Animal, Plant & Soil
Science
Lesson C2-3
The Skeletal System
Objectives

Examine the skeletal system, and
describe its functions.

Identify the components of bone,
discuss the three cell types found in
bones, and discuss how bones are
classified.
Objectives

Differentiate between moveable and
immoveable joints.

Discuss the chemical process in the
formation of bones and calcification.

Identify and recall the names of
bones found in livestock and
companion animals.
What is the skeletal system,
and what are its functions?
In mammals the skeletal system
consists of bones, teeth, joints, and
structures that connect bones to other
bones or muscles (e.g., ligaments,
tendons, and cartilage).
 The skeletal system
gives animals shape
and has the following
functions.

What is the skeletal system,
and what are its functions?

A. Support: Many bones of the body
provide support, but this is especially true
of the long bones.



For example, the long bones
in legs help support the trunk.
Bones other than long bones
also provide support.
For example, the first vertebra
supports the skull.
What is the skeletal system,
and what are its functions?

B. Protection: A vital function of the
skeletal system is the protection of vital
internal organs.


The skull protects the brain, and the rib cage
protects the heart, lungs, and abdominal
organs.
C. Movement: In combination with the
muscular system, the skeletal system
provides for bodily motion.

Skeletal muscles are attached to bones by
tendons that act as a lever to move bones.
What is the skeletal system,
and what are its functions?

D. Mineral storage: The outer layers of
bony tissues are used for the storage of
minerals (primarily calcium and
phosphorus).

Deposits and
withdrawals of mineral
ions from bone are
continuous, which
helps to maintain
blood levels of
calcium and
phosphorus.
What is the skeletal system,
and what are its functions?

E. Blood-cell formation: The inner core of
bone is a soft tissue called bone marrow.


Red marrow is a major site of blood cell and
platelet formation.
F. Energy storage: Yellow marrow is found
in the shaft of long bones and other
mature bones.

Yellow marrow consists mostly of fat and
serves as an energy reserve.
What are bone components? What
are the three cell types found in
bones? How are bones classified?
Bones are composed of inorganic and
organic materials and are classified by
shape.
 A. Sixty-five percent of bone is inorganic,
primarily calcium phosphate, which gives
bone its hardness and rigidity.
 B. The organic component consists of the
three cell types found in bones and
osteoid, which is primarily collagen and
gives bone its high tensile strength.

What are bone components? What
are the three cell types found in
bones? How are bones classified?

The three cell types found in bones are
osteoblasts, osteocytes, and osteoclasts.


1. The osteoblasts form a bone matrix by
secreting collagen, become enclosed in the
matrix, and develop into osteocytes.
2. Osteocytes are the principle bone cells that
maintain daily cellular activities (e.g.,
exchange of nutrients and wastes with blood).
What are bone components? What
are the three cell types found in
bones? How are bones classified?

3. Whereas osteoblasts
deposit bone, osteoclasts
secrete enzymes that
digest bone.


Bone is a living tissue that is
continually remodeled in
response to the body’s need
for calcium and for repairing
damaged tissue.
Osteoclasts are important in
the development, growth,
maintenance, and repair of
bone.
What are bone components? What
are the three cell types found in
bones? How are bones classified?
C. Bones are classified by
shape as long, short, flat,
sesamoid, and irregular.
 1. Long bones are
cylindrical in shape and
consist of a shaft with
two ends.



Found in limbs, long bones
typically support body weight
and act as levers.
The femur, or thighbone, is an example of a
long bone.
What are bone components? What
are the three cell types found in
bones? How are bones classified

2. Short bones are cube-like
in that they are nearly equal
in length and width.

Short bones are found in the
knee and hock and help to
absorb the shock of impact.
What are bone components? What
are the three cell types found in
bones? How are bones classified

3. Flat bones are typically thinner and
usually curved.

Flat bones (e.g., ribs, scapula, and some
bones in the skull) surround and protect vital
organs.
What are bone components? What
are the three cell types found in
bones? How are bones classified

4. Sesamoid bones are small and
embedded in tendons.


The patella (knee cap) is the only human
sesamoid bone.
5. Irregular bones have a variety of
shapes and sizes.

Vertebrae and some bones in the skull are
examples of irregular bones.
What is the difference between a
moveable and an immoveable
joint?
A joint, or articulation, is the union of
bone or cartilage.
 The classification of
joints is based on
joint structure and
mobility.
 Joints are classified
as fibrous,
cartilaginous, or
synovial.

What is the difference between a
moveable and an immoveable
joint?

A. Fibrous joints include those
united by connective tissue or
fused bone.


Fibrous joints, or fixed joints,
typically do not permit any type
of movement.
An example of this type of joint
is found in the skull.
What is the difference between a
moveable and an immoveable
joint?

B. Cartilaginous joints allow only slight
movement; these are joints in which the
bones are connected with cartilage.


An example of a cartilaginous joint is the area
between vertebrae.
This area has a pad of
cartilage that separates
and cushions vertebrae.
What is the difference between a
moveable and an immoveable
joint?
C. Synovial joints are freely movable
joints in which the bones are held together
(at the joints) by ligaments.
 Within the joint is synovial fluid, which
lubricates the joint and permits it to move
freely and without friction.
 Types of synovial joints
include ball-and-socket,
hinge, and pivot.

What is the difference between a
moveable and an immoveable
joint?

1. Ball-and-socket joints allow movement
in all directions.


For example, the ball of the femur fits into the
socket on the hip bone.
2. A hinge joint allows movement in one
axis.


The knee and elbow joints are
examples of hinge joints.
Hinge joints work similarly to a
hinged door in that they primarily
allow movement in one direction.
What is the difference between a
moveable and an immoveable
joint?

3. A pivot joint is found between the first
and second vertebrae.


It allows the head to be turned in more than
one direction.
A pivot joint allows
rotation around a point.
What is the chemical process in
the formation of bones and
calcification?
As mentioned previously, bone is a living
tissue that is continually remodeled in
response to the body’s need for calcium
and for repairing damaged tissue.
 In addition, bone is capable of growth.
 Bone begins development long before
birth as cartilage, which is a firm but
pliable tissue found in mature animals at
the ends of long bones and between
vertebrae.

What is the chemical process in
the formation of bones and
calcification?
Cartilage is also found in ears and noses.
 It is found in higher proportions in
younger animals because most cartilage is
transformed into bone as animals grow
and age.
 The process of transforming cartilage into
bone is called endochondral
ossification.
 Even after ossification, bones are ever
changing due to growth and remodeling.

What is the chemical process in
the formation of bones and
calcification?

A. Bones grow in length but they
also grow in thickness through a
process called appositional
growth.



Growth in length occurs in long
bones at the ends between the
epiphysis and diaphysis.
Long bones have two epiphysis
(enlarged ends) and one diaphysis
(shank).
The area of growth is called the
growth plate, or epiphysial–
diaphysial cartilage, and is where
cartilage is formed in layers.
What is the chemical process in
the formation of bones and
calcification?




The layers gradually become bone through
calcification, and a new layer of cartilage is
formed.
Calcification is the deposition of calcium salts
that harden, which is a process that continues
until adulthood.
Once the cartilage is replaced by bone, bone
growth stops.
Thus, animal growth stops, except for
fattening.
What is the chemical process in
the formation of bones and
calcification?

B. Once a bone has been formed, it is
continuously being remodeled.



Bone remodeling involves the action of
osteoblasts, osteoclasts, and two hormones:
the parathyroid hormone and calcitonin.
The parathyroid hormone (PTH) is secreted by
the parathyroid gland when blood calcium
levels are low.
PTH stimulates the osteoclast cells, which
causes the digestion or resorption of bone.
What is the chemical process in
the formation of bones and
calcification?


As a result, Ca++ is
released into the
bloodstream. Calcitonin is
secreted by the thyroid
gland when blood calcium
levels are high.
Calcitonin inhibits bone
resorption and increases
osteoblast activity, which
causes a deposition of
bone matrix.
What are the names of bones
commonly found in livestock and
companion animals?
There are many bones found in livestock
and companion animals that share the
same names as human bones.
 Veterinarians, livestock producers, and
even pet owners benefit from knowing the
names of these common bones.

What are the names of bones
commonly found in livestock and
companion animals?

A. The bone that surrounds and protects
the brain is known as the skull.



Similarly, bones that surround and protect the
spinal cord are known as vertebrae.
There are five types of vertebrae, beginning
near the skull with cervical and followed by
thoracic, lumbar, sacral, and coccygeal.
B. The two bones that make up the jaw
are known as the mandible and maxilla.

The maxilla is positioned above the mandible.
What are the names of bones
commonly found in livestock and
companion animals?






C. The shoulder blade is called the scapula.
In the front arm (or wing) of an animal, the large
single bone above the joint is called the
humerus.
Below the joint contains two bones: the ulna and
the radius.
The front foot bones are known as the carpals
and metacarpals, while the rear foot bones are
known as the tarsus and metatarsus.
The rear leg of the animal has a structure similar
to the front leg.
The large, single leg bone is called the femur,
and the two smaller leg bones below the knee
joint are the tibia and fibula.
What are the names of bones
commonly found in livestock and
companion animals?

D. Ribs are bones that surround and
protect the heart and lungs, the most vital
internal organs.


There are normally many ribs, surrounded with
muscle and connective tissue to give the chest
cavity movement and protection.
E. Many other bones throughout the
animal body each serve a specific
function.

Depending on the animal, hundreds of bones
can be found throughout the body.
Review

What is the skeletal system, and what are
its functions?

What are bone components? What are the
three cell types found in bones? How are
bones classified?

What is the difference between a
moveable and an immoveable joint?
Review

What is the chemical process in the
formation of bones and calcification?

What are the names of bones commonly
found in livestock and companion animals?