1. About It!” “Make No Bones Bones can tell us a lot about a person’s
physical and medical history.
Bone structure and connective
tissue account for about 25% of the
body’s weight.
Bone Formation and Growth
Early embryo - bones start out as
cartilage or fibrous structures.
The cartilage is gradually replaced
by calcified bone matrix.
Ossification - the process where mineral matter
starts to replace previously formed cartilage, thus
creating bone. (Usually starts during the 8th week of embryonic development.)
Infant bones are soft because ossification is
not complete. Continues through childhood.

2. You are born with about 300 bones bones but by the time you are an
adult, you have about 206 bones.
Many bones fuse together as you
grow.
Soft Spot
Soft Spot
(Fused)
The 206 bones are divided into 4 types based on their form.
1. Long Bones - constructed for weight-
bearing and movement. Examples
are the femur and the humerus
2. Short Bones - make flexible movement
possible. Examples are wrist bones
(carpals) and foot bones (tarsals).
3. Flat Bones - these bones help provide
organ protection and are important
sites for hemopoiesis (blood cell
formation.) Examples are skull
bones, sternum, and ribs.
4. Irregular Bones - odd shapes that do not fit
into the other three categories. They have
unique shapes related to their function.
Examples are the vertebrae and the ear bones.

3. Long Bones 1. Diaphysis  Also called the “shaft.” 2. Epiphyses
There are two major types of bone based on their
histological (tissue) structure:
1. Compact or Cortical Bone - mostly solid
bone matrix and cells with few spaces.
2. Spongy or Cancellous bone - has many
spaces within a lacy network of bone.
Long Bones
Long bones are hollow and shaped
like rods or shafts with rounded ends
Parts of the long bone are:
Epiphyses
Epiphyseal
Plate
1. Diaphysis
 Also called the “shaft.”
 Mostly compact or cortical bone.
 Strong yet light enough in weight
to permit easy movement.
Diaphysis
Epiphyseal
Plate
2. Epiphyses
 Mostly spongy or cancellous bone.
 Has many spaces filled with red
bone marrow which produces
red and white blood cells.
Epiphyses
3. Epiphyseal Plate
 Cartilage between the epiphyses and the diaphysis.
 Site of growth in bone length.
 Growth ceases when all epiphyseal cartilage is
transformed into bone.

4.  “Endo” means within and “osteum” means bones
4. Periosteum
 “Peri” means around and
“osteum” means bone
 Tough, white, vascular,
fibrous membrane on the
outside of a bone
 Contains blood vessels, lymph
vessels, and nerves
 Responsible for bone growth,
bone repair, and nutrition.
 If periosteum is removed, bone
will die.
Medullary
Cavity
Periosteum
Endosteum
5. Endosteum
 “Endo” means within and “osteum” means bones
 Membrane within the bone that lines the medullary
cavity.
 Osteoclasts (tear down bones) are located in this
cavity. They dissolve bone to keep the cavity.
6. Medullary Cavity
 Hollow space or cavity inside the diaphyses of the
bone that contains the yellow bone marrow.
 Yellow marrow started out as red marrow, but
gradually turns to fat cells in long bones.
 These fat cells can be converted to energy
when needed and some WBC’s are made here.

5.  Thin layer of cartilage
7. Articular Cartilage
 Thin layer of cartilage
covering each epiphysis
 Acts like a shock absorber
between bones
8. Haversian System (HC)
 Circulatory system within bone
 Contains blood vessels that run
parallel to the long axis of the
bone
 Provides nutrients to the
osteocytes (OC) and removes
waste. .

6. Osteoblasts How Bones Grow  Are the “bone-builders” and are
Our bones are constantly renewing themselves.
Up to 10% of your bones is eaten away
and replaced each year.
There are 3 basic types of bone cells:
Osteoblasts
 Are the “bone-builders” and are
responsible for building new bone
 These cells secrete bone matrix
Osteocytes
 Living bone cell located in the
lacunae (gaps) in the bone matrix.
 These are mature bone cells
 These cells live for about 20 years
Osteoclasts
 Are the “bone breakers”
 Are large phagocytic cells
 Tear down bones by excavating
channels within the bone
 Eat away bone in the medullary
cavity, preventing bone from
becoming too thick

7. Gerontological Conditions
 Bone mass peaks at about age 35,
after which there is a universal,
gradual loss of bone.
 Decreased activities and metabolic
changes (such as menopause and
decreased estrogen levels) contribute
to bone loss.
 Women lose more bone mass than
men.
 Bones also change in shape and
have reduced strength - leads to
increased change of fractures.
 Fractures are slower to heal because
new fibrous tissue develops more
slowly in the elderly.
 The ability of the collagen structure
to absorb energy is reduced - leads
to osteoarthritis.
 The articular cartilage decreases in
weight-bearing areas and has reduced
ability to heal.

8. Two Major Divisions Of The Skeletal System
I. Axial Skeleton
 80 bones of the head and trunk
 Many of these bones protect the
major organs of the body
 Consists of the bones which
run down the middle of the
body (it’s axis!)
II. Appendicular Skeleton
 Appendicular means “to
hang” and these bones
are attached to or “hang” from
the bones of the axial skeleton.
 Consists of the 126 bones of
the arms (upper appendages),
the legs (lower appendages), as
well as the bones of the hips and
shoulders.

9. Functions Of The Skeletal System
1. Support
Provides the framework to support the
body’s fat, muscles, and skin. Gives
shape to the body.
2. Protection
Protect delicate structures within them
(heart, lungs, brain) as well as
protecting bone marrow which is
responsible for forming blood cells.
3. Movement
Serves as a point of attachment for
skeletal muscles. As muscles contract and
shorten, they pull on bones and move them.
4. Storage
Stores most of the body’s calcium supply.
98% of the body’s extracellular calcium
is stored in bones. Excess calcium in the
blood, calcium goes into bone for storage.
Lack of calcium in blood and it goes
from bone to blood.

10. Functions Of The Skeletal System
(continued)
5. Hemiopoiesis (hee-mo-poy-EE-sis)
 “Hemo” means blood and “poiesis” means to make.
 Blood cell formation takes place in the red bone
marrow.
 The average life of a RBC is 120 days so your
body must produce 3 million new RBC’s every
second!
 If your body’s need for red blood cells is greater
than what the body can supply, some of the fatty
yellow matter can be converted to red marrow.
White blood cells are made in the Yellow Marrow

11. Functions Continued Vertebral Column: Bones Encloses Spinal Cord
Separated by pads of cartilage: intervertebral discs
Bones
12 pairs of ribs: 7 true, 3 false, 2 floating
Femur = longest, strongest bone in the body

12. Joints Ball & Socket Joint: Ball Shaped Head; Hip and Shoulder Example
Hinge Joint: Moves in One directions; Elbow and Knee Example
Pivot Joints: Rotate on arch shaped bones; Radius/Ulna Example
Gliding Joints: Flat Surfaces glide across each other; Vertebrae example
Suture: Immovable joint in skull
Synovial Fluid: Lubrication