Skeletal System: Bones & Skeletal Tissues

1. Skeletal System:Bones & Skeletal Tissues

2. Classification of Bones • Axial Skeleton • Skull, vertebral column, and rib cage • Protecting, supporting, or carrying other body parts • Appendicular Skeleton • Bones of upper and lower limbs and the girdles (shoulder & hip bones) that attach limbs to axial skeleton • Allow locomotion and manipulation of our environment

3. Types of Bones • Long bones • Short bones • Flat bones • Irregular bones

4. Long Bones • Length is longer than the width is wide • Designed to absorb stress from body weight • Found in: arms, forearms, hands, thighs, legs, and feet

5. Short Bones • About equal in length and width, roughly cube shaped • Found in: wrist and ankle

6. Flat Bones • Thin, flattened, and usually a bit curved • Found in: cranium, ribs, scapulae, and sternum

7. Irregular Bones • Complicated shapes that do not fit any of the previous three categories • Found in: hip bones, vertebrae and bones of the face

8. Functions of Bones • Support • Protection • Movement • Mineral Storage • Blood cell formation

9. Bones and Cartilages of the Human Body Figure 6.1

10. Gross Anatomy of Bones: Bone Textures • Compact bone – dense outer layer • Spongy bone – honeycomb of trabeculae (thin plates of bone interconnected with one another) filled with yellow bone marrow (rich in fatty tissue for energy storage

11. Structure of Long Bone • Long bones consist of a diaphysis and an epiphysis • Diaphysis • Tubular shaft that forms the axis of long bones • Composed of compact bone that surrounds the medullary cavity • Yellow bone marrow (fat) is contained in the medullary cavity

12. Structure of Long Bone • Epiphyses • Expanded ends of long bones • Exterior is compact bone, and the interior is spongy bone • Joint surface is covered with articular (hyaline) cartilage • Epiphyseal line separates the diaphysis from the epiphyses

13. Structure of Long Bone Figure 6.3

14. Bone Membranes • Periosteum – double-layered protective membrane • Outer fibrous layer is dense regular connective tissue • Inner osteogenic layer is composed of osteoblasts and osteoclasts • Richly supplied with nerve fibers, blood, and lymphatic vessels • Endosteum – delicate membrane covering internal surfaces of bone

15. Structure of Short, Irregular, and Flat Bones • Thin plates of periosteum-covered compact bone on the outside with endosteum-covered spongy bone on the inside • Have no diaphysis or epiphyses • Contain bone marrow between the trabeculae

16. Structure of a Flat Bone Figure 6.4

17. Location of Hematopoietic Tissue (Red Marrow) • In infants • Found in the medullary cavity and all areas of spongy bone • In adults • Found in the spongy bone of flat bones, and the head of the femur and humerus

18. Microscopic Structure of Bone: Compact Bone • Haversian system, or osteon – the structural unit of compact bone • Lamella – weight-bearing, column-like matrix tubes composed mainly of collagen • Haversian, or central canal – central channel containing blood vessels and nerves • Volkmann’s canals – channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal

19. Microscopic Structure of Bone: Compact Bone • Osteocytes – mature bone cells • Lacunae – small cavities in bone that contain osteocytes • Canaliculi – hairlike canals that connect lacunae to each other and the central canal

20. Microscopic Structure of Bone: Compact Bone Figure 6.6a, b

21. Chemical Composition of Bone: Organic • Osteoblasts – bone-forming cells • Osteocytes – mature bone cells • Osteoclasts – large cells that resorb or break down bone matrix • Osteoid – unmineralized bone matrix composed of proteoglycans, glycoproteins, and collagen

22. Bone Development • Osteogenesis and ossification – the process of bone tissue formation, which leads to: • The formation of the bony skeleton in embryos • Bone growth until early adulthood • Bone thickness, remodeling, and repair

23. Bone Development • Intramembranous Ossification • bones originate within sheetlike layers of connective tissues • broad, flat bones • skull bones (except mandible) • intramembranous bones • Endochondral Ossification • bones begin as hyaline cartilage • form models for future bones • most bones of the skeleton • endochondral bones

24. Formation of the Bony Skeleton • Begins at week 8 of embryo development • Hyaline cartilage that makes up fetal “bone” gets covered by osteoblasts • Eventually most cartilage gets converted to bone, except for articular cartilages and the epiphyseal plates

25. Bone Formation • Appositional growth—increase in diameter of bone • Long bone growth depends on a growth hormone during puberty • Growth occurs in the epiphyseal plate (junction of diaphysis with each epiphysis) until age 16-25, with the ossification of the epiphseal plate.

26. Long Bone Growth and Remodeling Figure 6.10

27. Bone Remodeling • Retains normal proportions and strength during long bone growth • Two Factors: • Calcium levels in the blood • Pull of gravity and muscles on the skeleton

28. Importance of Ionic Calcium in the Body • Calcium is necessary for: • Transmission of nerve impulses • Muscle contraction • Blood coagulation • Secretion by glands and nerve cells • Cell division

29. Factors Affecting Bone Development, Growth, and Repair • Deficiency of Vitamin A – retards bone development • Deficiency of Vitamin C – results in fragile bones • Deficiency of Vitamin D – rickets, osteomalacia • Insufficient Growth Hormone – dwarfism • Excessive Growth Hormone – gigantism, acromegaly • Insufficient Thyroid Hormone – delays bone growth • Sex Hormones – promote bone formation; stimulate ossification of epiphyseal plates • Physical Stress – stimulates bone growth

30. Homeostatic Imbalances • Rickets • Bones of children are inadequately mineralized causing softened, weakened bones • Bowed legs and deformities of the pelvis, skull, and rib cage are common • Caused by insufficient calcium in the diet, or by vitamin D deficiency

31. Homeostatic Imbalances • Osteoporosis • Group of diseases in which bone reabsorption outpaces bone deposit • Spongy bone of the spine is most vulnerable • Occurs most often in postmenopausal women • Bones become so fragile that sneezing or stepping off a curb can cause fractures

32. Bone Fractures (Breaks) • Bone fractures are classified by: • The position of the bone ends after fracture • The completeness of the break • The orientation of the bone to the long axis • Whether or not the bone ends penetrate the skin

33. Types of Bone Fractures • Compound (open) – bone ends penetrate the skin • Simple (closed) – bone ends do not penetrate the skin • Comminuted – bone fragments into three or more pieces; common in the elderly • Spiral – ragged break when bone is excessively twisted; common sports injury

34. Common Types of Fractures Table 6.2.1

35. Common Types of Fractures Table 6.2.2

36. Common Types of Fractures • Depressed – broken bone portion pressed inward; typical skull fracture • Compression – bone is crushed; common in porous bones • Greenstick – incomplete fracture where one side of the bone breaks and the other side bends; common in children

37. Common Types of Fractures Table 6.2.3

38. Treatment by Reduction • Closed reduction—bone ends are realigned and put back in place by physician. • Open reduction—bone ends are put together with pins or wires through surgery • After reduction, a cast follows to begin healing process (simple fracture 6-8 weeks)

39. Stages in the Healing of a Bone Fracture • Hematoma formation • Torn blood vessels hemorrhage • A mass of clotted blood (hematoma) forms at the fracture site • Site becomes swollen, painful, and inflamed Hematoma Hematoma formation 1 Figure 6.14.1

40. Stages in the Healing of a Bone Fracture External callus • Fibrocartilage callus forms • Granulation tissue (soft callus) forms a few days after the fracture • Capillaries grow into the tissue and phagocytic cells begin cleaning debris New blood vessels Internal callus (fibrous tissue and cartilage) Spongy bone trabeculae Fibrocartilaginous callus formation 2 Figure 6.14.2

41. Stages in the Healing of a Bone Fracture Bony callus of spongy bone • Bony callus formation • Fibrocartilage callus converts into a bony (hard) callus • Bone callus begins 3-4 weeks after injury, and continues until firm union is formed 2-3 months later 3 Bony callus formation Figure 6.14.3

42. Stages in the Healing of a Bone Fracture • Bone remodeling • Excess material on the bone shaft exterior and in the medullary canal is removed • Compact bone is laid down to reconstruct shaft walls Healing fracture Bone remodeling 4 Figure 6.14.4