Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 1 Chapter 7 Skeletal Tissues.

Mosby items and derived items © 2007, 2003 by Mosby, Inc.

Chapter 7Chapter 7Skeletal TissuesSkeletal Tissues


Types of BonesTypes of Bones• Structurally, there are four types of bones Structurally, there are four types of bones

(Figure 7-1):(Figure 7-1):

Long bones - ALong bones - A

Flat bones - BFlat bones - B

Short bones - CShort bones - C

Irregular bones - DIrregular bones - D

• Bones serve various needs, and their size, Bones serve various needs, and their size, shape, and appearance will vary to meet shape, and appearance will vary to meet those needsthose needs


Types of BonesTypes of Bones

• Bones vary in their proportions of compact Bones vary in their proportions of compact and cancellous (spongy) bone; compact bone and cancellous (spongy) bone; compact bone is dense and solid in appearance, whereas is dense and solid in appearance, whereas cancellous bone is characterized by open cancellous bone is characterized by open space partially filled with needle-like space partially filled with needle-like structuresstructures


Types of BonesTypes of Bones• Parts of a long bone Parts of a long bone

(Figure 7-2)(Figure 7-2)

DiaphysisDiaphysis

• Main shaft of long Main shaft of long bonebone

• Hollow, cylindrical Hollow, cylindrical shape and thick, shape and thick, compact bonecompact bone

• Function is to provide Function is to provide strong support without strong support without cumbersome weightcumbersome weight



• Parts of a long bone (cont.)Parts of a long bone (cont.)

EpiphysesEpiphyses

• Both ends of a long bone, made of cancellous bone filled Both ends of a long bone, made of cancellous bone filled with marrowwith marrow

• Bulbous shapeBulbous shape

• Function is to provide attachments for muscles and give Function is to provide attachments for muscles and give stability to jointsstability to joints




Articular cartilageArticular cartilage

• Layer of hyaline cartilage that covers the articular Layer of hyaline cartilage that covers the articular surface of epiphysessurface of epiphyses

• Function is to cushion jolts and blowsFunction is to cushion jolts and blows




PeriosteumPeriosteum

• Dense, white, fibrous membrane that covers boneDense, white, fibrous membrane that covers bone

• Attaches tendons firmly to bonesAttaches tendons firmly to bones

• Contains cells that form and destroy boneContains cells that form and destroy bone

• Contains blood vessels important in growth and repairContains blood vessels important in growth and repair

• Contains blood vessels that send branches into boneContains blood vessels that send branches into bone

• Essential for bone cell survival and bone formationEssential for bone cell survival and bone formation




Medullary (or marrow) cavityMedullary (or marrow) cavity

• Tubelike, hollow space in diaphysisTubelike, hollow space in diaphysis

• Filled with yellow marrow in adultFilled with yellow marrow in adult

Endosteum—thin epithelial membrane that lines Endosteum—thin epithelial membrane that lines medullary cavitymedullary cavity



• Short, flat, and irregular bonesShort, flat, and irregular bones

Inner portion is cancellous bone, covered on the Inner portion is cancellous bone, covered on the outside with compact boneoutside with compact bone

Spaces inside cancellous bone of a few irregular Spaces inside cancellous bone of a few irregular and flat bones are filled with red marrowand flat bones are filled with red marrow


Bone TissueBone Tissue

• Most distinctive form of connective tissueMost distinctive form of connective tissue

• Extracellular components are hard and Extracellular components are hard and calcifiedcalcified

• Rigidity of bone allows it to serve its Rigidity of bone allows it to serve its supportive and protective functionssupportive and protective functions

• Tensile strength is nearly equal to cast iron at Tensile strength is nearly equal to cast iron at less than one third the weightless than one third the weight



• Composition of bone matrixComposition of bone matrix

Inorganic saltsInorganic salts

• Hydroxyapatite—highly specialized chemical crystals of Hydroxyapatite—highly specialized chemical crystals of calcium and phosphate contribute to bone hardnesscalcium and phosphate contribute to bone hardness

• Slender, needle-like crystals are oriented to most Slender, needle-like crystals are oriented to most effectively resist stress and mechanical deformationeffectively resist stress and mechanical deformation

• Magnesium and sodium are also found in boneMagnesium and sodium are also found in bone



• Composition of bone matrix (cont.)Composition of bone matrix (cont.) Measuring bone mineral densityMeasuring bone mineral density

Organic matrixOrganic matrix

• Composite of collagenous fibers and an amorphous Composite of collagenous fibers and an amorphous mixture of protein and polysaccharides called mixture of protein and polysaccharides called ground ground substancesubstance

• Ground substance is secreted by connective tissue cellsGround substance is secreted by connective tissue cells

• Adds to overall strength of bone and gives some degree Adds to overall strength of bone and gives some degree of resilience to the boneof resilience to the bone


Microscopic Structure of the Bone Microscopic Structure of the Bone (Figure 7-3)(Figure 7-3)

• Compact boneCompact bone

Contains many cylinder-shaped Contains many cylinder-shaped structural units calledstructural units called osteons, osteons, oror Haversian systemsHaversian systems

Osteons surround canals that run Osteons surround canals that run lengthwise through bone and are lengthwise through bone and are connected by transverse connected by transverse Volkmann’s canalsVolkmann’s canals

Living bone cells are located in Living bone cells are located in these units, which constitute the these units, which constitute the structural framework of compact structural framework of compact bonebone

Osteons permit delivery of Osteons permit delivery of nutrients and removal nutrients and removal of waste productsof waste products


Microscopic Structure of the BoneMicroscopic Structure of the Bone• Compact bone (cont.)Compact bone (cont.)

Four types of structures make up Four types of structures make up each osteon:each osteon:

• Lamella—concentric, cylinder-shaped Lamella—concentric, cylinder-shaped layers of calcified matrixlayers of calcified matrix

• Lacunae—small spaces containing Lacunae—small spaces containing tissue fluid in which bone cells are tissue fluid in which bone cells are located between hard layers of the located between hard layers of the lamellalamella

• Canaliculi—ultrasmall canals radiating Canaliculi—ultrasmall canals radiating in all directions from the lacunae and in all directions from the lacunae and connecting them to each other and to connecting them to each other and to the Haversian canalthe Haversian canal

• Haversian canal—extends lengthwise Haversian canal—extends lengthwise through the center of each osteon and through the center of each osteon and contains blood vessels and lymphatic contains blood vessels and lymphatic vesselsvessels


Microscopic Structure of the BoneMicroscopic Structure of the Bone• Cancellous bones (Figure Cancellous bones (Figure

7-4)7-4)

No osteons in cancellous No osteons in cancellous bone; instead, it has bone; instead, it has trabeculaetrabeculae

Nutrients are delivered and Nutrients are delivered and waste products removed by waste products removed by diffusion through tiny diffusion through tiny canaliculicanaliculi

Bony spicules are arranged Bony spicules are arranged along lines of stress, along lines of stress, enhancing the bone’s enhancing the bone’s strengthstrength


Microscopic Structure of the BoneMicroscopic Structure of the Bone

• Blood supplyBlood supply

Bone cells are metabolically active and need a Bone cells are metabolically active and need a blood supply, which comes from the bone marrow blood supply, which comes from the bone marrow in the internal medullary cavity of cancellous bonein the internal medullary cavity of cancellous bone

Compact bone, in addition to bone marrow and Compact bone, in addition to bone marrow and blood vessels from the periosteum, penetrate blood vessels from the periosteum, penetrate bone and then, by way of Volkmann’s canals, bone and then, by way of Volkmann’s canals, connect with vessels in the Haversian canalsconnect with vessels in the Haversian canals


Microscopic Structure of the BoneMicroscopic Structure of the Bone

• Types of bone cellsTypes of bone cells

OsteoblastsOsteoblasts

• Bone-forming cells found in all bone surfacesBone-forming cells found in all bone surfaces

• Small cells synthesize and secrete osteoid, an important Small cells synthesize and secrete osteoid, an important part of the ground substancepart of the ground substance

• Collagen fibrils line up in osteoid and serve as a Collagen fibrils line up in osteoid and serve as a framework for the deposition of calcium and phosphateframework for the deposition of calcium and phosphate


Microscopic Structure of the BoneMicroscopic Structure of the Bone• Types of bone cells (cont.)Types of bone cells (cont.)

Osteoclasts (Figure 7-5)Osteoclasts (Figure 7-5)

• Giant multinucleate cellsGiant multinucleate cells

• Responsible for the active erosion Responsible for the active erosion of bone mineralsof bone minerals

• Contain large numbers of Contain large numbers of mitochondria and lysosomesmitochondria and lysosomes

Osteocytes—mature, Osteocytes—mature, nondividing osteoblast nondividing osteoblast surrounded by matrix, lying surrounded by matrix, lying within lacunae within lacunae (Figure 7-6)(Figure 7-6)


Bone MarrowBone Marrow

• Specialized type of soft, diffuse connective Specialized type of soft, diffuse connective tissue; called tissue; called myeloid tissuemyeloid tissue

• Site for the production of blood cellsSite for the production of blood cells

• Found in medullary cavities of long bones and Found in medullary cavities of long bones and in the spaces of spongy bonein the spaces of spongy bone



• Two types of marrow are present during a person’s Two types of marrow are present during a person’s lifetime:lifetime: Red marrowRed marrow

• Found in virtually all bones in an infant’s or child’s bodyFound in virtually all bones in an infant’s or child’s body

• Functions to produce red blood cellsFunctions to produce red blood cells

Yellow marrowYellow marrow

• As an individual ages, red marrow is replaced by yellow marrowAs an individual ages, red marrow is replaced by yellow marrow

• Marrow cells become saturated with fat and are no longer Marrow cells become saturated with fat and are no longer active in blood cell productionactive in blood cell production



• The main bones in an adult that still contain The main bones in an adult that still contain red marrow include the ribs, bodies of the red marrow include the ribs, bodies of the vertebrae, the humerus, the pelvis, and the vertebrae, the humerus, the pelvis, and the femurfemur

• Yellow marrow can alter to red marrow during Yellow marrow can alter to red marrow during times of decreased blood supply, such as times of decreased blood supply, such as with anemia, exposure to radiation, and with anemia, exposure to radiation, and certain diseasescertain diseases


Functions of BoneFunctions of Bone

• Support—bones form the framework of the body and Support—bones form the framework of the body and contribute to the shape, alignment, and positioning of contribute to the shape, alignment, and positioning of the body partsthe body parts

• Protection—bony “boxes” protect the delicate Protection—bony “boxes” protect the delicate structures they enclosestructures they enclose

• Movement—bones with their joints constitute levers Movement—bones with their joints constitute levers that move as muscles contractthat move as muscles contract

• Mineral storage—bones are the major reservoir for Mineral storage—bones are the major reservoir for calcium, phosphorus, and other mineralscalcium, phosphorus, and other minerals

• Hematopoiesis—blood cell formation is carried out by Hematopoiesis—blood cell formation is carried out by myeloid tissuemyeloid tissue


Regulation of Blood Calcium LevelsRegulation of Blood Calcium Levels

• Skeletal system serves as a storehouse for Skeletal system serves as a storehouse for about 98% of body calcium reservesabout 98% of body calcium reserves

Helps maintain constancy of blood calcium levelsHelps maintain constancy of blood calcium levels

• Calcium is mobilized and moves into and out of blood Calcium is mobilized and moves into and out of blood during bone remodelingduring bone remodeling

• During bone formation, osteoblasts remove calcium from During bone formation, osteoblasts remove calcium from blood and lower circulating levelsblood and lower circulating levels

• During breakdown of bone, osteoclasts release calcium During breakdown of bone, osteoclasts release calcium into blood and increase circulating levelsinto blood and increase circulating levels



• Skeletal system (cont.)Skeletal system (cont.) Homeostasis of calcium ion concentration Homeostasis of calcium ion concentration

essential for the following:essential for the following:

• Bone formation, remodeling, and repairBone formation, remodeling, and repair

• Blood clottingBlood clotting

• Transmission of nerve impulsesTransmission of nerve impulses

• Maintenance of skeletal and cardiac muscle contractionMaintenance of skeletal and cardiac muscle contraction



• Mechanisms of calcium homeostasisMechanisms of calcium homeostasis

Parathyroid hormoneParathyroid hormone

• Primary regulator of calcium homeostasisPrimary regulator of calcium homeostasis

• Stimulates osteoclasts to initiate breakdown of bone Stimulates osteoclasts to initiate breakdown of bone matrix and increase blood calcium levelsmatrix and increase blood calcium levels

• Increases renal absorption of calcium from urineIncreases renal absorption of calcium from urine

• Stimulates vitamin D synthesisStimulates vitamin D synthesis



• Mechanisms of calcium homeostasis (cont.)Mechanisms of calcium homeostasis (cont.)

CalcitoninCalcitonin

• Protein hormone produced in the thyroid glandProtein hormone produced in the thyroid gland

• Produced in response to high blood calcium levelsProduced in response to high blood calcium levels

• Stimulates bone deposition by osteoblastsStimulates bone deposition by osteoblasts

• Inhibits osteoclast activityInhibits osteoclast activity

• Far less important in homeostasis of blood calcium levels Far less important in homeostasis of blood calcium levels than parathyroid hormonethan parathyroid hormone


Development of BoneDevelopment of Bone

• Osteogenesis—development of bone from small Osteogenesis—development of bone from small cartilage model to an adult bonecartilage model to an adult bone

• Intramembranous ossificationIntramembranous ossification

Occurs within a connective tissue membraneOccurs within a connective tissue membrane

Flat bones begin when groups of cells differentiate into Flat bones begin when groups of cells differentiate into osteoblastsosteoblasts

Osteoblasts are clustered together in centers of ossificationOsteoblasts are clustered together in centers of ossification

Osteoblasts secrete matrix material and collagenous fibrilsOsteoblasts secrete matrix material and collagenous fibrils


Development of BoneDevelopment of Bone• Intramembranous Intramembranous

ossification (cont.)ossification (cont.) Large amounts of ground Large amounts of ground

substance accumulate around substance accumulate around each osteoblasteach osteoblast

Collagenous fibers become Collagenous fibers become embedded in the ground embedded in the ground substance and constitute the bone substance and constitute the bone matrixmatrix

Bone matrix calcifies when calcium Bone matrix calcifies when calcium salts are depositedsalts are deposited

Trabeculae appear and join in a Trabeculae appear and join in a network to form network to form spongy bonespongy bone

Apposition growth occurs by Apposition growth occurs by adding of osseous tissueadding of osseous tissue


Development of BoneDevelopment of Bone• Endochondral Endochondral

ossification (Figure 7-8)ossification (Figure 7-8)

Most bones begin as a Most bones begin as a cartilage model, with bone cartilage model, with bone formation spreading formation spreading essentially from the center essentially from the center to the endsto the ends

Periosteum develops and Periosteum develops and enlarges, producing a enlarges, producing a collar of bonecollar of bone

Primary ossification Primary ossification center formscenter forms

Blood vessel enters the Blood vessel enters the cartilage model at the cartilage model at the midpoint of the diaphysismidpoint of the diaphysis


Development of BoneDevelopment of Bone• Endochondral Endochondral

ossification (cont.)ossification (cont.) Bone grows in length Bone grows in length

as endochondral as endochondral ossification progresses ossification progresses from the diaphysis from the diaphysis toward each epiphysistoward each epiphysis

Secondary ossification Secondary ossification centers appear in the centers appear in the epiphysis, and bone epiphysis, and bone growth proceeds growth proceeds toward the diaphysistoward the diaphysis

Epiphyseal plate Epiphyseal plate remains between remains between diaphysis and each diaphysis and each epiphysis until bone epiphysis until bone growth in length is growth in length is complete (Figure 7-10)complete (Figure 7-10)


Development of BoneDevelopment of Bone• Endochondral ossification (cont.)Endochondral ossification (cont.)

Epiphyseal plate is composed of Epiphyseal plate is composed of four layers (Figure 7-9):four layers (Figure 7-9):

• ““Resting” cartilage cells—point of Resting” cartilage cells—point of attachment joining the epiphysis to attachment joining the epiphysis to the shaftthe shaft

• Zone of proliferation—cartilage cells Zone of proliferation—cartilage cells undergoing active mitosis, causing undergoing active mitosis, causing the layer to thicken and the plate to the layer to thicken and the plate to increase in lengthincrease in length

• Zone of hypertrophy—older, Zone of hypertrophy—older, enlarged cells undergoing enlarged cells undergoing degenerative changes associated degenerative changes associated with calcium depositionwith calcium deposition

• Zone of calcification—dead or dying Zone of calcification—dead or dying cartilage cells undergoing rapid cartilage cells undergoing rapid calcificationcalcification


Bone Growth and Resorption Bone Growth and Resorption (Figures 7-11 and 7-12)(Figures 7-11 and 7-12)

• Bones grow in diameter by the combined action of osteoclasts Bones grow in diameter by the combined action of osteoclasts and osteoblastsand osteoblasts

• Osteoclasts enlarge the diameter of the medullary cavityOsteoclasts enlarge the diameter of the medullary cavity

• Osteoblasts from the periosteum build new bone around the Osteoblasts from the periosteum build new bone around the outside of the boneoutside of the bone


Repair of Bone FracturesRepair of Bone Fractures• Fracture—break in the continuity of Fracture—break in the continuity of

a bonea bone

• Fracture healing (Figure 7-13)Fracture healing (Figure 7-13)

Fracture tears and destroys blood Fracture tears and destroys blood vessels that carry nutrients to vessels that carry nutrients to osteocytesosteocytes

Vascular damage initiates repair Vascular damage initiates repair sequencesequence

Callus—specialized repair tissue that Callus—specialized repair tissue that binds the broken ends of the fracture binds the broken ends of the fracture togethertogether

Fracture hematoma—blood clot Fracture hematoma—blood clot occurring immediately after the fracture, occurring immediately after the fracture, is then reabsorbed and replaced by is then reabsorbed and replaced by calluscallus


CartilageCartilage• CharacteristicsCharacteristics

Avascular connective tissueAvascular connective tissue

Fibers of cartilage are embedded in a firm gelFibers of cartilage are embedded in a firm gel

Has the flexibility of firm plasticHas the flexibility of firm plastic

No canal system or blood vesselsNo canal system or blood vessels

Chondrocytes receive oxygen and nutrients by diffusionChondrocytes receive oxygen and nutrients by diffusion

Perichondrium—fibrous covering of the cartilagePerichondrium—fibrous covering of the cartilage

Cartilage types differ because of the amount of matrix Cartilage types differ because of the amount of matrix present and the amounts of elastic and collagenous fiberspresent and the amounts of elastic and collagenous fibers


CartilageCartilage

• Types of cartilage (Figure Types of cartilage (Figure 7-14)7-14) Hyaline cartilageHyaline cartilage

• Most common typeMost common type

• Covers the articular surfaces of Covers the articular surfaces of bonesbones

• Forms the costal cartilages, Forms the costal cartilages, cartilage rings in the trachea, cartilage rings in the trachea, bronchi of the lungs, and the bronchi of the lungs, and the tip of the nosetip of the nose

• Forms from specialized cells in Forms from specialized cells in centers of chondrification, centers of chondrification, which secrete matrix materialwhich secrete matrix material

• Chondrocytes are isolated into Chondrocytes are isolated into lacunaelacunae


CartilageCartilage

• Types of cartilage (cont.)Types of cartilage (cont.)

Elastic cartilageElastic cartilage

• Forms external ear, epiglottis, and eustachian tubesForms external ear, epiglottis, and eustachian tubes

• Large number of elastic fibers confers elasticity and resiliencyLarge number of elastic fibers confers elasticity and resiliency

FibrocartilageFibrocartilage

• Occurs in symphysis pubis and intervertebral disksOccurs in symphysis pubis and intervertebral disks

• Small quantities of matrix and abundant fibrous elementsSmall quantities of matrix and abundant fibrous elements

• Strong and rigidStrong and rigid


CartilageCartilage

• Histophysiology of cartilageHistophysiology of cartilage

Gristle-like nature permits cartilage to sustain Gristle-like nature permits cartilage to sustain great weight or serve as a shock absorbergreat weight or serve as a shock absorber

Strong yet pliable support structureStrong yet pliable support structure

Permits growth in length of long bonesPermits growth in length of long bones


CartilageCartilage

• Growth of cartilageGrowth of cartilage

Interstitial or endogenous growthInterstitial or endogenous growth

• Cartilage cells divide and secrete additional matrixCartilage cells divide and secrete additional matrix

• Seen during childhood and early adolescence while Seen during childhood and early adolescence while cartilage is still soft and capable of expansion from cartilage is still soft and capable of expansion from withinwithin


CartilageCartilage

• Growth of cartilageGrowth of cartilage (cont.)(cont.)

Appositional or exogenous growthAppositional or exogenous growth

• Chondrocytes in the deep layer of the perichondrium Chondrocytes in the deep layer of the perichondrium divide and secrete matrixdivide and secrete matrix

• New matrix is deposited on the surface, increasing its sizeNew matrix is deposited on the surface, increasing its size

• Unusual in early childhood but, once initiated, continues Unusual in early childhood but, once initiated, continues throughout lifethroughout life


Cycle of Life: Skeletal TissuesCycle of Life: Skeletal Tissues

• Skeleton fully ossified by mid-twentiesSkeleton fully ossified by mid-twenties Soft tissue may continue to grow—ossifies more slowlySoft tissue may continue to grow—ossifies more slowly

• Adults—changes occur from specific conditionsAdults—changes occur from specific conditions Increased density and strength from exerciseIncreased density and strength from exercise

Decreased density and strength from pregnancy, nutritional Decreased density and strength from pregnancy, nutritional deficiencies, and illnessdeficiencies, and illness

• Advanced adulthood—apparent degenerationAdvanced adulthood—apparent degeneration Hard bone matrix replaced by softer connective tissueHard bone matrix replaced by softer connective tissue

Exercise can counteract degenerationExercise can counteract degeneration

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 1 Chapter 7 Skeletal Tissues.

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