Bone and Cartilage – its Structure and Physical Properties - Biomechanics of Hard Tissues - page 17

The skeleton supports soft parts of the body, enables the movements of body
and its members, and protects its internal organs (e.g., the skull protects the brain
and the ribs protect the heart and lungs). Bones together with tendons, ligaments,
joints, and skeletal muscles, steered by the nervous system, create forces and
motion of the entire body or its parts only. Another mechanical function of the
bone is linked to sound transduction in the ear and hearing. These mechanical
functions are the subject of study in biomechanics.
The bone owes its hardness to the osseous tissue, which can be regarded
as a composite material (mineralized organic matrix) formed of a mineral -
hydroxyapatite and a protein - collagen. The living cells are embedded in the
osseous tissue.
Bones are organs made up of bone tissue as well as marrow, blood vessels,
epithelium, and nerves, while the term bone tissue specifically refers to the mineral
matrix that forms the rigid sections of the organ.
1.2.3
Macroscopic Structure of Skeleton
The bones of the skeleton are joined to one another at different parts of their
surfaces, and such connections are termed joints or articulations . It happens that
the joints are immovable , as in the articulations between practically all the bones
of the skull; the adjacent margins of the bones are almost in contact, being
separated merely by a thin layer of fibrous membrane (sutural ligament). In certain
regions at the base of the skull, this fibrous membrane is replaced by a layer of
cartilage. In the freely movable joints, the surfaces are completely separated; the
bones forming the articulation are expanded for greater convenience of mutual
connection, covered by cartilage and enveloped by capsules of fibrous tissue. The
cells lining the interior of the fibrous capsule form an imperfect membrane - the
synovial membrane - which secretes a lubricating fluid. The joints are strengthened
by strong fibrous bands called ligaments , which extend between the bones forming
the joint.
Bones constitute the main elements of all the joints. In the long bones, the
extremities are the parts that form the articulations; they are built of spongy
cancellous tissues with a thin coating of compact substance. The layer of compact
bone that forms the joint surface, and to which the articular cartilage is attached,
is called the articular lamella . It differs from ordinary bone tissue in that it
contains no Haversian canals, and its lacunae are larger and have no canaliculi.
The vessels of the cancellous tissue, as they approach the articular lamella, turn
back in loops, and do not perforate it; this layer is consequently denser and
firmer than ordinary bone, and forms an unyielding support for the articular
cartilage.
Cartilage is a nonvascular structure found in various parts of the body: in adult
life, chiefly in the joints, in the parietes of the thorax, and in various tubes, such
as the trachea, bronchi, nose, and ears, which require to be kept permanently open
[63-73, 77].