Skeletal system axil & appendicular skeleton powerpoint (chapter 6)

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byby
Chitranjan kumarChitranjan kumar
Vinoba Bhave UniversityVinoba Bhave University
hazaribaghhazaribagh

 The skeleton, composed of bones,
cartilages, joints, and ligaments, accounts
for about 20% of body mass.
 There are 206 bones in the human body.

 The axial
skeleton forms
the long axis of
the body and
includes the
bones of the
skull, vertebral
column, and rib
cage.
 There are 80
bones in the
axial skeleton.

The Appendicular
skeleton consists of
the bones of the
upper and lower
limbs, and the
shoulder bones and
hip bones.
There are 126 bones
in the Appendicular
Skeleton.

The skull consists of two sets of bones – the
cranium and the facial bones. There are
eight cranial bones and fourteen facial
bones.
 The joints between bones of the skull are
immovable and called sutures.

•The SPHENOID BONE- acts like a bridge
between the cranial & facial bones

Only the mandible is attached by a freely
movable joint.
The hyoid bone is the only bone in the body
that does not articulate (match up with)
another bone. The hyoid bone acts as an
attachment point for several muscles that
help with speech and swallowing. The
hyoid bone is attached to the skull by
ligaments.

The vertebral column consists
of vertebrae separated by disks
of fibro-cartilage.
 7 cervical vertebrae
 12 thoracic vertebrae
 5 lumbar vertebrae
The bony thorax forms a cage
to protect major organs

SPINAL
(VERTEBRAL)
COLUMN
The spinal column
(or vertebral column)
extends from the
skull to the pelvis
and is made up of 33
individual bones
termed vertebrae.

The bony thorax is made up of three parts:
1)Sternum
2)Ribs
3)Thoracic vertebrae

You have three different types of ribs
 True ribs are the first seven pairs of ribs. True
ribs attach directly to the sternum by costal
cartilages.
 False ribs are the next five pairs. They either
attach indirectly to the sternum or not at all.
 Floating ribs are the last two pairs of false ribs.
They lack sternal attachments.

The 3 parts of the appendicular skeleton are:
1)Limbs (appendages)
2)Pectoral girdle (shoulder)
3)Pelvic girdle (pelvis)

The pectoral girdle (or shoulder) is composed
of two bones
1)Clavicle – collarbone
2)Scapula – Shoulder blade
The clavicle and the scapula allow the
upper limbs to have free movement

The arm is formed from a single bone, the
humerus.
The forearm has two bones: the ulna and
radius

The hand contains three types
of bones:
1)Carpals – wrists
2)Metacarpals – palm
3)Phalanges - fingers

The thigh has one bone – the femur.
The lower leg has two bones – the tibia and
fibula.

The foot has three types of bones:
1)Tarsals – ankle
2)Metatarsals – sole
3)Phalanges - toes

The pelvic girdle is made up of the hip bones.
The “hip bones” are composed of three pair of fused
bones – the ilium, ischium, and pubic bone.

The total weight of the upper body rests on
the pelvis.
The pelvic girdle protects several organs –
the reproductive organs, the urinary
bladder, and part of the large intestine.

Joints & ArticulationsJoints & Articulations

Classification Of JointsClassification Of Joints
 Classification By Function (degree of
movement possible):
1. Synarthroses (Syn=connected, immovable)
 Joints with little or no movement
 Skull sutures, cranium (minus the mandible))
1. Amphiarthroses (Amphi = on both sides, between)
 Slightly moveable joints
 Intervertebral discs, costosternal joints, cartilaginous
joints(vertebrate between spine)
1. Diarthroses (Diar=passing through, free moving)
 Freely moveable joints
 Shoulder, knee, hip, elbow, interphalangeal, tarsal, and
carpal joints

Joint ClassificationJoint Classification
 Classification by
structure:
1. Synovial joints:
 Bones separated
by a joint cavity;
lubricated by
synovial fluid;
enclosed in a
fibrous joint
capsule.
 Shoulder, hip,
elbow, knee,
carpal,
interphalangeal
How would we classify these
joints functionally?

Joint ClassificationJoint Classification
2. Fibrous joints:
– Bones held together by
collagenous fibers
extending from the
matrix of one bone into
the matrix of the next.
– No joint cavity
– Skull sutures, teeth in
joints, distal radioulnar
joints & tibiofibular
joints

Joint ClassificationsJoint Classifications
3. Cartilaginous joints:
– Bones held together by cartilage; no joint cavity
– Epiphyseal plates of long bones, costosternal joints, pubic
symphysis, intervertebral discs

Structure and FunctionStructure and Function
 Joints are designed for
their function.
 Let’s look at sutures as
our 1st
example:
– Name 4 sutures!
– What function do you
suppose sutures are
designed for?

(1) Immovable: fixed joint such as the cranium
(2) Ball-and-socket joints: such as the shoulder and hip joints, allow
backward, forward, sideways, and rotating movements.
(3) Hinge joints: such as in the fingers, knees, elbows, and toes, allow only
bending and straightening movements.
(4) Pivot joints: such as the neck joints, allow limited rotating movements.
(5) Sliding Joint: found in the vertebral column and allows small sliding
movements. The vertebrae have pads of cartilage between them, and the
bones slide over these pads. This is what makes the backbone so flexible.
(6) Ellipsoidal Joint: similar to a ball and socket joint. They allow the
same type of movement to a lesser magnitude such as the wrist
Types of Joints in theTypes of Joints in the
Human BodyHuman Body

 Now let’s talk about
synovial joints.
– 5 main structural
characteristics:
1. Articular cartilage
 What kind of cartilage
is it?
 Where do we find it?
 What does it do?

2. Articular capsule
– 2 layered. Surrounds both
articular cartilages and the
space btwn them.
– External layer is made of
dense irregular CT & is
continuous w/ the perisoteum.
– Inner layer is a synovial
membrane made of loose
connective tissue.
 It covers all internal joint
surfaces except for those areas
covered by the articular
cartilage.

3. Joint (Synovial) Cavity
– The potential space within
the joint capsule and articular
cartilage
3. Synovial Fluid
– A small amount of slippery
fluid occupying all free space
w/i the joint capsule
– Formed by filtration of blood
flowing thru capillaries in the
synovial membrane
– Synovial fluid becomes less
viscous as joint activity
increases.

5. Reinforcing Ligaments
– What kind of tissue are
they?
– What do you suppose their
function is?
– Double-jointed-ness
results from extra-stretchy
ligaments and joint
capsules. Is this
necessarily a good thing?

Other Synovial StructuresOther Synovial Structures
 The knee and hip joints have
cushioning fatty pads btwn
the fibrous capsule and the
synovial membrane or bone.
 Discs of fibrocartilage (i.e.,
menisci) which improve the
fit between bone ends, thus
stabilizing the joint.
– Found in the knee, jaw, and
sternoclavicular joint.
 Bursae are basically bags of
lubricant - fibrous
membrane bags filled with
synovial fluid. Often found
where bones, muscles,
tendons, or ligaments rub
together.

Types of SynovialTypes of Synovial
JointsJoints
1. Plane joints
– Articular surfaces are flat and
allow short slipping or gliding
movements.
– Intercarpal and intertarsal joints
1. Hinge joints
– A cylindrical projection of one
bone fits into a trough-shaped
surface on another (like a
hotdog in a bun)
– Movement resembles a door
hinge.
– Elbow joint – ulna and
humerus; Interphalangeal joints

Type of SynovialType of Synovial
JointsJoints
3. Pivot joints
– Rounded end of one bone
protrudes into a ring formed by
another bone or by ligaments of
that bone.
– Proximal radioulnar joint
– Atlas-axial joint
3. Condyloid joints
– Oval articular surface of one bone
fits into a complementary
depression on another.
– Radiocarpal joints
– Metacarpophalangeal joints

Types of SynovialTypes of Synovial
JointsJoints
5. Saddle joints
– Each articular surface has convex and
concave areas. Each articular surface
is saddle-shaped.
– Carpometacarpal joints of the
thumbs.
5. Ball-and-Socket joints
– Spherical or semi-spherical head of
one bone articulates with the cuplike
socket of another.
– Allow for much freedom of motion.
– Shoulder and hip joints.

The KneeThe Knee
 Largest and most complex
diarthrosis in the body.
 Primarily a hinge joint, but when
the knee is flexed, it is also
capable of slight rotation and
lateral gliding.
 Actually consists of 3 joints:
– Patellofemoral joint
– Medial and lateral tibiofemoral
joints
 The joint cavity is only partially
enclosed by a capsule – on the
medial, lateral, and posterior
sides.

The KneeThe Knee
 The lateral and medial
condyles of the femur
articulate with the
lateral and medial
condyles of the tibia.
– Between these structures,
we have the lateral and
medial menisci.
 Anteriorly, the patellar
ligament binds the tibia
(where?) to the inferior
portion of the patella.
The superior portion of
the patella is then
connected to the
quadriceps femoris
muscle

The KneeThe Knee At least a dozen bursae
are associated with the
knee.
 Multiple ligaments are
present.
– The fibular collateral
ligament extends from
the lateral epicondyle of
the femur to the head of
the fibula.
– The tibial collateral
ligament connects medial
epicondyle of the femur
to the medial condyle of
the tibial shaft and is also
fused to the medial
meniscus.
– Both of these ligaments
prevent excessive
rotation

The KneeThe Knee The anterior and posterior
cruciate ligaments are also
very important.
– ACL connects the anterior
intercondylar area of the tibia
to the medial side of the lateral
femoral condyle.
 Prevents forward sliding of the
tibia and hyperextension of the
knee.
– PCL connects the posterior
intercondylar area of the tibia
to the lateral side of the medial
femoral condyle.
 Prevents backward displacement
of the tibia or forward sliding of
the femur.

http://video.about.com/sportsmedicine/Anterior-Cruciate-Ligament.htm
http://video.about.com/sportsmedicine/Medial-Meniscus-Injury.htm
ACLACL VideosVideos

Articulations (Movements)Articulations (Movements)

Clinical
Conditions
 Arthritis describes about
100 different types of
inflammatory or
degenerative joint diseases.
 Osteoarthritis
– Most common arthritis.
– Normal joint use prompts the
release of cartilage-damaging
enzymes. If cartilage
destruction exceeds cartilage
replacement, we’re left with
roughened, cracked, eroded
cartilages.
 Eventually bone tissue thickensEventually bone tissue thickens
and forms spurs that can restrictand forms spurs that can restrict
movement.movement.
 Most common in C and L spine,Most common in C and L spine,
fingers, knuckles, knees, andfingers, knuckles, knees, and
hips.hips.

Clinical
Conditions
 Rheumatoid arthritis
– Chronic inflammatory
disorder
– Marked by flare-ups
– Autoimmune disease.
 Body creates antibodies
which attack the joint
surfaces
 The synovial membrane can
inflame and eventually
thicken into a pannus – an
abnormal tissue that clings to
the articular cartilage.

Gouty arthritis
– When nucleic acids are metabolized uric acid
is produced. Normally uric acid is excreted in
the urine.
– If blood [uric acid] rises due to decreased
excretion or increased production, it may
begin to form needle-shaped crystals in the
soft tissues of joints.
– Inflammation ensues causing painful arthritis.
Clinical
Conditions

Skeletal SystemSkeletal System
 Composed of the body’s bones and
associated ligaments, tendons, and
cartilages.
 Functions:
1. Support
 The bones of the legs, pelvic girdle, and vertebral
column support the weight of the erect body.
 The mandible (jawbone) supports the teeth.
 Other bones support various organs and tissues.
1. Protection
 The bones of the skull protect the brain.
 Ribs and sternum (breastbone) protect the lungs
and heart.
 Vertebrae protect the spinal cord.

Skeletal SystemSkeletal System
 Functions:
3. Movement
 Skeletal muscles use the bones as levers to
move the body.
3. Reservoir for minerals and adipose tissue
 99% of the body’s calcium is stored in bone.
 85% of the body’s phosphorous is stored in
bone.
 Adipose tissue is found in the marrow of
certain bones.
– What is really being stored in this case? (hint –
it starts with an E)
3. Hematopoiesis
 A.k.a. blood cell formation.
 All blood cells are made in the marrow of
certain bones.

BoneBone
ClassificationClassification
 There are 206 named bones in
the human body.
 Each belongs to one of 2 large
groups:
– Axial skeleton
 Forms long axis of the body.
 Includes the bones of the skull,
vertebral column, and rib cage.
 These bones are involved in
protection, support, and
carrying other body parts.
– Appendicular skeleton
 Bones of upper & lower limbs
and the girdles (shoulder bones
and hip bones) that attach them
to the axial skeleton.
 Involved in locomotion and
manipulation of the
environment.

BoneBone
ClassificationClassification
 4 types of bones:
1. Long Bones
 Much longer than they are wide.
 All bones of the limbs except for
the patella (kneecap),
and the bones of the wrist and
ankle.
 Consists of a shaft plus 2
expanded ends.
 Your finger bones are long bones
even though they’re
very short – how can this be?
1. Short Bones
 Roughly cube shaped.
 Bones of the wrist and the ankle.
Femur 
Carpal Bones

Bone ClassificationBone Classification
 Types of bones:
3. Flat Bones
 Thin, flattened, and usually
a bit curved.
 Scapulae, sternum,
(shoulder blades), ribs and
most bones of the skull.
3. Irregular Bones
 Have weird shapes that fit
none of the 3 previous
classes.
 Vertebrae, hip bones, 2
skull bones ( sphenoid
and the ethmoid bones).
Sternum
Sphenoid
Bone

Bone StructureBone Structure
 Bones are organs. Thus, they’re composed of
multiple tissue types. Bones are composed of:
– Bone tissue (a.k.a. osseous tissue).
– Fibrous connective tissue.
– Cartilage.
– Vascular tissue.
– Lymphatic tissue.
– Adipose tissue.
– Nervous tissue.

 All bones consist of a
dense, solid outer
layer known as
compact bone and an
inner layer of spongy
bone – a honeycomb
of flat, needle-like
projections called
trabeculae.
 Bone is an extremely
dynamic tissue!!!!
Above: Note the relationship btwn the
compact and spongy bone.
Below: Close up of spongy bone.

Note the gross differences between the spongy bone and the
compact bone in the above photo.
Do you see the trabeculae?

Compare compact and spongy bone as viewed with the light microscope

 Bone tissue is a type of
connective tissue, so it must
consist of cells plus a
significant amount of
extracellular matrix.
 Bone cells:
1. Osteoblasts
 Bone-building cells.
 Synthesize and secrete
collagen fibers and other
organic components of
bone matrix.
 Initiate the process of
calcification.
 Found in both the
periosteum and the
endosteum
The blue arrows indicate the
osteoblasts. The yellow arrows indicate
the bone matrix they’ve just secreted.

2.Osteocytes
 Mature bone
cells.
 Osteoblasts
that have
become
trapped by the
secretion of
matrix.
 No longer
secrete matrix.
 Responsible
for
maintaining
the bone
tissue.
Yellow arrows indicate
osteocytes – notice how
they are surrounded by the
pinkish bone matrix.
Blue arrow shows an
osteoblast in the process of
becoming an osteocyte.
On the right, notice how the osteocyte
is “trapped” within the pink matrix

3. Osteoclasts
– Huge cells derived from the fusion of as many as 50 monocytes (a type of
white blood cell).
– Cells that digest bone matrix – this process is called bone resorption and is
part of normal bone growth, development, maintenance, and repair.
– Concentrated in the endosteum.
– On the side of the cell that faces the bone surface, the PM is deeply folded
into a ruffled border. Here, the osteoclast secretes digestive enzymes (how
might this occur?) to digest the bone matrix. It also pumps out hydrogen
ions (how might this occur?) to create an acid environment that eats away at
the matrix. What advantage might a ruffled border confer?
– Why do we want a cell that eats away at bone? (Hint: bone is a very
dynamic tissue.)

•Here, we see a cartoon showing all 3 cell types. Osteoblasts and osteoclasts are indicated.
•Note the size of the osteoclast (compare it to the osteoblast), and note the ruffled border.
•Why is there a depression underneath the osteoclast?
•What is the name of the third cell type shown here?
•What do you think the tan material represents?

Bone Matrix:
– Consists of organic and inorganic
components.
– 1/3 organic and 2/3 inorganic by
weight.
 Organic component consists of several
materials that are secreted by the
osteoblasts:
– Collagen fibers and other organic materials
• These (particularly the collagen) provide
the bone with resilience and the ability
to resist stretching and twisting.

 Inorganic component
of bone matrix
– Consists mainly of 2
salts: calcium
phosphate and calcium
hydroxide. These 2
salts interact to form a
compound called
hydroxyapatite.
– Bone also contains
smaller amounts of
magnesium, fluoride,
and sodium.
– These minerals give
bone its characteristic
hardness and the
ability to resist
compression.
Three-dimensional array of
collagen molecules. The rod-
shaped molecules lie in a
staggered arrangement which
acts as a template for bone
mineralization. Bone mineral is
laid down in the gaps.
Note collagen fibers in longitudinal & cross section
and how they occupy space btwn the black bone cells.

This bone:
a. Has been demineralized
b. Has had its organic component removed

Long BoneLong Bone
StructureStructure
 Shaft plus 2 expanded ends.
 Shaft is known as the diaphysis.
– Consists of a thick collar of compact
bone surrounding a central marrow
cavity
 In adults, the marrow cavity contains
fat - yellow bone marrow.
 Expanded ends are epiphyses
– Thin layer of compact bone covering
an interior of spongy bone.
– Joint surface of each epiphysis is
covered w/ a type of hyaline cartilage
known as articular cartilage. It
cushions the bone ends and reduces
friction during movement.

Long BoneLong Bone
StructureStructure
 The external surface of the entire
bone except for the joint surfaces of
the epiphyses is covered by a
double-layered membrane known
as the periosteum.
– Outer fibrous layer is dense irregular
connective tissue.
– Inner cellular layer contains
osteoprogenitor cells and osteoblasts.
– Periosteum is richly supplied with
nerve fibers, lymphatic vessels and
blood vessels.
 These enter the bone of the shaft via a
nutrient foramen.
– Periosteum is connected to the bone
matrix via strong strands of collagen.

Long BoneLong Bone
StructureStructure
 Internal bone surfaces are covered with a delicate
connective tissue membrane known as the
endosteum.
– Covers the trabeculae of spongy bone in the marrow
cavities and lines the canals that pass through compact
bone.
– Contains both osteoblasts and osteoclasts.

Structure of Short, Irregular, andStructure of Short, Irregular, and
Flat BonesFlat Bones
 Thin plates of periosteum-covered
compact bone on the outside and
endosteum-covered spongy bone
within.
 Have no diaphysis or epiphysis
because they are not cylindrical.
 Contain bone marrow between
their trabeculae, but no marrow
cavity.
 In flat bones, the internal spongy
bone layer is known as the diploë,
and the whole arrangement
resembles a stiffened sandwich.

Bone MarrowBone Marrow
 Bone marrow is a general term for the
soft tissue occupying the medullary
cavity of a long bone, the spaces amid
the trabeculae of spongy bone, and the
larger haversian canals.
 There are 2 main types: red & yellow.
 Red bone marrow = blood cell
forming tissue = hematopoietic tissue
 Red bone marrow looks like blood but
with a thicker consistency.
 It consists of a delicate mesh of reticular
tissue saturated with immature red blood
cells and scattered adipocytes.
Notice the red marrow
and the compact bone

Distribution ofDistribution of
MarrowMarrow
 In a child, the medullary
cavity of nearly every bone is
filled with red bone marrow.
 In young to middle-aged
adults, the shafts of the long
bones are filled with fatty
yellow bone marrow.
– Yellow marrow no longer
produces blood, although in
the event of severe or chronic
anemia, it can transform back
into red marrow
 In adults, red marrow is
limited to the axial skeleton,
pectoral girdle, pelvic girdle,
and proximal heads of the
humerus and the femur.
Note the compact bone on the
bottom and marrow on the bottom.

MicroscopicMicroscopic
Structure ofStructure of
CompactCompact
BoneBone
 Consists of multiple
cylindrical structural
units known as
osteons or haversian
systems.
 Imagine these osteons
as weight-bearing
pillars that are
arranged parallel to
one another along the
long axis of a
compact bone.
The diagram below represents a long
bone shaft in cross-section. Each
yellow circle represents an osteon. The
blue represents additional matrix filling
in the space btwn osteons. The white in
the middle is the marrow cavity.

OsteonsOsteons
 Each osteon consists of a single
central canal, known as a
haversian canal, surrounded by
concentric layers of calcified
bone matrix.
– Haversian canals allow the passage
of blood vessels, lymphatic vessels,
and nerve fibers.
– Each of the concentric matrix
“tubes” that surrounds a haversian
canal is known as a lamella.
– All the collagen fibers in a particular
lamella run in a single direction,
while collagen fibers in adjacent
lamellae will run in the opposite
direction. This allows bone to better
withstand twisting forces.

Running perpendicular to the haversian canals are Volkmann’s canals.
They connect the blood and nerve supply in the periosteum to those
in the haversian canals and the medullary cavity.

OsteonsOsteons
 Lying in between intact
osteons are incomplete
lamellae called
interstitial lamellae.
These fill the gaps
between osteons or are
remnants of bone
remodeling.
• There are also circumferential lamellae that extend around the
circumference of the shaft. There are inner circumferential
lamellae surrounding the endosteum and outer circumferential
lamellae just inside the periosteum.

 Spider-shaped
osteocytes occupy small
cavities known as
lacunae at the junctions
of the lamellae. Hairlike
canals called canaliculi
connect the lacunae to
each other and to the
central canal.
 Canaliculi allow the
osteocytes to exchange
nutrients, wastes, and
chemical signals to each
other via intercellular
connections known as
gap junctions.

Here, we have a close up and a far
away view of compact bone. You
should be able to identify haversian
canals, concentric lamellae,
interstitial lamellae, lacunae, and
canaliculi.

MicroscopicMicroscopic
Structure ofStructure of
Spongy BoneSpongy Bone
 Appears poorly organized
compared to compact bone.
 Lacks osteons.
 Trabeculae align along
positions of stress and
exhibit extensive cross-
bracing.
 Trabeculae are a few cell
layers thick and contain
irregularly arranged
lamellae and osteocytes
interconnected by
canaliculi.
 No haversian or Volkmann’s
canals are necessary. Why?

BoneBone
DevelopmentDevelopment
 Osteogenesis (a.k.a.
ossification) is the
process of bone tissue
formation.
 In embryos this leads to
the formation of the
bony skeleton.
 In children and young
adults, ossification
occurs as part of bone
growth.
 In adults, it occurs as
part of bone remodeling
and bone repair.

Formation of the BonyFormation of the Bony
SkeletonSkeleton
 Before week 8, the human
embryonic skeleton is made of
fibrous membranes and hyaline
cartilage.
 After week 8, bone tissue
begins to replace the fibrous
membranes and hyaline
cartilage.
– The development of bone from a
fibrous membrane is called
intramembranous ossification.
Why?
– The replacement of hyaline
cartilage with bone is known as
endochondral ossification. Why?

Intramembranous OssificationIntramembranous Ossification
 Some bones of the skull (frontal, parietal, temporal, and occipital
bones), the facial bones, the clavicles, the pelvis, the scapulae, and
part of the mandible are formed by intramembranous ossification
 Prior to ossification, these structures exist as fibrous membranes
made of embryonic connective tissue known as mesenchyme.

 Mesenchymal cells first
cluster together and start
to secrete the organic
components of bone
matrix which then
becomes mineralized
through the crystallization
of calcium salts. As
calcification occurs, the
mesenchymal cells
differentiate into
osteoblasts.
 The location in the tissue
where ossification begins
is known as an
ossification center.
 Some osteoblasts are
trapped w/i bony pockets.
These cells differentiate
into osteocytes.

 The developing bone grows outward from the ossification center
in small struts called spicules.
 Mesenchymal cell divisions provide additional osteoblasts.
 The osteoblasts require a reliable source of oxygen and
nutrients. Blood vessels trapped among the spicules meet these
demands and additional vessels branch into the area. These
vessels will eventually become entrapped within the growing
bone.

 Initially, the intramembranous bone consists only of
spongy bone. Subsequent remodeling around trapped
blood vessels can produce osteons typical of compact
bone.
 As the rate of growth slows, the connective tissue around
the bone becomes organized into the fibrous layer of the
periosteum. Osteoblasts close to the bone surface become
the inner cellular layer of the periosteum.

Endochondral OssificationEndochondral Ossification
 Begins with the formation of a hyaline cartilage model which
will later be replaced by bone.
 Most bones in the body develop via this model.
 More complicated than intramembranous because the hyaline
cartilage must be broken down as ossification proceeds.
 We’ll follow limb bone development as an example.

Endochondral Ossification –Endochondral Ossification –
Step 1Step 1
 Chondrocytes near the center
of the shaft of the hyaline
cartilage model increase
greatly in size. As these cells
enlarge, their lacunae expand,
and the matrix is reduced to a
series of thin struts. These
struts soon begin to calcify.
 The enlarged chondrocytes
are now deprived of nutrients
(diffusion cannot occur
through calcified cartilage)
and they soon die and
disintegrate.

Endochondral Ossification – StepEndochondral Ossification – Step
22
 Blood vessels grow into the perichondrium surrounding the shaft
of the cartilage. The cells of the inner layer of the
perichondrium in this region then differentiate into osteoblasts.
 The perichondrium is now a periosteum and the inner osteogenic
layer soon produces a thin layer of bone around the shaft of the
cartilage. This bony collar provides support.

33
 Blood supply to the periosteum, and
capillaries and fibroblasts migrate into
the heart of the cartilage, invading the
spaces left by the disintegrating
chondrocytes.
 The calcified cartilaginous matrix
breaks down; the fibroblasts
differentiate into osteoblasts that replace
it with spongy bone.
 Bone development begins at this
primary center of ossification and
spreads toward both ends of the
cartilaginous model.
 While the diameter is small, the entire
diaphysis is filled with spongy bone.
Notice the primary
ossification centers in the
thigh and forearm bones
of the above fetus.

44
 The primary ossification center enlarges
proximally and distally, while osteoclasts break
down the newly formed spongy bone and open up
a medullary cavity in the center of the shaft.
 As the osteoblasts move towards the epiphyses,
the epiphyseal cartilage is growing as well. Thus,
even though the shaft is getting longer, the
epiphyses have yet to be transformed into bone.

55
 Around birth, most long bones
have a bony diaphysis surrounding
remnants of spongy bone, a
widening medullary cavity, and 2
cartilaginous epiphyses.
 At this time, capillaries and
osteoblasts will migrate into the
epiphyses and create secondary
ossification centers. The
epiphysis will be transformed into
spongy bone. However, a small
cartilaginous plate, known as the
epiphyseal plate, will remain at
the juncture between the epiphysis
and the diaphysis.
Articular
cartilage
Epiphyseal plate

Growth in BoneGrowth in Bone
LengthLength
 Epiphyseal cartilage
(close to the epiphysis)
of the epiphyseal plate
divides to create more
cartilage, while the
diaphyseal cartilage
(close to the diaphysis)
of the epiphyseal plate is
transformed into bone.
This increases the length
of the shaft.

•As a result osteoblasts begin
producing bone faster than the
rate of epiphyseal cartilage
expansion. Thus the bone grows
while the epiphyseal plate gets
narrower and narrower and
ultimately disappears. A remnant
(epiphyseal line) is visible on X-
rays (do you see them in the
adjacent femur, tibia, and fibula?)
At puberty, growth in bone length
is increased dramatically by the
combined activities of growth
hormone, thyroid hormone, and
the sex hormones.

Growth in Bone ThicknessGrowth in Bone Thickness
 Osteoblasts beneath the periosteum secrete bone
matrix on the external surface of the bone. This
obviously makes the bone thicker.
 At the same time, osteoclasts on the endosteum
break down bone and thus widen the medullary
cavity.
 This results in an increase in shaft diameter even
though the actual amount of bone in the shaft is
relatively unchanged.

FracturesFractures
 Despite its mineral strength,
bone may crack or even break
if subjected to extreme loads,
sudden impacts, or stresses
from unusual directions.
– The damage produced constitutes
a fracture.
 The proper healing of a
fracture depends on whether or
not, the blood supply and
cellular components of the
periosteum and endosteum
survive.

FractureFracture
RepairRepair
 Step 1:
A. Immediately after
the fracture,
extensive
bleeding occurs.
Over a period of
several hours, a
large blood clot,
or fracture
hematoma,
develops.
B. Bone cells at the
site become
deprived of
nutrients and die.
The site becomes
swollen, painful,
and inflamed.
• Step 2:
A. Granulation tissue is formed as the hematoma is
infiltrated by capillaries and macrophages, which begin
to clean up the debris.
B. Some fibroblasts produce collagen fibers that span the
break , while others differentiate into chondroblasts and
begin secreting cartilage matrix.
C. Osteoblasts begin forming spongy bone.
D. This entire structure is known as a fibrocartilaginous
callus and it splints the broken bone.

 Step 3:
A. Bone trabeculae
increase in number
and convert the
fibrocartilaginous
callus into a bony
callus of spongy
bone. Typically
takes about 6-8
weeks for this to
occur.
Fracture
Repair
• Step 4:
A. During the next several months, the bony callus is continually
remodeled.
B. Osteoclasts work to remove the temporary supportive structures
while osteoblasts rebuild the compact bone and reconstruct the
bone so it returns to its original shape/structure.

Fracture TypesFracture Types
 Fractures are often classified according to the position of the
bone ends after the break:
Open (compound)  bone ends penetrate the skin.
Closed (simple)  bone ends don’t penetrate the skin.
Comminuted  bone fragments into 3 or more pieces.
Common in the elderly (brittle
bones).
Greenstick  bone breaks incompletely. One side bent,
one side broken. Common in
children whose bone contains more
collagen and are less mineralized.
Spiral  ragged break caused by excessive twisting
forces. Sports injury/Injury of abuse.
Impacted  one bone fragment is driven into the

What kind of fracture is this?
It’s kind of tough to tell, but
this is a _ _ _ _ _ _ fracture.

Bone RemodelingBone Remodeling
 Bone is a
dynamic tissue.
– What does that
mean?
 Wolff’s law
holds that bone
will grow or
remodel in
response to the
forces or
demands placed
on it. Examine
this with the
bone on the left.

Check out the
mechanism of
remodeling on the right!
Why might you suspect
someone whose been a
powerlifter for 15 years to
have heavy, massive
bones, especially at the
point of muscle insertion?
Astronauts tend to
experience bone atrophy
after they’re in space for
an extended period of
time. Why?

Nutritional Effects on BoneNutritional Effects on Bone
 Normal bone growth/maintenance
cannot occur w/o sufficient dietary
intake of calcium and phosphate
salts.
 Calcium and phosphate are not
absorbed in the intestine unless the
hormone calcitriol is present.
Calcitriol synthesis is dependent on
the availability of the steroid
cholecalciferol (a.k.a. Vitamin D)
which may be synthesized in the skin
or obtained from the diet.
 Vitamins C, A, K, and B12 are all
necessary for bone growth as well.

HormonalHormonal
Effects on BoneEffects on Bone
 Growth hormone, produced
by the pituitary gland, and
thyroxine, produced by the
thyroid gland, stimulate bone
growth.
– GH stimulates protein synthesis
and cell growth throughout the
body.
– Thyroxine stimulates cell
metabolism and increases the
rate of osteoblast activity.
– In proper balance, these
hormones maintain normal
activity of the epiphyseal plate
(what would you consider
normal activity?) until roughly
the time of puberty.

Hormonal Effects on BoneHormonal Effects on Bone
 At puberty, the rising levels of sex hormones (estrogens in
females and androgens in males) cause osteoblasts to
produce bone faster than the epiphyseal cartilage can
divide. This causes the characteristic growth spurt as well
as the ultimate closure of the epiphyseal plate.
 Estrogens cause faster closure of the epiphyseal growth
plate than do androgens.
 Estrogen also acts to stimulate osteoblast activity.

Hormonal Effects on BoneHormonal Effects on Bone
 Other hormones that affect bone growth include
insulin and the glucocorticoids.
– Insulin stimulates bone formation
– Glucocorticoids inhibit osteoclast activity.
 Parathyroid hormone and calcitonin are 2
hormones that antagonistically maintain blood
[Ca2+
] at homeostatic levels.
– Since the skeleton is the body’s major calcium
reservoir, the activity of these 2 hormones affects bone
resorption and deposition.

CalcitoninCalcitonin
 Released by the C cells of the thyroid gland in response to high
blood [Ca2+
].
 Calcitonin acts to “tone down” blood calcium levels.
 Calcitonin causes decreased osteoclast activity which results in
decreased break down of bone matrix and decreased calcium
being released into the blood.
 Calcitonin also stimulates osteoblast activity which means
calcium will be taken from the blood and deposited as bone
matrix.
Notice the thyroid
follicles on the
right. The arrow
indicates a C cell

Calcitonin Negative FeedbackCalcitonin Negative Feedback
LoopLoop
Increased Blood [Ca2+
] Increased calcitonin release
from thyroid C cells.
Increased osteoblast activity
Decreased osteoclast activity

ParathyroidParathyroid
HormoneHormone
 PTH increases calcitriol synthesis which increases Ca2+
absorption in the small intestine.
 PTH decreases urinary Ca2+
excretion and increases urinary
phosphate excretion.
• Released by the cells of the
parathyroid gland in response to low
blood [Ca2+
].Causes blood [Ca2+
] to
increase.
• PTH will bind to osteoblasts and this
will cause 2 things to occur:
• The osteoblasts will decrease their activity
and they will release a chemical known as
osteoclast-stimulating factor.
• Osteoclast-stimulating factor will increase
osteoclast activity.

Increased PTH release
by parathyroid gland
Binds to osteoblast
causing decreased
osteoblast activity and
release of osteoclast-
stimulating factor
OSF causes increased
osteoclast activity
Decreased bone
deposition and increased
bone resorption
Increased calcitriol
synthesis
Increased intestinal
Ca2+
absorption
Decreased Ca2+
excretion
Increased Blood [Ca2+
]
Decreased Blood [Ca2+
]

Clinical ConditionsClinical Conditions
 Osteomalacia
– Literally “soft bones.”
– Includes many disorders in which
osteoid is produced but
inadequately mineralized.
 Causes can include insufficient
dietary calcium
 Insufficient vitamin D fortification
or insufficient exposure to sun
light.
 Rickets
– Children's form of osteomalacia
– More detrimental due to the fact
that their bones are still growing.
– Signs include bowed legs, and
deformities of the pelvis, ribs, and
skull.
What about the above x-ray is
indicative of rickets?

 Osteomyelitis
– Osteo=bone +
myelo=marrow +
itis=inflammation.
– Inflammation of bone and
bone marrow caused by
pus-forming bacteria that
enter the body via a
wound (e.g., compound
fracture) or migrate from
a nearby infection.
– Fatal before the advent of
antibiotics.

 Osteoporosis
– Group of diseases in which
bone resorption occurs at a
faster rate than bone deposition.
– Bone mass drops and bones
become increasingly porous.
– Compression fractures of the
vertebrae and fractures of the
femur are common.
– Often seen in postmenopausal
women because they
experience a rapid decline in
estrogen secretion; estrogen
stimulates osteoblast and
inhibits osteoclast activity.
 Based on the above, what
preventative measures might
you suggest?

 Gigantism
– Childhood hypersecretion
of growth hormone by the
pituitary gland causes
excessive growth.
 Acromegaly
– Adulthood hypersecretion
of GH causes overgrowth
of bony areas still
responsive to GH such as
the bones of the face, feet,
and hands.
 Pituitary dwarfism
– GH deficiency in children
resulting in extremely short
long bones and maximum
stature of 4 feet.

1.1. Credits:Credits:
2.2. Author:Author:
academic.pgcc.edu/~aimholtz/AandP/LectureNotes/ANacademic.pgcc.edu/~aimholtz/AandP/LectureNotes/AN
P1_Lec/Skeletal/P1_Lec/Skeletal/BoneTissueBoneTissue..pptppt

Essentials of Human Anatomy & Physiology
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Seventh Edition
Elaine N. Marieb
Chapter 6
The Skeletal System

The Skeletal SystemThe Skeletal System
Slide 5.1Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Parts of the skeletal system
• Bones (skeleton)
• Joints
• Cartilages
• Ligaments (bone to bone)(tendon=bone to
muscle)
• Divided into two divisions
• Axial skeleton
• Appendicular skeleton – limbs and girdle

Functions of BonesFunctions of Bones
• Support of the body
• Protection of soft organs
• Movement due to attached skeletal
muscles
• Storage of minerals and fats
• Blood cell formation

Bones of the Human BodyBones of the Human Body
• The skeleton has 206 bones
• Two basic types of bone tissue
•Compact bone
• Homogeneous
•Spongy bone
• Small needle-like
pieces of bone
• Many open spaces
Figure 5.2b

Classification of BonesClassification of Bones
Slide 5.4aCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Long bones
•Typically longer than wide
•Have a shaft with heads at both ends
•Contain mostly compact bone
• Examples: Femur, humerus

Slide 5.4bCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Short bones
•Generally cube-shape
•Contain mostly spongy bone
•Examples: Carpals, tarsals

Classification of Bones on theClassification of Bones on the
Basis of ShapeBasis of Shape
Slide 5.4cCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.1

• Flat bones
•Thin and flattened
•Usually curved
•Thin layers of compact bone around a layer
of spongy bone
•Examples: Skull, ribs, sternum

• Irregular bones
•Irregular shape
•Do not fit into other bone classification
categories
•Example: Vertebrae and hip

Classification of Bones on theClassification of Bones on the
Basis of ShapeBasis of Shape
Slide 5.5cCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.1

Gross Anatomy of a Long BoneGross Anatomy of a Long Bone
• Diaphysis
•Shaft
•Composed of
compact bone
• Epiphysis
•Ends of the bone
•Composed mostly of
spongy bone Figure 5.2a

Structures of a Long BoneStructures of a Long Bone
• Periosteum
• Outside covering of
the diaphysis
• Fibrous connective
tissue membrane
• Sharpey’s fibers
• Secure periosteum to
underlying bone
• Arteries
• Supply bone cells
with nutrients
Figure 5.2c

• Articular cartilage
•Covers the
external surface of
the epiphyses
•Made of hyaline
cartilage
•Decreases friction
at joint surfaces Figure 5.2a

• Medullary cavity
•Cavity of the shaft
•Contains yellow
marrow (mostly fat)
in adults
•Contains red marrow
(for blood cell
formation) in infants Figure 5.2a

Bone Markings - Page 119Bone Markings - Page 119
• Surface features of bones
• Sites of attachments for muscles, tendons,
and ligaments
• Passages for nerves and blood vessels
• Categories of bone markings
• Projections and processes – grow out from the
bone surface
• Depressions or cavities – indentations

Microscopic Anatomy of BoneMicroscopic Anatomy of Bone
SlideCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Osteon (Haversian System)
• A unit of bone
• Central (Haversian) canal
• Opening in the center of an osteon
• Carries blood vessels and nerves
• Perforating (Volkman’s) canal
• Canal perpendicular to the central canal
• Carries blood vessels and nerves

Figure 5.3

• Lacunae
• Cavities containing
bone cells
(osteocytes)
• Arranged in
concentric rings
• Lamellae
• Rings around the
central canal
• Sites of lacunae Figure 5.3

• Canaliculi
•Tiny canals
•Radiate from the
central canal to
lacunae
•Form a transport
system
Figure 5.3

Changes in the Human SkeletonChanges in the Human Skeleton
• In embryos, the skeleton is primarily hyaline
cartilage
• During development, much of this cartilage
is replaced by bone
• Cartilage remains in isolated areas
• Bridge of the nose
• Parts of ribs
• Joints

Bone GrowthBone Growth
• Epiphyseal plates allow for growth of long
bone during childhood
•New cartilage is continuously formed
•Older cartilage becomes ossified
•Cartilage is broken down
•Bone replaces cartilage

Bone GrowthBone Growth
• Bones are remodeled and lengthened
until growth stops
•Bones change shape somewhat
•Bones grow in width

Long Bone Formation and GrowthLong Bone Formation and Growth
Figure 5.4a

Types of Bone CellsTypes of Bone Cells
• Osteocytes
• Mature bone cells
• Osteoblasts
• Bone-forming cells
• Osteoclasts
• Bone-destroying cells
• Break down bone matrix for remodeling and
release of calcium
• Bone remodeling is a process by both
osteoblasts and osteoclasts

Bone FracturesBone Fractures
• A break in a bone
• Types of bone fractures
• Closed (simple) fracture – break that does not
penetrate the skin
• Open (compound) fracture – broken bone
penetrates through the skin
• Bone fractures are treated by reduction
and immobilization
• Realignment of the bone

Common Types of FracturesCommon Types of Fractures
Table 5.2

Repair of Bone FracturesRepair of Bone Fractures
• Hematoma (blood-filled swelling) is
formed
• Break is splinted by fibrocartilage to
form a callus
• Fibrocartilage callus is replaced by a
bony callus
• Bony callus is remodeled to form a
permanent patch

Stages in the Healing of a BoneStages in the Healing of a Bone
FractureFracture
Figure 5.5

The Axial SkeletonThe Axial Skeleton
• Forms the longitudinal part of the body
• Divided into three parts
•Skull
•Vertebral column
•Bony thorax

The Axial SkeletonThe Axial Skeleton
Figure 5.6

The SkullThe Skull
• Two sets of bones
•Cranium
•Facial bones
• Bones are joined by sutures
• Only the mandible is attached by a
freely movable joint

The SkullThe Skull
Figure 5.7

Bones of the SkullBones of the Skull
Figure 5.11

Human Skull, Superior ViewHuman Skull, Superior View
Figure 5.8

Human Skull, Inferior ViewHuman Skull, Inferior View
Figure 5.9

Paranasal SinusesParanasal Sinuses
• Hollow portions of bones surrounding
the nasal cavity
Figure 5.10

Paranasal SinusesParanasal Sinuses
• Functions of paranasal sinuses
• Lighten the skull
• Give resonance and amplification to voice
Figure 5.10

The Hyoid BoneThe Hyoid Bone
• The only bone that
does not articulate
with another bone
• Serves as a
moveable base for
the tongue
Figure 5.12

The Fetal SkullThe Fetal Skull
• The fetal skull is
large compared
to the infants
total body length
Figure 5.13

The Fetal SkullThe Fetal Skull
• Fontanelles –
fibrous membranes
connecting the
cranial bones
• Allow the brain
to grow
• Convert to bone
within 24 months
after birth
Figure 5.13

The Vertebral ColumnThe Vertebral Column
• Vertebrae
separated by
intervertebral discs
• The spine has a
normal curvature
• Each vertebrae is
given a name
according to its
location Figure 5.14

Structure of a Typical VertebraeStructure of a Typical Vertebrae
Figure 5.16

The Bony ThoraxThe Bony Thorax
• Forms a
cage to
protect
major
organs
Figure 5.19a

The Bony ThoraxThe Bony Thorax
• Made-up of
three parts
•Sternum
•Ribs
•Thoracic
vertebrae
Figure 5.19a

The Appendicular SkeletonThe Appendicular Skeleton
• Limbs (appendages)
• Pectoral girdle
• Pelvic girdle

The Appendicular SkeletonThe Appendicular Skeleton
Figure 5.6c

The Pectoral (Shoulder) GirdleThe Pectoral (Shoulder) Girdle
• Composed of two bones
•Clavicle – collarbone
•Scapula – shoulder blade
• These bones allow the upper limb to
have exceptionally free movement

Bones of the Shoulder GirdleBones of the Shoulder Girdle
Figure 5.20a, b

Bones of the Upper LimbBones of the Upper Limb
• The arm is
formed by a
single bone
•Humerus
Figure 5.21a, b

• The forearm
has two bones
• Ulna
• Radius
Figure 5.21c

• The hand
•Carpals – wrist
•Metacarpals –
palm
•Phalanges –
fingers
Figure 5.22

Bones of the Pelvic GirdleBones of the Pelvic Girdle
• Hip bones
• Composed of three pair of fused bones
• Ilium
• Ischium
• Pubic bone
• The total weight of the upper body rests on the
pelvis
• Protects several organs
• Reproductive organs
• Urinary bladder
• Part of the large intestine

The PelvisThe Pelvis
Figure 5.23a

Gender Differences of the PelvisGender Differences of the Pelvis
Figure 5.23c

Bones of the Lower LimbsBones of the Lower Limbs
• The thigh has
one bone
•Femur – thigh
bone
Figure 5.35a, b

• The leg has
two bones
•Tibia
•Fibula
Figure 5.35c

• The foot
•Tarsus – ankle
•Metatarsals –
sole
•Phalanges –
toes
Figure 5.25

JointsJoints
• Articulations of bones
• Functions of joints
•Hold bones together
•Allow for mobility
• Ways joints are classified
•Functionally
•Structurally

Functional Classification of JointsFunctional Classification of Joints
• Synarthroses – immovable joints
• Amphiarthroses – slightly moveable
joints
• Diarthroses – freely moveable joints

Structural Classification of JointsStructural Classification of Joints
• Fibrous joints
•Generally immovable
• Cartilaginous joints
•Immovable or slightly moveable
• Synovial joints
•Freely moveable

Fibrous JointsFibrous Joints
• Bones united by fibrous tissue –
synarthrosis or largely immovable.
Figure 5.27d, e

Cartilaginous Joints – mostlyCartilaginous Joints – mostly
amphiarthrosisamphiarthrosis
• Bones connected by cartilage
• Examples
•Pubic
symphysis
•Intervertebral
joints
Figure 5.27b, c

Synovial JointsSynovial Joints
• Articulating
bones are
separated by a
joint cavity
• Synovial fluid
is found in the
joint cavity
Figure 5.27f–h

Features of Synovial Joints-Features of Synovial Joints-
DiarthrosesDiarthroses
• Articular cartilage (hyaline cartilage)
covers the ends of bones
• Joint surfaces are enclosed by a fibrous
articular capsule
• Have a joint cavity filled with synovial
fluid
• Ligaments reinforce the joint

Structures Associated with theStructures Associated with the
Synovial JointSynovial Joint
• Bursae – flattened fibrous sacs
• Lined with synovial membranes
• Filled with synovial fluid
• Not actually part of the joint
• Tendon sheath
• Elongated bursa that wraps around a tendon

The Synovial JointThe Synovial Joint
Figure 5.28

Types of Synovial Joints Based onTypes of Synovial Joints Based on
ShapeShape
Figure 5.29a–c

Types of Synovial Joints Based onTypes of Synovial Joints Based on
ShapeShape
Figure 5.29d–f

Inflammatory ConditionsInflammatory Conditions
Associated with JointsAssociated with Joints
• Bursitis – inflammation of a bursa usually
caused by a blow or friction
• Tendonitis – inflammation of tendon sheaths
• Arthritis – inflammatory or degenerative
diseases of joints
• Over 100 different types
• The most widespread crippling disease in the
United States

Clinical Forms of ArthritisClinical Forms of Arthritis
• Osteoarthritis
• Most common chronic arthritis
• Probably related to normal aging processes
• Rheumatoid arthritis
• An autoimmune disease – the immune system
attacks the joints
• Symptoms begin with bilateral inflammation of
certain joints
• Often leads to deformities

Clinical Forms of ArthritisClinical Forms of Arthritis
• Gouty Arthritis
•Inflammation of joints is caused by a
deposition of urate crystals from the blood
•Can usually be controlled with diet

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