Unit 5
Bones
Some Bone Facts…
• One of the hardest and strongest materials in
body, but very light in weight
• Calcium helps to make your bones hard, and
collagen fibers help to make your bones slightly
flexible
• Smallest bone is in the middle ear, Largest bone
is the femur (thigh bone)
• Comprises approximately 20% of body weight
(varies)
• 206 total bones as an adult; 80 axial and 126
appendicular
Differences between Males &
Females…
• Male –
– Heavier, larger
– More defined markings
(such as eyebrow,
jaw)
– Deep pelvis
• Female
– Lighter, smaller
– Less defined markings
– Flatter, wider pelvis to
allow for childbirth
Let’s start off by talking about
bones on a tissue-level…
The 3 Types of Bone Cells
• Osteoblast: bone-forming cell
– Uses calcium from blood and forms collagen fibers to
build bone tissue
• Osteoclast: bone-destroying cell
– Breaks down bone matrix for remodeling using acids
and enzymes, releases calcium into blood
– Regulated by several hormones, including parathyroid
hormone (PTH) from the parathyroid gland, calcitonin
from the thyroid gland, and growth factor interleukin-6
• Osteocyte: mature bone cell
2 Types of Bone Tissue
• Compact Bone
– Homogeneous, dense,
smooth
– Composed of regular,
repeating patterns
– Has several major
components…
Parts of Compact Bone Tissue
• Lacunae
– Cavities containing bone cells
(osteocytes)
– Arranged in concentric rings
• Lamellae
– Rings around the central canal
– Sites of lacunae
• Canaliculi
– Tiny canals
– Connect lacuna (holding
osteocytes) to central canal
– Form a transport system
Parts of Compact Bone Tissue
• Osteon
– One system of lamella rings
• Haversian (Central) Canals
– Canal found at center of osteon
– Run parallel to bone
– Carries blood vessels and nerves through the bone
• Volkmann’s (Transverse/Perforating) Canals
– Connect Haversian Canals perpendicular to bone
2 Types of Bone Tissue
• Spongy Bone (sometimes called
Trabecular bone)
– Has very similar structures to Compact Bone,
but is not in set, dense pattern
– Much lighter, but still strong
– Has needle-like pieces and empty space in
bone
2 Major Sections of Long Bone
• Diaphysis
• Epiphysis
2 Major Sections of Long Bone
• Diaphysis
– Long Shaft
– Made of mostly compact bone
– Periosteum membrane (dense connective tissue)
covers the outside; contains blood vessels, some
nerve endings, osteoblasts, and osteoclasts
– Sharpey’s fibers hold Periosteum to the outer
diaphysis
– Has inner Medullary cavity filled with fat tissue
(Yellow Marrow); helps lighten the bone
– Endosteum separates Diaphysis and Medullary
cavity, contains osteoblasts & osteoclasts
2 Major Sections of Long Bone
• Epiphysis
– Ends of long bone
– Composed mainly of spongy bone covered
with a thin layer of compact bone
– Entire epiphysis covered by articular (hyaline)
cartilage, which provides smooth surface for
movement
– In adults, red marrow can be found here
(blood cells made from red marrow through
hematopoiesis)
2 Major Sections of Long Bone
• Diaphysis and
Epiphysis separated
by epiphyseal line
(which was once the
epiphyseal or growth
plate in young
children)
Bone Remodeling
• Bone remodeling is a process that involves bone
deposit and removal (resorption)
• Remodeling units are clusters of adjacent
osteoblasts and osteoclast
• In healthy adult, total bone mass remains
constant (meaning that deposits and removals
are happening at an equal rate)
• Bone remodeling occurs at a rate of 10% per
year
• Both happen in the adult on the periosteum and
endosteum surface
• Two control loops regulate bone remodeling…
Bone Remodeling
• Hormonal Mechanism: Calcium levels in blood
– If blood needs Ca+2, parathyroid hormone
(PTH) gets released to stimulate osteoclasts,
which will destroy bone to release more Ca+2
– If blood has too much Ca+2, calcitonin released
by thyroid gland to stimulate calcium deposited
back in bone
• Mechanical Mechanism: pull of gravity and
muscles
– Bones need to strengthen in areas where bulky
muscles attached and stress is felt
– Called Appositional Growth
– Bones become wider (but not thicker!) due to
osteoclast and osteoblast activity
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/
chapter6/animation__bone_growth_in_wid
th.html
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/
chapter6/animation__osteoporosis.html
How do bones change with age?
• Fetus
– Skeleton mostly hyaline cartilage
– Has approximately 300 cartilage “bones”, many which
fuse together
How do bones change with age?
• Before Birth / Young Child
(ages 0 to 3)
– Bones develop using
hyaline cartilage as
“model”
– Ossification: Bone
formation
• First, hyaline cartilage
covered with bone matrix by
osteoblasts
• Second, enclosed hyaline
cartilage is digested away,
leaving medullary cavity
– Medullary cavity filled with
Red Marrow (for Red Blood
Cell production)
How do Bones change with age?
• Child (ages 3 – 18)
– Epiphyseal plate (still made of cartilage, between diaphysis and
epiphysis) provides base for length growth
– Medullary cavity changes from Red Marrow to Yellow Marrow
– Hyaline cartilage remains in isolated areas (bridge of nose, ribs,
joints)
– More bone is made than lost
• Adult (ages 18-50, can vary)
– Epiphyseal plate cartilage hardens and turns to bone… now
known as epiphyseal line
– Bone created and destroyed at fairly equal rates (bone
remodeling)
– Bone still changing constantly in response to body changes
Newborn
1 Year
13 Years
18 years
How do Bones change with age?
• Elderly (ages 50 to ??)
– More bone is lost than is made
Trabeculae in
normal bone x40
Trabeculae in
osteoporotic bone
x40
How do bones repair themselves?
• If a fracture occurs, there are some main
steps that a bone takes to repair itself
– Hematoma (blood-filled swelling) forms due to
ruptured blood vessels in blood
– Fibrocartilage callus forms, acting as a splint
– Bony callus forms as osteoblasts and
osteoclasts replace fibrocartilage with spongy
bone
– Bone remodels in response to normal
stresses, forming a permanent patch
Fractures
• Closed (Simple)
Fracture: bone breaks
cleanly but does not
penetrate the skin
• Open
(Compound)Fracture:
broken bone ends
penetrate through the
skin
Fractures
•
Reduction: setting the fracture back into
place
– Closed Reduction: bone ends are coaxed
back into position by the physician’s hand
– Open Reduction: surgery is performed, and
the bone ends are secured with pins or
wires
– After bone reduced, bone immobilized with a
cast for 6 to 8 weeks
Types of Fractures
• Transverse: Cuts
directly across the
bone
• Oblique: Cuts at an
angle across the
bone
• Linear: often called a
“hairline” fracture,
does not displace the
bone
Fracture Types…
•
•
•
Comminuted: Bone
breaks into many
fragments, common
in elderly
Compression: bone
is crushed, common
in porous bones
Depression: Broken
bone portion is
pressed inward,
typical of skull
fracture
Comminuted Fracture
Compression Fracture
Depression Fracture
Fracture Types…
• Impacted: broken bone
ends are forced into
each other, common in
falls
• Spiral: ragged break
due to excessive
twisting, common
sports fracture
• Greenstick: bone
breaks incompletely,
common in children
Impacted Fracture
Spiral Fracture
Greenstick Fracture
Joints
•
The Function of Joints…
– Hold bones together securely
– Give the rigid skeleton mobility
• Can be classified functionally or
structurally…
Joints
•
Functional Classification… dependent on
how the joint moves
– Synarthroses – immovable joints
– Amphiarthroses – slightly moveable joints
– Diarthroses – freely moveable joints
– Immovable and slightly moveable joints
more common in axial skeleton, while freely
moveable joints more common in the limbs
Joints
• Structural Classification… dependent on
which thing separates the bony regions at
the joint!
– Fibrous: separated by dense (fibrous)
connective tissue
• Ex: Sutures of the Skull
• Usually immovable =
synarthroses
Joints
• Cartilaginous:
separated by
fibrocartilage
– Ex: vertebrae,
pubic symphysis
– Usually slightly
moveable =
amphiarthroses
Joints
• Synovial: separated
by fluid-filled sac
• Remember synovial
membranes from the
last unit???
• Usually freely
moveable =
diarthroses
Joints
•
Distinguishing Features of
Synovial Joint
– Articular cartilage (hyaline
cartilage) covers the ends of
bones
– Joint surfaces are enclosed
by synovial membrane and a
fibrous capsule
– Have a joint cavity filled with
synovial fluid – lubricates the
joint
– Ligaments reinforce the joint
Joints
• Types of Synovial Joints Include…
– Plane Joint
• Movement Allowed: slipping or gliding
• Example: intercarpal joints of wrist
• Non-Axial
– Hinge Joint
• Movement Allowed: angular movement in
one plane
• Example: elbow, phalanges
• Uni-Axial
Joints
– Pivot Joint
• Movement Allowed: rotates around long
axis
• Example: radioulnar joint
• Uni-axial
Skeletal System
– Condyloid Joint
• Movement Allowed: side-to-side and back
& forth, cannot rotate around long axis
• Example: knuckles
• Bi-axial
– Saddle Joint
• Movement Allowed: same as condyloid
• Example: thumb
• Bi-axial
Skeletal System
– Ball and Socket Joint
• Movement Allowed: rotation, most freely
moving
• Example: shoulder and hip
• Multi-axial
A few famous Synovial Joints…
• Temporomandibular Joint
– Where mandible and temporal
bone meet
– Problems with this joint leads to
jaw issues (popping, pain when
chewing, difficulty opening mouth,
headaches)
– Gliding and Hinge joint
A few famous Synovial Joints…
• Coxal Joint (Acetabulofemoral Joint)
– Occurs where the head of the femur fits into
the acetablum of the coxal bone
– With age, this joint can become very worn
down or broken at the neck of the femur,
requiring a hip replacement
– Ball and Socket Joint
A few famous Synovial Joints…
• Knee Joint
(Tibiofemoral Joint)
– Kneecap held on by a
patellar ligament
– Joint Cavity contains two
cartilages – the lateral
meniscus and the medial
meniscus
– The knee is held together
using SEVERAL ligaments
– Hinge and Pivot Joint
Joints
• Shoulder Joint
(Humeroscapular joint)
– The humerus and the
glenoid fossa of the scapula
are joined
– The shoulder is held
together using SEVERAL
ligaments
– Rotator cuff muscles also
help to hold this joint in place
– Ball and Socket Joint
The Skull
• Consists of the cranium and the bones of the
face
– The cranium encloses cranial cavity, protects the
brain
– Facial bones surround and protect the entrances to
the respiratory and digestive tracts, provides
attachment points for muscles to show feeling
Facial Bones
•
•
•
•
•
Maxillary bones
Mandible
Palatine bones
Nasal bones
Vomer
• Inferior nasal conchae
• Zygomatic bones
• Lacrimal bones
• Hyoid
Cranial Bones
• one occipital bone
• two temporal bones
– foramen magnum
• auditory ossicles
• two parietal bones
• one frontal bone
– frontal sinuses
• one sphenoid
• one ethmoid
Skull Sutures
• Lamboid: separate Occipital and Parietal
• Sagittal: separate Parietals
• Squamous: separate Temporal and
Parietal
• Coronal: separate Frontal and Parietal
Skull Sutures
Figure 7.3a, b
Paranasal Sinuses
• Hollow portions of bones surrounding the nasal
cavity
• Functions of paranasal sinuses:
• Lighten the skull
• Give resonance and amplification to voice
Mandible
Hyoid Bone
• The only bone that
does not articulate
with another bone
• Anchors using
ligaments to the
Temporal bone
• Serves as a moveable
base for the tongue
Foramen Magnum
• Hole in the
Occipital bone
that provides
passageway for
the spinal cord
Special Characteristics of the
Fetal Skull
• Infant’s face small in comparison to
cranium
• Skull large in comparison to infant’s body
• Skeleton unfinished; has areas of hyaline
cartilage that must be converted to bone
• Fontanels: fibrous membranes between
cranial bones that allow fetal skull to be
compressed during birth, allow brain to
grow
This is a joint between:
the lower end (1) and medial malleolus (2)
of the tibia and the lateral malleolus (3) of
the fibula
and the trochlear surface of the talus (4)
3-5 weeks in
utero. cartilage
model
6 weeks in utero.
Primary centre of
ossification
appears in shaft
which is
surrounded by a
collar of compact
bone.
2-5 years. Bone
marrow cavity is
formed in the
shaft and
secondary
centres of
ossification are
present in the
ends of the bone.
Adult. Adult bone.
Epiphyseal plates
are closed and
growth is finished.
8 months in
utero - birth.
Bone shaft is now
fully ossified.