a. Shaft (Diaphysis). In effect, the long bone has a shaft, with proximal and
distal ends. The shaft tends to be cylindrical in form.
(1) It has a cortex (outer portion) of dense bony tissue called compact bone
tissue. The cortex is usually thickest at the middle of the shaft.
(2) The inside of the shaft is usually hollow, except that it is filled with yellow
marrow (in adults, but red marrow in small children and infants).
b. Ends (Epiphyses). At the ends of the long bone, the cortex is much thinner.
Each end is filled with a lattice-or sponge-like network of bony tissue, called cancellous
bony tissue. The strands of bone forming this lattice are called trabeculae. The
trabeculae are aligned with the lines of applied forces, particularly tension and
compression. The spaces within the cancellous bony tissue are filled with red marrow.
c. Some Special Parts. The skeletal muscles pull and create tensions at their
attachments to the bone. These tensions will often cause the bone to react and form
spines, tubercles, ridges, and the like.
d. Articular Cartilages. The surface of each end of the bone is covered by an
articular cartilage. This cartilage is located where the bone contacts another bone at a
joint. The cartilage is made up of hyaline-type cartilage tissue. The articular cartilage
makes the movement between the bones smoother.
e. Periosteum. The periosteum surrounds the bone, except where the articular
cartilages are located. The periosteum is an envelope of the bone and consists mainly
of dense FCT. In fact, the periosteum may be considered the outermost portion of the
(1) However, the periosteum has a special layer of cells immediately
adjacent to the surface of the bone. Since this layer is able to produce bone material, it
is called the osteogenic layer of the periosteum.
(2) When a long bone is fractured or a portion of the bone is lost without
losing the periosteum, the fracture is healed by the combined action of the osteogenic
layer of the periosteum and the osteoblasts of the bone itself.
f. NAVL. Associated with the periosteum are the "service tissues." These are
the NAVL (nerves, arteries, veins, and lymphatics), which nourish and stimulate the
living tissues of the bone and periosteum.
(1) Neurovascular bundle. Branches from the main NAVL of the body go as
a unit to the bone. This unit, the neurovascular bundle, consists of NAVL within a
common fibrous connective sheath.