BONES AND BONE TISSUES

1. BONES AND BONE TISSUES CHAPTER 6 9/16/07

2. Introduction • One of the most remarkable tissues of the human body • Far from inert and lifeless, bones are living, dynamic structures • Bones serve a wide variety of very diverse functions within us • Noted for their strength and resiliency during life, bones will remain long after we are gone

3. Chapter Outline • Skeletal cartilages • Bones • Disorders of bones • The skeleton throughout life

4. Location and Basic Structure • Cartilages are found throughout the adult human body

5. Location and Basic Structure • Initially our skeleton is made up of fast growing cartilages and fibrous membranes • Gradually our skeletal cartilages are replaced by bone • Upon reaching adulthood the skeleton becomes almost fully ossified • Only a few cartilages remain in the adult skeleton

6. Location and Basic Structure • A typical cartilage is composed of connective tissue cartilage • It contains no nerves or blood vessels • It is surrounded by a layer of dense irregular connective tissue called the perichondrium which resists outward expansion of the tissue when subjected to pressure

7. Location and Basic Structure • Each type of cartilage contains a high proportion of water which makes them resilient after compression • Cartilage is 60-80% water • The water allows nutrients to diffuse rapidly through a loose matrix

8. Basic structure, type & location • There are three types of cartilage tissue: hyaline, elastic, and fibrocartilage • Each type consists of chondrocytes living in an extracellular matrix • Each contains a matrix of jellylike ground substance of complex sugar molecules that attract and hold water that is laced with connective tissue fibers

9. Hyaline cartilages • The most prevalent type of cartilage • Its high proportion of collagen fibers give it flexibility and resilience while providing support • Upon examination the tissue appears white, frosted, and smooth

10. Hyaline cartilages • The chondrocytes appear spherical • Each chondrocyte occupies a cavity in the matrix called a lacuna • The only type of fiber in the matrix is a collagen unit fibril

11. Hyaline cartilage locations • Articular - covers the end of bones • Costal - connect ribs to breastbone • Laryngeal - skeleton of larynx • Tracheal & bronchial - reinforce the respiratory passages • Fetal - forms the embryonic skeleton

12. Elastic cartilage • Elastic cartilage is similar to hyaline cartilage but its matrix contains many more elastic fibers in addition to collagen fibers • Its elastic fibers enable it to withstand repeated bending • Found only in the external ear and the epiglottis

13. Fibrocartilage • The tissue consists of parallel rows of thick collagen fibers alternating with rows of chondrocytes • Tissue is highly compressible and has great tensile strength • Found in thick pad-like structures like the menisci of the knee or the discs of the vertebral column

14. Growth of Cartilage • A cartilage grows in two ways • Appositional growth occurs when cells in the surrounding perichondrium secrete new matrix next to existing cartilage tissue (growth from the outside) • Interstitial growth occurs when the chondrocytes within the cartilage divide and secrete new matrix, expanding the cartilage (growth from within)

15. Growth of Cartilage • Cartilage stops growing in the late teens when the skeleton itself stops growing • Chondrocytes stop dividing and growth stops • Cartilage regenerates poorly in adults with most of the “healing” reflecting the ability of the remaining chondrocytes to secrete additional extracellular matrix

16. BONES SECTION II

17. Bones • Bones of the skeleton are organs that contain several different tissues • Bones are dominated by bone tissue but also contain • Nervous tissue and nerves • Blood tissue and vessels • Cartilage in articular cartilages • Epithelial tissue lining the blood vessels

18. Function of Bones: • Bones perform several important functions: • Support • Movement • Protection • Mineral storage • Blood cell formation and energy storage

19. Support Bones provide a hard framework that supports the body Bones provide support for internal organs Function of Bones

20. Movement Skeletal muscle attached to bones use the bones as levers to move the body Arrangement of bones and joints determine the movements possible Function of Bone

21. Protection Fused bones provide a brain case that protects this vital tissue Spinal cord is surrounded by vertebrae Rib cage protects vital organs Function of Bone

22. Mineral Storage Bone serves as a mineral reservoir Phosphate and calcium ions can be released into the blood steam for distribution Deposition and removal are ongoing Function of Bones

23. Blood cell formation Hematopoiesis occurs within the red marrow cavities of the long bones The yellow marrow cavities are involved in fat storage Function of Bones

24. CLASSIFICATION OF BONE SECTION III

25. Classification of Bone: • Bones vary in shape and size • The unique shape of each bone fulfills a particular need • Bones are classified by their shape as long, short, flat, or irregular bone • Bones differ in the distribution of compact and spongy osseous tissues

26. Classification of Bones

27. Classification:Long Bone • Long bones have a long shaft and two distinct ends • Classification is based on shape not size • Compact bone on exterior w/ spongy on the interior

28. Classification:Short Bones • Short bones are roughly cubelike • Thin compact bone layer surrounding spongy bone mass • Short bones are often carpal, tarsal and sesamoid bones

29. Classification:Flat Bones • Flat bones are thin, flattened and usually curved • Parallel layer of compact bone with spongy bone layer between • Skull, sternum and ribs are examples

30. Classification:Irregular Bone • Irregular bones don’t fit into the previous categories • Complicated shapes • Consist of spongy bone with a thin layer of compact • Examples are hip bones & vertebrae

31. Gross Anatomy of Bones SECTION IV

32. Gross Anatomy • Landmarks • Diaphysis • Proximal epiphysis • Distal epiphysis • Membranes • Periosteum • Endosteum

33. Diaphysis • Long tubular diaphysis is the shaft of the bone • Collar of compact bone surrounds a central medullary or marrow cavity • In adults, cavity contains fat

34. Epiphysis • The epiphyses are the ends of the bone • The joint surface of the epiphysis is covered with articular cartilage • Epiphyseal line separate diaphysis and epiphysis

35. Blood Vessels • Unlike cartilage bone is well vascularized • Nutrient arteries serve the diaphysis • The nutrient artery runs inward to supply the bone marrow and the spongy bony

36. Medullary cavity • The interior of all bones consists largely of spongy bone • The very center of the bone is an open or marrow cavity • The cavity is filled with yellow bone marrow

37. Membranes • Periosteum covers outer bone surfaces except the ends of the epiphysis • The membrane has two sublayers • Superficial layer • Osteogenic layer

38. Membranes • The superficial layer consists of dense irregular connective tissue which resists tension placed on a bone during bending • The osteogenic layer abuts the compact bone and contains bone-depositing cells called osteoblasts and osteoclasts that are responsible for bone remodeling

39. Membranes • During periods of bone growth or deposition the osteogenic cells differentiate into osteoblasts • Osteoblasts produce the bone tissue that forms the circumferential lamellae that encircle the perimeter of the bone

40. Membranes • Periosteum is richly supplied with nerves and blood vessels • The periosteum is supplied by branches of the nutrient artery and epiphyseal vessels

41. Membranes • The periosteum is secured to the underlying bone by perforating fibers (Sharpey’s fibers) • Thick bundles of collagen fibers run from the periosteum into the bone matrix

42. Membranes • Internal bone structures are covered by a thinner connective tissue membrane the endosteum • It also contains the osteoclasts and osteoblasts necessary for bone remodeling

43. Membranes • The endosteum covers the trabeculae of spongy bone and lines the central canals of osteons

44. Short, Irregular and Flat Bones • Bones consist of thin layers of compact bones over spongy bone • No shaft, epiphysis or marrow cavity • Spongy area between is a diploe • Flat sandwich of bone is common in bones of skull

45. Bone Design and Stress • The internal anatomy of each bone reflects the stresses most commonly placed upon it • Bones are subjected to compressive forces in weight bearing and tension forces when muscle pulls upon them • Often weight bearing loads are applied off center which threatened to bend the bone

46. Bone Design and Stress • Bending compresses the bone on one side and compresses it on the other • Compression and tension are greatest at the external surfaces of the bone

47. Bone Design and Stress • Compact bone occurs at the external surfaces to resist these tension and compression forces • Internal bone structures are not subjected to these forces and thus spongy bone is sufficient

48. Bone Design and Stress • As there are only limited tension and compression forces at the bone’s center the hollow medullary cavity does not impact a long bone’s weight bearing capacity

49. Bone Design and Stress • Spongy bone is not a random network of bone fragments • The trabeculae align along stress lines in an organized patterns of tiny struts that provide internal support for the bone

50. Bone Markings • Bones are shaped by the tissues that act upon and around them • Bones display bulges, depressions and holes which serve as sites of muscle, ligament and tendon attachment, points of articulation, or as conduits for blood vessels and nerves • Projections from the bone surface include heads, trochanters, spines, and others • Depressions include fossae, sinuses, foramina, and grooves