ABSTRACT
Bone is the primary reservoir of calcium and phosphate in the body. Lamellar bone forms the structural component of cortical and cancellous bone with stressorientated collagen fibres contributing to its anisotropic characteristics. Cortical bone is a subtype of lamellar bone and comprises 80 percent of the adult skeleton forming the envelope of cuboid bones. Osteocytes, lacunae and canaliculi in cancellous bone resemble those in cortical bone. Osteoblasts that become entrapped by calcified bone matrix are known as osteocytes. Lack of osteoclast activity is implicated in osteopetrosis, while overactivity is found in Paget's disease. A bone remodelling unit is an area of bone remodelled by a set of osteoblasts, osteoclasts and stromal supporting tissue. Capillaries enter at the sites of major muscle attachments, normally supplying the outer third of the cortex. Dietary calcium deficiency produces a progressive loss of bone mass. Calcitonin is secreted in response to elevated serum calcium and inhibited by decreased serum calcium.
