Chapter 6: Bones and Skeletal Tissues
Cartilage in
external ear
Cartilage in
Intervertebral
disc
Pubic
symphysis
Meniscus (padlike
cartilage in knee
joint)
Articular cartilage
of a joint
Epiglottis
Cartilages in Thyroid
cartilage
nose
Articular Cricoid
Cartilage cartilage
of a joint
Larynx
Trachea
Lung
Costal
cartilage
Respiratory tube cartilages
in neck and thorax
Bones of skeleton
Axial skeleton
Appendicular skeleton
Cartilages
Hyaline cartilages
Elastic cartilages
Fibrocartilages
Skeletal Cartilages
•
•
•
1.
Contain no blood vessels or nerves
Dense connective tissue girdle of
perichondrium contains blood vessels for
nutrient delivery to cartilage
3 types:
Hyaline cartilages
– Provide support, flexibility, and resilience
– Most abundant type
2. Elastic cartilages
– Similar to hyaline cartilages, but contain elastic
fibers
3. Fibrocartilages
– Collagen fibers—have great tensile strength
Growth of Cartilage
• Appositional
– Cells secrete matrix against the external face of
existing cartilage
• Interstitial
– Chondrocytes divide and secrete new matrix,
expanding cartilage from within
• Calcification of cartilage occurs during
– Normal bone growth
– Old age
Bones of the Skeleton
Two main groups, by location
• Axial skeleton: long axis of body:
skull, vertebral column, rib cage
• Appendicular skeleton: upper and
lower limbs that attach to axial
skeleton
Long bones: longer
than wide
Irregular bones:
complicated shapes
Types of bones
Flat bones:
thin, flat,
slightly
curved
Short bones
•Cube shaped
bones (in wrist
and ankle)
•Sesamoid
bones (within
tendons, e.g.,
patella)
Functions of Bones
•
•
•
•
•
Support for the body and soft organs
Protection for brain, spinal cord, and vital organs
Movement: Levers for muscle action
Storage of minerals (calcium and phosphorus)
Storage of growth factors (like insulin-like growth
factor) in bone matrix
• Blood cell formation (hematopoiesis) in marrow
cavities
• Triglyceride (energy) storage in bone cavities
Bone Markings
Bulges, depressions, and holes serve as
– Sites of attachment for muscles, ligaments,
and tendons
– Joint surfaces
– Conduits for blood vessels and nerves
Bone Markings: Projections
• Sites of muscle and ligament
attachment
– Tuberosity—rounded projection
– Crest—narrow, prominent ridge
– Trochanter—large, blunt, irregular
surface
– Line—narrow ridge of bone
– Tubercle—small rounded
projection
– Epicondyle—raised area above a
condyle
– Spine—sharp, slender projection
– Process—any bony prominence
Bone Markings
Projections that help to form joints
– Head: bony expansion carried on a narrow neck
– Facet: Smooth, nearly flat articular surface
– Condyle: Rounded articular projection
– Ramus: Armlike bar
Bone Markings: Depressions and Openings
• Meatus: Canal-like
passageway
• Sinus: Cavity within a
bone
• Fossa: Shallow, basinlike
depression
• Notch: indentation at
the edge of a structure
• Groove: Furrow
• Fissure: Narrow, slitlike
opening
• Foramen: Round or oval
opening through a bone
Bone Textures
Compact bone
Spongy bone
• Compact bone
– Dense outer layer
• Spongy (cancellous)
bone
– Honeycomb of
trabeculae
Structure of a Long Bone
• Diaphysis (shaft)
– Compact bone collar surrounds medullary (marrow)
cavity
– Medullary cavity in adults contains fat (yellow
marrow)
• Epiphyses
– Expanded ends
– Spongy bone interior
– Epiphyseal line (remnant of growth plate)
– Articular (hyaline) cartilage on joint surfaces
Articular
cartilage
Proximal
epiphysis
Diaphysis
Distal
epiphysis
Spongy bone
Epiphyseal
line
Compact bone
Medullary
cavity
Compact bone
Membranes of Bone
• Periosteum
– Outer fibrous layer
– Inner osteogenic layer
• Osteoblasts (bone-forming cells)
• Osteoclasts (bone-destroying cells)
• Osteogenic cells (stem cells)
– Nerve fibers, nutrient blood vessels, and lymphatic
vessels enter the bone via nutrient foramina
– Secured to underlying bone by Sharpey’s fibers
• Endosteum
– Delicate membrane on internal surfaces of bone
– Also contains osteoblasts and osteoclasts
Endosteum
Yellow bone marrow
Compact bone
Periosteum
Perforating
(Sharpey’s) fibers
Nutrient
arteries
Structure of short, irregular and flat bones
Spongy
bone called
diploë in
flat bones
•Periosteumcovered compact
bone on the
outside
•Endosteumcovers the
trabeculae
Trabeculae
Bone
marrow
between
trabeculae
Location of Hematopoietic Tissue (Red Marrow)
• Red marrow cavities of adults
– Trabecular cavities of the heads of the
femur and humerus
– Trabecular cavities of the diploë of flat
bones
• Red marrow of newborn infants
– Medullary cavities and all spaces in spongy
bone
Microscopic Anatomy of Bone
Osteogenic cell
Stem cells in
periosteum and
endosteum that give
rise to osteoblasts
Osteoblast
Matrix-synthesizing
cell responsible
for bone growth
Microscopic Anatomy of Bone
Osteocyte
Mature bone cell
that maintains the
bone matrix
Osteoclast
Bone-resorbing cell
Compact Bone: Haversian system, or osteon—structural unit
Structures
in the
central
canal
Artery with
capillaries
Vein
Nerve fiber
•Central (Haversian) canal
•Contains blood
vessels and nerves
•Lamellae
Lamellae
Collagen
fibers
run in
different
directions
•Weight-bearing
•Column-like matrix
tubes
Twisting
force
Compact
bone
Central
(Haversian) canal
Osteon
Circumferential
lamellae
Osteocyte
in a lacuna
Perforating (Volkmann’s)
canal: Perpendicular to
central canal. Connects
blood vessels and nerves
of the periosteum with
central canal
Endosteum lining bony canals
and covering trabeculae
Lamellae
Nerve
Vein
Artery
Canaliculi
Spongy bone
Lamellae
Central
canal
Lacunae
Perforating (Sharpey’s) fibers
Periosteal blood vessel
Periosteum
Lacuna (with
osteocyte)
Interstitial lamellae
Microscopic Anatomy of Bone: Spongy Bone
• Trabeculae
– Align along lines of stress to resist stress
– No osteons
– Contain irregularly arranged lamellae, osteocytes,
and canaliculi
– Capillaries in endosteum supply nutrients
Composition of Bone
Organic
• Osteogenic cells, osteoblasts, osteocytes, osteoclasts
• Osteoid—organic bone matrix secreted by osteoblasts
– Ground substance (proteoglycans, glycoproteins)
– Collagen fibers
• Provide tensile strength and flexibility
Inorganic
• Hydroxyapatites (mineral salts)
– 65% of bone by mass
– Mainly calcium phosphate crystals
– Responsible for hardness and resistance to
compression
Bone Development
• Osteogenesis (ossification)—bone tissue
formation
• Stages
– Bone formation—begins in the 2nd month of
development
– Postnatal bone growth—until early adulthood
– Bone remodeling and repair—lifelong
Two Types of Ossification
1.
Intramembranous ossification
–
–
Membrane bone develops from fibrous membrane
Forms flat bones, e.g. clavicles and cranial bones
2. Endochondral ossification
–
–
Cartilage (endochondral) bone forms by replacing
hyaline cartilage
Forms most of the rest of the skeleton
Intramembranous ossification
1
Collagen
fiber
Mesenchymal
cell
Ossification
center
Osteoid (bone
Matrix)
Ossification centers
appear in the fibrous
connective tissue
membrane.
• Selected centrally
located mesenchymal cells
cluster and differentiate
into osteoblasts, forming
an ossification center.
Osteoblast
2
Bone matrix (osteoid)
is secreted within the
fibrous membrane and
Osceocytes
calcifies.
• Osteoblasts begin to
Osteoid
secrete osteoid, which is
Newly calcified calcified
bone matrix
within a few days.
• Trapped osteoblasts
become osteocytes.
Osteoblast
3
4
Woven bone and periosteum form.
Mesenchyme • Osteoid laid down between
blood vessels in a random
condensing
to form the manner. The result is a
periosteum network of trabeculae called
woven bone.
Vascularized mesenchyme
Trabeculae of •condenses
and becomes the
woven bone
periosteum.
Blood vessel
Lamellar bone replaces woven bone, just deep to the
periosteum. Red marrow appears.
• Trabeculae just deep to the
periosteum thicken, and are
Fibrous
later replaced with mature
periosteum
lamellar bone, forming compact
bone plates.
Osteoblast • Spongy bone (diploë),
consisting of distinct
trabeculae, persists internally
Plate of
and its vascular tissue becomes
compact bone red marrow.
Diploë (spongy
bone) cavities
contain red
marrow
Endochondral ossification
Childhood to
•Uses hyaline cartilage blueprint
adolescence
•Hyaline cartilage breaks down
Birth
Articular
Before ossification
Secondary cartilage
Week 9
Hyaline
cartilage
Area of
deteriorating
cartilage matrix
ossification
Month 3 center
Epiphyseal
blood vessel
Spongy
bone
formation
Spongy
bone
Medullary
cavity
Epiphyseal
plate
cartilage
Bone
collar
1
Blood
vessel of
periosteal
Primary
ossification bud
center
3
Bone collar
forms
around
hyaline
cartilage
model.
4
2 Cartilage in Periosteal bud Diaphysis gets
longer, medullary
the center of invades the
cavity forms,
the diaphysis internal
cavities and
ossification
calcifies and
spongy bone
continues. 2o
then develops begins to form. ossification
cavities.
center develops.
5
Epiphyses ossify.
After, hyaline
cartilage is only
in the epiphyseal
plates and articular
cartilages.
Postnatal Bone Growth
How bones widen (appositional growth):
• Osteoblasts beneath periosteum secret bone matrix
• Osteoclasts on bone surface remove bone
How bones widen
• Cartilage divide and hypertrophy and are eventually
replaced by bone (see next slide)
Hormonal regulation of bone growth
• Growth hormone stimulates epiphyseal plate activity
• Thyroid hormone modulates activity of growth
hormone
• Testosterone and estrogens (at puberty)
– Promote adolescent growth spurts
– End growth by inducing epiphyseal plate closure
 GH stimulates the
lengthening of
bones at the
epiphyseal plate.
 GH stimulates
osteoblast activity &
the proliferation
of epiphyseal cartilage.
 New bone tissue
replaces cartilage in
this region.
 GH stimulates bone
thickness by activating
osteoblasts under the
periosteum.
Articular
cartilage
Bone of
epiphysis
Epiphyseal
plate
Bone of
diaphysis
Marrow cavity
Cartilage
Calcified
cartilage
Bone
Bone of epiphysis
Diaphysis
Epiphyseal plate
Resting
chondrocytes
Cartilage
Calcified
cartilage
Bone
Chondrocytes
undergoing
cell division
chondrocytes
enlarging
Causes
thickening
of
epiphyseal
plate
Calcification of
extracellular matrix
(chondrocytes die)
Dead chondrocytes cleared
away by osteoclasts
Osteoblasts swarming up
from diaphysis and
depositing bone over
persisting remnants of
disintegrating cartilage
Bone remodeling:continuous deposition and resorption of bone
Why? 1. To make bones stronger
2. To maintain Ca 2+ homeostasis
• Calcium is necessary for: transmission of nerve impusles,
muscle contraction, blood coagulation, secretion by glands,
cell division
• Primarily controlled by parathyroid hormone (PTH)
 Blood Ca2+ levels

Parathyroid glands release PTH

PTH stimulates
osteoclasts to degrade bone matrix and
2+
release Ca

 Blood Ca2+ levels
• Calcitonin is secreted by C cells in the thyroid gland to
prevent plasma Calcium from being too high
Response to Mechanical Stress
Load here (body weight)
• Wolff’s law: A bone grows or
remodels in response to forces
or demands placed upon it
• Observations supporting
Wolff’s law:
Head of
– Handedness (right or left
femur
handed) results in bone of
one upper limb being thicker
and stronger
– Curved bones are thickest
where they are most likely
Compression
to buckle
Tension
here
– Trabeculae form along lineshere
of stress
– Large, bony projections
Point of
occur where heavy, active
no stress
muscles attach
•
Bone fractures may be classified by four “either/or”
classifications:
1. Position of bone ends after fracture:
• Nondisplaced—ends retain normal position
• Displaced—ends out of normal alignment
2. Completeness of the break
• Complete—broken all the way through
• Incomplete—not broken all the way through
3. Orientation of the break to the long axis of the bone:
• Linear—parallel to long axis of the bone
• Transverse—perpendicular to long axis of the bone
4. Whether or not the bone ends penetrate the skin:
• Compound (open)—bone ends penetrate the skin
• Simple (closed)—bone ends do not penetrate the
skin
All fractures can be classified based on these criteria:
–Location
–External appearance
–Nature of the break
Some common types of fractures
Comminuted: Bone broken into
3 or more pieces.
Common in people with brittle
bones, such as elderly
Compression: Bone is
crushed. Common in porous
bones (i.e. osteoporotic bone)
subjected to fall or other
trauma
More types of fractures
Spiral: Ragged break from
twisting force on a bone,
common in
sports injury
Epiphyseal: Epiphysis
separates from the
diaphysis along the
epiphyseal plate. Tends to
occur where cartilage cells
are dying
and
calcification
of the
matrix is
occurring
Depressed: Broken bone is
pressed inward. Typical in
a skull fracture.
Greenstick: Bone breaks
incompletely, like a broken
twig. Only one side of the
shaft
breaks.
Common
in kids
Stages in the Healing of a Bone Fracture
Internal
callus
Hematoma (fibrous
tissue and
cartilage)
1 A hematoma forms.
Bony
callus of
spongy
bone
3 Bony callus forms.
2 Fibrocartilaginous
callus forms.
External
callus
New
blood
vessels
Spongy
bone
trabecula
Healed
fracture
4 Bone remodeling occurs.
Homeostatic Imbalances
• Osteomalacia and rickets
– Calcium salts not deposited
– Rickets (childhood disease) causes bowed legs and
other bone deformities
– Cause: vitamin D deficiency or insufficient dietary
calcium
• Paget’s disease
– Excessive and haphazard bone formation and
breakdown, usually in spine, pelvis, femur, or skull
– Pagetic bone has very high ratio of spongy to compact
bone and reduced mineralization
– Unknown cause (possibly viral)
– Treatment includes calcitonin and biphosphonates
Osteoporosis
•Loss of bone mass—bone
resorption outpaces deposit
•Spongy bone of spine and neck of
femur become most susceptible
to fracture
•Risk factors: Lack of estrogen,
calcium or vitamin D; petite body
form; immobility; low levels of
TSH; diabetes mellitus
Treatment and prevention:
•Calcium, vitamin D, and fluoride supplements
• Weight-bearing exercise throughout life
•Hormone (estrogen) replacement therapy slows bone loss
•Some drugs (Fosamax, SERMs, statins) increase bone
mineral density
Developmental Aspects of Bones
• Embryonic skeleton ossifies predictably so fetal age
easily determined from X rays or sonograms
• At birth, most long bones are well ossified (except
epiphyses)
• Nearly all bones completely ossified by age 25
• Bone mass decreases with age beginning in 4th decade
• Rate of loss determined by genetics and
environmental factors
• In old age, bone resorption predominates