1. CHAPTER 6

2.  Babies have ~ 300 bones  Adults have ~ 206 bones  Humans and Giraffes have the same # of bones in the neck  Longest bone = femur  Smallest bone = inner ear

3. 1. Support – structural framework 2. Protection of internal organs 3. Blood Cell Production (hematopoiesis) 4. Movement – skeletal muscle attaches to bone 5. Mineral Homeostasis (calcium and phosphorous)

4. 2 main divisions of the skeletal system 1. Axial skeleton (head, neck, trunk) – 80 bones 2. Appendicular skeleton (limbs) – 126 bones USE TEXTBOOK TO LABEL SKELETONS IN PACKET

5. 1. Long bones (bones of arms and legs) 2. Short bones (bones of wrist and ankle) 3. Flat bones (skull, ribs, shoulder blades) 4. Irregular bones (vertebrae)

7.  Diaphysis: central shaft  Epiphysis: forms joint with another bone  Articular Cartilage (Hyaline)  Medullary cavity: Hollow chamber filled with bone marrow  Periosteum: Covers outside of bone  Endosteum: Lines medullary cavity

8. Bone Tissue types 1. Compact Bone ▪ Solid ▪ Forms the diaphysis of long bones ▪ Contains yellow marrow 2. Spongy Bone (Cancellous bone) ▪ Resembles a network of bony rods separated by spaces ▪ Fills the epiphysis of long bones ▪ Contains red marrow ▪ Reduces the weight of the skeleton

9. Coverings 1. Periosteum ▪ Outer surface of bone ▪ Tendons and ligaments fuse to connect muscles and bones ▪ Isolates bone from other bone ▪ Provides route for vessels and nerves ▪ Participates in growth and repair 2. Endostium ▪ Lines marrow cavity ▪ Active only during growth and repair

10. Cells 1. Osteocytes ▪ mature bone cells ▪ Exchange nutrients and wastes with blood 2. Osteoclasts – (clast = break) ▪ Release enzymes to dissolve bone matrix 3. Osteoblasts (blast = precursor) ▪ Produce new bone

11. Bone Matrix (secreted by osteocytes) 1. Organic Components (33.3%) ▪ Collagen fibers provide resilience against stretching and twisting 2. Inorganic components (66.7%) ▪ Mg, F, Na, Ca, P ▪ Hydroxyapatite (calcium phosphate and calcium hydroxide) ▪ Provide hardness and resist compression

12. Other Features 1. Lacunae ▪ Small pockets which house osteocytes 2. Lamellae = “thin plates” ▪ Sheets of calcified matrix 3. Canaliculi = “small channels” ▪ Connect lacunae with blood vessels

13. Features specific to compact bone 1. Osteon (Haversion System) ▪ Basic functional unit of compact bone ▪ Osteocytes arranged in concentric layers 2. Central canal ▪ Houses blood vessels 3. Perforating Channels (Volkmann’s Canals) ▪ Link blood vessels of the central canal with the periosteum and marrow cavity

14. Organization of OSTEON  Central (haversion) canals run the length of the bone  Adjacent Haversion canals are connected via Volkmann’s canals  Around the central canals are concentric lamellae  Between the lamellae are spaces called lacunae  Lacunae contain osteocytes  Lacunae are connected in all directions via canaliculi

15. Features specific to spongy bone 1. trabeculae ▪ Support and protect the cells of red bone marrow, important for blood formation

16. COMPACT BONE

17. COMPACT BONE

18. COMPACT BONE

19.  SPONGY BONE

21.  Ossification = the process of replacing other tissues with bone  Skeleton begins as cartilage  Calcification = the deposition of calcium salts  Occurs during ossification but can also occur in other tissues besides bone  Bone Formation occurs in 3 situations 1. Growth during development 2. Remodeling of bones 3. Repair of fractures

22. 1. Intramembranous ossification – continues to age 2 ▪ Flat bones of the skull. Lower jaw and collar bones ▪ Bone develops from fibrous connective tissue ▪ Ossification center = where bone growth begins ▪ Growth is outward from the center

23. Intramembranous ossification

24. 2. Endochondral ossification – continues to age 25 ▪ “inside” “cartilage” ▪ Most bones of the body grow this way ▪ Bone develops from hyaline cartilage 1.Chondrocytes enlarge, calcify and differentiate into osteoblasts 2.Osteoblasts form spongy bone at the diaphysis (primary ossification center) 3.Growth continues outward in both directions 4.Secondary ossification center at epiphysis

25. Endochondral ossification

26. Growth During puberty:  Sex hormones speed up osteoblast activity = rapid growth  Epihyseal cartilage completely replaced with bone  Epiphyseal line = former location of epiphyseal cartilage; still evident by X-Ray through adulthood  Appositional Growth continues (increase in diameter)

27.  Ongoing replacement of old bone with new bone  Due to the action of osteoclasts (breakdown of bone) and osteoblasts (building of bone)

28. 1. Fracture hematoma – blood leaks from broken blood vessels in bone 2. Callus Formation – fibroblasts invade the tissue and produce collagen fibers 3. Bony Callus Formation – osteoblasts begin to build spongy bone 4. Bone remodeling – compact bone replaces spongy bone

31.  Calcium = most abundant mineral in the body  Stored in skeleton (bone matrix)  Necessary for muscle and nerve  Tightly regulated

32.  When blood calcium is low  Parathyroid hormone (PTH)  increases activity of osteoclasts (bone breakers)  decreases activity of osteoblasts (bone builders)  stimulates calcitrol, a hormone that promotes absorption of calcium from food  Elevates blood Ca2+

33.  When blood calcium is high  Calcitonin (CT)  stimulates osteoblasts (bone builders)  inhibits osteoclasts (bone breakers)  promotes bone formation  decreases blood Ca 2+  Decreases blood Ca 2+

34.  Calcium Regulation

35.  Minerals, especially calcium and phosphate  Vitamin D3 stimulates absorption of calcium  Rickets – vitamin D3 deficiency – causes bone to soften  Vitamin A stimulates osteoblasts  Vitamin C for synthesis of collagen  Scurvy – vitamin - C deficiency

37.  Process = bony projection or bump  Ramus = curved portion of a bone (ram’s horn)

38.  Trochanter = large rough projection  Tuberosity = small rough projection  Tubercle = small rounded projection  Crest = prominent ridge  Line = low ridge  Spine = pointed process

39.  Head = epiphysis  Neck = connection between epiphysis and diaphysis  Condyle = smooth, rounded bump that forms joint with another bone  Trochlea = small, grooved pulley shaped process  Facet = small flat articular surface

40.  Fossa = shallow groove or depression  Sulcus = narrow grove

41.  Foramen = rounded passageway for blood vessels and nerves  Canal or Meatus = passageway through bone  Fissure = elongated cleft  Sinus = chamber within bone usually filled with air