The Skeletal System Bones, joints, and connective tissues

Skeletal System Functions Support Protection of organs Framework for movement Mineral storage (calcium & phosphate) Hematopoiesis (Blood cell production in bone marrow)

Axial vs. Appendicular Skeleton Axial: Skull, rib cage, vertebrae Appendicular: Limbs and girdles (shoulder, pelvic)

Skeletal cartilage Properties of cartilage: Made of mostly water Contains cells called chondrocytes Avascular and has no nerve endings (heals very slowly) Stops growing during adolescence (deteriorates from this point on) 3 different types

Types of Cartilage (see figure 6.1) Fibrocartilage - resists very high compression forces (in knee and between vertebrae) Hyaline - Most common 1) articular - at joints 2) costal - (connect ribs to sternum) 3) respiratory - larynx and trachea 4) nasal Elastic - least common type - very flexible (external ear and epiglottis)

Types of Bones (see figure 6.2 pg.178)

Structure of a Long Bone Epiphyses - end of long bone Diaphysis - shaft Articular cartilage - covers epiphyses (provides cushion and lubrication at joints) Periosteum - double membrane surrounding bone Endosteum - lines inner cavities of bone

Structure of a Long Bone Medullary cavity - contains bone marrow Spongy (trabecular) bone - contains red marrow (found in epiphyses) Compact (cortical) bone - found in diaphysis Epiphyseal plate - hyaline cartilage from which bone growth occurs in childhood and adolescence

Microscopic Anatomy of Compact Bone (see Figure 6.6 on pg.183) Haversian Canal

Chemical Composition of Bone Organic component (35%): bone cells and osteoid Osteoid - secreted by osteoblasts (most collagen as well as other protein compounds) Responsible for bone flexibility Inorganic component (65%): mineral component Hydroxyapatites - Ca 3 (PO 4 ) 2 aka calcium phosphate Responsible for hardness of bone

Cell Types Osteoblasts - bone building cells Osteoclasts - resorb (break down) bone (secrete HCl) Osteocytes - mature bone cells (maintain bone matrix)

What is Ossification? Ossification (also osteogenesis) means “bone formation” Starts before birth and extends throughout life Types: - intramembranous ossification (forms bones of the skull as well as clavicles) - endochondral ossification (forms all bones below the skull and clavicles)

Endochondral Ossification Replacement of hyaline cartilage with bone - see Figure 6.8 on pg 185 Ossification begins in the middle of the bone (primary ossification center) At birth, epiphyses remain mostly cartilaginous By early childhood, hyaline cartilage only remains in the epiphyseal plate and covering the epipyses (articular cartilage)

Post-natal Bone Growth Growth occurs from the epiphyseal plate (see left side of Figure 6.10 on pg.187) Diaphysis also increases in width as bone lengthens (gives bone more stability) Regulated by growth hormone (hGH) in childhood Growth spurt in teen years cause by androgens (sex hormones): testosterone (males) estrogen (females) Bone growth at epipyseal plate

Post-natal Bone Growth After epiphyseal plate has completely ossified, bones can only grow in width (appositional growth) Bone remodeling occurs throughout life Bone deposit (osteoblasts) and bone resorption (osteoclasts) balance each other out in healthy young adults See right side of Figure 6.10 on pg 187 Bone growth at epipyseal plate

Bone Remodeling Bone deposit and bone resorption of the adult skeleton Occurs to prevent bones from becoming brittle Spongy bone is replaced every 3-4 years; compact every 10 years

Control of Bone Remodeling Mechanical stress weight bearing activity leads to bone deposit to strengthen areas most in need (Wolff’s Law) Hormonal control (see figure 6.12 on pg. 189) Calcitonin - stimulates bone deposit Parathyroid hormone (PTH) - stimulates bone resorption

Types of fractures (pg.191) Nondisplaced vs. displaced Complete vs. incomplete Linear vs. transverse Open (compound) vs. closed (simple) * Fractures are treated with closed reduction (hands are used to align bone ends) or open reduction (screws, rods, wires, etc are used to keep bone ends together)

What is a joint? Area where two bones meet

Ligaments and Tendons Ligaments Connect two bones together at a joint Tendons Connect muscles to bones

Joint Classification (structural) fibrous - bone ends joined by fibrous tissue (ex. Sutures in skull, teeth in sockets) cartilaginous - bone ends joined by cartilage (ex. Vertebral joints, pubic symphysis) synovial - bone ends covered by cartilage and surrounded by a fluid filled joint capsule lined with a membrane (all joints of the limbs and most joints in the body)

Joint Classification (functional) Synarthroses - immovable joints (ex. Sutures in skull) Amphiarthroses - slightly movable (ex. Vertebral joints) Diarthroses - movable (most joints)

Joint Classification (functional) Synarthroses - immovable joints (ex. Sutures in skull) Amphiarthroses - slightly movable (ex. Vertebral joints) Diarthroses - movable (most joints)

Synovial joint movements and types of synovial joints Movements allowed by synovial joints See pages Types of Synovial joints Plane, pivot, hinge, condyloid, saddle, ball-and-socket See pages

Synovial Joints - a type of diarthrotic joint

Bursae and Tendon Sheaths Function to reduce friction during joint movement Bursae are fluid filled sacs found where ligaments, muscles, tendons, skin, and bones rub together. Tendon sheaths wrap around tendons that are subjected to friction

Synovial joint movements and types of synovial joints Movements allowed by synovial joints See pages Types of Synovial joints Plane, pivot, hinge, condyloid, saddle, ball-and-socket See pages