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Copyright 2009, John Wiley & Sons, Inc.
Chapter 6:The Skeletal System:
Bone Tissue
Copyright 2009, John Wiley & Sons, Inc.
Functions of Bone and Skeletal System
n Supportn Protectionn Assistance in Movementn Mineral Homeostasisn Blood Cell Production(Hemopoiesis)
q Triglyceride Storageq Yellow bone marrow
n Triglycerides stored in adipose cellsq Serves as a potential chemical energy reserve
Copyright 2009, John Wiley & Sons, Inc.
Structure of Bone
q Diaphysisq Epiphysisq Metaphysis
n Epiphyseal growth plateq Articular cartilage
n Perforating fibersq Periosteum q Medullary cavityq Endosteum
n Long Bone Anatomy (Humerus)
Copyright 2009, John Wiley & Sons, Inc.
Histology of Bone Tissuen Extracellular matrix surrounding widely
separated cellsq Matrix
n 25% watern 25% collagen fibersn 50% crystallized mineral salts
n The most abundant mineral salt is calcium phosphate
Copyright 2009, John Wiley & Sons, Inc.
Histology of Bone Tissuen A process called calcification is initiated
by bone-building cells called osteoblasts
n Mineral salts are deposited and crystalize in the framework formed by the collagen fibers of the extracellular matrix
n Bone’s flexibility depends on collagen fibers
Copyright 2009, John Wiley & Sons, Inc.
Histology of Bone Tissuen Four types of cells are present in bone tissuen Osteogenic cells
q Undergo cell division; the resulting cells develop into osteoblasts
n Osteoblastsq Bone-building cellsq Synthesize extracellular matrix of bone tissue
n Osteocytesq Mature bone cellsq Exchange nutrients and wastes with the blood
Histology of Bone Tissuen Osteoclasts
q Release enzymes that digest the mineral components of bone matrix (resorption)
q Regulate blood calcium level
Copyright 2009, John Wiley & Sons, Inc.
Histology of Bone Tissuen Bone may be categorized as:
q Compactq Spongy
Copyright 2009, John Wiley & Sons, Inc.
Histology of Bone Tissuen Compact Bone
q Resists the stresses produced by weight and movement
q Components of compact bone are arranged into repeating structural units called osteons or Haversian systems
q Osteons consist of a central (Haversian) canal with concentrically arranged lamellae, lacunae, osteocytes, and canaliculi
Copyright 2009, John Wiley & Sons, Inc.
Histology of Bone Tissuen Osteon
q Central canals run longitudinally through boneq Around the central canals are concentric
lamellaen Rings of calcified matrix (like the rings of a tree
trunk)q Between the lamellae are small spaces called
lacunae which contain osteocytesq Radiating in all directions from the lacunae are
tiny canaliculi filled with extracellular fluid
Copyright 2009, John Wiley & Sons, Inc.
Histology of Bone Tissuen Osteon
q Canaliculi connect lacunae, forming a system of interconnected canalsn Providing routes for nutrients and oxygen to reach
the osteocytes
q The organization of osteons changes in response to the physical demands placed on the skeleton
Copyright 2009, John Wiley & Sons, Inc.
Copyright 2009, John Wiley & Sons, Inc.
Histology of Bone Tissuen Spongy Bone
q Lacks osteonsq Lamellae are arranged in a lattice of thin
columns called trabeculaen Spaces between the trabeculae make bones
lightern Trabeculae of spongy bone support and protect
the red bone marrown Hemopoiesis (blood cell production) occurs in
spongy bone
Copyright 2009, John Wiley & Sons, Inc.
Histology of Bone Tissuen Spongy Bone
q Within each trabecula are lacunae that contain osteocytes
q Osteocytes are nourished from the blood circulating through the trabeculae
q Interior bone tissue is made up primarily of spongy bone
q The trabeculae of spongy bone are oriented along lines of stressn helps bones resist stresses without breaking
Copyright 2009, John Wiley & Sons, Inc.
Blood and Nerve Supply of Bonen Bone is richly supplied with blood
q Periosteal arteries accompanied by nerves supply the periosteum and compact bone
q Epiphyseal veins carry blood away from long bones
n Nerves accompany the blood vessels that supply bonesq The periosteum is rich in sensory nerves
sensitive to tearing or tension
Copyright 2009, John Wiley & Sons, Inc.
Bone Formationn The process by which bone forms is
called ossificationn Bone formation occurs in four situations:
q 1) Formation of bone in an embryoq 2) Growth of bones until adulthoodq 3) Remodeling of boneq 4) Repair of fractures
Copyright 2009, John Wiley & Sons, Inc.
Bone Formationn Formation of Bone in an Embryo
q Cartilage formation and ossification occurs during the sixth week of embryonic development
1
Blood capillary
Ossification center
Mesenchymal cellOsteoblast
Collagen fiber
Development of ossification center
Mandible
Flat boneof skull
1
Blood capillary
Ossification center
Mesenchymal cellOsteoblast
Osteocyte in lacuna
Canaliculus
Osteoblast
Newly calcified bonematrix
Development of ossification center
Calcification
Mandible
Flat boneof skull
2
Collagen fiber
1
Blood capillary
Ossification center
Mesenchymal cellOsteoblast
Development of ossification center
Calcification
Mandible
Flat boneof skull
2
Collagen fiber
Osteocyte in lacuna
Canaliculus
Osteoblast
Newly calcified bonematrix
MesenchymecondensesBlood vessel
Spongy bonetrabeculaeOsteoblast
Formation of trabeculae3
1
Blood capillary
Ossification center
Mesenchymal cellOsteoblast
MesenchymecondensesBlood vessel
Spongy bonetrabeculaeOsteoblast
Periosteum
Spongy bone tissue
Compact bone tissue
Development of ossification center
Calcification Formation of trabeculae
Development of the periosteum
Mandible
Flat boneof skull
3
4
2
Collagen fiber
Osteocyte in lacuna
Canaliculus
Osteoblast
Newly calcified bonematrix
Copyright 2009, John Wiley & Sons, Inc.
Bone Formationn Formation of Bone in an Embryo
q Bone formation follows one of two patternsn Intramembranous ossification
q Flat bones of the skull and mandible are formed in this way
q “Soft spots” that help the fetal skull pass through the birth canal later become ossified forming the skull
n Endochondral ossificationq The replacement of cartilage by boneq Most bones of the body are formed in this way including
long bones
1 Development ofcartilage model
Hyalinecartilage
Perichondrium
Proximalepiphysis
Distalepiphysis
Diaphysis
1 Development ofcartilage model
Growth ofcartilage model
2
Hyalinecartilage
Uncalcifiedmatrix
Calcifiedmatrix
Perichondrium
Proximalepiphysis
Distalepiphysis
Diaphysis
1 Development ofcartilage model
Development ofprimary ossificationcenter
Growth ofcartilage model
2 3
Hyalinecartilage
Uncalcifiedmatrix
Calcifiedmatrix
Nutrientartery
Perichondrium
Proximalepiphysis
Distalepiphysis
Diaphysis
Periosteum
Primaryossificationcenter
Spongybone
1
Hyalinecartilage
CalcifiedmatrixPeriosteum(covering compact bone)
Uncalcifiedmatrix
Calcifiedmatrix
Medullarycavity
Nutrientartery and vein
Nutrientartery
Perichondrium
Proximalepiphysis
Distalepiphysis
Diaphysis
Development ofcartilage model
Development ofprimary ossificationcenter
Development ofthe medullarycavity
Growth ofcartilage model
Periosteum
Primaryossificationcenter
2 3 4
Spongybone
Uncalcifiedmatrix
1 Development ofcartilage model
Development ofprimary ossificationcenter
Development ofthe medullarycavity
Growth ofcartilage model
2 3 4
Hyalinecartilage
CalcifiedmatrixPeriosteum(covering compact bone)
Uncalcifiedmatrix
Calcifiedmatrix
Medullarycavity
Nutrientartery and vein
Nutrientartery
Perichondrium
Proximalepiphysis
Distalepiphysis
Diaphysis
Periosteum
Primaryossificationcenter
Secondaryossificationcenter
Nutrientartery and vein
Uncalcifiedmatrix
Epiphysealartery andvein
Development of secondaryossification center
5
Spongybone
Uncalcifiedmatrix
1
Articular cartilage
Spongy bone
Epiphyseal plate
Secondaryossificationcenter
Nutrientartery and vein
Uncalcifiedmatrix
Epiphysealartery andvein
Formation of articular cartilageand epiphyseal plate
Development of secondaryossification center
Development ofcartilage model
Development ofprimary ossificationcenter
Development ofthe medullarycavity
Growth ofcartilage model
2 3 4
5 6
Hyalinecartilage
Uncalcifiedmatrix
CalcifiedmatrixPeriosteum(covering compact bone)
Uncalcifiedmatrix
Calcifiedmatrix
Medullarycavity
Nutrientartery and vein
Nutrientartery
Perichondrium
Proximalepiphysis
Distalepiphysis
Diaphysis
Periosteum
Primaryossificationcenter
Spongybone
Copyright 2009, John Wiley & Sons, Inc.
Bone Growth During Infancy, Childhood and Adolescence
n Growth in Lengthn The growth in length of long bones
involves two major events:q 1) Growth of cartilage on the
epiphyseal plateq 2) Replacement of cartilage by
bone tissue in the epiphyseal plate
Bone Growth During Infancy, Childhood and Adolescence
n Osteoclasts dissolve the calcified cartilage, and osteoblasts invade the area laying down bone matrix
n The activity of the epiphyseal plate is the way bone can increase in length
n At adulthood, the epiphyseal plates close and bone replaces all the cartilage leaving a bony structure called the epiphyseal line
Copyright 2009, John Wiley & Sons, Inc.
Bone Growth During Infancy, Childhood and Adolescencen Growth in Thickness
q Bones grow in thickness at the outer surfacen Remodeling of Bone
q Bone forms before birth and continually renews itself
q The ongoing replacement of old bone tissue by new bone tissue
q Old bone is continually destroyed and new bone is formed in its place throughout an individual’s life
Copyright 2009, John Wiley & Sons, Inc.
Bone Growth During Infancy, Childhood and Adolescencen A balance must exist between the actions of
osteoclasts and osteoblasts
q If too much new tissue is formed, the bones become abnormally thick and heavy
q Excessive loss of calcium weakens the bones, as occurs in osteoporosis
q Or they may become too flexible, as in rickets and osteomalacia
Copyright 2009, John Wiley & Sons, Inc.
Factors Affecting Bone Growth and Bone Remodelingn Normal bone metabolism depends on several factorsn Minerals
q Large amounts of calcium and phosphorus and smaller amounts of magnesium, fluoride, and manganese are required for bone growth and remodeling
n Vitaminsq Vitamin A stimulates activity of osteoblastsq Vitamin C is needed for synthesis of collagenq Vitamin D helps build bone by increasing the
absorption of calcium from foods in the gastrointestinal tract into the blood
q Vitamins K and B12 are also needed for synthesis of bone proteins
Copyright 2009, John Wiley & Sons, Inc.
Factors Affecting Bone Growth and Bone Remodelingn Hormones
q During childhood, the hormones most important to bone growth are growth factors (IGFs), produced by the livern IGFs stimulate osteoblasts, promote cell division at the
epiphyseal plate, and enhance protein synthesis
q Thyroid hormones also promote bone growth by stimulating osteoblasts
q Insulin promotes bone growth by increasing the synthesis of bone proteins
Copyright 2009, John Wiley & Sons, Inc.
Factors Affecting Bone Growth and Bone Remodelingn Hormones
q Estrogen and testosterone cause a dramatic effect on bone growthn Cause of the sudden “growth spurt” that occurs
during the teenage yearn Promote changes in females, such as widening of
the pelvisn Shut down growth at epiphyseal plates
q Parathyroid hormone, calcitriol, and calcitonin are other hormones that can affect bone remodeling
Copyright 2009, John Wiley & Sons, Inc.
Fracture and Repair of Bonen Fracture Types
q Open (compound) fracturen The broken ends of the bone protrude through the skin
q Closed (simple) fracturen Does not break the skin
q Comminuted fracturen The bone is splintered, crushed, or broken into pieces
q Greenstick fracturen A partial fracture in which one side of the bone is broken and the other side
bendsq Impacted fracture
n One end of the fractured bone is forcefully driven into anotherq Pott’s fracture
n Fracture of the fibula, with injury of the tibial articulationq Colles’ fracture
n A fracture of the radius in which the distal fragment is displacedq Stress fracture
n A series of microscopic fissures in bone
Fracture and Repair of Bone
Copyright 2009, John Wiley & Sons, Inc.
Fracture and Repair of Bonen Calcium and phosphorus needed to strengthen and
harden new bone after a fracture are deposited only gradually and may take several months
n The repair of a bone fracture involves the following stepsq 1) Formation of fracture hematoma
n Blood leaks from the torn ends of blood vessels, a clotted mass of blood forms around the site of the fracture
q 2) Fibrocartilaginous callus formationn Fibroblasts invade the fracture site and produce collagen
fibers bridging the broken ends of the boneq 3) Bony callus formation
n Osteoblasts begin to produce spongy bone trabeculae joining portions of the original bone fragments
q 4) Bone remodelingn Compact bone replaces spongy bone
Copyright 2009, John Wiley & Sons, Inc.
Fracture and Repair of Bone
Compact boneSpongy bone
Periosteum
Fracture hematoma
Fracturehematoma
BonefragmentOsteocyte
Red bloodcell
Blood vessel
Formation of fracture hematoma
Phagocyte
Osteon
1
Phagocyte
Osteoblast
Fibroblast
Fibrocartilaginouscallus
Collagen fiberChondroblastCartilage
Fibrocartilaginous callus formation2
Compact boneSpongy bone
Periosteum
Fracture hematoma
Fracturehematoma
BonefragmentOsteocyte
Red bloodcell
Blood vessel
Formation of fracture hematoma
Phagocyte
Osteon
1
Bony callus
Spongy boneOsteoblast
Bony callus formation
Osteocyte
3
Compact boneSpongy bone
Periosteum
Fracture hematoma
Fracturehematoma
BonefragmentOsteocyte
Red bloodcell
Blood vessel
Formation of fracture hematoma
Phagocyte
Osteon
1
Phagocyte
Osteoblast
Fibroblast
Fibrocartilaginouscallus
Collagen fiberChondroblastCartilage
Fibrocartilaginous callus formation2
Spongy boneOsteoblast
Osteoclast
New compactbone
Bony callus formation Bone remodeling
Osteocyte
3 4
Compact boneSpongy bone
Periosteum
Fracture hematoma
Fracturehematoma
BonefragmentOsteocyte
Red bloodcell
Blood vessel
Formation of fracture hematoma
Phagocyte
Osteon
1
Phagocyte
Osteoblast
Fibroblast
Fibrocartilaginouscallus
Collagen fiberChondroblastCartilage
Fibrocartilaginous callus formation2
Bony callus
Copyright 2009, John Wiley & Sons, Inc.
Bone’s Role in Calcium Homeostasisn Bone is the body’s major calcium reservoirn Levels of calcium in the blood are maintained
by controlling the rates of calcium resorption from bone into blood and of calcium deposition from blood into boneq Both nerve and muscle cells depend on
calcium ions (Ca2+) to function properlyq Blood clotting also requires Ca2+
q Many enzymes require Ca2+ as a cofactor
Copyright 2009, John Wiley & Sons, Inc.
Bone’s Role in Calcium Homeostasisn Actions that help elevate blood Ca2+ level
q Parathyroid hormone (PTH) regulatesCa2+ exchange between blood and bone tissuen PTH increases the number and activity of
osteoclastsn PTH acts on the kidneys to decrease loss of
Ca2+ in the urinen PTH stimulates formation of calcitriol a
hormone that promotes absorption of calcium from foods in the gastrointestinal tract
Bone’s Role in Calcium Homeostasis
Copyright 2009, John Wiley & Sons, Inc.
Bone’s Role in Calcium Homeostasisn Actions that work to decrease blood Ca2+
level
q The thyroid gland secretes calcitonin (CT) which inhibits activity of osteoclasts
q The result is that CT promotes bone formation and decreases blood Ca2+ level
Copyright 2009, John Wiley & Sons, Inc.
Exercise and Bone Tissuen Bone tissue alters its strength in response to
changes in mechanical stressq Under stress, bone tissue becomes stronger through
deposition of mineral salts and production of collagen fibers by osteoblasts
q Unstressed bones diminishes because of the loss of bone minerals and decreased numbers of collagen fibers
n The main mechanical stresses on bone are those that result from the pull of skeletal muscles and the pull of gravity
n Weight-bearing activities help build and retain bone mass
Copyright 2009, John Wiley & Sons, Inc.
Aging and Bone Tissuen The level of sex hormones diminishes during
middle age, especially in women after menopauseq A decrease in bone mass occursq Bone resorption by osteoclasts outpaces bone
deposition by osteoblastsn Female bones generally are smaller and less
massive than malesq Loss of bone mass in old age has a greater
adverse effect in females
Aging and Bone Tissuen There are two principal effects of aging on bone tissue:
q 1) Loss of bone massn Results from the loss of calcium from bone matrixn The loss of calcium from bones is one of the symptoms in
osteoporosisq 2) Brittleness
n Results from a decreased rate of protein synthesisn Collagen fibers gives bone its tensile strengthn The loss of tensile strength causes the bones to become very brittle
and susceptible to fracture
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