What is the Bone?

Connective tissue  Organic matrix (cells & proteins)  Inorganic elements (calcium hydroxyapatite)

Modeling and Remodeling of Bone The balance of bone formation and resorption determines skeletal mass.

 From the preadolescent years to the end of the second decade of life, bone size and bone mass increase rapidly.  The peak bone mass attained by approximately 30 years.  There is steady decrement in skeletal mass after 30 years.

Factors effecting Bone mass  Genetic factors  Environmental factors: Calcium and Vitamin D Exercise Smoking

CALCIUM REQUIREMENTS  For pre-menopausal women years old: 1,000-1,200 milligrams per day.  For pregnant or lactating women:1,500 milligrams per day  For men ages 25-65: 1,000 milligrams per day.  For all people (women and men) over age 65: 1,500 milligrams per day.

Vitamin D

Sources of Vitamin D  Sun light and ultraviolet light  Diet

REQUIREMENTS  Variable and depends in part upon sun exposure  The Recommended Dietary Allowance (RDA) of vitamin D for adults through age 70 years is 600 IU  After 70 years RDA increases to 800 IU  For pregnant and lactating mothers RDA is 600 IU

VITAMIN D DEFICIENCY  Impaired availability of vitamin D, secondary to inadequate dietary vitamin D, fat malabsorptive disorders, and/or lack of sun exposure  Impaired hydroxylation by the liver to produce 25-OH vitamin D  Impaired hydroxylation by the kidneys to produce 1,25- dihydroxyvitamin D  End organ insensitivity to vitamin D metabolites

VITAMIN D DEFICIENCY  Lack of vitamin D activity leads to reduced intestinal absorption of calcium and phosphorus.  Persistent vitamin D deficiency leads to secondary hyperparathyroidism, which causes phosphaturia and demineralization of bones (osteomalacia in adults and rickets in children).

OSTEOMALACIA Decreased mineralization of newly formed osteoid

CLINICAL MANIFESTATIONS  Asymptomatic  Diffuse bone pain  Polyarthralgias  Muscle weakness, and difficulty walking  Fractures

Diagnosis  Elevated Alkaline phosphatase  Reduced Serum calcium and phosphorus  Decrease 25-hydroxyvitamin D (calcidiol) <15 ng/ml  Elevated PTH  Osteopenia on X-ray  Bone biopsy

Osteoporosis  Low bone mass with micro architectural disruption and fragility, resulting in an increased risk of fracture  Normal serum calcium and phosphorus  Decreased bone mass can occur because peak bone mass is low, bone resorption is excessive, or bone formation during remodeling is decreased.

CAUSES  Hormone deficiency  Hormone excess  Immobilization  Genetic disorder  Tobacco/ alcoholism  Miscellaneous

CLINICAL MANIFESTATIONS Osteoporosis has no clinical manifestations until there is a fracture

DIAGNOSIS  bone mineral density (BMD) by Dual energy x-ray Absorptiometry (DXA)  CT scan of bones