Page 85 - Anatomy and Physiology of Farm Animals, 8th Edition

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he study of the bones that make up the the hard layer that constitutes the exterior
Compact (dense or cortical) bone is
Tskeleton, or framework of the body, is
VetBooks.ir osteology. The skeleton gives a basis for the of most bones and forms almost the entire
shaft of long bones.
external structure and appearance of most
vertebrate animals as we know them Cancellous (spongy) bone is composed
(Figs. 4‐1 and 4‐2). All mammals share a of spicules arranged to form a porous net-
basic body plan with striking similarities work. The spaces are usually filled with
in skeletal structure. Differences reflect marrow.
adaptations to specific lifestyles. The medullary cavity (marrow cavity)
The skeleton of a living animal is made is the space surrounded by the cortex of a
up of bones that are themselves living long bone. In young animals it is filled with
structures. They have blood vessels, lym- red marrow (hematopoietic tissue), which
phatic vessels, and nerves; they are subject gradually is replaced by yellow marrow
to disease; they can undergo repair; and (fat) as the animal ages.
they adjust to changes in stress. The func- Epiphysis refers to either end of a long
tions of bones include providing protec- bone. The end closest to the body is the
tion, giving rigidity and form to the body, proximal epiphysis, and the end farthest
acting as levers, storing minerals, and from the body is the distal epiphysis.
forming the cellular elements of blood. The diaphysis is the cylindrical shaft of
a long bone between the two epiphyses.
The metaphysis of a mature bone is the
Functions of Bones flared area adjacent to the epiphysis.
Epiphyseal cartilage or disk (physis) is
Protection of vital organs is one of the a layer of hyaline cartilage within the meta-
important functions of bones. The central physis of an immature bone that separates
nervous system is protected by the skull the diaphysis from the epiphysis. This is
and vertebral column; the heart and lungs, the only area in which a bone can lengthen.
by the rib cage; and internal parts of the Articular cartilage is a thin layer of
urogenital system, by the pelvis. hyaline cartilage that covers the articular
In the vertebrates, locomotion, defense, (joint) surface of a bone.
offense, grasping, and other activities of Periosteum is a fibrous membrane that
this type depend largely upon the action of covers the surface of a bone except where
muscles that attach to levers. Almost with- articular cartilage is located. Osteoblasts
out exception, these levers are made of (bone‐producing cells) of the periosteum
bone and are integral parts of the skeleton. are responsible for increases in the diameter
The entire skeleton serves as a dynamic of bones, and activity of periosteal cells is
storage area for minerals, particularly important in the healing of fractures. The
calcium and phosphorus. These minerals periosteum is vascular and well‐innervated.
are deposited and withdrawn as needed in Endosteum is a fibrous membrane that
the ongoing homeokinetic process. Blood lines the marrow cavity and osteonal canals
formation is not strictly a function of bone (osteons) of a bone. Erosion of existing
itself but of the marrow within the cavity of bone by osteoclasts (bone‐destroying
long bones and the spongy substance of all cells) in the endosteum determines the size
young bones. of the marrow cavity and the thickness of
the diaphyseal cortex. Both periosteum
and endosteum contain osteoblasts and
Terminology osteoclasts (see Chapter 5).
Many of the projections from and
Certain terms (Fig. 4‐3) routinely used in depressions in bones have general names
reference to bones, particularly long bones, that depend to some extent on their
include the following. size and function. Both projections and