Human Anatomy

1. © 2012 Pearson Education, Inc.
5
The Skeletal System:
Osseous Tissue and
Skeletal Structure
PowerPoint®
Lecture Presentations prepared by
Steven Bassett
Southeast Community College
Lincoln, Nebraska

2. © 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
• Bone tissue, or osseous tissue, is the
major component of the skeletal system.

3. © 2012 Pearson Education, Inc.
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

4. © 2012 Pearson Education, Inc.
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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Structure of Bone
• Bones (osseous tissue)
• Supporting connective tissue
• Specialized cells
• Solid matrix
• Outer lining
• Called the periosteum, Continuous with the deep
fascia
• Inner lining
• Called the endosteum

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Structure of Bone
• The Histological Organization of Mature Bone
• Matrix
• Calcium phosphate:
• eventually converts to hydroxyapatite crystals
• Hydroxyapatite crystals resist compression
• Collagen fibers
• Make up 1/3 of the bone matrix
• Contribute to the tensile strength of bones
• Bone cells
• Contribute only 2% of the bone mass

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Structure of Bone
• The Cells of Mature Bone
• Osteocytes
• Mature bone cells
• Maintain the protein and mineral content of the matrix
• They are contained in lacunae
• 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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Structure of Bone
• The Cells of Mature Bone (continued)
• 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
• Giant multinucleated cells, 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
MatrixOsteoclast
Medullary
cavity
Osteoclast: Multinucleate cell
that secretes acids and enzymes
to dissolve bone matrix

10. © 2012 Pearson Education, Inc.
Figure 5.1c Histological Structure of a Typical Bone
Canaliculi
Concentric
lamellae
Osteon
Lacunae
Osteons
A thin section through
compact bone; in this
procedure the intact matrix
and central canals appear
white, and the lacunae and
canaliculi are shown in black.
LM × 220
Central canal

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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 5.1b Histological Structure of a Typical Bone
Osteon
Lacunae
Central
canals
Lamellae
A scanning electron
micrograph of several osteons
in compact bone
Osteons SEM × 182

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Structure of Bone
• 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
• its basic functional unit is the osteon
• Osteon consists of:
• Central canal
• Canaliculi
• Osteocytes
• Lacunae
• Lamellae
• Spongy bone (porous/ trabecular bone)
• Spongy bone forms an open network of struts and plates (trabeculae).
Trabeculae does not contain central canal within.

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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
ArteryVein

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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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Structure of Bone
• Structural Differences
• Compact bone
• Consists of osteons
• Makes up the dense, solid portion of bone
• Spongy bone
• Trabeculae are arranged in parallel struts
• Trabeculae form branching plates
• Trabeculae form an open network
• Creates the lightweight nature of bones

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Structure of 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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Facts about compact and spongy
bones
• The structural unit of compact bone is
osteon.
• The structural unit of spongy bone is
trabeculae.
• The layers of bone in compact bone is
called lamellea. There are concentric,
interstitial and circumferential lamellae.

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Figure 5.3a Anatomy of a Representative Bone
Articular
surface of
head of femur
Epiphysis
Metaphysis
Diaphysis
(shaft)
Metaphysis
Epiphysis
Medullary
cavity
Posterior view Sectional view
The femur, or thigh bone, in superficial and sectional views. The femur has a
diaphysis (shaft) with walls of compact bone and epiphyses (ends) filled with
spongy bone. A metaphysis separates the diaphysis and epiphysis at each
end of the shaft. The body weight is transferred to the femur at the hip joint.
Because the hip joint is off center relative to the axis of the shaft, the body
weight is distributed along the bone so that the medial portion of the shaft is
compressed and the lateral portion is stretched.
Spongy bone
Compact bone

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Figure 5.3b Anatomy of a Representative Bone
An intact femur chemically cleared
to show the orientation of the
trabeculae in the epiphysis

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Figure 5.3c Anatomy of a Representative Bone
Articular surface
of head of femur
A photograph showing the
epiphysis after sectioning
Compact bone
Medullary cavity
Cortex
Trabeculae
of spongy
bone

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Structure of Bone
• Organization of Compact and Spongy Bone
• Epiphysis
• Each end of the long bones
• Made of the spongy bone.
• Diaphysis
• Shaft of the long bones
• contains marrow cavity, which holds the red or yellow bone marrow. Red
bone marrow is the source of producing RBCs, WBCs, and platelets.
• Metaphysis
• Narrow growth zone between the epiphysis and the diaphysis
 (formerly epiphyseal plate). Epiphyseal plate is contributing in longitudinal
growth of the bone in prepubertal age. After puberty it becomes ossified and
the longitudinal growth of the bone stops.
 Metaphysis connecting the epiphysis to diaphysis.

23. © 2012 Pearson Education, Inc.
Figure 5.3a Anatomy of a Representative Bone
Articular
surface of
head of femur
Epiphysis
Metaphysis
Diaphysis
(shaft)
Metaphysis
Epiphysis
Medullary
cavity
Posterior view Sectional view
The femur, or thigh bone, in superficial and sectional views. The femur has a
diaphysis (shaft) with walls of compact bone and epiphyses (ends) filled with
spongy bone. A metaphysis separates the diaphysis and epiphysis at each
end of the shaft. The body weight is transferred to the femur at the hip joint.
Because the hip joint is off center relative to the axis of the shaft, the body
weight is distributed along the bone so that the medial portion of the shaft is
compressed and the lateral portion is stretched.
Spongy bone
Compact bone

24. © 2012 Pearson Education, Inc.
Structure of Bone
• 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

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Structure of Bone
• The Periosteum and Endosteum
• 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
• Osteogenesis
• Bone formation
• Calcification
• The deposition of calcium ions into the bone
tissue

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Bone Development and Growth
 Before six weeks of development the skeleton is
cartilage.
 Osteogenesis is bone formation.
 Ossification is bone replacing existing tissue
 The two types of Ossification:
 Intramembraneous ossification, such as flat bones.
 Endochondreal ossification, such as long bones.
This ossification begins with hyaline cartilage.
 Calcification is the process of depositing calcium salts
into tissues.

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Figure 5.5 Histology of Intramembranous Ossification
Mesenchymal cells aggregate, differentiate into osteoblasts,
and begin the ossification process. The bone expands as a
series of spicules that spread into surrounding tissues.
Bone matrix
Osteoblast
Osteoid
Embryonic connective tissue
Mesenchymal cell
Blood
vessel
Osteocyte in lacuna
Blood vessel Osteoblasts Spicules LM × 32
As the spicules interconnect, they
trap blood vessels within the bone.
Osteocytes
in lacunae
Blood
vessels
Osteoblast
layer
Blood vessel
Over time, the bone
assumes the structure of
spongy bone. Areas of
spongy bone may later be
removed, creating
medullary cavities.
Through remodeling,
spongy bone formed in this
way can be converted to
compact bone.
LM × 32

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Figure 5.7 Anatomical and Histological Organization of Endochondral Ossification
As the cartilage enlarges,
chondrocytes near the
center of the shaft
increase greatly in size.
The matrix is reduced to a
series of small struts that
soon begin to calcify. The
enlarged chondrocytes
then die and disintegrate,
leaving cavities within the
cartilage.
Blood vessels grow
around the edges of the
cartilage, and the cells of
the perichondrium convert
to osteoblasts. The shaft
of the cartilage then
becomes ensheathed in a
superficial layer of bone.
Blood vessels penetrate the
cartilage and invade the central
region. Fibroblasts migrating
with the blood vessels
differentiate into osteoblasts
and begin producing spongy
bone at a primary center of
ossification. Bone formation
then spreads along the shaft
toward both ends.
Epiphysis
Diaphysis
Blood
vessel
Medullary
cavity
Primary
ossification
center
Superficial
bone
Spongy
bone
Bone
formation
Medullary
cavity
Metaphysis
See
Figure 5.9
Enlarging
chondrocytes within
calcifying matrix
Hyaline cartilage
Remodeling occurs as growth
continues, creating a medullary
cavity. The bone of the shaft
becomes thicker, and the cartilage
near each epiphysis is replaced by
shafts of bone. Further growth
involves increases in length (Steps 5
and 6) and diameter (see Figure 5.9).
Steps in the formation of a long bone from a hyaline cartilage model
Epiphyseal
cartilage matrix
Cartilage cells
undergoing division
Zone of
proliferation
Zone of
hypertrophy
Medullary
cavity
Osteoblasts Osteoid
Epiphyseal cartilage
Light micrograph showing the
zones of cartilage and the
advancing osteoblasts at an
epiphyseal cartilage
LM × 250
Soon the epiphyses are filled with
spongy bone. An articular cartilage
remains exposed to the joint cavity;
over time it will be reduced to a thin
superficial layer. At each metaphysis,
an epiphyseal cartilage separates the
epiphysis from the diaphysis.
Articular cartilage
Spongy
bone
Epiphyseal
cartilage
Diaphysis
Capillaries and osteoblasts
migrate into the epiphyses,
creating secondary
ossification centers.
Hyaline cartilage
Epiphysis
Metaphysis
Periosteum
Compact
bone
Secondary
ossification
center

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Figure 5.8 Epiphyseal Cartilages and Lines
X-ray of the hand of a young child. The arrows
indicate the locations of the epiphyseal cartilages.
X-ray of the hand of an adult. The arrows indicate the
locations of epiphyseal lines.

32. © 2012 Pearson Education, Inc.
Figure 5.6 Fetal Intramembranous and Endochondral Ossification
Intramembranous
ossification
produces the
roofing bones of
the skull
Temporal
bone
Mandible
Clavicle
Scapula
Humerus
Femur
Vertebrae
Hip bone
(ilium)
Endochondral
ossification
replaces cartilages
of embryonic skull
Primary ossification
centers of the
diaphyses (bones
of the lower limb)
Future
hip bone
At 10 weeks the fetal skull clearly shows
both membrane and cartilaginous bone,
but the boundaries that indicate the limits
of future skull bones have yet to be
established.
At 16 weeks the fetal skull shows the irregular
margins of the future skull bones. Most
elements of the appendicular skeleton form
through endochondral ossification. Note the
appearance of the wrist and ankle bones at 16
weeks versus at 10 weeks.
Parietal bone
Frontal bone
Metacarpal bones
Phalanges
Radius
Ulna
Cartilage
Fibula
Tibia
Phalanx
Metatarsal bones
Ribs

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Bone Development and Growth
Factors Regulating Bone Growth
 Ions
 Calcium, phosphate, magnesium, citrate, carbonate, sodium
 Vitamins
 Vitamins A and C
 Vitamin D derivatives
 Parathyroid hormone (PTH) acts to increase the overall availability of
calcium ions in the blood. Decreased levels of blood calcium stimulates
the secretion of PTH.
 Increased osteoclast activity is the direct result of PTH levels.
 Calcitonin is the antagonist of PTH.
 Growth hormone and thyroxine increase osteoblast activity leading to
bone growth.
 Sex hormones increase bone growth dramatically during puberty.

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Remodeling and bone maintenance

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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

36. © 2012 Pearson Education, Inc.
Clinical Note 5.3 Fractures and Their Repair (Part 3 of 4)
Fracture
hematoma
Dead
bone
Bone
fragments
Spongy bone of
external callus
Periosteum
Immediately after the fracture,
extensive bleeding occurs.
Over a period of several
hours, a large blood clot, or
fracture hematoma, develops.
Repair
of a
fracture
An internal callus forms as
a network of spongy bone
units the inner edges, and
an external callus of
cartilage and bone
stabilizes the outer edges.

37. © 2012 Pearson Education, Inc.
Clinical Note 5.3 Fractures and Their Repair (Part 4 of 4)
Internal
callus
External
callus
External
callus
A swelling initially marks
the location of the fracture.
Over time, this region will
be remodeled, and little
evidence of the fracture
will remain.
The cartilage of the external
callus has been replaced by bone,
and struts of spongy bone now
unite the broken ends. Fragments
of dead bone and the areas of
bone closest to the break have
been removed and replaced.

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Anatomy of Skeletal Elements
• There are seven broad categories of bones
according to their shapes
• Long bone: humerus
• Flat bone: cranial bones or scapula.
• Wormian bone: develops between the sutures of
cranium.
• Pneumatized bone: ethmoid bone.
• Irregular bone: vertebrae.
• Short bones: carpals and tarsals.
• Sesamoid bone: patella

39. © 2012 Pearson Education, Inc.
Figure 5.11 Shapes of Bones
Irregular Bones
Sutural
bone
Sutures
Pneumatized BonesSutural Bones
Air cellsEthmoid
Vertebra
Carpal
bones
Humerus
External tableParietal bone
Internal
table
Diploë
(spongy bone)
Patella
Short Bones
Flat Bones
Long Bones
Sesamoid Bones

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Integration with other systems
The skeletal system is closely linked to other body
systems.
The skeletal system is a reservoir for calcium, phosphate,
and other minerals.
The growth and development of bones is under control of
several factors including diet, hormones, muscle
attachments and mechanical stress. Lack of any of these
factors causes weak bones and increases the chance of
break in the bone or Fracture.
The most common type of fracture in children is called
Green stick fracture.

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Anatomy of Skeletal Elements
• Bone markings include:
• Projections
• Depressions
• Fissures
• Foramina
• Canals (meatuses)

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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