Page 261 - Atlas of Histology with Functional Correlations

SECTION 2 Bone

CHARACTERISTICS OF BONE

Similar to cartilage, bone is also a special form of connective tissue consisting of
cells, connective tissue fibers, and extracellular matrix. In contrast to

cartilage, minerals accumulate and are deposited in the cartilage matrix causing
calcification of the developing bones. Consequently, bones become hard and can
bear more weight, serve as a rigid skeleton for the body, and provide attachment
sites for muscles and organs.

Because of their strength, bones also protect the brain in the skull, the heart
and lungs in the thorax, and the urinary and reproductive organs between the
pelvic bones. In addition, adult bones with red marrow function in
hematopoiesis (blood cell formation). Bones also serve as reservoirs for
calcium, phosphate, and other essential minerals. Almost all (99%) of the

calcium in the body is stored in bones, from which the body draws its daily
calcium needs.

BONE MICROARCHITECTURE

All adult bones exhibit similar histology consisting of cells, bony matrix, and the

neurovascular bundle (blood vessels, nerves, and lymphatics). Examination of
bone in cross section shows two types: compact bone and cancellous (spongy)
bone (Fig. 7.18). In long bones, the outer cylindrical part is the dense compact
bone. The inner surface of the bone adjacent to the marrow cavity is the
cancellous (spongy, not dense) bone with numerous interconnecting areas;

however, both types of bone have a similar microscopic appearance. In
newborns, the marrow cavities of long bones are red and produce blood cells. In
adults, the marrow cavities of long bones are yellow and filled with adipose (fat)

cells.

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