Anatomy 32
Chapter 6
Bone and Skeletal Tissues
I. Cartilage- A versatile
connective tissue that
supports body structures.
Cartilage also lays down the
initial skeletal structure.
A. Location and basic
structure- found throughout
the body, has different
functions according to its
location. Cartilage contains
a great amount of water and
low blood vessels and it can
reshape easily. Although
there are three main types
of cartilage there are eight
major body locations:
1. external ear
2. nasal
3. articulate cartilage
(ends of bones)
4. costal cartilage
5. larynx cartilage
6. tracheal cartilage
7. vertebral discs
8. pubic symphysis
B. Classification of cartilage- based on its composition, flexibility, and density.
1. Hyaline cartilage-most abundant, lines joints, bluish, chondrocytes
and collagen.
2. Elastic cartilage- has chondrocytes, collagen, and elastin fibers. It is
highly elastic, tolerates repeated bending.
3. Fibrocartilage-intermediate between hyaline and dense regular
connective tissue. Thick collagen fiber rows alternate with
chondrocyte rows, embedded in matrix. Support high
compression and tension. Found in areas that bear weight,
between vertebrates and knees.
During lab you will study histology slides of the three types of
cartilage. Pay close attention to the structural differences.
C. Growth of cartilage- appositional growth stems from the perichondrium
towards center while interstitial growth stems from center towards
perichondrium. Calcified cartilage occurs when calcium deposits form within
the cartilage- this can cause pain or reduce the range of motion of a joint.
II. Bones are classified as connective tissue but are also organs. Bones have
bone cells embedded in a matrix that has a high concentration collagen and
minerals but little water
A. Functions of bones- there are five major functions performed by bones:
1. Support- they give shape to the body, hold it up, bare its weight,
and contain organs
2. Protection- bones surround soft tissue organs to provide support
3. Movement- bone joints and skeletal muscle work together with
bones to make movement possible
4. Storage- the hard matrix the make up bones store minerals like
calcium and phosphate, when needed by the body they are released
into the blood stream. The bone marrow inside long bone stores fats.
5. Blood Formation- bone marrow is the site of blood cell and immune
system cell formation .
B. Classification of bonesdespite the large array of
bones in the body most
bones are classified into four
types:
1. Long bones-these are
bones that more length than
width and has a shaft plus
two ends. A long bone does
not have to be a big bone.
2. Short bones- these are
cubed shaped and include
sesamoid bones (small short
bones) such as the patella.
3. Flat bones- thin, flat, and
curved such as the skull or
ribs
4. Irregular bones- these are
bones that have various
shapes within a single bone
piece. SESAMOID BONES
C. Gross Anatomy of
bones-in these sections
we study the general
characteristics of
compact bone and
cancellous bone (spongy
bone). All bones are
innervated with
lymphatic vessels,
nerves, and blood
vessels. They are
surrounded on the
outside by a membrane
called periosteum and
the inner cavities are
lined with endosteum.
The periosteum attaches
to the bone surface by
sharpey’s fibers. All
bones contain the
following living cells:
Osteoclast- bone
destroying cells, help
to release minerals
into blood stream
Osteoblast- bone
generation cells that
lay down more matrix
Osteocyte- mature
bone cell, maintains
bone matrix
1. Compact and spongy bone- compact bone appears as
a dense solid mass as seen on the shaft and edges of
long bones. Spongy bone (cancellous) is porous because
of the trabeculae structure and is usually surrounded by a
layer of compact bone. It is found on the end of long
bones. Compact bone may hold yellow bone marrow while
spongy bone holds red bone marrow.
SEE DEVELOPING BONE SLIDE
TO COMPARE COMPACT BONE,
SPONGY BONE, CARTILAGE,
AND EPIPHYSEAL PLATE
2. Structure of typical
long bone- the shaft is
2
called the diaphysis and
.
the ends are called the
epiphysis.
S Each of these
areas thas its own blood
supply.r The nutrient
artery uand vein serve
c
the diaphysis
and enter
t the nutrient
through
u There are also
foramen.
r
epiphyseal arteries and
e
veins. Long bones also
have an
o internal cavity
called fthe medullary
cavity filled with bone
t The ends of
marrow.
y
long bones
are lined with
hyalinep cartilage to
i joint movement.
facilitate
c
a
l
3. Structure of short,
irregular, and flat
bones- although not
cylindrical they are
like long bones in the
compact bone
surrounds spongy
bone.
4. Bone design and stressas bones bare weight
they are compressed
and as they bend in one
direction they
experience tension
(stretching) in the other
direction. Long bones
are designed to
withstand this by having
compact bones on the
external region of the
bone. Because these
forces do not exists
internally the inside of
the bone has bone
marrow or spongy bone
which also reduces
bone mass. Trabeculae
follow certain stress line
to also provide support.
D. Microscopic structure of bone- in this
section we study the microscopic organization
of bone.
1. compact bone- this dense structure
is composed of structures called osteon
(harvesian system), it is a group of concentric
tubes that in cross-section appear as rings.
They are made up of lamella (layer if bone
matrix with collagen running in one direction).
Circular lamella is called concentric and parallel
lamella is called interstitial lamella. Within the
lamella is a network of osteocytes embedded in
lacunae and connected by canaliculi ( little
canals). These cells are maintained alive by
nutrients and oxygen provided by blood vessels
passing through the center of the osteon called
the central or harvasian canal and the
volkman’s canal (transverse to diaphysis) .
Circumferential lamellae follow the
circumference of the bone.
2. spongy bone- the trabeculae of
spongy bone is made of lamella and ostecytes
but not osteons because the trabeculae are so
small.
E. Chemical Composition -healthy bone is half as strong as steel in resisting
compression and equally strong in resisting tension. Bone is composed of the
following: 35% organic components- cells, fibers, and ground substance
65% inorganic components- minerals, mostly calcium phosphate.
F. Bone Development- the
bone framework is first laid
down as cartilage and then
changes to bone this
process is called
osteogenesis or
ossification. The skeleton
changes throughout the
entire life of the individual.
1. Intramembranous
ossification- this is a
process in which bone is
not laid out first in
cartilage, it happens in
membrane bone that form
the skull and clavicle.
a. –Week 8 of
development cells cluster
within mesenchyme
membranes and
become osteoblast.
They secrete the osteoid
(bone matrix) forming
woven
bone tissue
which thicks into
trabeculae. The outer
trabeculae thicken to form
compact bone. There
is no lamella in this type of
bone.
http://www.e-radiography.net/articles/ossification/ossification.htm
• 2. Endochondral ossification- This process begins late into the second
month of development and is completed in adulthood. There are four
stages:
– Stage 1- By week 8 the cartilage model has perichondrium that
becomes bone forming periosteum and a bone collar forms around
the diaphysis
– Stage 2- The chondrocytes signal calcification at the center of the
diaphysis. Calcification of the cartilage deprives the cells of nutrients.
Once they die, cartilage disintegrates leaving a cavity at the center
that influences elongation and provides a space for the primary
ossification center.
– Stage 3- The primary ossification center forms at the diaphysis by
the third month of development. The periosteal bud includes nutrient
blood vessels, bone cells, and bone marrow forming cells; it invades
the calcification area. Trabeculae is laid out to eventually meet with
bone collar in the diaphysis. Osteoclast help to remodel bone and
form the medullary cavity.
– Stage 4- Before birth or shortly after, the epiphyses forms secondary
ossification centers and the ends of the bones ossify. Secondary
follows the same mechanisms as in primary ossification. At this point
hyaline cartilage remains on the surface of joints and at the growth
plates.
• http://www.e-radiography.net/articles/ossification/ossification.htm
Bone growth
Linear growth of long bones takes place at the
epiphyseal plates- sex hormones eventually inactivate
epilhyseal plates.
Epiphysis
is the end
of a long
bone.
Bone growth
Epiphyseal plate is the
site of bone growth.
Dividing
chondrocytes
add length
to bone.
Chondrocytes
produce
cartilage.
Old
chondrocytes
disintegrate.
Diaphysis
Compact
bone
Chondrocyte
Cartilage
Direction of growth
Diaphysis
is the
shaft of a
long bone.
Osteoblasts lay
down bone on
top of cartilage.
Newly calcified Osteoblast
bone
Figure 23-19
G. Anatomy of epiphyseal
growth areas- these are
areas known as the “growth
plates”. The bone continues
to elongate. The
chondroblasts are organizes
as large columns forming
four zones
1- Cells divide rapidly
pushing the older cells away,
thus elongating the bone.
2- In this zone the older
chondrocyte enlarge to
signal calcification
3 & 4- cells die and
disintegrate forming
trabeculae at the epiphysisdiaphysis junction
H. Bone remodeling- Compact bone is entirely replaced every 10 years and
spongy bone every 3-4 years. Not all areas of a single bone are replaced at the
same time. Osteoblast perform bone deposition by producing bone matrix and
osteoclast re-absorb bone by releasing hydrochloric acid and dissolving the
minerals.
I. Repair of bone fractures- If the bone does
not pierce the skin it is a simple fracture, if
it does then it’s a compound fracture.
There are six types of fractures (pg 138) :
Communited-3+ fragments
Depressed- inward depression
Compression-crushed
Epiphysieal-plate tears
Greenstick-partial break
Spiral-due to twisting force
Ossification steps in a fracture:
1. Hematoma formation-broken blood vessels release blood that form a clot
2. Fibrocartilaginous callus formation-periosteum and endosteum form many
bone-forming cells that invade the clot creating a callus containing
fibrocartilage and hyaline cartilage.
3. Bony callus formation-trabeculae form in callus by enchondrial ossification, it
becomes the bony callus. This takes about 2 months.
4. Bone remodeling-the callus is removed by osteoclast removing excess bone
mass and compact bone is laid out.
III. Disorders of Bones
A. Osteoporosis-(bone porous condition) low bone mass due to
deterioration and bone reabsorption is faster than bone deposition.
Fractures occur easily, especially in the vertebrae, femur, or hip. It
happens more in women than in men and more often in Caucasian
women. Low estrogen levels, poor diet, and not enough exercise can lead
to osteoporosis.
B.
Osteomalacia and Rickets- (soft tissue) weakening of the bone resulting
from lack of vitamin D or calcium phosphate. Osteomalacia occurs in the
adults, the bone does not have a proper amount of minerals and
calcification does not occur causing weak bones. Rickets is the childs’ form
but is more severe because bones are still developing. May cause bowed
legs or malformities in head and ribs. Bones become thick and abnormally
long
C. Paget’s Disease-( disorder in newly formed bone) bones become soft and
weak because new bone is layed out faster than it matures and less
mineralization. Bones thicken irregularly happens before age 40 and may
result from a viral infection.
D. Osteosarcoma-(bone cancer) affects people 10-25, originates in long limb
bones. The tumor develops in the regions near growthplates and is of
osteoblast origin.
Osteoporosis
IV. The Skeleton Throughout Life- Mesoderm give rise to
embryonic mesenchyme which forms membranes and
cartilage
Cartilage- grows quickly in youth, stops in adulthood,
and calcifies in old age.
Bone- ossification begins before birth, after birth
movement and tension provided by muscle forms
markings, children are more likely to injure bones at
the growth plate.
--At age 18 women stop growing and men stop at
age 21.
--During growth bone deposition is faster than bone
re-absorption, during adult they happen at equal
rates, during old age re-absorption predominates
and blood supply drops result in bone death. This
can be influence by sex and race.