SKELETAL SYSTEM

SKELETAL SYSTEM FUNCTIONS Support (Primary function) Movement (Passive) Protection of Vital Organs Mineral Storage Blood Cell Formation (Hematopoiesis or Hemopoiesis)

OSSEOUS TISSUE Cancellous (spongy) Bone Compact (dense) Bone Bone Cells -Osteoblasts – Secrete to form bone -Osteocytes *Mature bone cells *“Trapped” osteoblasts -Osteoclasts – destroy bone *Enzymes digest protein *Acids dissolve minerals *Forms Marrow Cavity; Involved in Remodelling

CANCELLOUS OR SPONGY BONE -Open spaces, light weight -Lattice arrangement -Made of microscopic trabeculae subunits -Location of bone marrow -Site of blood cell formation (red marrow) -Within epiphyses of long bones

COMPACT OR DENSE BONE -Dense, Ivory-like -Forms the outside layer of bones -Forms Diaphyses of long bones -Made of microscopic osteon (Haversian system) subunits

Axial skeleton Appendicular skeleton STRUCTURAL CLASSIFICATION: APPENDICULAR AND AXIAL

STRUCTURAL CLASSIFICATION BASED ON BONE SHAPE

Long Bone Irregular Bone Flat Bone Short Bones STRUCTURAL CLASSIFICATION BASED ON TYPE OF BONE

ANATOMY OF A LONG BONE Periosteum Epiphysis Diaphysis Compact bone Spongy bone Medullary cavity Endosteum Nutrient foramen Epiphyseal line Epiphysis Diaphysis Spongy bone Compact bone Medullary cavity Epiphyseal line

BONE DEVELOPMENT Ossification = replacement of other tissues with bone Begins about the 6th week of gestation Size increases until late teens (females) to mid-twenties (males) Requires Ca 2+ Ossification processes include: -Intramembranous bone formation -Endochondral bone formation

GENERAL FEATURES OF INTRA- MEMBRANOUS BONE FORMATION *Occurs in flat bones of skull, clavicles *Begins with collagenous fiber membrane model *Membrane calcifies into compact bone *Fontanels (“Soft spot”, not yet ossified)

THE PROCESS OF INTRA- MEMBRANOUS BONE FORMATION *C.T. Cells cluster & centers of ossification appear *Cells differentiate into osteoblasts *Osteoblasts secrete a matrix, forming trabeculae *Calcium salts are deposited

*Trabeculae fuse into spongy bone lattice *Lattice fills with red bone marrow *Eventually, peripheral trabeculae thicken into compact bone (periosteal ossification) THE PROCESS OF INTRA- MEMBRANOUS BONE FORMATION CONTINUED

*Occurs in remainder of skeleton *Begins with hyaline cartilage model *Cartilage is replaced by bony tissue GENERAL FEATURES OF ENDOCHONDRAL BONE FORMATION

THE PROCESS OF ENDOCHONDRAL BONE FORMATION FORMATION OF BONE COLLAR -Cartilage model is covered by perichondrium -Perichondrium becomes periosteum -A “collar” of bone is produced around the diaphysis

THE PROCESS OF ENDOCHONDRAL BONE FORMATION CALCIFICATION OF DIAPHYSEAL CARTILAGE -Hypertrophy of chondrocytes -Surrounding matrix calcifies -Diffusion disabled, chondrocytes die -Cartilaginous matrix disintegrates

THE PROCESS OF ENDOCHONDRAL BONE FORMATION CONTINUED FORMATION OF PRIMARY OSSIFICATION CENTER -Diaphysis penetrated by blood vessels, osteoblasts, osteoclasts -Marrow cavity formed by osteoclasts -Trabeculae form (Spongy bone) -Cartilage model grows at ends, elongating bone

THE PROCESS OF ENDOCHONDRAL BONE FORMATION CONTINUED FORMATION OF SECONDARY CENTER OF OSSIFICATION -Blood vessels reach epiphyses -Secondary ossification centers develop -Spongy bone is formed -Cartilage is replaced by bone, except at articular surfaces -Cartilage remains at epiphyseal plate (metaphysis) until growth is complete

FRACTURES AND THEIR REPAIR Definition: Any break in a bone Repair may take months Types include -Simple (skin not broken) -Compound (bone protrudes through skin) -Greenstick (shaft bent/broken) -Spiral (twisting force, ragged break) -Comminuted (shattered into fragments)

STEPS IN FRACTURE REPAIR -Broken blood vessels form a fracture hematoma -C.T. and Capillaries invade site, form fibrocartilage callus -Repair cells (osteoblasts) are activated in about 48 hours -Bony callus replaces fibrocartilage callus -Bony callus is remodeled by osteoclasts

BONES AS LEVERS Lever: A rigid rod that moves about a fixed point Fulcrum: The fixed point around which a lever moves (joints) Forces: Act to move levers at two points -Resistance: Force to be overcome -Effort or Work: Force required to overcome resistance; supplied by skeletal muscles

CLASSES OF LEVERS First Class: The fulcrum is between the effort/force and the resistance -Seesaw -Tilting head backward

FIRST CLASS LEVER F R E R E R E R E R E R E R E

CLASSES OF LEVERS CONTINUED Second Class: Resistance is between the fulcrum and the effort/force -Wheelbarrow -Rising up on one’s toes

SECOND CLASS LEVER F R E R E R E R E R E R E R E R E

Third Class: The effort/force is between the fulcrum and the resistance -Most common type in the human body -Flexing the elbow CLASSES OF LEVERS CONTINUED

THIRD CLASS LEVER F R E R E R E R E R E E R R E R E

ARTICULATIONS: CLASSIFICATION BY FUNCTION

ARTICULATIONS: CLASSIFICATION BY STRUCTURE

ARTICULATIONS: EXAMPLES Sutures Functional: Synarthrosis Structural: Fibrous Knee Functional: Diarthrosis Structural: Synovial Pubic symphysis Functional: Amphiarthrosis Structural: Cartilagenous

STRUCTURE OF A SYNOVIAL JOINT Articular cartilage – cover bone ends Synovial membrane – lines joint capsule Synovial fluid – lubricates & nourishes cartilage Synovial cavity Joint capsule – fibrous C.T. Ligaments – reinforce joint Bursae – synovial sacs at other sites of friction

TYPES OF SYNOVIAL JOINTS Classified based on shape of articular surfaces Gliding (plane) Hinge Pivot Ellipsoidal (condyloid) Saddle Ball-and-socket