Skeletal
System
Our support system
Two Types of Bone
There
are two
types of bone
 Compact
bone
The outer more
dense portion of
bone
Composed of
cylinder of dense
white osseous
tissue
Sponge
Bone
Despite its name it
is relatively hard
and strong
Name given
because of the
appearance of its
cross section.
It provides support
for bone marrow
and reduces the
density of bone
 All
bone is covered in
periosteum which is a
tough membrane that
contains a network of
blood vessels to supply
nutrients, and nerves
which signal pain.
 Periosteum also works
with tendons and
ligament to attach
bone together.
Histology and Bone Growth
Osteoprogenitor
cells
nonspecialized
cells found in
periosteum,
endosteum,
and central
canal of
compact
bones; can
turn into other
types of cells
as needed
Osteoblasts
cells
that actually
form bones; arise
from nonspecialized
osteoprogenitor
cells and are cells
that secrete a
matrix of calcium
with other minerals
that give bone its
typical
characteristics
 Osteocytes
 considered
mature bone cells that started as
osteoblasts; osteoblasts surround themselves
with matrix to then become mature osteocytes
 Osteoclasts
 believed
to originate from a type of white
blood cell called monocyte found in red bone
marrow; job is to tear down bone material and
help move calcium and phosphate into blood;
and aids in remodeling
 Osteon:
consisting of concentric bone layers
called lamellae and the central canal
 Lamellae: A thin layer of calcified matrix around a
central canal
 Central Canal: hollow tube with central to an
osteon and provides an opening for blood vessels
and nerves into the bone.
 Osteocytes
live in little “caves” called lacuna.
 From their lacuna osteocytes reaches through
canaliculi or little tunnels to connect with one
another or a blood supply.
Anatomy of a long Bone
Long
bones are made up of a
diaphysis and two epiphysis.
Proximal
Closer
to the trunk
Distal
Further
from the trunk
Long
bones contain both yellow and
red bone marrow.
 Yellow
marrow is located in the shafts of
the long bones.
Yellow bone marrow contains mostly fat
cells and works as an energy reserve
 Red Marrow is found in spongy bone, the
ends of long bones, Ribs, vertebrae, the
sternum and the pelvis.
From specialized stem cells it produces
red blood cells, platelets, and white
blood cells.
Bone Growth
 Most



bones develop from cartilage
In the second month of fetal development, much of
the skeleton is made of cartilage during, and in the
third month, osteocytes begin to develop and release
minerals that lodge in the spaces between the
cartilage cells, turning the cartilage to bone.
Ossification: the process by which cartilage is slowly
replaced by bone as a result of the deposition of
minerals
Many area remain cartilage to lend flexibility and
support to the body.
Bone Growth
There
are two forms of bone
growth intramembranous
ossification and endochondral
ossification.
Intramembranous
ossification is how
flat bones form
Endochondral is how long /short
bones form
Endochondral Ossification
 First
there is a cartilage model that forms
 Next osteoblasts are produced by the
perichondrium and they form what is known
as a bone collar around the middle of the
cartilage
Encircling it like a napkin ring; providing
physical reinforcement
What was perichondrium is now periosteum
Primary ossification center arises
 Blood vessels penetrate the bony collar and
will the primary ossification center into the
primary marrow cavity. And the secondary
ossification cent shows up.
Endochondral Ossification

The secondary ossification cent becomes hollowed
out by the same process as the primary one creating
a secondary marrow cavity in the epiphysis.
 At
the time of birth infant bones primarily look like step
four.

During infancy and childhood, the epiphyses fill with
spongy bone.
 Cartilage
is then limited to the articular cartilage covering
each joint and the epiphyseal.
Bone Elongation and
Appositional Growth
 Bones
continue to develop after a person’s
birth
 During early childhood and late adolescence
bone cells gradually replace the cartilage of
the epiphyseal plate in long bones

Such as the one on the arms and legs
 Epiphyseal
plate is composed of cartilage cells
that divide and form columns, pushing older
cells toward the middle of the bone

As older cells die the are replaced by new bone
cells.
 After
a late adolescents the epiphyseal
plate ossifies.
Appositional
Growth (or widening of
the bone)is where new bone is layed
on the outside of the bone by
osteoblasts and old bone is being
broken down by osteoclast in the
middle.
Joints
 Joint:
the place where two bones meet
 Three major types of joints:



Fixed
Semimovable
Movable
Joints
 Joint:
the place where two bones meet
 Three major types of joints:



Fixed
Semimovable
Movable
Fixed Joint
 Fixed
joints prevent movement
 Found in the skull where they permit no
movement of those bones

Small amount of connective tissue in a fixed
joint also helps absorb impact to prevent
the bones from breaking
Semimovable Joints
 Semimovable
movement


joints permit limited
Found in the vertebral column; allow the
body to bend and twist
Also found in the rib cage; connect the
upper ten pairs of ribs to the sternum
Movable joints
 Movable
joints enable the body to
perform a wide range of movements and
activities

Include:
 Hinge
 Ball-and-socket
 Pivot
 Saddle
 Gliding
Movable Joints
 Hinge
joint: found in the elbow
 Ball-and-socket: shoulder joint
 Pivot joint: formed between the top two
vertebrae in the neck
 Saddle: found at the base of each thumb
 Gliding: fount between the small bones of
your foot
Joint Structure
 Joints
are subjected to a great deal of
pressure and stress, but their structure is
well suited to meet these demands

Bones that come into contact are covered
with cartilage
 Protects
against friction
Joint Structure
 Ligaments:
tissue

tough bands of connective
Hold the bones of the joint in place
 Synovial
fluid: lubricating substance that
helps protect the ends of bones from
damage by friction
Joint Structure
 Knee
joint is the most susceptible because
it carries the body’s weight
Joint Structure
 Arthritis:
used to describe disorders that
cause painful, swollen joints
 Two forms of arthritis:


Rheumatoid arthritis: develops when the
immune system begins to attack body
tissues
Osteoarthritis: degenerative joint disease in
which cartilage becomes thinner and
rougher, so bones rub against each other