Bones and Skeletal Tissues: Structure and Function

1. Bell Work!!! (5 Minutes from the bell!!) Look at the pictures above, do you think these two people have the same number of bones, or does one have more than the other? If different, who has more? Are bones a living tissue or merely a non-living collection of minerals to support/protect our other organ systems? Support your answer.

2. Bones and Skeletal Tissues Part A

3. Skeletal Cartilages • Consist primarily of water this is what allows it to spring back to its original shape after being compressed. • Contain no blood vessels or nerves • Surrounded by dense irregular connective tissue, the perichondrium • contains blood vessels for nutrient delivery to cartilage • acts as a girdle to resist outward expansion

4. Skeletal Cartilages • Hyaline cartilages • Provide support, flexibility, and resilience • Most abundant type • Elastic cartilages • Similar to hyaline cartilages, but contain more stretchy elastic fibers • Better able to stand up to repeated bending • Only found in the external ear and the epiglottis • Fibrocartilages • Collagen fibers—have great tensile strength • Areas subjected to heavy pressure and stretch- menisci (knee)

5. Epiglottis Larynx Thyroid cartilage Cartilage in external ear Cartilages in nose Trachea Cricoid cartilage Lung Articular Cartilage of a joint Cartilage in Intervertebraldisc Costal cartilage Respiratory tube cartilages in neck and thorax Bones of skeleton Pubic symphysis Axial skeleton Meniscus (padlike cartilage in knee joint) Appendicular skeleton Cartilages Articular cartilage of a joint Hyaline cartilages Elastic cartilages Fibrocartilages Figure 6.1

6. Growth of Cartilage • Cartilage grows in two ways: • Appositional “growth from the outside” • Cells secrete matrix against the external face of existing cartilage • Interstitial “growth from the inside” • Chondrocytes divide and secrete new matrix, expanding cartilage from within • Under certain conditions calcification of cartilage (calcium salts are deposited in the matrix) occurs during • Normal bone growth • Old age • THIS IS NOT BONE 2 separate tissues!

7. Regions of the Skeleton • Two main groups, by location • Axial skeleton (brown) • Skull, vertebral column, and rib cage • Appendicular skeleton (yellow) • Bones of the upper and lower limbs and the girdles. Figure 6.1

8. Classification of Bones by Shape • Long bones • Longer than they are wide • All limb bones except the patella, wrist, and ankle bone are long bones. • Short bones • Cube-shaped bones (in wrist and ankle) • Sesamoid bones (within tendons  patella)

9. Classification of Bones by Shape • Flat bones • Thin, flat, slightly curved • Sternum, scapulae, ribs, and most skull bones • Irregular bones • Complicated shapes that fit none of the other classes • Vertebrae and hip bones

10. Bell Work!!! (5 Minutes from the bell!!) • What are the 2 divisions of the human skeleton? • What are the 4 classifications of bone shape? • 6 functions of Bones?

11. Functions of Bones • Support • For the body and soft organs (framework) • Protection • For brain, spinal cord, and vital organs • Movement • Levers for muscle action muscles use bones as levers to move the body.

12. Functions of Bones • Storage • Minerals (calcium and phosphorus) and growth factors • Blood cell formation (hematopoiesis) in marrow cavities • Triglyceride (energy) storage in bone cavities

13. Bone Markings • Bulges, depressions, and holes serve as • Sites of attachment for muscles, ligaments, and tendons • Joint surfaces • Channels for blood vessels and nerves

14. Bone Markings: Projections Table 6.1

15. Bone Markings: Projections • Projections (grow outward from bone surface) that help to form joints

16. Bone Markings: Depressions and Openings

17. Bone Textures • Compact bone • Dense outer layer that looks smooth and solid • Spongy bone • Honeycomb of trabeculae internal layer filled with bone marrow

18. Structure of a Long Bone • Diaphysis (shaft) • Forms the long axis of the bone • Constructed from a thick compact bone collar that surrounds a central medullary (marrow) cavity • Medullary cavity in adults contains fat (yellow marrow)

19. Structure of a Long Bone • Epiphyses • Bone ends • Compact bone exterior & spongy bone interior • Epiphyseal line • remnant of growth plate- a disc of hyaline cartilage that grows during childhood to lengthen the bone • Articular (hyaline) cartilage on joint surfaces

20. Articular cartilage Compact bone Proximal epiphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) (b) Diaphysis Distal epiphysis (a) Figure 6.3a-b

21. Membranes of Bone • Periosteum • Covers the entire external surface of bones • Outer fibrous layer dense irregular connective tissue • Inner osteogeniclayer mainly bone forming cells • Nerve fibers, nutrient blood vessels, and lymphatic vessels enter the bone via nutrient foramina • Secured to underlying bone by perforating “Sharpey’s” fibers • Tufts if collagen fibers that extend from the fibrous layer into the bone matrix

22. Membranes of Bone • Endosteum • Delicate connective tissue membrane on internal surfaces of bone • Covers the trabeculae of spongy bone and lines the canals that pass through compact bone • Also contains osteoblasts and osteoclasts

23. Structure of Short, Irregular, and Flat Bones • All consist of: • Periosteum-covered compact bone on the outside • Endosteum-covered spongy bone within • Spongy bone called diploë in flat bones • Bone marrow between the trabeculae

24. Location of Hematopoietic Tissue (Red Marrow) • Red marrow cavities of adults • Trabecular cavities of the heads of the femur and humerus • Trabecular cavities of the diploë of flat bones • In most adult long bones the fat containing medullary cavity extends well into the epiphysis and little red marrow is present  blood cell production occurs in the heads of the femur (thigh bone) and humerus (long bone of arm) • The red marrow found in the diploë of flat bones (sternum) or some irregular bone (hip) is much more active in hematopoiesis and these sites are routinely used for obtaining bone marrow biopsies when problems with blood forming tissue are suspected. • Red marrow of newborn infants • Medullary cavities and all spaces in spongy bone

25. Microscopic Anatomy of Bone • Cells of bones • Osteogenic cells • Stem cells in periosteum and endosteum that give rise to osteoblasts • Osteoblasts • Bone-forming cells • Osteocytes • Mature bone cells • Osteoclasts • Cells that break down bone matrix

26. Microscopic Anatomy of Bone: Compact Bone • Although compact bone looks solid it is riddled with passageways for nerves, blood vessels, and lymphatic vessels • Osteons—structural units • “Tiny pillars” • Lamellae • Weight-bearing • Column-like matrix tubes • Haversiancanal • Contains blood vessels and nerves

27. Microscopic Anatomy of Bone: Compact Bone • Perforating (Volkmann’s) canals • At right angles to the central canal • Connects blood vessels and nerves of the periosteum and central canal • Lacunae—small cavities that contain osteocytes • Canaliculi—hairlike canals that connect lacunae to each other and the central canal

28. Microscopic Anatomy of Bone: Spongy Bone • Trabeculae • Align along lines of stress • No osteons • Contain irregularly arranged lamellae, osteocytes, and canaliculi • Capillaries in endosteum supply nutrients

29. Chemical Composition of Bone: Organic • Osteogenic cells, osteoblasts, osteocytes, osteoclasts • Osteoid—organic bone matrix secreted by osteoblasts • Ground substance (proteoglycans, glycoproteins) • Collagen fibers • Provide strength and flexibility

30. Chemical Composition of Bone: Inorganic • Hydroxyapatites (mineral salts) • Tiny, tightly packed crystals in and around the collagen fibers in the extracellular matrix • 65% of bone by mass • Mainly calcium phosphate crystals • Responsible for hardness and resistance to compression