SKELETAL SYSTEM

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

OSSEOUS C.T. Compact (dense) Bone -Hard & heavy -Forms surface & diaphysis -Osteons = building blocks Cancellous (spongy) Bone -Lightweight -Fills epiphyses, Contains red marrow -Trabeculae = building blocks Matrix -Mineral Salts (hardness) -Collagen (strong & flexible)

Two Types of Bone

Compact Bone

Spongy 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 Remodeling

Osteoblasts & Osteocytes

Osteoclast

SKELETAL DIVISIONS Axial Appendicular

Classification: Shape & Location Long Short Flat Irregular Sesamoid (develop in tendons; patella) Sutural (between cranial bones)

Torus Bones

LONG BONE ANATOMY Diaphysis = shaft made of compact bone Epiphyses = ends filled with spongy bone containing red marrow Articular cartilage covers epiphyses Epiphyseal line indicates earlier location of epiphyseal (growth) plate

LONG BONE ANATOMY Periosteum is C.T. covering bone Nutrient Foramina – holes allowing for penetration of arteries Medullary cavity contains yellow marrow Endosteum is C.T. lining medullary cavity

BONE DEVELOPMENT Ossification = replacement of other connective tissue with bone Begins during the 2 nd month of gestation Size increases until late teens (females) to mid-twenties (males) Ossification processes include: -Intramembranous bone formation -Endochondral bone formation

INTRAMEMBRANOUS OSSIFICATION Occurs in flat bones of skull, clavicles, mandible Begins with fibrous C.T. membrane Membrane calcifies & ossifies into bone Fontanels -“Soft spot”, not yet ossified -Allows for birth & brain growth

Process of Intramembranous Ossification Embryonic C.T. cells cluster & differentiate Osteoblasts form & produce matrix = ossification center Newly formed matrix calcifies Osteocytes form

Process of Intramembranous Ossification Trabeculae form; periosteum forms from surrounding condensed embryonic C.T. Surface trabeculae fill with matrix, forming compact bone

ENDOCHONDRAL OSSIFICATION Occurs in remainder of skeleton Begins with hyaline cartilage model Cartilage is replaced by bony tissue Steps include: -Bone collar forms -Cartilage in shaft calcifies -Primary Ossification center forms in shaft -Secondary Ossification centers in epiphyses

THE PROCESS OF ENDOCHONDRAL BONE FORMATION FORMATION OF BONE COLLAR -Cartilage model is covered by perichondrium -Cells in perichondrium become osteoblasts & secrete bony matrix -Perichondrium becomes periosteum -A “collar” of bone is produced around the diaphysis

Formation of Bone Collar & Primary Ossification Center

Formation of Secondary Ossification Centers

Epiphyseal Plates & Articular Cartilage

APPOSITIONAL GROWTH Bone Widens Osteoclasts enlarge medullary cavity Osteoblasts add bone to surface of diaphysis

BONE REMODELING Replacement of old bone with new bone Involves resorption (osteoclasts) & deposition (osteoblasts) Alters bone shape in response to stress Benefits: -Allows for growth -Removes injured bone -New bone is more resistant to fracture

FRACTURES AND THEIR REPAIR Definition: Any break in a bone Repair may take months Requires: -Adequate minerals -Vitamins -Hormones -Weight-bearing exercise

STEPS IN FRACTURE REPAIR Broken blood vessels form a hematoma (blood clot) C.T. and Capillaries invade site; C.T. cells form fibrocartilage callus Bony callus of spongy bone replaces fibrocartilage callus Bony callus is remodeled

Types of Fractures Open (Compound) – Broken bone ends protrude through the skin Closed (Simple) – Bone does not penetrate the skin

Types of Fractures Comminuted – splintered, crushed; small pieces between broken ends. Elderly. Most difficult to treat. Greenstick – Partial fracture; one side breaks, other side bends. Children.

Types of Fractures Impacted – One end of fractured bone forcefully driven into other end Spiral – fracture spirals around long bone axis from twisting force

Types of Fractures Pott’s – distal end of fibula, tibia or both Colles’ – distal end of radius

Types of Fractures Stress Fracture -Fracture without visible break -Microscopic fissures -No apparent damage to surrounding tissues -Result from repeated, strenuous activities -Can result from reduced calcium deposition in disease -25% involve tibia

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

CLASSIFICATION OF JOINTS Structural -Based on what tissues or structures are found between the bones -Fibrous, Cartilagenous, Synovial Functional -Based on amount of movement (& amount of movement is determined by structures found between bones) -Freely movable, Slightly movable, Immovable

ARTICULATIONS: CLASSIFICATION BY STRUCTURE

ARTICULATIONS: CLASSIFICATION BY FUNCTION

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 – covers bone ends Synovial membrane – lines joint capsule Synovial fluid – lubricates & nourishes cartilage Synovial cavity – space between the bones 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