Veterinary Technology
Chapter 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.
Terms









calcification
carpals
cartilage
cartilaginous joints
diaphysis
endochondral
ossification
epiphysis
femur









fibrous joint
fibula
flat bones
humerus
joint
long bones
mandible
maxilla
metacarpals
Terms










metatarsus
osteoblasts
osteoclasts
osteocytes
osteoid
radius
red marrow
ribs
scapula
sesamoid bones










short bones
skeletal system
skull
synovial fluid
synovial joints
tarsus
tibia
ulna
vertebrae
yellow marrow
How many bones do humans
have?





When you were born you had over 300 bones. As
you grew, some of these bones began to fuse
together. The result? An adult has only 206
bones!
You have over 230 moveable and semi-moveable
joints in your body.
The human hand has 27 bones; your face has 14!
The longest bone in your body? Your thigh bone,
the femur -- it's about 1/4 of your height.
The smallest is the stirrup bone in the ear which
can measure 1/10 of an inch.
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?

1. 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?

2. 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.
What is the skeletal system,
and what are its functions?

3. 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?

4. Blood-cell formation: The inner core
of bone is a soft tissue called bone
marrow. Bone marrow is made in this
hollow center called the medullary cavity.


Red marrow is a major site of blood cell and
platelet formation.
5. 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.
Bone Structure
C. Bones are classified by
shape:
 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.
Bone Structure

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
and make up the fingers and toes.

Bone Structure

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.
Bone Structure

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).
Bone Structure of a Long Bone
-page 30
Outer shell composed of dense (compact)
bone.
 Underneath, the spongy (cancellous) bone


Where is it found? Read 2nd paragraph!
Medullary Cavity = hollow center of the
diaphysis (shaft).
 Periosteum = thin layer of connective
tissue.


Blends into tendons and ligaments, binding
them to the bone
Bone Structure of a Long Bone
-page 30

A dried bone is
composed of about
70% inorganic
minerals, and 30%
organic
compounds.


Calcium and
phosphorus
Bone Structure of a Long Bone

There are 3 types of bone cells:
 Osteoblasts: lay down the collagen
matrix, become enclosed in the matrix
and develop into osteocytes…
 Osteocytes: responsible for maintaining
the bone matrix
 Osteoclasts: large cells that release the
minerals from the bone.
Bone Structure of a Long Bone


Disease conditions
of bones?
Bone is composed
of a collection of
microscopic units
called osteons.
 Center = canal
 In canal = blood
vessels, nerves
Joints and Movement
A joint, or articulation, is the union of
bone or cartilage.
 The classification of
joints is based on
joint structure and
mobility.
 3 types of joints

Joints and Movement

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. Cartilage 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.
Growth plate in young animals
Joints and Movement
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.

Joints and Movement

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.
Joints and Movement

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.
Joints and Movement
Several terms are used to describe the motion
within a joint:
- Flexion: the angle b/t the two bones gets
smaller
- Extension: the angle b/t the two bones
increases
- Abduction: when a part is moved away from
the body
- Adduction: when a part is moved closer to the
body
Axial vs. Appendicular Skeletons
Skeleton can be divided into two main
sections:
 1.axial skeleton: contains skull,
vertebrae, ribs and sternum
 2.appendicular skeleton: contains
bones of the limbs



The total number of bones in the APP varies
b/t species
“Typical” dog has 320 total bones.



Length of tail?
With or without dewclaw? (first digit)
Horses have a total of 205 bones
Axial Skeletons

The bone that surrounds and protects the
brain is known as the skull (cranium).



Composed of numerous flat bones
Shape based on species
The two bones that make up the jaw are
known as the mandible and maxilla.


Mandible = lower
Maxilla = upper
Axial Skeletons

Similarly, bones that surround and protect the
spinal cord are known as vertebrae.


The column is broken down into divisions,
beginning and the head and moving to the tail.






Read page 34 first 3 paragraphs
1. atlas=first vertebrae; up and down motion of head
2. axis=second vertebra; back and fourth motion
Thoracic = attached to ribs, joint to sternum
Lumbar=lower back
Sacrum= group of 3 fused sacral vertebrae,
joints to the pelvis
Caudal (coccygeal) = tail

This number may greatly vary due to species
Appendicular Skeletons

The number and size of bones in the APP
has many differences.


A dog has 4 or 5 toes, a horse only has 1
High-Rise Syndrome = cats

Great flexibility in scapula, fall a great distance
= lower jaw hits ground to absorb shock.
Appendicular Skeleton






The shoulder blade is called the scapula.
In the front arm of an animal, the large single
bone above the joint is called the humerus.
Below the joint contains two bones: the
ulna(smaller) and the radius(heavy bone.
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(heavy bone) and
fibula(smaller).
Appendicular Skeleton

The pelvis is made of two halves, then
each half then is divided into a region:



Ilium
Ischium
pubis
Bone Growth and Remondeling

Ossification: cartilage is replaced by bone
tissue.
Happens as the growth plate in young animals
grows.
 For proper development, the rate of limb
growth must match!
 Bassett Hounds =
premature closing of distal
growth plate in the ulna
Subluxates = partially dislocate

Bone Growth and Remodeling

Radiographs (the actual picture) are
produced when a stream of x-rays are
passed through a body part.


Dense structures allow a small amount of xrays to pass through and show up as light on a
radiograph. Lead prevents x-rays
The 5 stages of density: (least to most)





1.
2.
3.
4.
5.
air (lungs) = darkest
fat (adipose)
soft tissue or muscle
bone
mineral = lightest or white on a radiograph
Relation of Bones, Muscles and
Movement
Muscles are included in this chapter b/c
the work with bones to allow animals to
move.
 Muscles are described by the point of their
attachment:




Origin: the fixed attachment point(more distal)
Insertion: the moveable point(
They are also described based on their
type of motion they cause:

Extensors: cause bone to move into straighter
alignment or open the joint
Relation of Bones, Muscles and
Movement
Muscles are included in this chapter b/c
the work with bones to allow animals to
move.
 Muscles are described by the point of their
attachment:




Origin: the fixed attachment point(more distal)
Insertion: the moveable point(
They are also described based on their
type of motion they cause:

Extensors: cause bone to move into straighter
alignment or open the joint
Clinical Practice

Fractures: occur when the physical force
exerted on the bone is stronger than the
bone itself.


are common; the average person has two
during a lifetime.
Your risk of fracture depends, in part, on your
age.
Clinical Practice



Simple Fracture:
bone is broken into
two, clean pieces.
Comminuted
Fracture: results in
many fragments of
bone.
Compound (open)
Fracture: when one
of the ends of the
bone ends punctures
thought the skin.
Clinical Practice

In order for a fracture to heal, the bone
ends must be put back in alignment and
held without movement.


Bone plate
Intramedullary pin
Clinical Practice

Hip Dysplasia: the ball and socket joint
of the hip becomes diseased.





Socket becomes shallow
More common in large dogs
Genetics ??
Nutrition ??
Degenerative Joint Disease: cartilage
lining becomes worn down.

Pain, lameness, have trouble getting around
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?