appendicular skeleton: attaches to the central part

     • 126 bones

     • Incl: extremities & pelvis

6. Bone Composition

1. • 1/3 organic - provides bone elasticity

   • 2/3 inorganic - provides hardness/strength & opaque appearance

1. Compact bone: makes up the hard, dense outer layer of all bones 

2. Cancellous bone: a less dense, latticework of trabeculae of inner bone 

• Trabeculae: latticework at the end of long bones described as porous or spongy, 

3. Periosteum: thin, fibrous membrane covering the entire surface of a bone, except the articular (joint) surface containing blood vessels & nerves 

• Articular surfaces: covered with hyaline cartilage 

  • Provides blood supply for nourishing the bones to promote growth and repair 

  • Serves as an attachment point for tendons & ligaments 

4. Epiphysis: region at each end of a bone 

• Wider than the shaft in long bones 

• Epiphyseal plate: cartilaginous material in the growing bone where longitudinal growth occurs  

  • Ossifies during adolescence to become mature 

  • Disappears in adult bones 

5. Metaphysis: widening region of the long bone that serves as a transition from the epiphysis to diaphysis; function is to support the epiphysis 

6. Diaphysis: main shaft of a bone, composed of an outer layer of compact bone, giving it strength 

• Medullary canal: hollow center which, among other features, decreases the weight of the bone, containing marrow & blood vessels 

• Endosteum: a membrane lining the medullary canal, containing osteoclasts 

• Osteoclasts: type of bone cell primarily responsible for bone resorption 

  • Resorption: a process by which old bone is broken down so it can be replaced with new bone 

• Osteoblasts: type of bone cell primarily responsible for the formation of bone 

1. Long bones: tube-shaped with a shaft filled with bone marrow length is greater than their width, serving as the largest bone in the body 

   • Makes up most of the appendicular skeleton 

   • Covered by hyaline cartilage layer on the articular surface of the epiphysis 

   • Ex. Femur, humerus, radius 

2. Short bones: have more equal dimensions of height, length, and width, resembling a cube 

   • Thin layer of compact bone covering cancellous bone with marrow cavity in the middle 

   • Ex. Carpal bones of the wrist & tarsals of the foot 

3. Flat bones: broad surface, not very thick, and tend to be curved rather than a flat surface; main sites of blood formation 

   • Ex. Ilium, scapula, & cranial bones 

4. Irregular bones: have a variety of shapes, allowing them to fulfill particular functions 

   • Ex. Vertebral bones 

5. Sesamoid bones (accessory bones): small bones located where tendons cross the ends of long bones in the extremities 

   • Protect tendons from excessive wear, improving muscle function 

   • Ex. The tendon of the flexor hallucis longus, spanning the plantar surface of the foot to attach to the great toe 

   • Located on either side of the tendon near the head of the first metatarsal, providing a protective groove for the tendon to pass through 

• No long or short bones in the axial skeleton 

• Innominate bones are the only irregular bones in the appendicular skeleton

1. Fracture: broken bone/cracked bone; interruption in the continuity of a bone caused by trauma or pathology (disease) 

   • Can interfere with bone growth if occurs early on to disrupt the epiphyseal plate 

   • Can cause osteoporosis in elderly 

2. Osteoporosis: condition characterized by loss of normal bone mass which can weaken a bone to fracture by everyday forces 

   • Bone density measures bone mass 

   • Vertebrae are common sites 

3. Osteopenia: condition of reduced bone mass, less severe than osteoporosis 

4. Osteomyelitis: infection of the bone caused by bacteria 

   • Risk increases when the bone breaks the skin (open fracture) 

5. Legg-Calve-Perthes disease: slippage at the epiphyseal plate occurs, causing interruption of blood supply to the femoral head --> bone necrosis (death) 

6. Slipped capital femoral epiphysis: occurs when the head of the femur becomes displaced as a result of separation at the epiphyseal plate 

7. Osgood-Schlatter disease: occurs in children at the tendinous attachment of the quadriceps tendon to the tibial tuberosity 

Types of Fractures

1. Avulsion: Attachment sites of tendons or ligaments separate from the body of the bone

2. Closed: Bone fractured, skin intact

3. Comminuted: Multiple fragments of bone

4. Complete: Complete separation of bone fragments

5. Complicated: Bone fracture with associated injury of surrounding tissue such as nerves, arteries, or veins 

6. Greenstick: Bone is bent on one side and separated at the opposite side; occurs mostly in children 

7. Hairline/stress: Minor lines of fracture, often as the result of repetitive microtrauma; no separation of bone 

8. Incomplete: Fracture does not disrupt complete cross-section of bone 

9. Overriding: Fracture in which segments slide past each other 

10. Open (compound): Skin punctured or torn as a result of the fracture 

11. Simple: Fracture in which only the bone is damaged; surrounding soft tissue is uninjured 

12. Spiral: Fracture line has spiral shape as it encircles the bone 

13. Spontaneous: Fracture with no apparent traumatic cause 

14. Transverse: Fracture perpendicular to long axis of bone