Bones and Skeletal Tissues

1. 6 Bones and Skeletal Tissues

3. I. Cartilage • A. Found throughout adult body • 1. external ear • 2. nose • 3. articular (joints) cartilages and costal cartilage • 4. cartilages in the: • a. larynx and trachea • b. intervertebral discs • c. pubic symphysis • d. articular discs

4. B. Perichondrium • 1. surrounds cartilages • 2. resists outward pressure • 3. functions in growth and repair of cartilage • 4. consists primarily of water • 5. is a resilient tissue • 6. springs back to original shape

5. II. Types of Cartilage • A. Hyaline cartilage • 1. most abundant cartilage • 2. chondrocytes appear spherical • 3. collagen unit fibril is the only type of fiber in the matrix • 4. ground substance holds a large amount of water • 5. provides support through flexibility • 6. Locations – surface of bones at joints

6. B. Elastic cartilage • 1. Contains many elastic fibers • 2. Able to tolerate repeated bending • 3. Locations—epiglottis and cartilage of external ear • C. Fibrocartilage • 1. resists strong compression and strong tension • 2. an intermediate between hyaline and elastic cartilage • 3. Locations—pubic symphysis, anulus fibrosus

7. Flat bone(sternum) Long bone(humerus) Irregular bone(vertebra), rightlateral view Short bone(talus)

8. Chondrocyte in a lacuna Chondrocyte in a lacuna Matrix Elastic fibers Lacuna Gelatinousground substance Perichondrium Hyaline cartilage (260) Elastic cartilage (350) Chondrocyte in a lacuna Collagenfibers Fibrocartilage (320)

9. III. Growth of Cartilage • A. Appositional growth • 1. chondroblasts - produce new cartilage • B. Interstitial growth • 1. chondrocytesdivide and secrete new matrix • 2. stops growing when the skeleton stops growing

10. IV. Tissues in Bone A. bones contain several types of tissues B. dominated by bone connective tissue C. contain nervous tissue and blood connective tissue D. contain cartilage in articular cartilages E. contain epithelial tissue lining blood vessels

11. VI. Bone Tissue A. organic components = cells, fibers, and ground substance B. inorganic components = mineral salts (Calcium Phosphate) C. Extracellular Matrix 1. unique composition of matrix 2. gives bone exceptional properties 3. 35%—organic components a. contribute to flexibility and tensile strength 4. 65%—inorganic components a. exceptional hardness, resist compression

12. D. Cells • 1. osteogenic cells - stem cells - differentiate into osteoblasts • 2. osteoblasts - produce and secrete bone matrix (osteoid) • 3. osteocytes - keep bone matrix healthy; primary cell in bone • 4. osteoclasts – chew up old bone during remodeling • a. responsible for resorption of bone • b. are derived from a line of white blood cells • c. Secrete hydrochloric acid and lysosomal enzymes

13. VII. Classification of Bones A. Long bones - longer than wide; a shaft plus ends example: femur and humerus B. Short bones - roughly cube-shaped example: carpals C. Flat bones - thin and flattened, usually curved example: frontal bone of cranium D. Irregular bones - various shapes example: vertebra

14. VIII. Bone Markings Depressions and Openings A. fissure - cleft-like opening between adjacent parts of bones through which vessels & nerves pass B. foramen - hole through which blood vessels, nerves, ligaments can pass C. meatus - tunnel-like passageway through a bone D. sinus - cavity within a bone with narrow opening E. sulcus - groove or depression for vessels, nerve, tendon F. fossa - depression in/on a bone; generally at a joint G. process - prominent projection or point of attachment

15. Articular Processes (of the joints) H. condyle - large, rounded articular (joint) prominence I. head - rounded projection supported by a cylinder of a bone (neck) J. facet - smooth, flat surface on a bone

16. Processes for Attachment (tendons, ligaments, etc.) K. tubercle - small, rounded process L. tuberosity - large, rounded, usually rough process M. trochanter - large, blunt projection (only on the femur) N. line - less prominent ridge than a crest O. spine - sharp, slender process P. epicondyle - prominence found "above" a condyle

17. IX. Gross Anatomy of Bones • A. Compact bone - dense outer layer of bone • B. Spongy bone (cancellous) - internal network of bone • 1. trabeculae- little “beams” of bone; make it like a sponge • 2. open spaces between trabeculae are filled with marrow

18. Articularcartilage Compact bone vs. Spongy bone Proximalepiphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity(lined byendosteum) Diaphysis Distalepiphysis

19. Compact bone vs. Spongy bone Spongy bone(diploë) Compact bone Trabeculae

20. C. Spongy bone • 1. is less complex than compact bone • 2. trabeculae contain layers of lamellae and osteocytes • 3. are too small to contain osteons

21. Spongy bone Trabeculae

22. Articularcartilage Compact bone Proximalepiphysis Spongy bone Endosteum Epiphysealline Endosteum Periosteum Compact bone Medullarycavity(lined byendosteum) Yellowbone marrow Diaphysis Compact bone Periosteum Perforatingcollagen fiberbundles Nutrientarteries Distalepiphysis

23. X. Gross Structure of Bones • A. Long Bones • 1. diaphysis- “shaft” of a bone • 2. epiphysis- end of a bone • 3. blood vessels - well vascularized • 4. medullary cavity - hollow cavity filled with yellow marrow • 5. membranes – periosteum and endosteum • F. Flat bones, short bones, and irregular bones • 1. contain bone marrow but no marrow cavity • 2. diploë - internal spongy bone of flat bones

24. Articularcartilage Proximalepiphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity(lined byendosteum) Anatomy of Long Bone Diaphysis Distalepiphysis

25. XI. Microscopic Structure of Compact Bones • A. Compact bone • ► osteon– has passage for blood vessels, lymph vessels, and nerves • 1. long cylindrical structures • 2. structurally resemble rings of a tree in cross section • 3. parts: • a. lamellae (rings) • b. central canal (longitudinal) • c. perforating canals (perpendicular) • d. canaliculi • e. lacunae (holes)

26. Articularcartilage Proximalepiphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity(lined byendosteum) Diaphysis Distalepiphysis

27. Compact bone Spongy bone Perforating(Volkmann’s) canal Central(Haversian) canal Endosteum Osteon(Haversian system) Circumferentiallamellae Perforating collagen fiber bundles Periosteal blood vessel Lamellae Periosteum

28. Nerve Vein Lamellae Artery Centralcanal Canaliculi Osteocytein a lacuna Lacunae

29. XII. Bone Development • A. ossification (osteogenesis) - bone tissue formation • 1. membrane bones - formed directly from mesenchyme

30. B. Intramembranous ossification (from fibrous membrane) • 1. ossification center - where osteoblastsconcentrate • 2. osteoblasts secrete collagen fibers for matrix • 3. calcification - Ca salts secreted to cement matrix • 4. osteoblasts surrounded and turn into --> osteocytes • 5. trabeculae - result when hardened bone forms • 6. spongy bone now in place with red marrow • 7. in time, spongy bone reconstructed -> compact bone

31. Figure 6.10 Intramembranous ossification: Development of a flat bone of the skull in the fetus. 1 2 4 3 Mesenchymalcell Osteoblast Osteoid Collagenfiber Ossificationcenter Osteocyte Newly calcifiedbone matrix Osteoid Osteoblast Bone matrix (osteoid) is secreted within thefibrous membrane and calcifies. Ossification centers appear in the fibrousconnective tissue membrane. • Osteoblasts begin to secrete osteoid, which is calcified within a few days. • Selected centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center. • Trapped osteoblasts become osteocytes. Fibrousperiosteum Mesenchymecondensingto form theperiosteum Osteoblast Plate ofcompact bone Trabeculae ofwoven bone Diploë (spongybone) cavitiescontain redmarrow Blood vessel Lamellar bone replaces woven bone, justdeep to the periosteum. Red marrow appears. Woven bone and periosteum form. • Accumulating osteoid is laid down between embryonic blood vessels in a random manner. The result is a network (instead of lamellae) of trabeculae called woven bone. • Trabeculae just deep to the periosteum thicken and are later replaced with mature lamellar bone, forming compact bone plates. • Spongy bone (diploë), consisting of distinct trabeculae, persists internally, and its vascular tissue becomes red marrow. • Vascularized mesenchyme condenses on the external face of the woven bone and becomes the periosteum.

32. C. Endochondral Ossification • 1. all bones except some bones of the skull and clavicles • 2. bones are modeled in hyaline cartilage • 3. forms late in second month of embryonic development • 4. continues forming until early adulthood

33. D. Anatomy of Epiphyseal Growth Areas • 1. in epiphyseal plates (growth plates) of growing bones: • What happens? • a. cartilage is organized for quick, efficient growth • b. cartilage cells form tall stacks • c. chondroblasts at the top of stacks divide quickly • d. pushes the epiphysis away from the diaphysis • e. lengthens entire long bone

34. 2. epiphyseal growth areas • What happens? • 1. proliferation zone (surface) • 2. hypertrophic zone ▼ • 3. calcification zone ▼ • 4. ossification zone (bottom)

35. Figure 6.12 Organization of the cartilage within the epiphyseal plate of a growing long bone. 2 1 3 4 Resting zone Proliferationzone Cartilage cellsundergo mitosis. Hypertrophiczone Older cartilage cellsenlarge. X-ray image of right knee,anterior view. Proximalepiphyseal plate of thetibia enlarged inpart (b). Calcificationzone Matrix becomescalcified; cartilagecells die; matrixbegins deteriorating. Calcifiedcartilagespicule Ossificationzone Osseoustissue New bone is forming. Photomicrographof cartilage in theepiphyseal plate (125). Diagram of the zoneswithin the epiphysealplate.

36. 1. older chondrocytes signal surrounding matrix to calcify 2. older chondrocytes then die and disintegrate 3. leaves long trabeculae (spicules) of calcified cartilage on diaphysis side 4. trabeculae are partly eroded by osteoclasts 5. osteoblasts then cover trabeculae with bone tissue 6. trabeculae finally eaten away from their tips by osteoclasts

37. Endochondral ossification of a long bone. 1 2 5 4 3 Childhood toadolescence Articularcartilage Birth Secondaryossificationcenter Spongybone Month 3 Epiphysealblood vessel Week 9 Area ofdeterioratingcartilage matrix Epiphysealplatecartilage Hyalinecartilage Medullarycavity Spongyboneformation Bonecollar Bloodvessel ofperiostealbud Primaryossificationcenter Bone collarforms around thediaphysis of thehyaline cartilagemodel. The periostealbud invades theinternal cavities,and spongy bonebegins to form. The diaphysiselongates, and amedullary cavityforms as ossificationcontinues. Secondaryossification centersappear in theepiphyses. The epiphysesossify. Whencompleted, hyalinecartilage remainsonly in theepiphyseal platesand articularcartilages. Cartilage in thecenter of the diaphysis calcifiesand then developscavities.

38. X-ray image of right knee, anterior view. Proximal epiphyseal plate of the tibia enlarged in part (b).

39. E. Postnatal Growth of Endochondral Bones • 1. During childhood and adolescence: • What happens? • a. bones lengthen entirely by growth of the epiphyseal plates • b. cartilage replaced with bone tissue as quickly as it grows • c. epiphyseal plate maintains constant thickness • d. whole bone lengthens

40. 2. As adolescence draws to an end • What happens? • a. chondroblasts divide less often • b. epiphyseal plates become thinner • c. cartilage stops growing • d. replaced by bone tissue • e. long bones stop lengthening when diaphysis & epiphysis fuse • f. growing bones widen as they lengthen

41. g. osteoblasts - add bone tissue to external surface of diaphysis • h. osteoclasts - remove bone from internal surface of diaphysis • i. crawls along bone surfaces • ii. breaks down bone tissue • iii. secretes concentrated HCl • iv. lysosomal enzymes are released • v. derived from hematopoietic stem cells • i. Appositional growth - growth by addition of bone tissue to surface

42. XIII. Hormonal Regulation of Bone Growth • A. Growth hormone - produced by the pituitary gland • 1. stimulates epiphyseal plates • B. Thyroid hormone - ensures skeleton proper proportions • C. Sex hormones (estrogen and testosterone) • 1. promote bone growth • 2. later induces closure of epiphysealplates • 3. can be used for bone density in elderly

43. XIV. Bone Remodeling • A. Bone is a dynamic living tissue • 1. 500 mg of calcium may enter/leave adult skeleton each day • 2. bone matrix and osteocytes continually removed and replaced • 3. cancellous bone of the skeleton is replaced every 3–4 years • 4. compact bone is replaced every 10 years • 5. bone deposit and removal: • a. occurs at periosteal and endosteal surfaces • 6. bone deposition—accomplished by osteoblasts • 7. bone reabsorption—accomplished by osteoclasts

44. XV. Disorders of Bones • A. Osteoporosis • 1. characterized by low bone mass • 2. bone reabsorption outpaces bone deposition • 3. occurs most often in women after menopause • B. Osteomalacia • 1. “softening” of bone • 2. occurs in adults—bones are inadequately mineralized • C. Rickets - occurs in children - analogous to osteomalacia • D. Osteosarcoma - form of bone cancer

45. Osteoporosis Normal bone Osteoporotic bone

46. Rickets