Building Material

1. Building Material

2. Functions of the skeletal system • __________________(support for body, attachment for soft tissues) • Storage of _______________ (calcium and phosphate) • Calcium most abundant mineral in body (~2–4 lb) • 98% stored in bones • Blood ____________ production (all formed elements of blood) • Protection (delicate tissues and organs surrounded by bone) • ____________________ (act as levers with skeletal muscles to move body)

3. Quick Review • Six categories based on shape • ____________ bones • Thin, roughly parallel surfaces • Examples: cranial bones, sternum • Sutural bones (Wormian bones) • Irregular bones formed between cranial bones • Number, size, and shape vary • ___________ bones • Relatively long and slender • Examples: various bones of the limbs

4. Six categories based on shape (continued) • Irregular bones • Complex shapes • Examples: vertebrae, bones of pelvis, facial bones • _______________ bones • Small, flat, and somewhat shaped like sesame seed • Develop in tendons of knee, hands, and feet • Individual variation in location and number • Short bones • Small and boxy • Examples: bones of the wrist (carpals) and ankles (tarsals)

5. Functions of Bone • Bones are important mineral reservoirs • Mostly _____________________________ but other ions as well • Calcium • Most abundant mineral in body • 1–2 kg (2–4 lb) • ~__________% deposited in skeleton • Variety of physiological functions • Concentration variation greater than 30–35% affects neuron and muscle function • Normal daily fluctuations are <10%

6. Levels controlled by activities of: • Intestines • Absorb calcium and phosphate under hormonal control • Bones • Remodeling by osteoblasts and osteoclasts • Kidneys • Calcium and phosphate loss in urine under hormonal control • As a calcium reserve, skeleton has primary role in calcium _________________________ • Has direct effect on shape and length of bones • Release of calcium into blood weakens bones • Deposit of calcium salts strengthens bones

7. Factors that increase blood calcium levels • ____________________ hormone • Responses • Bones: stimulates osteoclasts to release calcium • Intestines: enhances calcitriol effects and increases calcium absorption • Kidneys: increase release of hormone calcitriol, which causes calcium reabsorption in kidneys

8. Factors that decrease blood calcium levels • ___________________ • Responses • Bone: decrease osteoclast activity • Intestines: decreased absorption with decreasing PTH and calcitriol • Kidneys: inhibits calcitriol release and calcium reabsorption

10. Long bone features • ______________________ (expanded ends) • Consist largely of _________________ bone (trabecular bone) • Network of struts and plates • Resists forces from various directions and directs body weight to diaphysis and joints • Outer covering of ______________________ bone • Strong, organized bone • Articular _________________________ • Covers portions of epiphysis that form articulations • Avascular and receives resources from synovial fluid

11. Long bone features (continued) • _____________________________ (connects epiphysis to shaft) • ______________________ (shaft) • Contains medullary cavity (marrow cavity) • Filled with marrow • Red bone marrow (red blood cell production) • Yellow bone marrow (adipose storage)

12. Figure 6.2 1 - 2 Coronal sections through a right femur, showing the boundaries of a long bone’s major regions, plus the bone’s internal organization and how it distributes the forces applied to the bone The epiphysis consists largely of spongy bone, also called trabecular bone. Spongy bone consists of an open network of struts and plates that resembles latticework with a thin covering, or cortex, of compact bone. Body weight (applied force) The epiphysis (e-PIF-i-sis) is an expanded area found at each end of the bone. The metaphysis (me-TAF-i-sis; meta, between) is a narrow zone that connects the epiphysis to the shaft of the bone. The wall of the diaphysis consists of a layer of compact bone. Tension on lateral side of shaft The medullary cavity (medulla, innermost part), or marrow cavity, is a space within the hollow shaft. In life, it is filled with bone marrow, a highly vascular tissue. Red bone marrow is highly vascular and involved in the production of blood cells. Yellow bone marrow is adipose tissue important in the storage of energy reserves. The diaphysis (shaft) is long and tubular. Compression on medial side of shaft Metaphysis Epiphysis

14. Figure 6.2 3 A longitudinal section of the humerus, showing the extensive|network of blood vessels in long bones An articular cartilage covers portions ofthe epiphysis that articulate with other bones. The cartilage is avascular, and itrelies primarily on diffusion from thesynovial fluid to obtain oxygen andnutrients and eliminate wastes. Epiphyseal arteryand vein The metaphyseal artery (red) andmetaphyseal vein (blue) carry blood toand from the area of the metaphysis and tothe epiphysis through epiphyseal arteriesand veins. Metaphysis Most bones have only onenutrient artery (shown inred) and one nutrient vein(shown in blue), but a fewbones, including the femur,have more than one of each. Periosteum Compactbone Medullarycavity A nutrient foramen is a tunnel that penetrates thediaphysis and providesaccess for the nutrient arteryand/or vein. Branches ofthese large vessels supplythe osteons of thesurrounding compact bonebefore entering andsupplying the tissues of themedullary cavity. Metaphysealartery and vein Metaphysis

15. Bone vasculature • Growth and maintenance requires extensive _______________________ supply • Vascular features • Nutrient artery/vein (commonly one each/bone) • Nutrient __________________(tunnel providing access to marrow cavity) • Also supplies osteons of compact bone with blood • Metaphyseal artery/vein • Carry blood to/from metaphysis • Connects to epiphyseal arteries/veins

16. _____________________ features • Smaller blood vessels (supply superficial osteons) • Lymphatic vessels (collect lymph from bone and osteons) • ____________________ nerves (innervate diaphysis, medullary cavity, and epiphyses)

18. Bone cells • Four bone cell types • __________________________ (osteo-, bone + cyte, cell) • Mature bone cells that cannot divide • Most numerous bone cell type • Maintain protein and mineral content of adjacent matrix • Dissolve matrix to release minerals • Rebuild matrix to deposit mineral crystals • Occupy ____________________(pocket) • Separated by layers of matrix (lamellae) • Connected with canaliculi

19. ______________________ (blast, precursor) • Produce new bony matrix (osteogenesisor ossification) • Begins with release of proteins and other organic components to produce unmineralized matrix (= osteoid) • Then assists in depositing calcium salts to convert osteoid to bone • Become osteocytes once surrounded by bony matrix

20. Figure 6.3 1 - 2 The structures of osteocytes and osteoblasts within a long bone The layers of matrix are called lamellae (lah-MEL-lē; singular, lamella, a thin plate). Narrow passageways called canaliculi penetrate the lamellae, radiating through the matrix and connecting lacunae to one another and to various blood vessels that supply nutrients. Osteocytes account for most of the cell population in bone. Each osteocyte occupies a lacuna, a pocket sandwiched between layers of matrix. Osteocytes cannot divide, and a lacuna never containsmore than one osteocyte. Osteoblast Osteoid

21. _________________________ cells (progenitor, ancestor) • Mesenchymal (stem) cells that produce cells that differentiate into osteoblasts • Important in fracture repair • Locations • Inner lining of periosteum • Lining endosteum in medullary cavity • Lining passageways containing blood vessels

22. ______________________ (clast, to break) • Remove and remodel bone matrix • Giant cells with ______________+ nuclei • Derived from same stem cells as macrophages • Release acids and proteolytic enzymes to dissolve matrix and release stored minerals • = Osteolysis(lysis, loosening)

23. Figure 6.3 3 - 4 The structures of osteocytes and osteoblasts within a long bone Endosteum Osteoprogenitor cell Osteoclast

25. Building a bone • Bone _________________ • Collagen fibers account for ~1/3 bone weight • Provide _________________ • Calcium phosphate (Ca3(PO4)2) accounts for ~2/3 bone weight • Interacts with calcium hydroxide (Ca(OH)2) to form crystals of hydroxyapatite (Ca10(PO4)6(OH)2) salts • Incorporates other salts (calcium carbonate, CaCO3) and ions (Na, Mg2, F) • Provides _______________________

26. _________________ bone • Functional unit is _________________ • Organized concentric lamellae around a central canal • Osteocytes (in lacunae) lie between lamellae • Central canal contains small blood vessels • Canaliculi connect lacunae with each other and central canal • Strong along its length

27. Figure 6.4 1 - 2 The structure of compact bone, as shown in the shaft of a long bone Capillary and venule Central canal Concentric lamellae Canaliculi radiating through the lamellae interconnect the lacunae of the osteons with one another and with the central canal. Endosteum Central canal Periosteum Circumferential lamellae Osteon Vein Interstitial lamellae Artery Compact bone LM x 375 The osteocytes occupy lacunae that lie between the lamellae. In preparing this micrograph, a small piece of bone was ground down until it was thin enough to transmit light. In this process, the lacunae and canaliculi are filled with bone dust, and thus appear black. Central canal Perforating canal

28. Typical long bone organization • Periosteum (outermost layer) • Compact bone (outer bone tissue layer) • ___________________________ lamellae (circum-, around + ferre, to bear) • Outer and inner surfaces of compact bone layer • Interstitial lamellae • Fill spaces between osteons • _______________________________ • Contain central canals (parallel to bone surface) • Connected by perforating canals (perpendicular) • Spongy bone (innermost layer)

29. _______________________ bone • Located where bones not heavily stressed or in many directions • Lamellae form struts and plates (trabeculae) creating an open network • _______________________ weight of skeleton • No blood vessels in matrix • Nutrients reach osteons through ___________________________________ open to trabeculae surfaces

30. Figure 6.4 3 – 4 The structure of spongy bone, as shown in the head of the femur Trabeculae of spongy bone Canaliculi opening on surface Endosteum Lamellae

31. _____________________ bone growth • Increases bone diameter of existing bones • Does not form original bones • Osteoprogenitor cells differentiate into osteoblasts that ____________ bone matrix under periosteum • Adds successive _____________________ of circumferential lamellae • Trapped _____________________ become osteocytes • Deeper lamellae recycled and replaced by osteons • Osteoclasts remove matrix at inner surface to enlarge medullary cavity

32. Figure 6.5 1 Increase in bone diameter resulting from appositional growth Additional circumferential lamellae are deposited, and the bone continues to increase in diameter. Periosteum

34. Figure 6.5 2 Enlargement of the medullary cavity with increased bone diameter resulting from appositional growth Bone matrix is removed by osteoclasts Bone deposited by superficial osteoblasts Infant Child Adult Young adult

35. _________________ • Two layers • _________________________ outer layer • _____________________________ inner layer • Functions • ________________ bone from surrounding tissues • Route for blood and nervous supply • Actively participate in bone growth and _____________________

36. ____________________ fibers • Created by osteoblasts in periosteum cellular layer • Strongly connect tendons, ligaments, and joint capsules to bone through periosteum

37. Figure 6.5 3 Structure of the periosteum Circumferential lamellae Fibrous layer of periosteum Cellular layer of periosteum Canaliculi Osteocyte in lacuna Perforating fibers

38. __________________ • Incomplete cellular layer lining medullary cavity • Covers spongy bone and lines central canals • Consists of simple layer of osteoprogenitor cells • Where incomplete, osteoclasts and osteoblasts remodel matrix

39. Figure 6.5 4 Structure of the endosteum Endosteum Osteoclast Circumferential lamella Osteocyte Osteoprogenitor cell Osteoid Osteoblast

40. Fetal bone developement • Initial bone formation in embryo begins with ______________________ • Replaced by bone through endochondral(endo-, inside + chondros, cartilage) _______________________________ • Uses cartilage as small model • Bone grows in diameter and length • Diameter growth involves appositional bone deposition

41. Steps of endochondral ossification • In shaft, _______________________ enlarge and matrix ossifies • Chrondrocytes die, leaving cavities within cartilage • ___________________ vessels grow around cartilage edge and osteoblasts form to create a superficial layer of bone • Blood vessels penetrate central region • Allow entering fibroblasts to change into osteoblasts • Spongy bone produced (_______________________________ ossification center) and spreads toward bone ends

42. _____________________ cavity created as cartilage replaced by osseous tissue • Bone grows in length and diameter • __________________ ossification centers form as capillaries and osteoblasts migrate into epiphyses • Epiphyses fill with __________________ bone • Only articular cartilage (on epiphyses) and epiphyseal cartilage (in metaphysis) remain

43. Figure 6.6 1 – 6 The process of endochondral ossification Hyaline cartilage Articular cartilage Spongy bone Epiphysis Enlarging chondrocytes within calcifying matrix Metaphysis Epiphysis Epiphyseal cartilage Medullary cavity Medullary cavity Periosteum Blood vessel Primary ossification center Diaphysis Compact bone Superficial bone Diaphysis Spongy bone Formation of an epiphyseal cartilage between epiphysis and diaphysis Metaphysis Bone formation Secondary ossification center Hyaline cartilage Further growth in length and diameter Enlargement of chondrocytes Formation of superficial layer of bone Production of spongy bone at a primary ossification center Formation of secondary ossification centers

44. Bone grows in _________________ at epiphyseal cartilage • Chondrocytes actively produce more cartilage on epiphysis side • Osteoblasts _____________________ replace cartilage with bone on shaft side • As long as both processes are equally active, bone lengthening continues • At puberty, hormones increase bone growth and epiphyseal cartilage is replaced • Leaves _____________________________________________________in adults

45. Intramenbranous ossification • Steps of intramembranous ossification • _____________________________ cells secrete osteoid matrix • Differentiate into osteoblasts • Osteoid matrix becomes mineralized • Forms _________________________________ • Bone grows out in small struts (____________________________) • Osteoblasts become trapped and mature into osteocytes • Mesenchymal cells produce more osteoblasts • Blood vessels enter and become trapped in developing bone

46. Further membranous bone development • __________________ bone formed initially • Remodeling around blood vessels forms osteons of compact bone • Periosteum forms, lined with osteoblasts • Begins at approximately ____________ week of embryonic development • Examples: • Roofing bones of skull • Lower jaw • Collarbone • Sesamoid bones such as patella

47. Figure 6.7 4 16 weeks of development 10 weeks of development Flat bones of the skull Intramembranous ossification centers that produce the roofing bones of the skull Primary ossification centers of the long bones of the lower limb Future hip bone Long bones of the limbs The extent of intramembranous and endochondrial ossification occurring between 10 and 16 weeks of development

48. Abnormal Bone Growth • Endocrine and metabolic problems can affect the skeletal system

49. Figure 6.8 1 • Reduction in _______________ hormone leads to reduced epiphyseal cartilage activity and short bones

50. Figure 6.8 2 • Epiphyseal cartilage grows unusually slowly