Bones, kidneys and sun
Vitamin D made by the sun, bones that renew themselves all life long, and the stones that form in the kidneys.
Vitamin D and sun 
How long in the sun to make vitamin D? City, month, time of day and skin type: the sun making vitamin D in the skin, animated.
Bones through life 
Why do bones become fragile with age? Bone dug out then filled in, and bone mass from age 5 to 90, in women and in men.
Kidney stones 
How does a kidney stone form, and does it pass on its own? What you drink, the crystals that grow, and the stone moving down the ureter depending on its size.
How long in the sun to make vitamin D? City, month, time of day and skin type: the sun making vitamin D in the skin, animated.
Bones through life Why do bones become fragile with age? Bone dug out then filled in, and bone mass from age 5 to 90, in women and in men.
Kidney stones How does a kidney stone form, and does it pass on its own? What you drink, the crystals that grow, and the stone moving down the ureter depending on its size.