Chapter 5: The Skeletal System (Page 133 – 181)
Os-/osteo- : bone
Ortho-: joints/articulations
Skeletal System is divided into 2 divisions:
 Axial: skull, face, ribs, and back

Appendicular: shoulder, pelvis, arms, hands, legs, and feet
Skeletal system includes: Bones and …

Cartilage

Joints

Ligaments and tendons
…that provide flexibility, stabilize, or connect.
Five primary functions:
1. Blood cell production = Hematopoiesis
2. Protection
3. Levers for movement
4. Storage of minerals calcium and phosphorus AND storage of adipose tissue/fat
5. Framework/Support
Classification of Bones
206 bones in adult skeleton
 Based on composition
1. Compact: dense
2. Spongy: porous; holds red (blood) and yellow (adipose/fat) marrow

Base on Bone Shape
4 MAIN categories
 Long bone: longer than it is wide
Arms and legs, hands and feet
 Short bone: as long as it is wide
Wrists and ankles
 Flat bone: flat and slightly curved; good at offering protection
Skull and ribs
 Irregular bones: don’t fit in any other category
Vertebrae, face, pelvis
2 “other” categories
 Sutural bones: fill in gaps between bones of the skull during infancy
Soft spots on infant skull called FONTANELLES
 Sesamoid bones: bones buried inside a tendon; built in response to stress
Kneecaps (patella) are sesamoid bones

Structure of Long Bone
Diaphysis: shaft of the long bone; composed of COMPACT bone.
Compact bone is DENSE; tightly connected and filled with calcium.

Epiphysis: expanded area at ends of long bone; composed mainly of SPONGY bone.
Details: shape of the ends allows for different articulations between bones.
Epiphyseal Line: growth plate; area of new bone growth; made of cartilage.
Spongy bone is porous and allows for living bone marrow to fill in the spaces.

Medullary canal, AKA marrow cavity; contains: either red blood cell bone marrow or yellow
adipose/fat tissue marrow. Dependent on age. 0 – 20 years it is filled with RED MARROW
20 + years it is filled with YELLOW MARROW
Flat Bones
 Resembles a spongy bone sandwich. How?
Flat bones are composed of 2 layers of compact bone, one on the outer edge and one on the inner
edge with a layer of spongy bone in between. This structure allows for the bone to be molded to
a shape that satisfies the need for protection. Think of the shape of your skull and the way it
wraps around the brain. This “mold-ability” is due to the spongy bone layer in the center.