Chapter 5 The Skeletal System: Osseous Tissue and Skeletal...
Transcript of Chapter 5 The Skeletal System: Osseous Tissue and Skeletal...
© 2012 Pearson Education, Inc.
Chapter 5
The Skeletal System:
Osseous Tissue and
Skeletal Structure
© 2012 Pearson Education, Inc.
Introduction
• The skeletal system is made of:
• Skeletal bones
• Cartilage
• Ligaments
• Connective tissue to stabilize the skeleton
• Bones are dynamic organs, which consist
of several tissue types and interacts with all
organ systems
• Continually rebuilds and remodels itself
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Introduction
• Functions of the skeletal system
• Support • Provides the framework for the attachment of other
organs
• Storage of minerals • Calcium ions: 98% of the body’s calcium ions are
in the bones
• Phosphate ions
• Blood cell production • Bone marrow produces erythrocytes, leukocytes,
and platelets
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Introduction
• Functions of the skeletal system (continued)
• Leverage
• Muscles pull on the bones to produce movement
• Protection
• Ribs protect heart and lungs
• Skull protects the brain
• Vertebrae protect the spinal cord
• Pelvic bones protect the reproductive organs
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• 3 types:
• Hyaline=most
abundant; flexible
and resilient
• Elastic=highly
bendable
• Fibro=resists
compression and
tension
Cartilages:
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Cartilages:
• 3 Major functions of Cartilages
• Supporting soft tissues
• Providing a gliding surface at articulations
(joints), where two bones meet
• Providing a model for the formation of most of
the bones in the body
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Structure of Bone
• Bones (osseous
tissue)
• Supporting connective
tissue
• Specialized cells
• Solid matrix
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The Histological Organization of Bone
• The matrix
• Calcium phosphate eventually converts to hydroxyapatite crystals
• Make up 2/3 of the bone weight
• Hydroxyapatite crystals resist compression
• Collagen fibers
• Contribute to the tensile strength of bones
• Collagen and hydroxyapatite make bone tissue extremely strong
• Bone cells
• Contribute only 2% of the bone mass
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The Cells of Mature Bone
• Osteocytes
• Mature bone cells, reside in spaces called lacunae
(interconnected by canaliculi)
• Maintain the protein and mineral content of the matrix
• Osteoblasts
• Immature bone cells
• Found on the inner and outer surfaces of bones
• Produce osteoid, which is involved in making the
matrix
• Osteoblasts are involved in making new bone. This is
a process called osteogenesis
• Osteoblasts can convert to osteocytes
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The Cells of Mature Bone
• Osteoprogenitor cells
• Found on the inner and outer surfaces of bones
• Differentiate to form new osteoblasts
• Heavily involved in the repair of bones after a
break
• Osteoclasts
• Secrete acids, which dissolve the bones thereby
causing the release of stored calcium ions and
phosphate ions into the blood
• This process is called osteolysis
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Figure 5.1a Histological Structure of a Typical Bone
Osteocyte: Mature bone cell
that maintains the bone matrix
Osteoblast
Matrix
Matrix
Canaliculi Osteocyte
Osteoid
Osteoblast: Immature bone
cell that secretes organic
components of matrix The cells of bone
Endosteum Osteoprogenitor cell
Medullary
cavity
Osteoprogenitor cell:
Stem cell whose divisions produce
osteoblasts
Matrix Osteoclast
Medullary
cavity
Osteoclast: Multinucleate cell
that secretes acids and enzymes
to dissolve bone matrix
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Two types of osseous tissue
• Compact bone (dense bone) • Compact bones are
dense and solid
• Forms the walls of bone outlining the medullary cavity
• Medullary cavity consists of bone marrow
• Spongy bone (trabecular bone) • Open network of plates
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Compact vs. Spongy bone
• Structural Differences
• Compact bone • Consists of osteons
• Makes up the dense, solid portion of bone
• Central canal contains blood vessles and nerves
• Volkmann’s canals carry blood to central canal
• Spongy bone • Trabeculae are arranged in thick branching plates
• Creates the lightweight nature of bones
• No central canal
• Blood enters from bone marrow into tracecular spaces
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Figure 5.2a-c The Internal Organization in Representative Bones
Spongy bone
Blood vessels
Compact bone
Medullary cavity
Endosteum
Periosteum
Gross anatomy
of the humerus
Compact
bone
Spongy
bone
Medullary
cavity
Concentric
lamellae
Interstitial
lamellae
Capillary
Small vein
Circumferential
lamellae
Osteons
Periosteum
Collagen fiber
orientation
Concentric
lamellae
Central
canal
Endosteum
The organization of collagen
fibers within concentric lamellae
Trabeculae of
spongy bone
Central
canal
Diagrammatic view of the histological
organization of compact and spongy bone
Perforating
canal
Artery Vein
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Microscopic view of the compact bone
• The Osteon
• It is the basic unit of
compact bones
• Consists of:
• Central canal
• Canaliculi
• Osteocytes
• Lacunae
• Lamellae (layers of
calcified matrix)
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Figure 5.1d Histological Structure of a Typical Bone
A single osteon at higher
magnification
Osteon LM 343
Canaliculi
Concentric
lamellae
Osteon
Lacunae
Central canal
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Figure 5.2d The Internal Organization in Representative Bones
Canaliculi
opening
on surface
Location and structure of spongy bone. The photo
shows a sectional view of the proximal end of the femur.
Trabeculae of
spongy bone
Lamellae
Endosteum
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Compact vs. Spongy bone
• Functional Differences
• Compact bone
• Conducts stress from one area of the body to
another area of the body
• Generates tremendous strength from end to end
• Weak strength when stress is applied to the side
• Spongy bone
• Trabeculae create strength to deal with stress from
the side
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Structure of Bone
• Organization of Compact
and Spongy Bone
• Epiphysis (spongy)
• Each end of the long
bones
• Diaphysis (walls filled
with compact)
• Shaft of the long bones
• Metaphysis
• Narrow growth zone
between the epiphysis and
the diaphysis
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The Periosteum and Endosteum • Periosteum
• Outer surface of the bone
• Isolates and protects the bone from surrounding tissue
• Provides a route and a place for attachment for circulatory and nervous supply
• Actively participates in bone growth and repair
• Attaches the bone to the connective tissue network of the deep fascia
• Endosteum
• Inner surface of bone
• Lines the medullary cavity
• Consists of osteoprogenitor cells
• Actively involved in repair and growth
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Figure 5.4ab Anatomy and Histology of the Periosteum and Endosteum
The endosteum is an incomplete
cellular layer containing osteoblasts,
osteoprogenitor cells, and osteoclasts.
Joint capsule
Osteoblasts
Osteoid
Osteocyte
Osteoprogenitor
cell
Endosteum
Giant
multinucleate
osteoclast
Bone
matrix
Compact bone
Fibrous layer
of periosteum
Cellular layer
of periosteum
Endosteum
The periosteum contains outer
(fibrous) and inner (cellular) layers.
Collagen fibers of the periosteum are
continuous with those of the bone,
adjacent joint capsules, and attached
tendons and ligaments.
Circumferential
lamellae
Cellular layer
of periosteum
Fibrous layer
of periosteum
Canaliculi
Lacuna
Osteocyte
Perforating
fibers
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Bone Development and Growth
• Before six weeks of development, the
skeleton is cartilage
• Cartilage cells will be replaced by bone cells
• This is called ossification
• Osteogenesis
• Bone formation
• Calcification
• The deposition of calcium ions into the bone
tissue
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Bone Development and Growth
• There are two types of ossification
• Intramembranous ossification
• Bone develops from a fibrous membrane
• Involved in the development of clavicle, mandible,
skull, and face
• Endochondral ossification
• Bone forms by replacing hyaline cartilage
• Involved in the development of limbs, vertebrae,
and hips
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Bone Development and Growth
• Intramembranous ossification
• Mesenchymal cells differentiate to form
osteoblasts
• Osteoblasts begin secreting a matrix
• Osteoblasts become trapped in the matrix
• Osteoblasts differentiate and form osteocytes
• More osteoblasts are produced, thus move
outward
• Eventually, spongy bone and compact bone is
formed
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Bone Development and Growth
• Endochondral ossification • The developing bone begins as cartilage cells
• Requires breakdown of hyaline cartilage prior to ossification
• Invasion of hyaline cartilage by the osteoblasts, they begin to develop spongy bone in the diaphysis (primary center of ossification)
• Formation of the medullary cavity (secondary center of ossification) in epiphysis
• Ossification of the epiphysis, with hyaline cartilage remaining only in the epiphyseal plates
(New cartilage is added at the epiphyseal side, where osseous tissues replaces older cartilage at the diaphyseal side)
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Bone Development and Growth
• Epiphyseal plate
• Endochondral ossification
of a long bone occurs in
progressive stages.
• Bone growth is complete
when each epiphyseal
plate has ossified and the
epiphyseal line has formed.
• Epiphyseal plate
ossification occurs between
the ages of 10 and 25.
• The width of this zone gets
narrower as we age
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Long Bone Growth and Remodeling
• Growth in length – cartilage continually grows and is replaced by bone (increases length at the epiphyseal cartilage)
• Appositional bone growth (enlarging the diameter of bone)
• Osteoblasts begin to produce matrix, thus creating concentric rings
• As osteoblasts are laying down more bone material, osteoclasts are dissolving the inner bone, thus creating the marrow cavity
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Figure 5.9b Appositional Bone Growth
Bone resorbed
by osteoclasts
Bone deposited
by osteoblasts Child Infant
Young adult Adult A bone grows in diameter as new bone is added to the outer surface. At the same
time, osteoclasts resorb bone on the inside, enlarging the medullary cavity.
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Bone remodeling
When adult bone size has been reached, the bone continues to reshape itself
throughout a person’s lifetime in a constant process of bone resorption and deposition.
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• Nutrition • Calcium ions, Phosphate ions, Magnesium ions,
Citrate, Carbonate ions, Sodium ions
• Vitamins A, C, D (calcitriol)
• Hormones • Parathyroid hormone
• Thyroid hormone
• Growth hormone
• Sex hormones (estrogen & testosterone)
Factors Regulating Bone Growth
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• Hormones: Parathyroid gland
• Releases parathyroid hormone
• Stimulates osteoclasts & osteoblasts
• Increases calcium ion absorption from the small
intestine to the blood
• Hormones: Thyroid gland
• Releases calcitonin
• Inhibits osteoclasts
• Removes calcium ions from blood and adds it to bone
Factors Regulating Bone Growth
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Factors Regulating Bone Growth
• Hormones: Thyroid gland
• Releases thyroxine (T4)
• Increases osteoblasts activity
• Maintains normal activity of the epiphyseal cartilage
• Hormones: Pituitary gland
• Releases growth hormone (somatotropin)
• Increases osteoblasts activity
• Maintains normal activity of the epiphyseal cartilage
• Hormones: Reproductive organs
• Increases osteoblasts activity
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Bone Maintenance, Remodeling, and Repair
• Aging and the Skeletal System
• When we are young, osteoblast activity
balances with osteoclast activity
• When we get older, osteoblast activity slows
faster than osteoclast activity
• When osteoclast activity is faster than
osteoblast activity, bones become porous
• Estrogen keeps osteoclast activity under
control
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Bone Maintenance, Remodeling, and Repair
• Aging and the Skeletal System
• As women age, estrogen levels drop
• Osteoclast control is lost
• Osteoclasts are overactive
• Bones become porous
• This is osteoporosis
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Bone Maintenance, Remodeling, and Repair
• Injury and Repair
• When a bone is
broken, bleeding
occurs
• A network of spongy
bone forms
• Osteoblasts are overly
activated, thus
resulting in enlarged
callused area
• This area is now
stronger and thicker
than normal bone
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Anatomy of Skeletal Elements
• There are seven broad categories of bones according to their shapes
• Sutural bones
• Irregular bones
• Short bones
• Pneumatized bones
• Flat bones
• Long bones
• Sesamoid bones
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Figure 5.11 Shapes of Bones
Irregular Bones
Sutural
bone
Sutures
Pneumatized Bones Sutural Bones
Air cells Ethmoid
Vertebra
Carpal
bones
Humerus
External table Parietal bone
Internal
table
Diploë
(spongy bone)
Patella
Short Bones
Flat Bones
Long Bones
Sesamoid Bones
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Anatomy of Skeletal Elements
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Figure 5.12a Examples of Bone Markings (Surface Features)
Trochanter
Head
Neck
Femur
Facet
Tubercle
Condyle
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Figure 5.12b Examples of Bone Markings (Surface Features)
Fissure
Ramus
Process
Foramen
Skull, anterior view
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Figure 5.12c Examples of Bone Markings (Surface Features)
Canal
Sinuses
Meatus
Skull, sagittal section
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Figure 5.12d Examples of Bone Markings (Surface Features)
Humerus
Condyle
Trochlea
Fossa
Tuberosity
Neck
Sulcus
Head Tubercle
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Figure 5.12e Examples of Bone Markings (Surface Features)
Crest
Pelvis
Spine
Line
Foramen
Fossa
Ramus
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Table 5.1 Common Bone Marking Terminology