Activated vitamin D acts on which organ to stimulate calcium absorption?

Activated vitamin D, specifically in its form as calcitriol, primarily functions to enhance the absorption of calcium in the small intestine. This is a crucial role because vitamin D facilitates the uptake of calcium from dietary sources, ensuring that the body maintains adequate levels of this essential mineral for various physiological processes, including bone health and muscle function.

In the small intestine, calcitriol increases the expression of proteins that are involved in transporting calcium across the intestinal cell membranes, thereby promoting more efficient calcium absorption into the bloodstream. This action is vital, especially when dietary calcium intake may be insufficient.

While vitamin D does have effects on other organs, such as the kidneys where it can help regulate calcium excretion and reabsorption, the primary site of calcium absorption stimulated by activated vitamin D is the small intestine. Therefore, recognizing the unique role of the small intestine is key to understanding how vitamin D contributes to mineral homeostasis in the body.