Provide the framework and internal core structure for the attachment of muscles
Bone is a living rigid tissue which forms the support structures for the rest of
the body. The process of bone formation is called
ossification.
The matrix of bone contains a dense arrangement of collagen fibres together with
mineral salts of calcium, magnesium and phosphates.
The calcium salts give bone its hardness and rigidity while collagen fibres give
bones its flexibility and strength.
Functions of bone
To serve as a firm
support framework for the whole body.
To
protect such delicate structures as the brain and spinal cord
To serve as levers, working with attached muscles to
produce movement.
To serve as a
storehouse for
calcium salts , which may be reabsorbed into the blood if there is not enough calcium in the
diet,
To
produce blood cells in the red marrow.
Microscopic structure of a long bone
Numerous hollow tunnels called
Haversian canals occur within the matrix of bone tissue and run parallel with the length of the
bone. Under the microscope they appear as black circles against a lighterbackground.
Each Haversian canal is surrounded by concentric rings of compact bone called
lamellae
Each of these layers contains a ring of fluid-filled cavities called
lacunae. Each of these lacuna will contain a number of bone cells called
osteocytes.
The lacunae are linked to each other and to the Haversian canal by a system of
very tiny interconnecting canals called
canaliculi. Strands of cytoplasm extend through these canals which supply the osteocytes
with oxygen and nutrients and remove waste products
The Haversian canals, lacunae, osteocytes and canaliculi together form a unit
called a
Haversion System and a number of these systems make up compact bone.
Apart from osteocytes which are embedded in the lacunae of bone there are two
other types of bone cells
Osteoblasts : Bone forming cells. These cells allow the bone to change and remodel its shape
as the organism grows and responds to stresses. If a bone is broken
or if strengthening is needed, bone cells lay down new tissue and repair damaged
tissue
Osteoclasts: Special bone cells for destroying and reabsorbing bone tissue.
Cartilage
Main features
cartilage is a tough semi-transparent flexible tissue
it is enclosed by a fibrous capsule called the
perichondrium
consists of living cells called
chondrocytes which secrete a rubbery protein matrix called
chondrin
chondrocytes occur in small fluid-filled spaces called
lacunae which are scattered throughout the matrix.
There are
no blood vessels or nerves in the matrix.
Cartilage and bone
Infant and young children do not have bones like those of adults. Their bones
are made mostly of
cartilage, a firm elastic fibrous material.
As the individual grows and matures, the cartilage is gradually replaced by bone
cells which deposit crystals of calcium carbonate and calcium phosphate.
This process called
ossification greatly increases the strength of the bone.
Bones usually continue to grow through adolescence. During this time a layer of
cartilage still exists between the head and shaft at either end of thebone.
The growth of the bone does not interfere with the way joints fit together.Eventually once all the cartilage has become ossified bone growth will stop
Types of cartilage
Hyaline Cartilage:
Appearance: glass-like, bluish-white in colour, few fibres present
Location:
at the ends of bones as articular cartilage
where the ribs are joined to the sternum
forms rings in the trachea
larynx and tip of nose
as temporary cartilage in bones.
Functions:
reduces friction at the joints.
allows a degree of movement during breathing
keeps the trachea open.
Forms permanent structures
Allows for bones to increase in length.
Fibrocartilage
Appearance: has numerous white collagen fibres in the matrix.
Location:
as cartilaginous discs between the vertabrae
in the rim of sockets of ball and socket joints
between the pubic bones
Functions:
act as shock absorbers
make the cavity deeper without hampering movement
allows for limited movement
Elastic cartilage
Appearance: has a network of yellow elastic fibres in the matrix.
Location:
in the pinna of the ear
in the epiglottis
Functions:
maintains the shape of the ear but also allows for changes in shape.
strengthens the epiglottis which prevents food from entering the trachea.
Ligaments
Ligaments consist of white collagen fibres and a network of yellow elastic
fibres.
The collagen fibres are less orderly and more randomly arranged than in tendons
and ligaments have varying amounts of elastic fibres.
Ligaments join bone to bone and they also control the degree of movement allowed
between the two bones. This is achieved by the amount of elasticity in aligament i.e. a ligament will only stretch enough to allow a particular
movement to happen.
The more elastic fibres in the ligament the greater the articulation between two
bones. Thus the attachment of ligaments between bones keep the bones of a jointin position.
By restricting bone movement ligaments will prevent any dislocation during
normal actions.
Tendons
Attach muscles to bones and facilitate the various positions of the body related
to movement and balance.
Tendons consist of non elastic collagen fibres only.
These are densely packed, arranged in parallel bundles and are extremely strong,
less flexible and more resistant to stress
