Essentials of Human Anatomy
The Skeletal System 1
Chapter 5
Dr Fadel Naim
Ass. Prof. Faculty of Medicine
IUG
1
Bone
• Bones are organs
• Bones are composed of all tissue types.
• Their primary component is osseous
connective tissue.
• The matrix is sturdy and rigid due to
calcification (also called mineralization).
Function of Bones
• Support: form the framework that supports the
body and cradles soft organs
• Protection: provide a protective case for the
brain, spinal cord, and vital organs
• Movement: provide levers for muscles
• Mineral storage: reservoir for minerals, especially
calcium and phosphorus
• Blood cell formation: hematopoiesis occurs
within the marrow cavities of bones
• Energy storage (fat in yellow marrow)
Support and Protection
• Bones provide structural support and
serve as a framework for the entire body.
• Bones protect many delicate tissues and
organs from injury and trauma.
Movement
• Muscles attach to the bones of the
skeleton
– contract and pull on bone
– functions as a series of levers.
Storage of Mineral and Energy Reserves
• More than 90% of the body’s reserves of the
minerals calcium and phosphate are stored and
released by bone.
– Calcium: needed for
• muscle contraction
• blood clotting
• nerve impulse transmission.
– Phosphate: needed for
• ATP utilization
• structure of nucleic acids (DNA, RNA)
Hematopoiesis
Blood Cell Formation
• Blood cell production in red bone marrow
– located in some spongy bone.
• Red bone marrow contains stem cells
– form all of the blood cell types.
Bone Classification
A.
•
•
•
•
Long Bones
Short Bones
Flat Bones
Irregular Bones
Sesamoid (Round) Bones
Classification of Bones: By Shape
• Long bones –
longer than
they are wide
(e.g.,
humerus)
Classification of Bones: By Shape
• Short bones
– Cube-shaped
bones of the
wrist and ankle
– Bones that form
within tendons
(e.G., Patella)
Classification of Bones: By Shape
• Flat bones –
thin, flattened,
and a bit
curved (e.g.,
sternum, and
most skull
bones)
Classification of Bones: By Shape
• Irregular
bones –
bones with
complicated
shapes (e.g.,
vertebrae and
hip bones)
Classification of Bones
• Axial skeleton – bones
of the skull, vertebral
column, and rib cage
• Appendicular skeleton
– bones of the upper
and lower limbs,
shoulder, and hip
Bone Structure - External
 Cartilage
protection for
joints
Bone Structure - External
Epiphyses
Expanded ends of long bones
Exterior is compact bone, and
the interior is spongy bone
Epiphyse
Joint surface is covered with
articular (hyaline) cartilage
location of red bone marrow
Epiphyseal line separates the
diaphysis from the epiphyses
Bone Structure - External
Diaphysis
Tubular shaft that forms
the axis of long bones
Composed of compact
bone that surrounds the
medullary cavity
Yellow bone marrow
(fat) is contained in the
medullary cavity
Diaphysis
Bone Structure - Internal
• Spongy Bonered marrow
Bone Structure - Internal
• Compact bone
Compact and Spongy Bone
Bone Structure - Internal
• Medullary Cavityyellow marrow
Bone Structure - Internal
• Epiphiseal Plate
“Growth Plate”
Parts of a Long Bone
• epiphysis
• distal
• proximal
• diaphysis
• compact bone
• spongy bone
• articular cartilage
• periosteum
• endosteum
• medullary cavity
• trabeculae
• marrow
• red
• yellow
Structure of Short, Irregular, and Flat Bones
• Thin plates of
periosteum-covered
compact bone on the
outside with
endosteum-covered
spongy bone on the
inside
• Have no diaphysis or
epiphyses
• Contain bone marrow
between the
trabeculae
Bone Membranes
• Periosteum – double-layered protective
membrane
– Outer fibrous layer is dense regular connective
tissue
– Inner osteogenic layer is composed of
osteoblasts and osteoclasts
– Richly supplied with nerve fibers, blood, and
lymphatic vessels, which enter the bone via
nutrient foramina
– Secured to underlying bone by Sharpey’s fibers
• Endosteum – delicate membrane covering
internal surfaces of bone
Blood and Nerve Supply of Bone
• Periosteal arteries
– Supply periosteum
• Nutrient arteries
– Enter through nutrient foramen
– Supplies compact bone of diaphysis
& red marrow
• Metaphyseal & epiphyseal aa
– Supply red marrow & bone tissue of
epiphyses
Bone Markings:
Projections ( Sites of Muscle and Ligament Attachment)
•
•
•
•
Tuberosity – rounded projection
Crest – narrow, prominent ridge of bone
Trochanter – large, blunt, irregular surface
Line – narrow ridge of bone
Bone Markings:
Projections ( Sites of Muscle and Ligament Attachment)
• 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 of bone
Bone Markings:
Depressions and Openings
•
•
•
•
•
•
Meatus – canal-like passageway
Sinus – cavity within a bone
Fossa – shallow, basinlike depression
Groove – furrow
Fissure – narrow, slitlike opening
Foramen – round or oval opening through
a bone
The Histologic Types:
•
•
•
•
•
•
Compact bone ( cortical)
Spongy bone ( cancellous)
Lamellar bone: regular – mature
Woven bone: irregular – immature – fetus
- fracture
Osteoid
Callus: fracture healing
Compact Bone:
• Haversian system, or osteon – the
structural unit of compact bone
– Lamella – weight-bearing, column-like matrix
tubes composed mainly of collagen
– Haversian, or central canal – central channel
containing blood vessels and nerves
– Volkmann’s canals – channels lying at right
angles to the central canal, connecting blood
and nerve supply of the periosteum to that of the
Haversian canal
Compact Bone
• Osteocytes – mature bone cells
• Lacunae – small cavities in bone that
contain osteocytes
• Canaliculi – hairlike canals that connect
lacunae to each other and the central
canal
Compact Bone:
Spongy (cancellous) Bone
Does not contain osteons. •
trabeculae surrounding red marrow spaces •
Cell Types of Bone
4 types of cells in bone tissue
• Osteoprogenitor cells:
– Undifferentiated cells
– Can divide become osteoblasts
– Found in inner layer of periosteum and
endosteum
• Osteoblasts:
– Form matrix & collagen fibers but can’t divide
• Osteocytes:
– Mature cells that no longer secrete matrix
• Osteoclasts:
– Huge cells from fused monocytes (WBC)
– Function in bone resorption at surfaces such as
endosteum
Bone Development
Osteogenesis and ossification:
• The process of bone tissue formation, which
leads to:
– The formation of the bony skeleton in embryos
– Bone growth until early adulthood
– Bone thickness, remodeling, and fracture repair
Bone Growth - Ossification
• Cartilage template laid down.
• Osteoblasts (bone building cells)
located in Ossification Centers.
Bone Growth Ossification
• Primary Ossification Center in
diaphasis.
• Secondary Ossification Centers in
epiphisis.
Bone Growth - Ossification
• Grow toward one another, cartilage
remains between them.
• As long as cartilage remains
undamaged, growth can occur.
Formation of the Bony
Skeleton
• Begins at week 8 of embryo development
• Intramembranous ossification – bone
develops from a fibrous membrane
• Endochondral ossification – bone forms
by replacing hyaline cartilage
Endochondral Ossification
• Begins in the second month of
development
• Uses hyaline cartilage “bones” as models
for bone construction
• Requires breakdown of hyaline cartilage
prior to ossification
Stages of Endochondral Ossification
• Formation of bone collar
• Cavitation of the hyaline cartilage
• Invasion of internal cavities by the
periosteal bud, and spongy bone formation
• Formation of the medullary cavity;
appearance of secondary ossification
centers in the epiphyses
• Ossification of the epiphyses, with hyaline
cartilage remaining only in the epiphyseal
plates
Stages of Endochondral Ossification
Secondary
ossification
center
Epiphyseal
blood vessel
Deteriorating
cartilage matrix
Hyaline
cartilage
Spongy
bone
formation
Primary
ossification
center
Bone
collar
Articular
cartilage
Spongy
bone
Medullary
cavity
Epiphyseal
plate
cartilage
Blood
vessel of
periostea
l bud
1 Formation
of bone
collar
around
hyaline
cartilage
model.
2 Cavitation
of the
hyaline
cartilage
within the
cartilage
model.
3 Invasion of
internal cavities
by the
periosteal bud
and spongy
bone formation.
4 Formation of the
medullary cavity as
ossification continues;
appearance of
secondary ossification
centers in the
epiphyses in
preparation for stage 5.
5 Ossification of the
epiphyses; when
completed, hyaline
cartilage remains
only in the
epiphyseal plates
and articular
cartilages
Long Bone Growth and Remodeling
• Growth in length – cartilage continually
grows and is replaced by bone
• Remodeling – bone is resorbed and added
by appositional growth
Bone Growth in Length
• Epiphyseal plate or cartilage growth
plate
– Cartilage cells are produced by mitosis
on epiphyseal side of plate
– Cartilage cells are destroyed and
replaced by bone on diaphyseal side of
plate
• Between ages 18 to 25, epiphyseal
plates close
– Cartilage cells stop dividing and bone
replaces the cartilage (epiphyseal line)
• Growth in length stops at age 25
Remodeling
• Occurs all the time.
• Stresses change, bones adapt.
• Osteoclasts remove bone, Osteoblasts build
bone, Osteocytes maintain bone
• Mineral deposits in Spongy Bone form to
hold the stress best.
• 5-10% bone / year.
Osteoclast in lacuna;
Control of Remodeling
• Two control loops regulate bone
remodeling
– Hormonal mechanism maintains calcium
homeostasis in the blood
– Mechanical and gravitational forces acting on
the skeleton
Developmental Aspects of Bones
• The embryonic skeleton ossifies in a
predictable timetable that allows fetal age to
be easily determined from sonograms
• At birth, most long bones are well ossified
(except for their epiphyses)
• By age 25, nearly all bones are completely
ossified
• In old age, bone resorption predominates
Fracture
• A disruption in the integrity of
a living bone involving injury
to:
–
–
–
–
Bone
Bone marrow
Periosteum
Adjacent soft tissues
Types of Fractures
• green stick
• fissured
• comminuted
• transverse
• oblique
• spiral
•Pathologic
•Stress
•Occult
Fracture Healing
– Bone is the only tissue in the human body
other than liver that heals by regeneration
instead of by scarring.
– For regeneration to occur the bone must
be immobilized to allow uninterrupted
formation of new bone.
Fracture Healing
• Primary healing
– Non displaced fractures, fractures with
compressive fixation across the fracture site
– Osteoblasts traverse the fracture site and lay
down lamellar bone without forming immature
bone when there is direct contact between cortical
bone ends
• Secondary healing
– No compression across fracture site, motion can
occur
– Fracture callus forms to stop motion, stage of
consolidation and remodeling
Primary Bone Healing
Secondary Bone Healing
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Fracture hematoma
(72 hours)
Granulation tissue
(3-14 days)
Callus formation
(7-14 days)
Ossification
(3 weeks- 6 months)
Consolidation
(3 weeks- 6 months)
Remodeling
(Up to 1 year)
Rickets
• a generalized metabolic bone disorder
• characterized by a failure of or delay in
calcification of the cartilaginous growth plate in
children whose epiphyses have not yet fused.
• it is primarily a disease affecting endochondral
calcification
• manifests clinically and radiographically with
widening and deformation of the metaphyseal
regions of long bones
THE END