6.2 2.2.3 associated tissues

Associated tissues

Bones

• 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
• The fibres give tendons a white shiny appearance.
• There is a minimal amount of matrix present.