Lamellar bone is the characteristic component of the normal adult skeleton. Woven bone and lamellar bone are easily identified under a polarizing microscope. The arrangement of collagen fibers in each produces a unique pattern of birefringence and probably determines the specific structural effects of the two tissue types. Woven bone contains nonparallel arrays of collagen fibers arranged in an irregular, haphazard pattern. There is a high concentration of cells per unit of matrix, and the cells present a variety of shapes and sizes.
Lamellar bone is characterized by an orderly array of collagen fibers aligned in parallel.
There are relatively few cells per unit of matrix, the cells are uniform in size and shape, and they are found in lacunae aligned parallel to the long axis of the collagen fibers. In lamellar bone, most of the mineral phase is located in hole zones created by the specific, staggered packing arrangement of collagen molecules. The mineral component in woven bone is found in or between collagen fibrils and in membrane-bound vesicles. Hormones act on skeletal cells directly and indirectly by modifying the synthesis, activation, and receptor binding of locally active factors or by regulating the concentrations of specific binding proteins, which in turn modulate the effects of these factors. One of the systemic hormones with important effects on bone cell function is PTH, which stimulates bone resorption.