The adult human skeleton is composed of 206 bones. At birth, there are approximately 270 bones, with the final adult count decreasing as a portion of these bones fuse during phases of skeletal growth and maturation. Bone is a metabolically active connective tissue that provides structural support, facilitates movement, and protects vital organs. It plays an important role in regulating mineral and acid-base balance homeostasis. It also provides the environment for hematopoiesis (blood cell production) within the bone marrow. Bone is composed of an extracellular matrix and bone cells (osteocytes).[1][2]
Bone Cells
Bone cells make up about 10% of total bone volume. There are four types of cells:
Bone Extracellular Matrix
This makes up 90% of overall bone volume. It consists of inorganic (mineral) and organic matrices.[7]
Bone Remodeling
This is a physiological process in which old or damaged bone is removed by osteoclasts and then replaced by new bone formed by osteoblasts. There is a tight coupling of bone formation to bone resorption to ensure no net change in bone mass or quality after each remodeling. It requires coordinated action of the four types of bone cells. The process involves four major distinct but overlapping phases:
Osteoporosis[9][10][11][12][13][14]
This is a common disorder of bone remodeling which is characterized by low bone mass and structural deterioration of bone. It causes bone fragility and increased vulnerability to fractures. There are two types of osteoporosis:
Primary Osteoporosis:
Type I (Postmenopausal Osteoporosis)
Type II (Age-Related Osteoporosis or Senile Osteoporosis)
Glucocorticoid-induced Osteoporosis (Secondary Osteoporosis)
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