Everything Life Sciences Grade 10

FACT

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.

Bones DUMMY

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.

Figure 7.17: A diagram of a section of compact bone showing Haversian canals.

Microscopic structure of a long bone

Numerous hollow tunnels calledHaversian canalsoccur within the matrix of bone tissue

and run parallel to the length of the bone. Under the microscope they appear as black

circles against a lighter background. 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 an Haversian

System and a number of these systems make up compact bones.

Cartilage DUMMY

Main features

Cartilage is a tough semi-transparent flexible tissue that consists of a tough matrix or jelly-

like substance. The matrix is made up of collagen (a protein) and proteins with special

carbohydrate chains called proteoglycans. Cartilage is enclosed by a fibrous capsule called

208 7.4. Musculoskeletal tissues