Chapter 5 Skeletal System: Bones, Functions and Microscopic Anatomy
Skeletal System includes joints, bones, cartilage, ligaments The skeleton has two sub-divisions of 206 bones : Axial —forms the longitudinal axis of the skeleton Appendicular —forms the limbs and girdles
Axial Subdivision Think of a straight line down From the top of the head through the pelvis: --Head --Vertebrae --Ribcage
Appendicular Subdivision Think arms and legs
Functions of the Skeletal System Functions of the bones: Support Protection —protect soft organs Movements —bones are used as levers by muscles to move the body Storage —fat is stored in the internal cavities of bones Minerals are also stored : Calcium & Phosphorus Blood Cell Formation —Hematopoiesis occurs within marrow cavities
Shapes of Bones There are 4 distinct shapes of bones in the body: --Long --Short --Flat --Irregular
Long Bones typically longer than they are wide Mostly made up of compact bone Ex.) bones of the arm and leg
Short Bones cube shaped & mostly spongy bone Ex.) bones of the wrist and ankle
Flat Bones thin, flat and usually curved * 2 layers of compact bone, over 1 layer of spongy bone (Pelvis, Scapula, Cranium)
Irregular Bones Those bones that don’t fit into the other categories **Ex.) Vertbrae and Hip bones
Bone Tissue In the body, there are two forms of bone tissue: Compact Bone—Dense Tissue that smooth look Spongy Bone—Composed of small needlelike pieces of bone and space
Compact Bone
Spongy Bone
Bone Markings Bone Markings Bumps, holes and ridges on bone that serve a specific purpose 2 Categories 1.) Projections / Processes —grow out from the surface 2.) Depressions / Cavities —indentations into the bone
Structure of a Long Shaft Bone Diaphysis —Shaft of a long bone Epiphysis —the end of a long shaft bone Periosteum —connective tissue membrane covering the diaphysis shaft Sharpey’s Fibers —connect the periosteum to the diaphysis (acts as a glue to anchor the periosteum)
Structure of a Long Shaft Bone Articular Cartilage —covers the epiphysis surface provides a smooth slippery surface that decreases friction at joint surfaces Epiphyseal Line —found in adult bones, in the epiphysis Epiphyseal Plate —found in developing, young bones
Structure of a Long Shaft Bone Medullary Cavity —the central cavity of the long shaft of long bones Yellow marrow —storage area of fat in the cavity of the shaft in adults Red Marrow —forms red blood cells (in medullary cavity in young bones)
Microscopic Anatomy of the Bone Osteocytes —mature bone cells are found in lacuna Lacuna —tiny cavities found within the matrix Lamellae —concentric circles of matrix surrounding an artery and canal Haversian System (Osteon)—central canal + matrix rings Canaliculi —Radiating canals that connect all bone cells to the nutrient supply Volkmann’s Canals —run into the compact bone at right angles to the shaft