The Skeletal System

1. The Skeletal System Bones, joints, and connective tissues

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

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

4. 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

5. 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)

6. Types of Bones (see figure 6.2 pg.178)

7. 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

8. 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

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

10. 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 - Ca3(PO4)2 aka calcium phosphate • Responsible for hardness of bone

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

12. 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)

13. 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)

14. 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

15. 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

16. 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

17. 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

18. 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)

19. What is a joint? • Area where two bones meet

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

21. 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)

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

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

24. Synovial joint movements and types of synovial joints Movements allowed by synovial joints • See pages 260-263 Types of Synovial joints • Plane, pivot, hinge, condyloid, saddle, ball-and-socket • See pages 264-265

25. Synovial Joints - a type of diarthrotic joint

26. 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

27. Synovial joint movements and types of synovial joints Movements allowed by synovial joints • See pages 260-263 Types of Synovial joints • Plane, pivot, hinge, condyloid, saddle, ball-and-socket • See pages 264-265