2. Skeletal System (Osteology)

OSTEOLOGY

study of skeleton such as bones, joints, and connective

tissue.

1. Support

2. Locomotion

3. Protection

4. Storage

5. Haemopoiesis

functions of the skeletal system

Support

it acts as an internal ‘scaffold’ upon which the body is built

Locomotion

it provides attachment for muscles, which operate a

system of levers, i.e. the bones, to bring about movement

Protection

it protects the underlying soft parts of the body, e.g. the

brain is encased in the protective bony cranium of the skull

Storage

it acts as a store for the essential minerals calcium and

phosphate

Haemopoiesis

haemopoietic tissue forming the bone marrow

manufactures the blood cells.

Appendicular skeleton

Axial skeleton

Splanchnic skeleton

skeleton are considered to be made up of three parts:

Appendicular skeleton

bones of the thoracic limb and pelvic limbs.

Axial skeleton

it consists of skull, vertebral column, ribs, and sternum

Splanchnic skeleton

small bones seen in the tissues of an organs or other structures.

os penis/baculum

os clitoridis/ baubellum

os cordis

os rostrale

os phrenic

Examples of splanchnic skeleton

Bones

Cartilages

Tendons

Joints (articulation)

Components of skeleton

Bones

rigid organ that constitutes part of

the skeleton in most vertebrate animals.

Cartilages

non-vascular type of supporting

connective tissue that is found throughout the

body.

Tendons

fibrous connective tissue that

attaches muscle to bone.

Joints (articulation)

areas where two or

more bones meet

average count for the canine skeleton

Long bones

Short bones

Flat bones

Irregular bones

Bones are classified based on their general shape:

Long bones

• are typical of the limb bones and also include bones of the metacarpus/metatarsus and phalanges

• they have a shaft containing a medullary cavity filled with bone marrow

• e.g., femur,humerus

Short bones

• have an outer layer of compact bone with a core of cancellous bone and no medullary cavity

• e.g., carpal and tarsal bones

Flat bones

• have an outer layer of compact bone with a layer of cancellous or spongy bone inside

• there is no medullary cavity

Irregular bones

• have a similar structure to short bones but a less uniform shape and are unpaired

• e.g., vertebrae

Sesamoid bones

Pneumatic bones

Splanchnic bones

Some specialized types of bones:

Sesamoid bones

• are sesame seed-shaped bones that develop within a tendon that runs over an underlying bony prominence

• e.g. patella associated with stifle joint

Pneumatic bones

• contain air-filled spaces known as sinuses that have the effect of reducing the weight of the bones

• e.g. maxillary and frontal bones

Splanchnic bone

• bone that develops in a soft organ and is unattached to the rest of the skeleton

• e.g. the os penis (bone within the penis of the dog and cat)

Ossification

process by which the bones is formed

Intramembranous ossification

Endochondral ossification

two types of ossification

Intramembranous ossification

is the process by which the flat bones of the skull are formed. The osteoblasts lay down bone between two layers of fibrous connective tissue. There is no cartilage template or ‘model’.

Endochondral ossification

• involves the replacement of a hyaline cartilage model within the embryo by bone.

• process starts in the developing embryo but is not completed fully until the animal has reached maturity and growth has ceased.

• The long bones of the limb develop by this method.

Osteoblasts

cells responsible for laying down new bone.

Osteoclasts

cells that destroy or remodel bone

Stages of endochondral ossification

Steps of endochondral ossification

Steps of endochondral ossification

Compact bone

• It is dense, white and hard and forms the outer shell of the bone

• Bone is arranged in the form of concentric system called “Haversian system”

Cancellated or Spongy bone

• It is made up of delicate plates, which intercrosses each other forming a meshwork with spaces containing marrow

• Haversian systems are absent.

Medullary Cavity

Also known as bone marrow cavity, it is the space in the diaphysis containing the marrow

Epiphysis

Two enlarged ends of the long bone (proximal and distal extremities)

Metaphysis

The joining point of the diaphysis and epiphysis in a mature bone

Diaphysis

cylindrical shaft of a long bone between two epiphysis.

Epiphyseal cartilage

“growth plate” , is the cartilaginous plate between the diaphysis and epiphysis of immature long bones.

Periosteum

is the fibrous covering around the bone that is not covered by articular cartilage.

Endosteum

is the fibrous tissue lining the medullary cavity of the bone.

Cortex

compact bone surrounding the medullary cavity

Articular surface

are smooth layer of hyaline cartilage covering the epiphysis where one bone forms a joint with another bone

Apophysis

process/ any outgrowth of the bone

Nutrient foramen

a small opening in the bone that serves as a passageway for blood vessels, providing essential nutrients and oxygen to keep the bone healthy and promoting repair and growth.

Diagram of Blood and Nerve Supply to Bone Blood vessels and nerves enter the bone through the nutrient foramen

BONY FEATURES

Bones have many external features depending on it’s specific function, it can either be a projection or depression.

Projection

is any bony feature that protrudes from the major bone part

Depression

is a shallow or deep concavity/depressed part of the bone

 Articular projection

 Non-articular projections

 Articular depressions

 Non-articular depressions

Types of Bony Features

Head

Condyles

Trochlea

Facets

What are the articular projections?

Head

• rounded articular processes

• (e.g head of the humerus/femur)

Condyles

• large articular prominence

• (e.g occipital condyles of the skull)

Trochlea

• pulley-shaped structures

• (e.gtrochlea of femur)

Facets

• smooth, flat articular surfaces

• (e.garticular facets of a thoracic vertebra for rib attachment)

Process

Tuberosity/tuber

Spine

Tubercle

What are the non-articular projections?

Process

• general term for bony projections

• (e.g zygomaticprocess of temporal bone)

Tuberosity/tuber

• a large, usually roughened process

• (e.g deltoid tuberosity of the humerus)

Spine

• sharp, slender process

• (e.g scapula)

Tubercle

small, rounded process

(e.g greater tubercle of humerus)

Cotyloid

Glenoidcavity

What are the articular depressions?

Cotyloid

• deep articular depression

• (e.g acetabulum of os coxae/hip joint)

Glenoid cavity

shallow articular concavity

Fovea

Fossa

Foramen

What are the non-articular depressions?

Fovea

a shallow, non-articular depression (e.gfovea capitison the head of the femur)

Fossa-

large, non-articular depression, usually they are wide in terms of area of attachment of muscles

Foramen

• an opening through a bone

• (e.g infraorbital foramen, obturator foramen, foramen magnum)