1. Copyright © John Wiley & Sons, Inc. All rights reserved. Chapters 6 Bone Tissue Lecture slides prepared by Curtis DeFriez, Weber State University

2. Copyright © John Wiley & Sons, Inc. All rights reserved. Introduction  The skeletal system has 6 important functions:  Provide support by acting as a structural framework and a point of attachment for tendons and ligaments  Protect the internal organs (brain, chest, etc.)  Assist body movements (in conjunction with muscles)  Store and release salts of calcium and phosphorus  Participate in blood cell production (hematopoiesis)  Store triglycerides in adipose cells of yellow marrow

3. Copyright © John Wiley & Sons, Inc. All rights reserved.  Bone is a dynamic tissue – it is always remodeling (building up and breaking down).  Like all organ systems (and as part of the even larger musculoskeletal organ system), the skeletal system is made of several different tissues.  The two major tissues are bone (osseous tissue) and cartilage. Tissues of the Skeletal System

4. Copyright © John Wiley & Sons, Inc. All rights reserved. Tissues of the Skeletal System  Bone is a highly vascularized C.T. with a hard, mineralized extracellular matrix. It is found in the body in two different arrangements:  Compact bone – most of the bone in this graphic is compact bone.  Spongy bone is seen as the less organized tissue along the left margin (with the spicules).

5. Copyright © John Wiley & Sons, Inc. All rights reserved. Tissues of the Skeletal System  Compact bone is good at providing protection and support.  It forms the diaphysis of long bones, and the external layer of all bones.  Spongy bone is lightweight and provides tissue support.  It forms much of the epiphysis and the internal cavity of long bones. Compact bone Spongy bone

6. Copyright © John Wiley & Sons, Inc. All rights reserved. Tissues of the Skeletal System  Cartilage is a poorly vascularized C.T. with a matrix composed of chondroitin sulfate and various fibers.  Fiber types distinguish hyaline cartilage from fibrocartilage or elastic cartilage. Hyaline cartilage

7. Copyright © John Wiley & Sons, Inc. All rights reserved.  Articular cartilage is the thin layer of hyaline cartilage covering the epiphysis of long bones.  Articular cartilage is found where the bone forms an articular (joint) surface - where one bone moves against another bone. Tissues of the Skeletal System Hyaline cartilage is the articular cartilage of this long bone

8. Copyright © John Wiley & Sons, Inc. All rights reserved.  The periosteum is a tough sheath of dense, irregular connective tissue on the outside of the bone.  It contains osteoblasts that help the bone grow in thickness, but not in length.  It also assists with fracture repair and serves as an attachment point for tendons and ligaments. Tissues of the Skeletal System

9. Copyright © John Wiley & Sons, Inc. All rights reserved.  The medullary cavity is a space within the diaphysis of long bones that contains fatty yellow bone marrow in adults.  The endosteum is a membrane that lines the medullary cavity.  The endosteum is composed of osteoclasts, osteoblasts, and connective tissue. Structure of Bone

10. Copyright © John Wiley & Sons, Inc. All rights reserved. Tissues of the Skeletal System  The perichondrium is a dense irregular connective tissue membrane that surrounds cartilage.  Chondrocytes are cells that form cartilage.  As we will soon see, many of the major bones are formed from cartilage (the remainder do not go through a cartilaginous stage.) Perichondrium Periosteum

11. Copyright © John Wiley & Sons, Inc. All rights reserved. Tissues of the Skeletal System  The various cells in osseous tissues are shown in the bottom graphic:

12. Copyright © John Wiley & Sons, Inc. All rights reserved.  Osteoblasts are bone building cells: They synthesize and secrete collagen fibers and other organic components.  Osteocytes are mature osteoblasts (maintenance).  Osteoclasts are large bone breakdown cells.  As white blood cells, osteoclasts migrated from the bone marrow to become “fixed macrophages” in the substance of the bone. Tissues of the Skeletal System

13. Copyright © John Wiley & Sons, Inc. All rights reserved. Tissues of the Skeletal System  Besides bone and cartilage, the skeletal system contains other important tissues:  Epithelium (endothelium) form the capillary walls  Nerves (the periosteum is especially tender)  Red marrow – hematopoiesis  Yellow marrow – fat storage

14. Copyright © John Wiley & Sons, Inc. All rights reserved. Chemical Constituents of Bone  Bone is 25% water, 25% organic proteins, 50% mineral salts (hydroxyapatite crystals).  Organic constituents Collagen fibers provide flexibility and tensile strength.  Inorganic hydroxyapatite crystals (mineral salts) Calcium Phosphate (Ca 3 PO 4 ) 2 Calcium Carbonate (CaCO 3 – marble) Other trace elements: magnesium, fluoride, sulfate

15. Copyright © John Wiley & Sons, Inc. All rights reserved.  The humerus in the arm is a typical long bone. Bone Structure

16. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Structure  The diaphysis is the shaft or body of a long bone.  The epiphyses form the distal and proximal ends of a long bone.  The metaphyses are the areas where the epiphyses and diaphysis join.

17. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Structure  In adolescents, through the end of active growth, the epiphysis of the long bones contains hyaline cartilage and forms an “epiphyseal growth plate”.  The growth plate is always actively dividing and causing the bone to elongate from each end.

18. Copyright © John Wiley & Sons, Inc. All rights reserved.  In adults, the epiphyseal cartilage is no longer present and elongation of bones has stopped.  The epiphyseal growth plate becomes an “epiphyseal line”, as growing cartilage is replaced by calcified bone. The epiphyseal line is visible externally and on X-rays. Bone Structure

19. Copyright © John Wiley & Sons, Inc. All rights reserved. Histology of Bone Tissue  Compact Bone contains units called osteons or Haversian systems formed from concentric lamellae (rings of calcified matrix).  Interstitial lamellae between osteons are left over fragments of older osteons.

20. Copyright © John Wiley & Sons, Inc. All rights reserved.  Outer circumferential lamellae encircle the bone beneath the periosteum.  Inner circumferential lamellae encircle the medullary cavity. Histology of Bone Tissue

21. Copyright © John Wiley & Sons, Inc. All rights reserved.  Lacunae are small spaces between the lamellae which house osteocytes.  Canaliculi are small channels filled with extracellular fluid connecting the lacunae. Histology of Bone Tissue

22. Copyright © John Wiley & Sons, Inc. All rights reserved. Histology of Bone Tissue  Blood and lymphatic vessels are found in the osteon’s Central canal.  Perforating (Volkmann’s) canals allow transit of these vessels to the outer cortex of the bone.

23. Copyright © John Wiley & Sons, Inc. All rights reserved. Histology of Bone Tissue  Spongy bone lacks osteons. Instead, lamellae are arranged in a lattice of thin columns called trabeculae.  Trabeculae of spongy bone support and protect the red bone marrow and are oriented along lines of stress (helps bones resist stresses without breaking).  Hematopoiesis (blood cell production) occurs in spongy bone.

24. Copyright © John Wiley & Sons, Inc. All rights reserved. Histology of Bone Tissue  Within each trabecula of spongy bone are lacunae.  As in compact bone, lacunae contain osteocytes that nourish the mature bone tissue from the blood circulating through the trabeculae.

25. Copyright © John Wiley & Sons, Inc. All rights reserved. Histology of Bone Tissue  The interior of long bones is made up primarily of spongy bone. The use of spongy bone lessens overall bone weight.

26. Copyright © John Wiley & Sons, Inc. All rights reserved.  Bone is richly supplied with blood; Periosteal arteries and veins supply the periosteum and compact bone.  Nerves accompany the blood vessels (this is often the case.)  The periosteum is rich in sensory nerves sensitive to tearing or tension (as anyone who has bruised their shin will tell you!) Blood and Nerve Supply of Bone

27. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation  Ossification or osteogenesis is the process of forming new bone. Bone formation occurs in four situations:  Formation of bone in an embryo  Growth of bones until adulthood  Remodeling of bone  Repair of fractures

28. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation  Osteogenesis occurs by two different methods, beginning about the 6 th week of embryonic development.  Intra-membranous ossification produces spongy bone. This bone may subsequently be remodeled to form compact bone.  Endochondral ossification is a process whereby cartilage is replaced by bone. Forms both compact and spongy bone.

29. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation  Intra-membranous ossification is the simpler of the two methods.  It is used in forming the flat bones of the skull, mandible, and clavicle.  Bone forms from mesenchymal cells that develop within a membrane – without going through a cartilage stage (recall that mesenchyme is the tissue from which almost all other C.T. develop.)  Many ossification centers.

30. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation

31. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation

32. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation

33. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation

34. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation

35. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation  Endochondral ossification is the method used in the formation of most bones, especially long bones.  It involves replacement of cartilage by bone.  There are one primary and two secondary centers of growth.

36. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation

37. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation

38. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation

39. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation

40. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation

41. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation

42. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation

43. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation  Ossification contributing to bone length is usually complete by 18-21 years of age.  Bones can still continue to thicken and are capable of repair even after the epiphyseal growth plates have closed.

44. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation  Human growth hormone is one of the body’s many anabolic hormones. Among other things, its secretion will stimulate bone growth, muscle growth, loss of fat, and increased glucose output in the liver.  The use of growth hormone has been increasing in popularity among athletes due to the numerous “benefits” associated with its use; side effects are often not thought of when young athletes use these drugs.

45. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Formation Interactions Animation  Bone Formation Bone Formation You must be connected to the internet to run this animation

46. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Growth and Remodeling  A balance must exist between the actions of osteoclasts and osteoblasts.  If too much new tissue is formed, the bones become abnormally thick and heavy (acromegaly).  Excessive loss of calcium weakens the bones, as occurs in osteoporosis.  They may also become too “soft”, as seen in the bone diseases rickets and osteomalacia.

47. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Growth and Remodeling Interactions Animation  Bone Remodeling Bone Remodeling You must be connected to the internet to run this animation

48. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Growth and Remodeling Normal bone metabolism depends on several factors:  Minerals are an essential component.  Large amounts of calcium and phosphorus and smaller amounts of magnesium, fluoride, and manganese are required for bone growth and remodeling.

49. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Growth and Remodeling  Vitamins are also necessary for normal bone metabolism:  Vitamin A stimulates activity of osteoblasts.  Vitamin C is needed for synthesis of collagen.  Vitamin D is essential to healthy bones because it promotes the absorption of calcium from foods in the gastrointestinal tract into the blood.  Vitamins K and B 12 are needed for synthesis of bone proteins.

50. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Growth and Remodeling  Hormones are key contributors to normal bone metabolism.  During childhood, the hormones most important to bone growth are human growth hormone (hGH) and growth factors called IGFs (produced by the liver). Both stimulate osteoblasts, promote cell division at the epiphyseal plate, and enhance protein synthesis.  Thyroid hormones and insulin also promote bone growth by stimulating osteoblasts and protein synthesis.

51. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Growth and Remodeling  Hormones continued…  The sex hormones (estrogen and testosterone) cause a dramatic effect on bone growth, such as the sudden “growth spurt” that occurs during the teenage years. The sex hormones also promote widening of the pelvis in the female skeleton. They are also responsible for closing the epiphyseal plates at the end of puberty.

52. Copyright © John Wiley & Sons, Inc. All rights reserved. Bone Growth and Remodeling  Hormones continued…  Parathyroid hormone (PTH) and calcitonin are critical for balancing the levels of calcium and phosphorus between blood and bone. Maintaining a normal serum Ca 2+ level takes precedence over mineralizing bone (usually both can be done) – can you suggest an explanation why this is true?

53. Copyright © John Wiley & Sons, Inc. All rights reserved. Calcium Homeostasis  Day to day control of calcium regulation mainly involves:  PTH stimulates osteoclastic activity and raises serum calcium level.  Calcitonin (thyrocalcitonin), and to a lesser extent hGH and the sex hormones, stimulate osteoblastic activity and lower serum calcium level.  Vitamin D is needed for absorption of the Ca 2+ and PO 4 – ions from the small intestine, and reabsorption of those same ions in the kidneys.

54. Copyright © John Wiley & Sons, Inc. All rights reserved. Calcium Homeostasis The role of regulating serum Ca 2+ levels and mineralizing bone is under hormonal control, and is carefully balanced. I made this little diagram… but I’m not sure where I got the figures from. Can we reproduce this? PTH Calcitonin hGH Testosterone

55. Copyright © John Wiley & Sons, Inc. All rights reserved. Calcium Homeostasis

56. Copyright © John Wiley & Sons, Inc. All rights reserved. Fracture and Repair  The naming of fractures can be confusing because of the many different criteria that are used.  Some schemes describe the anatomical appearance of the fracture: Partial, complete (fx is all the way through the bone), closed (simple), open (fx punctures the skin), “Green stick” (a small linear break in the bone cortex), impacted, comminuted, spiral, transverse, displaced

57. Copyright © John Wiley & Sons, Inc. All rights reserved. Fracture and Repair  Anatomical appearance – like breaking a green twig Greenstick

58. Copyright © John Wiley & Sons, Inc. All rights reserved. Fracture and Repair  Anatomical appearance – the distal part is shoved up into the proximal part. Impacted

59. Copyright © John Wiley & Sons, Inc. All rights reserved. Fracture and Repair  Anatomical appearance – though not seen here, one or both bones are “open” to the outside. Open (compound)

60. Copyright © John Wiley & Sons, Inc. All rights reserved. Fracture and Repair  Naming fractures, continued…  Other fractures are classified by the disease or mechanism which produced the fracture. Pathological fracture (usually from a cancerous process or severe chronic disease), compression fracture (produced by extreme forces such as in trauma) Stress fracture (produced from repeated strenuous activities such as running)

61. Copyright © John Wiley & Sons, Inc. All rights reserved. Fracture and Repair  Naming fractures, continued…  Still other fractures describe a common pattern of injury, often involving more than one bone, and usually denoted by an eponym (someone’s name): Colles’ fracture of the distal radius Pott’s fracture of the distal fibula

62. Copyright © John Wiley & Sons, Inc. All rights reserved. Fracture and Repair  Eponyms – Colles’ is a fracture of the distal radius ± ulna. Colles’

63. Copyright © John Wiley & Sons, Inc. All rights reserved. Once a bone is fractured, repair proceeds in a predictable pattern:  The first step, which occurs 6-8 hours after injury, is the formation of a fracture hematoma as a result of blood vessels breaking in the periosteum and in osteons. Fracture and Repair

64. Copyright © John Wiley & Sons, Inc. All rights reserved.  The second and third steps involve the formation of a callus (takes a few weeks, to as many as six months).  Phagocytes remove cellular debris and fibroblasts deposit collagen to form a fibro- cartilaginous callus... Fracture and Repair

65. Copyright © John Wiley & Sons, Inc. All rights reserved. Fracture and Repair ... which is followed by osteoblasts forming a bony callus of spongy bone.

66. Copyright © John Wiley & Sons, Inc. All rights reserved. Fracture and Repair  The final step takes several months and is called remodeling :  Spongy bone is replaced by compact bone.  The fracture line disappears, but evidence of the break remains.

67. Copyright © John Wiley & Sons, Inc. All rights reserved. Exercise and Bone Tissue  Under mechanical stress, bone tissue becomes stronger through deposition of mineral salts and production of collagen fibers by osteoblasts. Unstressed bones, on the other hand, become weaker.  Astronauts in space suffer rapid loss of bone density.  The main mechanical stresses on bone are those that result from the pull of skeletal muscles and the pull of gravity (weight-bearing activities).

68. Copyright © John Wiley & Sons, Inc. All rights reserved. Aging and Bone Tissue  A decrease in bone mass occurs as the level of sex hormones diminishes during middle age (especially in women after menopause).  Bone resorption by osteoclasts outpaces bone deposition by osteoblasts.  Since female bones are generally smaller and less massive than males to begin with, old age has a greater adverse effect in females.

69. Copyright © John Wiley & Sons, Inc. All rights reserved. Aging and Bone Tissue  There are two principal effects of aging on bone tissue:  Loss of bone mass The loss of calcium from bones is one of the symptoms in osteoporosis.  Brittleness Collagen fibers give bone its tensile strength, and protein synthesis decreases with age. The loss of tensile strength causes the bones to become very brittle and susceptible to fracture.

70. Copyright © John Wiley & Sons, Inc. All rights reserved. Aging and Bone Tissue  Osteoporosis is a condition where bone resorption outpaces bone deposition.  Often due to depletion of calcium from the body or inadequate intake

71. Copyright © John Wiley & Sons, Inc. All rights reserved. End of Chapter 6 Copyright 2012 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information herein.