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The SkeletalSystem:

Bone Tissue6.1-6.4

Chapter 6 - The Skeletal System:Bone Tissue• 6.1 Functions of Bone & the Skeletal System• 6.2 Structure of Bone• 6.3 Histology of Bone Tissue• 6.4 Blood & Nerve Supply of Bone• 6.5 Bone Formation• 6.6 Fracture & Repair of Bone• 6.7 Bone’s Role in Calcium Homeostasis• 6.8 Exercise & Bone Tissue• 6.9 Aging & Bone Tissue

The Big Idea• Bone Tissue & Homeostasis

– Bone tissue is continuously growing, remodeling,and repairing itself. It contributes to homeostasisof the body by providing support andprotection, producing blood cells, and storingminerals and triglycerides

6.1 Functions of Bone and the SkeletalSystem• Objectives

• Describe the six main functions of theskeletal system

• A bone is made up of several different tissues

– Bone or osseous tissue

– Cartilage

– Dense connective tissue

– Epithelium

– Adipose tissue

– Nervous tissue

• The entire framework of bone and their cartilagesconstitutes the skeletal system

• The skeletal system has 6 important functions:• Provide support by acting as a structural

framework and a point of attachment for tendonsand 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

6.2 Structure of Bone• Objectives

• Describe the structure and functions of eachpart of a long 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 (Ca3PO4)2

• Calcium Carbonate (CaCO3 – marble)•Other trace elements: magnesium, fluoride,

sulfate

• 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 organsystem), the skeletal system is made ofseveral different tissues• The two major tissues are bone

(osseous tissue) and cartilage

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• Bone is a highly vascularized CT with a hard,mineralized extracellular matrix

• Bone is found in the body in two differentarrangements

• Compact bone

• Spongy bone

• Compact bone is good atproviding protection and support

• It forms the diaphysis of longbones, and the external layer ofall bones

• Spongy bone is lightweight andprovides tissue support

• It forms much of the epiphysisand the internal cavity of longbones

• Cartilage is a poorly vascularized CT with amatrix composed of chondroitin sulfate andvarious fibers

• Fiber types distinguish hyaline cartilage fromfibrocartilage or elastic cartilage

• Articular cartilage is the thin layerof hyaline cartilage covering theepiphysis of long bones

• Articular cartilage is foundwhere the bone forms anarticular (joint) surface - whereone bone moves againstanother bone

• The periosteum is a tough sheathof dense, irregular connectivetissue on the outside of the bone

• It contains osteoblasts that helpthe bone grow in thickness, butnot in length

• It also assists with fracturerepair and serves as anattachment point for tendonsand ligaments

• The medullary cavity is aspace within the diaphysis oflong bones that containsfatty yellow bone marrow inadults

• The endosteum is amembrane that lines themedullary cavity• The endosteum is

composed of osteoclasts,osteoblasts, andconnective tissue

• The perichondrium is a denseirregular connective tissuemembrane that surroundscartilage

• Chondrocytes are cells thatform cartilage

• Many of the major bones areformed from cartilage

• The humerus in the arm is atypical long bone

• 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

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• In adolescents, through theend of active growth, theepiphysis of the long bonescontains hyalinecartilage andforms an “epiphyseal growthplate”

• The growth plate isalways actively dividingand causing the bone toelongate from each end

• In adults, the epiphysealcartilage is no longer presentand elongation of bones hasstopped• The epiphyseal growth

plate becomes an“epiphyseal line”,as growingcartilage is replaced bycalcified bone• The epiphyseal line is

visible externally and onX-rays

6.3 Histology of Bone Tissue• Objectives

• Explain why bone tissue is classified as aconnective tissue

• Describe the cellular composition of bonetissue and the functions of each type of cell

• Compare the structural and functionaldifferences between compact and spongybone tissue

• Bone tissue consists of widely separated cellssurrounded by large amounts of extracellularmatrix

• There are four principal types of cells in bonetissue

– Osteogenic cells

– Osteoblasts (bone building cells)

– Osteocytes (maintain daily activity of bone)

– Osteoclasts (bone destroying cells)

• The extracellular matrix of bone containsabundant mineral salts and collagen fibers

• Osteoblasts are bone building cells: They synthesizeand secrete collagen fibers and other organiccomponents

• Osteocytes are mature osteoblasts (maintenance)

• Osteoclasts are large bone breakdown cells

• As white blood cells, osteoclasts migrated fromthe bone marrow to become “fixedmacrophages” in the substance of the bone.

• Besides bone and cartilage, theskeletal system contains otherimportant tissues:

• Epithelium (endothelium) formthe capillary walls

• Nerves (the periosteum isespecially tender)

• Red marrow – hematopoiesis

• Yellow marrow – fat storage

Compact 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

• Outer circumferential lamellae encircle the bonebeneath the periosteum

• Inner circumferential lamellae encircle themedullary cavity

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• Lacunae are small spaces between the lamellaewhich house osteocytes

• Canaliculi are small channels filled withextracellular fluid connecting the lacunae

• Blood and lymphatic vessels are found in theosteon’s Central canal

• Perforating (Volkmann’s) canals allow transit ofthese vessels to the outer cortex of the bone

• Compact bone tissue lies over spongy bone tissuein the epiphyses and makes up most of the bonetissue of the diaphysis

• Compact bone is the strongest form of bone andprotects, supports, and resists stress

Spongy 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 areoriented along lines of stress (helpsbones resist stresses without breaking)

• Hematopoiesis (blood cell production)occurs in spongy bone

• Within each trabecula of spongy bone arelacunae

• As in compact bone, lacunae containosteocytes that nourish the mature bonetissue from the blood circulating through thetrabeculae

• The interior of the epiphysis in long bones is madeup primarily of spongy bone

– The use of spongy bone lessens overall boneweight

• Also forms most of the structure in short, flat, andirregular bones

6.4 Blood and Nerve Supply of Bone• Objectives

• Describe the blood and nerve supply of bone

• Bone is richly supplied withblood• Periosteal, nutrient,

metaphyseal, and epiphysealarteries and veins

• Nerves accompany bloodvessels• The periosteum is rich in

sensory nerves sensitive totearing or tension