The skeletal system

1. Ch. 5 The skeletal system

2. Functions of Bones • Support • For the body and soft organs • Protection • For brain, spinal cord, and vital organs • Movement • Levers for muscle action

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

4. Classification of Bones by Shape • Long bones • Longer than they are wide • All limb bones except carpals and tarsals, patella • Short bones • Cube-shaped bones (in wrist and ankle) • Sesamoid bones (within tendons, e.g., patella)

5. Classification of Bones by Shape • Flat bones • Thin, flat, slightly curved • Examples: Sternum, scapulae, ribs most skull bones • Irregular bones • Complicated shapes • Examples: coxal, vertebrae

6. Figure 6.2

7. Bone Markings: Projections • Sites of muscle and ligament attachment • Tuberosity—rounded projection • Crest—narrow, prominent ridge • Trochanter—large, blunt, irregular surface • Tubercle—small rounded projection • Epicondyle—raised area above a condyle • Spine—sharp, slender projection • Process—any bony prominence

8. Bone Markings: Projections • Projections that help to form joints • Head • Bony expansion carried on a narrow neck • Facet • Smooth, nearly flat articular surface • Condyle • Rounded articular projection • Ramus • Armlike bar

9. Meatus Canal-like passageway Sinus Cavity within a bone Fossa Shallow, basinlike depression Groove Furrow Fissure Narrow, slitlike opening Foramen Round or oval opening through a bone Bone Markings: Openings

10. Bone Textures • Compact bone • Dense outer layer of bone • Composed of osteons • Spongy bone • Internal to compact bone & composed of trabeculae

11. Membranes of Bone • Periosteum • Surrounds entire outer surface of compact bone, except joint surfaces • Contains: Osteoblasts and osteoclasts • Secured to compact bone by Sharpey’s fibers • Endosteum • Lines internal surfaces of bone and also contains osteoblasts and osteoclasts

12. Structure of a Long Bone • Diaphysis (shaft) • Compact bone collar surrounds medullary (marrow) cavity

13. Structure of a Long Bone • Epiphyses • Expanded ends • Spongy bone interior • Epiphyseal line (remnant of growth plate) • Articular (hyaline) cartilage on joint surfaces

14. 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

15. Structure of Short, Irregular, and Flat Bones • Endosteum covered spongy bone surrounded/sandwiched by compact bone covered in periosteum

16. Spongy bone (diploë) Compact bone Trabeculae Figure 6.5

17. Microscopic Anatomy of Bone: Compact Bone • Osteon—structural unit • Lamellae • Weight-bearing portion • Column-like matrix tubes • Central Canal • Contains blood vessels and nerves

18. Artery with capillaries Structures in the central canal Vein Nerve fiber Lamellae Collagen fibers run in different directions Twisting force Figure 6.6

19. 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

20. Spongy bone Compact bone Central (Haversian) canal Perforating (Volkmann’s) canal Endosteum lining bony canals and covering trabeculae Osteon (Haversian system) Circumferential lamellae (a) Perforating (Sharpey’s) fibers Periosteal blood vessel Lamellae Periosteum Nerve Vein Lamellae Artery Central canal Lacuna (with osteocyte) Canaliculi Osteocyte in a lacuna Lacunae Interstitial lamellae (b) (c) Figure 6.7a-c

21. Nerve Vein Lamellae Artery Central canal Canaliculus Lacunae Osteocyte in a lacuna (b) Figure 6.3b

22. Microscopic Anatomy of Bone: Spongy Bone • Composed of trabeculae • No osteons • Spaces between trabeculae are filled with bone marrow

23. Chemical Composition of Bone: Organic • Bone cells (osteoblasts, osteocytes, osteoclasts) • Osteoid—organic bone matrix (secreted by osteoblasts) and: • Ground substance • Collagen fibers

24. Chemical Composition of Bone: Inorganic • Hydroxyapatites (mineral salts) • 65% of bone by mass • Mainly calcium phosphate crystals • Responsible for hardness and resistance to compression

25. Bone Formation, Growth and Remodeling • Ossification- bone formation • Stages • Bone formation begins in the 2nd month of development • Postnatal bone growth - until early adulthood • Bone remodeling and repair - lifelong

26. Month 3 Birth Childhood toadolescence Week 9 Articularcartilage Secondaryossificationcenter Spongybone Epiphysealblood vessel Area ofdeterioratingcartilage matrix Epiphysealplatecartilage Hyalinecartilage Medullarycavity Spongyboneformation Bonecollar Bloodvessel ofperiostealbud Primaryossificationcenter 1 2 3 4 5 Bone collarforms aroundhyaline cartilagemodel. Cartilage in thecenter of thediaphysis calcifiesand then developscavities. The periostealbud inavades theinternal cavitiesand spongy bonebegins to form. The diaphysis elongatesand a medullary cavityforms as ossificationcontinues. Secondaryossification centers appearin the epiphyses inpreparation for stage 5. The epiphysesossify. Whencompleted, hyalinecartilage remains onlyin the epiphysealplates and articularcartilages.

27. Growth in Length of Long Bones • Interstitial growth: • Increase in the length of long bones

28. Growth in Width of All Bones • Appositional Growth • Bones must widen as they lengthen, but must continue to widen after interstitial growth has ended

29. Control of Remodeling • What controls continual remodeling of bone? • Hormonal mechanisms that maintain calcium homeostasis in the blood • Mechanical and gravitational forces

30. Hormonal Control of Blood Ca2+ • Primarily controlled by parathyroid hormone (PTH)  Blood Ca2+ levels  Parathyroid glands release PTH  PTH stimulates osteoclasts to degrade bone matrix and release Ca2+   Blood Ca2+ levels

31. Calcium homeostasis of blood: 9–11 mg/100 ml BALANCE BALANCE Stimulus Falling blood Ca2+ levels Thyroid gland Osteoclasts degrade bone matrix and release Ca2+ into blood. Parathyroid glands Parathyroid glands release parathyroid hormone (PTH). PTH

32. Response to Mechanical Stress • Curved bones are thickest where they are most likely to buckle • Trabeculae form along lines of stress • Large, bony projections occur where heavy, active muscles attach

33. Load here (body weight) Head of femur Tension here Compression here Point of no stress Figure 6.13

34. Stages in the Healing of a Bone Fracture • Hematoma forms • Torn blood vessels hemorrhage • Clot (hematoma) forms and site becomes swollen, painful, and inflamed

35. Hematoma 1 A hematoma forms. Figure 6.15, step 1

36. Stages in the Healing of a Bone Fracture • The Break is Splinted by a soft callus • Phagocytic cells clear debris • Fibroblasts secrete collagen fibers to connect bone ends = soft callus • Osteoblasts begin forming spongy bone within 1 week • New blood vessels grow into injured area

37. Externalcallus Internalcallus(fibroustissue andcartilage) Newbloodvessels Spongybonetrabecula 2 Fibrocartilaginouscallus forms. Figure 6.15, step 2

38. Stages in the Healing of a Bone Fracture • Bony callus formation • New trabeculae form a bony or hard callus • Bony callus formation continues until firm union is formed in ~2 months

39. Bonycallus ofspongybone 3 Bony callus forms. Figure 6.15, step 3

40. Stages in the Healing of a Bone Fracture • Bone remodeling • In response to mechanical stressors over several months • Final structure resembles original

41. Healedfracture 4 Bone remodelingoccurs. Figure 6.15, step 4

42. Homeostatic Imbalances • Read about Osteoporosis its risk factors, symptoms and characteristics

43. The skull

44. The Skeleton • Two Major Divisions of the Skeletal System: Axial and Appendicular • The Axial Skeleton Includes Three Regions: • Skull and associated bones (auditory ossicles and hyoid) • Vertebral column • Thoracic cage

45. Cranium Skull Facial bones Clavicle Thoracic cage (ribs and sternum) Scapula Sternum Rib Humerus Vertebra Vertebral column Radius Ulna Sacrum Carpals Phalanges Metacarpals Femur Patella Tibia Fibula Tarsals Metatarsals (a) Anterior view Phalanges Figure 7.1a

46. The Skull • Two sets of bones • Cranial bones (8) • Enclose the brain in the cranial cavity • Calvaria: • Cranial base: anterior, middle, and posterior cranial fossae

47. The Skull • Facial bones • Cavities for: special sense organs for sight, taste, and smell • Provide sites of attachment for: teeth and muscles of facial expression • All skull bones are joined by: sutures except the temperomandibular joint(TMJ)

48. Bones of cranium (cranial vault) Coronal suture Squamous suture Facial bones Lambdoid suture

49. Anterior cranial fossa Middle cranial fossa Posterior cranial fossa (b) Superior view of the cranial fossae

50. Frontal Bone Frontal bone • Forms most of forehead • Superior wall of orbits Parietal bone (a) Anterior view Figure 7.4a