Skeletal System - Quick Reference

Skeletal System

Framework of the body; consists of bones and supporting tissues.

Axial Skeleton

One of the two primary divisions of the skeleton.

Appendicular Skeleton

One of the two primary divisions of the skeleton.

Functions of Bones

Support, protection, movement, storage (fat, calcium, phosphorus), and hematopoiesis.

Hematopoiesis

Blood cell formation, occurring in the marrow.

Number of Bones in Adults

206 bones.

Types of Osseous Tissue

Compact Bone and Spongy Bone.

Bone Shapes

4 shapes: Long, Short, Flat, Irregular.

Long Bones

Typically longer than wide; include shaft (diaphysis) and two ends (epiphyses/heads); mostly compact bone. Examples: limb bones (excluding patella, carpal, and tarsal bones).

Short Bones

Generally cube-shaped; mostly spongy bone. Examples: wrist and ankle bones; sesamoid bones (e.g., patella).

Flat Bones

Thin, flattened, curved; two thin layers of compact bone with a middle layer of spongy bone. Examples: most skull bones, ribs, sternum.

Irregular Bones

Do not fit into other categories. Examples: Vertebrae, Sacrum, Ethmoid, Sphenoid, Palatine, Temporal, Inferior nasal concha, Zygomatic, Hyoid, Maxilla, Mandible.

Diaphysis

The main length or shaft of a long bone; composed of compact bone.

Periosteum

Outer covering of the diaphysis; secured to bone by Sharpey's fibers.

Epiphyses

The ends (heads) of a long bone; thin layer of compact bone enclosing spongy bone.

Articular Cartilage

Hyaline cartilage covering the epiphyses; reduces friction at joints.

Epiphyseal Line

Remnant of the epiphyseal plate in adults; indicates where growth in length occurred.

Endosteum

Inner lining of the medullary (marrow) cavity of the shaft.

Medullary Cavity

Cavity within the diaphysis; contains yellow marrow (fat) in adults.