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 Functions of Bone and Skeletal System
 Structure of Bone
 Histology of BoneTissue
 Blood and Nerve Supply of Bone
 Bone Formation
 Bone’s Role in Calcium Homeostasis
 Exercise and BoneTissue
 Aging and BoneTissue
 Support
 Protection
 Assistance in Movement
 Mineral Homeostasis
 Blood Cell Production
 Triglyceride Storage

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 Diaphysis
 Epiphyses
 Metaphyses
▪ Epiphyseal growth plate
 Articular cartilage
 Periosteum
▪ Perforating fibers
 Medullary cavity
 Endosteum
 Long Bone Anatomy
(Humerus)
 Extracellular matrix surrounding widely
separated cells
 Matrix
▪ 25% water
▪ 25% collagen fibers
▪ 50% crystallized mineral salts
 The most abundant mineral salt is calcium
phosphate
 A process called calcification is initiated by
bone-building cells called osteoblasts
 Mineral salts are deposited and crystalize in
the framework formed by the collagen fibers
of the extracellular matrix
 Bone’s flexibility depends on collagen fibers

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 Four types of cells are present in bone tissue
 Osteogenic cells
 Undergo cell division; the resulting cells develop
into osteoblasts
 Osteoblasts
 Bone-building cells
 Synthesize extracellular matrix of bone tissue
 Osteocytes
 Mature bone cells
 Exchange nutrients and wastes with the blood
 Osteoclasts
 Release enzymes that digest the mineral components of
bone matrix (resorption)
 Regulate blood calcium level

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 Bone is richly supplied with
blood
 Periosteal arteries
accompanied by nerves
supply the periosteum and
compact bone
 Epiphyseal veins carry
blood away from long bones
 Nerves accompany the blood
vessels that supply bones
 The periosteum is rich in
sensory nerves sensitive to
tearing or tension
 The process by which bone forms is called
ossification
 Bone formation occurs in four situations:
 1) Formation of bone in an embryo
 2) Growth of bones until adulthood
 3) Remodeling of bone
 4) Repair of fractures

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 Formation of Bone in an Embryo
 Bone formation follows one of two patterns
▪ Intramembranous ossification
▪ Flat bones of the skull and mandible are formed in this way
▪ “Soft spots” that help the fetal skull pass through the birth
canal later become ossified forming the skull
▪ Endochondral ossification
▪ The replacement of cartilage by bone
▪ Most bones of the body are formed in this way including long
bones
1
Blood capillary
Ossification center
Mesenchymal cell
Osteoblast
Collagen fiber
Development of ossification center
Mandible
Flat bone
of skull
1
Blood capillary
Ossification center
Mesenchymal cell
Osteoblast
Osteocyte in lacuna
Canaliculus
Osteoblast
Newly calcified bone
matrix
Development of ossification center
Calcification
Mandible
Flat bone
of skull
2
Collagen fiber
1
Blood capillary
Ossification center
Mesenchymal cell
Osteoblast
Development of ossification center
Calcification
Mandible
Flat bone
of skull
2
Collagen fiber
Osteocyte in lacuna
Canaliculus
Osteoblast
Newly calcified bone
matrix
Mesenchyme
condenses
Blood vessel
Spongy bone
trabeculae
Osteoblast
Formation of trabeculae3
1
Blood capillary
Ossification center
Mesenchymal cell
Osteoblast
Mesenchyme
condenses
Blood vessel
Spongy bone
trabeculae
Osteoblast
Periosteum
Spongy bone tissue
Compact bone tissue
Development of ossification center
Calcification Formation of trabeculae
Development of the periosteum
Mandible
Flat bone
of skull
3
4
2
Collagen fiber
Osteocyte in lacuna
Canaliculus
Osteoblast
Newly calcified bone
matrix
1 Development of
cartilage model
Hyaline
cartilage
Perichondrium
Proximal
epiphysis
Distal
epiphysis
Diaphysis
1 Development of
cartilage model
Growth of
cartilage model
2
Hyaline
cartilage
Uncalcified
matrix
Calcified
matrix
Perichondrium
Proximal
epiphysis
Distal
epiphysis
Diaphysis
1 Development of
cartilage model
Development of
primary ossification
center
Growth of
cartilage model
2 3
Hyaline
cartilage
Uncalcified
matrix
Calcified
matrix
Nutrient
artery
Perichondrium
Proximal
epiphysis
Distal
epiphysis
Diaphysis
Periosteum
Primary
ossification
center
Spongy
bone
1
Hyaline
cartilage
Calcified
matrix
Periosteum
(covering
compact bone)
Uncalcified
matrix
Calcified
matrix
Medullary
cavity
Nutrient
artery and vein
Nutrient
artery
Perichondrium
Proximal
epiphysis
Distal
epiphysis
Diaphysis
Development of
cartilage model
Development of
primary ossification
center
Development of
the medullary
cavity
Growth of
cartilage model
Periosteum
Primary
ossification
center
2 3 4
Spongy
bone
Uncalcified
matrix
1 Development of
cartilage model
Development of
primary ossification
center
Development of
the medullary
cavity
Growth of
cartilage model
2 3 4
Hyaline
cartilage
Calcified
matrix
Periosteum
(covering
compact bone)
Uncalcified
matrix
Calcified
matrix
Medullary
cavity
Nutrient
artery and vein
Nutrient
artery
Perichondrium
Proximal
epiphysis
Distal
epiphysis
Diaphysis
Periosteum
Primary
ossification
center
Secondary
ossification
center
Nutrient
artery and vein
Uncalcified
matrix
Epiphyseal
artery and
vein
Development of secondary
ossification center
5
Spongy
bone
Uncalcified
matrix
1
Articular cartilage
Spongy bone
Epiphyseal plate
Secondary
ossification
center
Nutrient
artery and vein
Uncalcified
matrix
Epiphyseal
artery and
vein
Formation of articular cartilage
and epiphyseal plate
Development of secondary
ossification center
Development of
cartilage model
Development of
primary ossification
center
Development of
the medullary
cavity
Growth of
cartilage model
2 3 4
5 6
Hyaline
cartilage
Uncalcified
matrix
Calcified
matrix
Periosteum
(covering
compact bone)
Uncalcified
matrix
Calcified
matrix
Medullary
cavity
Nutrient
artery and vein
Nutrient
artery
Perichondrium
Proximal
epiphysis
Distal
epiphysis
Diaphysis
Periosteum
Primary
ossification
center
Spongy
bone

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 Growth in Length
 The growth in length of long
bones involves two major events:
 1) Growth of cartilage on the
epiphyseal plate
 2) Replacement of cartilage by
bone tissue in the epiphyseal
plate
 Osteoclasts dissolve the calcified cartilage, and osteoblasts invade
the area laying down bone matrix
 The activity of the epiphyseal plate is the way bone can increase in
length
 At adulthood, the epiphyseal plates close and bone replaces all the
cartilage leaving a bony structure called the epiphyseal line
 Growth in Thickness
 Bones grow in thickness at the outer surface
 Remodeling of Bone
 Bone forms before birth and continually renews
itself
 The ongoing replacement of old bone tissue by
new bone tissue
 Old bone is continually destroyed and new bone is
formed in its place throughout an individual’s life

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 A balance must exist between the actions of
osteoclasts and osteoblasts
 If too much new tissue is formed, the bones become
abnormally thick and heavy
 Excessive loss of calcium weakens the bones, as occurs
in osteoporosis
 Or they may become too flexible, as in rickets and
osteomalacia
 Normal bone metabolism depends on several factors
 Minerals
 Large amounts of calcium and phosphorus and smaller
amounts of magnesium, fluoride, and manganese are
required for bone growth and remodeling
 Vitamins
 Vitamin A stimulates activity of osteoblasts
 Vitamin C is needed for synthesis of collagen
 Vitamin D helps build bone by increasing the absorption of
calcium from foods in the gastrointestinal tract into the
blood
 Vitamins K and B12 are also needed for synthesis of bone
proteins
 Hormones
 During childhood, the hormones most important to bone
growth are growth factors (IGFs), produced by the liver
▪ IGFs stimulate osteoblasts, promote cell division at the epiphyseal
plate, and enhance protein synthesis
 Thyroid hormones also promote bone growth by
stimulating osteoblasts
 Insulin promotes bone growth by increasing the synthesis
of bone proteins

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 Hormones
 Estrogen and testosterone cause a dramatic
effect on bone growth
▪ Cause of the sudden “growth spurt” that occurs during
the teenage year
▪ Promote changes in females, such as widening of the
pelvis
▪ Shut down growth at epiphyseal plates
 Parathyroid hormone, calcitriol, and calcitonin are
other hormones that can affect bone remodeling
 Fracture Types
 Open (compound) fracture
▪ The broken ends of the bone protrude through the skin
 Closed (simple) fracture
▪ Does not break the skin
 Comminuted fracture
▪ The bone is splintered, crushed, or broken into pieces
 Greenstick fracture
▪ A partial fracture in which one side of the bone is broken and the other side bends
 Impacted fracture
▪ One end of the fractured bone is forcefully driven into another
 Pott’s fracture
▪ Fracture of the fibula, with injury of the tibial articulation
 Colles’ fracture
▪ A fracture of the radius in which the distal fragment is displaced
 Stress fracture
▪ A series of microscopic fissures in bone

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Compact bone
Spongy bone
Periosteum
Fracture hematoma
Fracture
hematoma
Bone
fragment
Osteocyte
Red blood
cell
Blood vessel
Formation of fracture hematoma
Phagocyte
Osteon
1
Phagocyte
Osteoblast
Fibroblast
Fibrocartilaginous
callus
Collagen fiber
Chondroblast
Cartilage
Fibrocartilaginous callus formation2
Compact bone
Spongy bone
Periosteum
Fracture hematoma
Fracture
hematoma
Bone
fragment
Osteocyte
Red blood
cell
Blood vessel
Formation of fracture hematoma
Phagocyte
Osteon
1
Bony callus
Spongy bone
Osteoblast
Bony callus formation
Osteocyte
3
Compact bone
Spongy bone
Periosteum
Fracture hematoma
Fracture
hematoma
Bone
fragment
Osteocyte
Red blood
cell
Blood vessel
Formation of fracture hematoma
Phagocyte
Osteon
1
Phagocyte
Osteoblast
Fibroblast
Fibrocartilaginous
callus
Collagen fiber
Chondroblast
Cartilage
Fibrocartilaginous callus formation2
Spongy bone
Osteoblast
Osteoclast
New compact
bone
Bony callus formation Bone remodeling
Osteocyte
3 4
Compact bone
Spongy bone
Periosteum
Fracture hematoma
Fracture
hematoma
Bone
fragment
Osteocyte
Red blood
cell
Blood vessel
Formation of fracture hematoma
Phagocyte
Osteon
1
Phagocyte
Osteoblast
Fibroblast
Fibrocartilaginous
callus
Collagen fiber
Chondroblast
Cartilage
Fibrocartilaginous callus formation2
Bony callus

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 Bone is the body’s major calcium reservoir
 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 bone
 Both nerve and muscle cells depend on calcium
ions (Ca2+) to function properly
 Blood clotting also requires Ca2+
 Many enzymes require Ca2+ as a cofactor
 Actions that work to decrease blood Ca2+
level
 The thyroid gland secretes calcitonin (CT) which
inhibits activity of osteoclasts
 The result is that CT promotes bone formation
and decreases blood Ca2+ level

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 Bone tissue alters its strength in response to
changes in mechanical stress
 Under stress, bone tissue becomes stronger through
deposition of mineral salts and production of collagen
fibers by osteoblasts
 Unstressed bones diminishes because of the loss of bone
minerals and decreased numbers of collagen fibers
 The main mechanical stresses on bone are those
that result from the pull of skeletal muscles and the
pull of gravity
 Weight-bearing activities help build and retain bone
mass
 The level of sex hormones diminishes during
middle age, especially in women after menopause
 A decrease in bone mass occurs
 Bone resorption by osteoclasts outpaces bone
deposition by osteoblasts
 Female bones generally are smaller and less
massive than males
 Loss of bone mass in old age has a greater
adverse effect in females
 There are two principal effects of aging on bone
tissue:
 1) Loss of bone mass
▪ Results from the loss of calcium from bone
matrix
▪ The loss of calcium from bones is one of the
symptoms in osteoporosis
 2) Brittleness
▪ Results from a decreased rate of protein
synthesis
▪ Collagen fibers gives bone its tensile strength
▪ The loss of tensile strength causes the bones to
become very brittle and susceptible to fracture

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