1. © 2012 Pearson Education, Inc. Lecture Presentation by Lee Ann Frederick University of Texas at Arlington Chapter 6 Osseous Tissue and Bone Structure © 2015 Pearson Education, Inc. Lecture Presentation by LeeAnn Frederick University of Texas at Arlington Modified by James R. Jabbur Pauline P. Ward Houston Community College

2. © 2012 Pearson Education, Inc. Learning Outcomes 6-1Describe the primary functions of the skeletal system. 6-2 Classify bones according to shape and internal organization, giving examples of each type, and explain the functional significance of each of the major types of bone markings. 6-3 Identify the cell types in bone, and list their major functions. An Introduction to the Skeletal System

3. © 2012 Pearson Education, Inc. Learning Outcomes 6-4 Compare the structures and functions of compact bone and spongy bone. 6-5 Compare the mechanisms of endochondral ossification and intramembranous ossification. 6-6 Describe the remodeling and homeostatic mechanisms of the skeletal system. 6-7 Discuss the effects of exercise, hormones, and nutrition on bone development and on the skeletal system.

4. © 2012 Pearson Education, Inc. Learning Outcomes 6-8 Explain the role of calcium as it relates to the skeletal system. 6-9 Describe the types of fractures, and explain how fractures heal. 6-10 Summarize the effects of the aging process on the skeletal system.

5. © 2012 Pearson Education, Inc. An Introduction to the Skeletal System The Skeletal System includes: Bones and Cartilage Ligaments and Connective Tissues Adipose (fat) Vasculature (blood) Nervous tissue

6. © 2012 Pearson Education, Inc. 6-1 Functions of the Skeletal System The Skeletal System has six primary functions 1.Physical support (framework using long bones) 2.Storage of minerals (calcium and phosphate) 3.Storage of fat (yellow marrow) 4.Blood Cell production (red marrow – hematopoetic) 5.Protection (organ guardianship using flat bones) 6.Leverage (force of motion using long bones)

7. © 2012 Pearson Education, Inc. 6-2 Classification of Bones Bones are classified by their: Shape Bone Markings Internal tissue organization (compact or spongy)

8. © 2012 Pearson Education, Inc. Short bone: small & thick Carpal and tarsal bones Flat bone: thin & plate-like Bones of the cranium, sternum, scapula and ribs Long bone: long and thin Bones of arm, leg, hand, feet, fingers and toes Irregular bone: complex shapes Bones of the spinal vertebrae and face Sesamoid bone: small & flat Bones wrapped inside of a tendon – near joints of the hand, knee (patella) and feet Sutural bone: small & irregular Found between cranial bones There are six types of bone shape

9. © 2012 Pearson Education, Inc. …a little more about the structure of long and flat bones Structure of a Long Bone Diaphysis (pr. di-AF-i-sis) Is the “shaft” of a long bone Consists of a heavy wall of compact bone (or dense bone), and A central cavity that is filled with yellow bone marrow in adults (medullary, or marrow, cavity) Epiphyses (pr. ē-PIF-i-ses) Are the two wide parts at each end that articulate with other bones They are covered with a compact bone cortex, and A central cavity that is mostly spongy bone (cancellous or trabecular) with a red bone marrow filling OF NOTE: Articular cartilage covers parts of the epiphyses that articulate with other bones Metaphyses (pr. me-TAF-i-ses) Are where diaphysis and epiphyses meet It has a cartilagenous epiphyseal plate (pre-pubescent) which is the site of expansive bone growth (genesis)

10. © 2012 Pearson Education, Inc. Structure of a Flat Bone Resembles a sandwich of spongy bone that is between two layers of compact bone Within the cranium, the layer of spongy bone between the compact bone is called the diploë (pr. dip-low-ë) An example is the parietal bone of the skull

11. © 2012 Pearson Education, Inc. Bone Markings refer to surface characteristics of bone: They help in naming parts of bone, and being landmarks for physicians and scientists to locate internal structures Depressions, grooves or tunnels run along and into bone These indicate conduits for vascular and nervous tissue Elevations or projections form out from the bone Where tendons and ligaments attach (very strong!) Where adjacent bones articulate (at joints)

12. © 2012 Pearson Education, Inc. ***We will do this in lab and coming lectures!***

13. © 2012 Pearson Education, Inc. 6-3 Bone (Osseous) Tissue Bone is a dense, supportive connective tissue that is composed of a solid extracellular matrix with several types of specialized cells

14. © 2012 Pearson Education, Inc. Components of the Solid Matrix 1.Calcium Salts are an inorganic component of the solid matrix Two thirds of the bone matrix is calcium phosphate Calcium phosphate reacts with calcium hydroxide and calcium carbonate to form crystals of hydroxyapatite, Ca 10 (PO 4 ) 6 (OH) 2 other minerals are also reactive in this matrix (fluoride, potassium, magnesium), which can pose health-related concerns (radioactive isotopes) The crystals are very hard and resist compression, but they are inflexible and can be broken with a side-way impact 2.Collagen fibers are the organic component of the solid matrix One third of the bone matrix is collagen They are flexible and tough; they can be twisted and bent But they offer little resistance to compression Together, calcium salts and collagen fibers interlock with each other, giving bone its strength, flexibility and shatter-resistant properties…

15. © 2012 Pearson Education, Inc. Bone-specific Cell types Bone Cells make up only 2% of bone mass Bone contains four types of cells 1.Osteoprogenitor (osteogenic) cells 2.Osteoblasts 3.Osteocytes 4.Osteoclasts

16. © 2012 Pearson Education, Inc. Osteoprogenitor cells are mesenchymal stem cells that divide and differentiate to produce osteoblasts They are located in endosteum, the inner cellular layer of periosteum (which is the outer cellular layer of bone) These cells assist in fracture repair

17. © 2012 Pearson Education, Inc. Osteoblasts are immature bone cells that secrete compounds which form the osteoid matrix (osteogenesis) The osteoid matrix is fluid; it is not yet calcified to form bone Osteoblasts that are surrounded by bone become osteocytes

18. © 2012 Pearson Education, Inc. Osteocytes are mature bone cells that maintain bone matrix Osteocytes reside in lacunae between layers (lamellae) of the matrix; they are connected by cytoplasmic extensions through canaliculi They do not divide, but help maintain and repair damaged bone

19. © 2012 Pearson Education, Inc. Osteoclasts secrete acids and protein-digesting enzymes that dissolve the bone matrix and release stored minerals (osteolysis) They are giant, multinucleate cells (many nuclei per cell) Derived from stem cells that produce macrophages

20. © 2012 Pearson Education, Inc. the great balance: homeostasis Bone building (by osteoblasts) and bone recycling (by osteoclasts) must balance  homeostasis! More breakdown than building, bones become weak Exercise, particularly weight-bearing exercise, causes osteoblasts to build bone

21. © 2012 Pearson Education, Inc. 6-4 Types of Bone: Compact and Spongy Compact Bone composes 80% of bone It is dense, supporting body weight and movement The osteon is the basic unit of compact bone: Osteocytes reside in a lacunae cavity and are arranged in concentric lamellae, which surround a central canal that contains blood vessels and nerves Perforating canals are perpendicular to the central canal and carry blood vessels into the bone and the marrow Canaliculi are narrow passageways containing cytoplasmic extensions of osetocytes; they connect osteocytes to each other and to the vasculature Circumferential and Interstitial lamellae are wrapped around the long bone or between the osteons There are two types of bone, compact and spongy… Concentric lamellae Central canal Osteon Perforating canals Circumferential lamellae Interstitial lamellae

22. © 2012 Pearson Education, Inc. NOTE: the criss-crossed orientation of collagen fibers (strength) and the canaliculi networking of osteocytes from the central canal

23. © 2012 Pearson Education, Inc. NOTE: Look at how few lacunae (the residence of osteocytes) there are in the osteon! Remember that mature bone only has a cellular content of about 2%!

24. © 2012 Pearson Education, Inc. Spongy Bone composes 20% of bone and is lighter than compact bone Spongy bone does not have osteons, it is composed of an open network of trabeculae that can withstand stress from many directions Concentric lamellae are present, but are not arranged as osteons The trabeculae have no blood vessels, they are fed by canaliculi The space between the trabeculae is filled with red bone marrow, blood vessels and nerves Forms red blood cells by the process of hematopoesis Supplies nutrients to the osteocytes in the lamellae Concentric Lamellae Trabeculae of spongy bone Canaliculi opening on surface

25. © 2012 Pearson Education, Inc. Except for joint cavities, compact bone is covered with a membrane of periosteum The outer layer is fibrous, dense irregular connective tissue It provides protection and repair to bone Anchors blood vessels and nerves Serves as an attachment site for ligaments and tendons The inner layer is a cellular layer containing cells (osteogenic, osteoblasts and osteoclasts) Sharpey’s Fibers (perforating fibers) are collagen fibers that anchor the periosteum to bone and with fibers of joint capsules, tendons and ligaments

26. © 2012 Pearson Education, Inc. The endosteum in an incomplete cellular layer that lines the medullary (marrow) cavity of compact bone It covers the trabeculae of spongy bone and lines central canals It contains osteoblasts, osteogenic cells and osteoclasts It is active in bone growth and repair

27. © 2012 Pearson Education, Inc. A word about bone marrow: soft connective tissue Adult Bone Marrow Distribution Red bone marrow Contains hematopoietic (hemopoietic) stem cells for the production of red blood cells, white blood cells and platelets It is used in bone marrow transplantation (commonly pulled from the hip bone of the donor) Children contain mostly red bone marrow in the medullary cavity & epiphyses of long bones and spongy bone of flat bones In adults, red bone marrow is restricted to mostly flat bones – the skull, vertebrae, ribs, sternum and ilium

28. © 2012 Pearson Education, Inc. Adult Bone Marrow Distribution Yellow bone marrow Is widespread in adults and consists of fat (adipose) cells that store energy reserves: It is found in the medullary cavity and epiphyses of long bones and in the spongy bone of flat bones It is not found in skull flat bones, the vertebrae, ribs, sternum and ilium, the proximal epiphysis of the humerus and the femur Yellow bone marrow is not hematopoetic

29. © 2012 Pearson Education, Inc. Human bones form until age 25 (osteogenesis); the process of bone formation is called ossification Ossification begins in the fetus with mesenchymal tissue that will undergo transformation to form bones. There are two main forms of ossification: Endochondral ossification is an expansive process – the replacement of dividing hyaline cartilage with osseous tissue Intramembranous ossification is a layered process – the direct development of osseous tissue from mesenchyme or fibrous connective tissue 6-5 Bone Formation and Growth https://www.youtube.com/watch?v=NM8zQLJ1ipQ

30. © 2012 Pearson Education, Inc. Endochondral Ossification (Most bones are formed by this process…) 1.As an embryo, mesenchymal cells differentiate into chondroblasts, which lay down a cartilage matrix mold and differentiate into chondrocytes 2.As the cartilage expands (enlarges), chondrocytes near the center of the shaft greatly increase in size 3.The mold of cartilage matrix then begins to calcify into supportive “struts” and the enlarged chondrocytes die, leaving gaping cavities within the cartilage (this is the origin of the medullary cavity)

31. © 2012 Pearson Education, Inc. 1.Blood vessels begin to grow around the central edges of perichondrium, which is centrally localized cartilage tissue 2.Nourishment by the blood, along with differentiating factors, causes the perichondrial cartilage to differentiate into periosteal bone 3.The cartilage shaft is now ensheathed in a superficial layer of bone

32. © 2012 Pearson Education, Inc. 3 1.Blood vessels penetrate the cartilage and invade the central region 2.Fibroblasts migrate with the blood vessels and differentiate into osteoblasts, producing a medullary cavity of spongy bone at the primary ossification center 3.Bone formation now spreads along the shaft to both ends

33. © 2012 Pearson Education, Inc. 1.Remodeling takes place as growth continues, expanding the medullary cavity 2.In addition, the osseous tissue of the shaft becomes thicker, and the cartilage near each end (epiphysis) is replaced by bone. 3.Thus, further bone growth involves increases in length (interstitial growth) and diameter (appositional growth) Appositional growth is performed by osteoclasts of the endosteum, which deposit layers of circumferential lamellae on the outer surface of bone along periosteum

34. © 2012 Pearson Education, Inc. 1.Capillaries and osteoblasts migrate into the epiphyses (into the ends of bone) 2.This results in the generation of secondary ossification centers Take note of the location of the metaphysis, this is where the real magic happens! pronounced: EP-IF-A-SIS MET-AF-A-SIS DI-AF-I-SIS

35. © 2012 Pearson Education, Inc. 1.Once again, nourishment by the blood, along with differentiating factors, causes the epiphyses to become filled with spongy bone 2.(MAGIC TIME!) The metaphysis is a narrow cartilage-rich region, referred to as epiphyseal cartilage (or the epiphyseal plate) 3.This structure separates the epiphyses (tips) from the diaphysis (shaft) 4.On the “shaft” side, osteoblasts continue to invade the degenerating cartilage and replace it with new bone 5.Meanwhile, new cartilage is produced at the same rate on the “tip” side (the figure explains it well)

36. © 2012 Pearson Education, Inc. 1.At puberty, higher levels of sex hormones reduce “tip” cartilage production while stimulating “shaft” bone production (causing a dramatic increase in bone growth) 2.As a result, the epiphyseal cartilage gets more narrow, until it disappears (this is termed epiphyseal closure), causing the formation of an epiphyseal line, signifying the stopping point of bone formation 3.This line is clearly visible in radiographs (next slide…) NOTE: articular cartilage remains to cushion bone in joint sockets

37. © 2012 Pearson Education, Inc. An x-ray showing epiphyseal plate in a child (arrows) An x-ray showing epiphyseal lines in an adult (arrows) NOTE: Appositional bone growth can still occur after puberty (bones can still get thicker, just not longer)

38. © 2012 Pearson Education, Inc. Intramembranous Ossification is also referred to as dermal ossification It produces dermal bones, such as the mandible (lower jaw), the clavicle (collarbone) and the flat bones of the skull 1 Bone matrix Osteoid Mesenchymal cell Ossification center Blood vessel Osteoblast During fetal development, mesenchymal cells cluster together, differentiate into osteoblasts, and start to secrete organic components of the matrix (osteoid fluid). The resulting osteoid fluid becomes mineralized with calcium salts forming the bone matrix of the ossification center. Parietal bone Occipital bone Frontal bone Mandible

39. © 2012 Pearson Education, Inc. 2 Osteocyte Spicules As ossification proceeds, some osteoblasts are trapped inside bony pockets, where they differentiate into osteo- cytes, maintaining and expanding the matrix. The developing bone grows out from the ossification center in small struts called spicules, which interconnect ossification centers. 3 Blood vessel trapped within bone matrix Blood vessels begin to branch within the region and grow between the spicules. The rate of bone growth accelerates with oxygen and a reliable supply of nutrients. As spicules interconnect, they trap blood vessels within the bone.

40. © 2012 Pearson Education, Inc. 4 Continued deposition of bone by osteoblasts located close to blood vessels results in a plate of spongy bone with blood vessels weaving throughout. Fibrous periosteum 5 Blood vessels trapped within bone matrix Cellular periosteum Subsequent remodeling around blood vessels produces osteons typical of compact bone. Osteoblasts on the bone surface along with connective tissue around the bone become the periosteum. Areas of spongy bone are remodeled forming the diploë and a thin covering of compact (cortical) bone.

41. © 2012 Pearson Education, Inc. …another perspective on the process

42. © 2012 Pearson Education, Inc. Blood Supply of Mature Bones 1.Nutrient Vessels (arteries and veins) Is a single pair of large blood vessels (the femur has more than one pair) It enters the diaphysis through the nutrient foramen 2.Metaphyseal Vessels Supply the epiphyseal cartilage, facilitating bone expansion in childhood and adolescence 3.Periosteal Vessels Supply blood to superficial osteons and secondary ossification centers, facilitating appositional growth lymph and nerve also innervate the periosteum Nutrient foramen Perforating canal Metaphyseal vessels Periosteal vessels Nutrient vessels

43. © 2012 Pearson Education, Inc. 6-6 Bone Remodeling Bone continually undergoes changes; this is the process of remodeling (Bone is built by osteoblasts; recycled by osteoclasts) During development: deposition > resorption (growth) At maturity: deposition = resorption (maintainance) During aging: resorption > deposition (loss)

44. © 2012 Pearson Education, Inc. 6-7 Exercise, Hormones, and Nutrition Effects of Exercise on Bone Exercise, particularly weight-bearing exercise, causes osteoblasts to build bone; heavily stressed bones become thicker and stronger Bone Degeneration Bone degenerates quickly; up to one third of bone mass can be lost in a few weeks of inactivity (just imagine what happens when you are in a coma)

45. © 2012 Pearson Education, Inc. Normal Bone Growth and Maintenance Depend on Nutritional and Hormonal Factors Minerals – Calcium and phosphorous; smaller amounts of magnesium, fluoride, iron and manganese are needed for remodeling and growth Vitamins –Vitamin C needed for normal production of collagen. –Folic Acid and Vitamin B for protein production. –Vitamin A stimulates osteoblasts –Vitamins K and B 12 help synthesize other bone proteins

46. © 2012 Pearson Education, Inc. Hormones –Human growth hormone, which is produced by the pituitary gland, stimulates osteoblasts. This increases protein synthesis and cell division at the epiphyseal plate and periosteum. –Thyroid hormones (T3 and T4), produced by the thyroid gland, also stimulates osteoblasts (results as above) –Sex hormones (estrogen and androgens) are produced in the gonads. They initially stimulate bone growth by increasing osteoblast activity, resulting in a growth spurt at puberty. But as their secretions increase, epiphyseal plates become ossified to form epiphyseal lines, terminating growth –Parathyroid hormone, produced in the thyroid, stimulates osteoclast activity, resulting in increased bone resorption and calcium reabsorption in the kidney, increasing blood calcium levels –Calcitonin, produced in the thyroid, inhibits osteoclast activity, preserving bone and increasing calcium secretion in the kidney (lower blood calcium) –Calcitriol (activated Vitamin D 3 ), which is produced in the kidneys, helps absorb calcium and phosphorus from the digestive tract. Insufficient vitamin D can result in rickets in children, or osteomalacia in adults

47. © 2012 Pearson Education, Inc.

48. Pituitary dwarfismMarfan’s syndrome

49. © 2012 Pearson Education, Inc. 6-8 Calcium Homeostasis The skeleton is a calcium reserve Bones store calcium and other minerals Calcium is the most abundant mineral in the body and is vital for several bodily functions, including: Nerve conduction Muscle contraction Blood coagulation Cell-signaling Cofactors in enzymatic reactions

50. © 2012 Pearson Education, Inc. Composition of Bone Bone Contains … 99% of the body’s Calcium 4% of the body’s Potassium 35% of the body’s Sodium 50% of the body’s Magnesium 80% of the body’s Carbonate 99% of the body’s Phosphate Calcium 39% Potassium 0.2% Sodium 0.7% Magnesium 0.5% Carbonate 9.8% Phosphate 17% Total inorganic components 67% Organic compounds (mostly collagen) 33%

51. © 2012 Pearson Education, Inc. The concentration of calcium ion must be tightly regulated in bodily fluids (bloodstream) Homeostasis is maintained by two hormones: Parathyroid Hormone (PTH) Produced by parathyroid glands in neck Increases calcium ion levels by: 1.Stimulating osteoclasts, increasing bone resorption 2.Increasing intestinal absorption of calcium 3.Decreasing calcium excretion at kidneys Calcitonin Secreted by C cells (parafollicular cells) in thyroid Decreases calcium ion levels by: 1.Inhibiting osteoclast activity, decreasing bone resorption 2.Increasing calcium excretion at kidneys

52. © 2012 Pearson Education, Inc. Bone ResponseIntestinal ResponseKidney Response Parathyroid Gland Response Factors That Increase Blood Calcium Levels These responses are triggered when plasma calcium ion concentrations fall below 8.5 mg/dL. Low Calcium Ion Levels in Plasma (below 8.5 mg/dL) Low calcium plasma levels cause the parathyroid glands to secrete parathyroid hormone (PTH). Osteoclasts stimulated to release stored calcium ions from bone Osteoclast Bone Rate of intestinal absorption increases Kidneys retain calcium ions PTH more calcitriol Calcium released Calcium absorbed quickly Calcium conserved Decreased calcium loss in urine ↑Ca 2+ levels in bloodstream

53. © 2012 Pearson Education, Inc. Bone Response Intestinal Response Kidney Response Thyroid Gland Response Factors That Decrease Blood Calcium Levels These responses are triggered when plasma calcium ion concentrations rise above 11 mg/dL. HIgh Calcium Ion Levels in Plasma (above 11 mg/dL) Parafollicular cells (C cells) in the thryoid gland secrete calcitonin. Osteoclasts inhibited while osteoblasts continue to lock calcium ions in bone matrix Bone Rate of intestinal absorption decreases Kidneys allow calcium loss Calcitonin less calcitriol Calcium stored Calcium absorbed slowly Calcium excreted Increased calcium loss in urine ↓Ca 2+ levels in bloodstream

54. © 2012 Pearson Education, Inc. 6-9 Fractures Fractures are cracks or breaks in bones that are caused by physical stress Fractures are repaired in four steps: Fracture hematoma formation : Immediately after fracture, extensive bleeding causes a large clot to form (fracture hematoma). 1 Callus formation: Internal and External calluses form, producing an internal spongy bone network and an external seal of cartilage and bone. 2 Spongy bone formation: The external seal of cartilage is replaced by bone; struts of spongy bone unite the broken ends. Fragments of dead bone have been removed. 3 Compact bone formation. Initial swelling subsides with remodeling. Almost as good as new! 4 Dead boneBone fragmentsPeriosteum Spongy bone of external callus Spongy bone of internal callus Cartilage of external callus Internal callusExternal callus External callus

55. © 2012 Pearson Education, Inc. the types of fractures… (Be able to match a description of the type of fracture with its name, this would make a great question on the lab exam, eh?…) Fractures are named according to their external appearance, location and the nature of the crack or the break in the bone The broadest general categories are: Closed (simple) fractures that are completely internal and can only be visualized by x-rays Open (compound) fractures that project through the skin, which can complicate the condition with secondary infection Many fractures fall into more than one category, because terms overlap…

56. © 2012 Pearson Education, Inc. Transverse fractures break a bone shaft along its long axis ulna

57. © 2012 Pearson Education, Inc. Displaced fractures produce new and abnormal bone arrangements. (Nondisplaced fractures retain the normal alignment)

58. © 2012 Pearson Education, Inc. Compression fractures occur in vertebrae subjected to extreme stresses. (like falling on your backside in an abrupt “sitting” manner)

59. © 2012 Pearson Education, Inc. Spiral fractures are produced by twisting stresses that spread along the length of the bone. tibia

60. © 2012 Pearson Education, Inc. Epiphyseal fractures tend to occur where the bone matrix is undergoing calcification and the chondrocytes are dying. Clean transverse fractures heal well (for obvious reasons) if treated properly. femur

61. © 2012 Pearson Education, Inc. Comminuted fractures shatter the affected area into many bony fragments. femur

62. © 2012 Pearson Education, Inc. Greenstick fractures are a partial fracture, where one side of the shaft is broken and the other side is bent. This happens frequently in children. radius

63. © 2012 Pearson Education, Inc. Colles fractures are a break in the distal portion of the radius. (typically caused by extending your hand to cushion a fall)

64. © 2012 Pearson Education, Inc. Pott’s fractures occur at the ankle and affect both bones of the leg. (this is a common sports injury)

65. © 2012 Pearson Education, Inc. 6-10 Adverse Effects on the Skeletal System Bones become thinner and weaker with age Osteopenia begins between the ages of 30 and 40 Demineralization and decollagenation occur Women lose 8% of bone mass per decade, men 3% The epiphyses, vertebrae and jaws are most affected, resulting in fragile limbs, a reduction in height and tooth loss Osteoporosis is a severe loss in bone mass Bone resorption far outweighs deposition, due to a drop in estrogen and testosterone Over age 45, occurs in: 29% of women, 18% of men The femur, vertebrae and wrist are most affected

66. © 2012 Pearson Education, Inc. Figure 6-18 The Effects of Osteoporosis on Spongy Bone SEM  25 Normal spongy bone Spongy bone in osteoporosis SEM  21

67. © 2012 Pearson Education, Inc. Cancer contributes to bone Loss Cancerous tissues release osteoclast-activating factor, stimulating the degradation of bone, causing severe osteoporosis (Why would a cancer want to degrade bone?)

68. © 2012 Pearson Education, Inc. Osteoporosis: Traditional Treatments Calcium and vitamin D supplements Increased exercise Estrogen-replacement therapy in menopausal women (may increase breast cancer, stroke, heart disease) Osteoporosis: Newer Treatments SERMs: Selective Estrogen Receptor Modulators (Evista, tamoxifen) Biphosphonate drugs(Fosamax)-destroy osteoclasts Prolia: injected antibody that interferes with formation of osteoclasts Osteoporosis: The key is prevention Weight-bearing exercise and diet containing adequate amount of calcium and vitamin D throughout life and especially when young