Chapter 6 The Skeletal System

FUNCTIONS OF THE SKELETAL SYSTEM Supports and gives shape to the body Protects internal organs Helps make movements possible Stores calcium Hemopoiesis, or blood cell formation

TYPES OF BONES Four major types, according to overall shape of the bone Long—Example: humerus (upper arm) Short—Example: carpals (wrist) Flat—Example: frontal (skull) Irregular—Example: vertebrae (spinal cord) Some also recognize a sesamoid (round) bone category Example: patella (kneecap)

STRUCTURE OF LONG BONES Structural components (Figure 6-1) Diaphysis or shaft—hollow tube of hard compact bone Medullary cavity—hollow area inside diaphysis bone that contains yellow marrow Epiphyses, or ends of the bone—spongy bone that contains red bone marrow Articular cartilage—covers epiphyses and functions as a cushion Periosteum—strong membrane covering bone everywhere except at joint surfaces Endosteum—lining of medullary cavity

MICROSCOPIC STRUCTURE OF BONE AND CARTILAGE Bone types (Figure 6-2) Spongy Texture results from needlelike threads of bone called trabeculae surrounded by a network of open spaces Found in epiphyses of bones Spaces contain red bone marrow Compact Structural unit is an osteon—calcified matrix arranged in multiple layers or rings called concentric lamella Composed of osteocytes, lacunae, and canaliculi Covered by periosteum

MICROSCOPIC STRUCTURE OF BONE AND CARTILAGE Cartilage (Figure 6-4) Cell type called chondrocyte Matrix is gel-like and lacks blood vessels

BONE FORMATION AND GROWTH (Figures 6-5 and 6-6) Early bone development (before birth) consists of cartilage and fibrous structures Cartilage models gradually replaced by calcified bone matrix—process called endochondral ossification Osteoblasts form new bone, and osteoclasts resorb bone

DIVISIONS OF SKELETON Skeleton composed of the following divisions and their subdivisions: Axial skeleton Skull Spine (vertebral column) Thorax Appendicular skeleton Upper extremities, including shoulder (pectoral) girdle Lower extremities, including hip (pelvic) girdle Location and description of bones—see Figures 6-7 to 6-17 and Tables 6-2 to 6-6