Figure

Calcium (Ca) flux between body compartments. Ca balance is a complex process involving bone, intestinal absorption of dietary Ca, and renal excretion of Ca. The parathyroid glands, by their production of parathyroid hormone, and the liver, through its participation in vitamin D metabolism, also are integral organs in the maintenance of Ca balance. (From Kumar [1]; with permission.)

T-lymphocyte

T-lymphocyte

^Osteocalcin Osteopontin Alkaline Phosphatase

Bone

Monoblast

^Osteocalcin Osteopontin Alkaline Phosphatase

Bone

Monoblast

Effects of 1,25-dihydroxy-vitamin D3 (calcitriol) on bone. In addition to the effects on parathyroid cells, the kidney, and intestinal epithelium, calcitriol has direct effects on bone metabolism. Calcitriol can promote osteoclast differentiation and activity from monocyte precursor cells. Calcitriol also promotes osteoblast differentiation into mature cells. (From Holick [8]; with permission.)

DNA binding

Hinge region

Calcitiriol binding gly—asp 30

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