Where is calcium primarily absorbed in the human body?

Calcium is primarily absorbed in the small intestine, which is responsible for nutrient absorption following food intake. The small intestine has specialized structures, such as villi and microvilli, that increase its surface area and facilitate the absorption of various nutrients, including calcium.

Calcium absorption in the small intestine occurs mainly in the duodenum and jejunum, where the presence of vitamin D enhances the absorption process. Vitamin D increases the expression of calcium-binding proteins in the intestinal cells, allowing for more efficient uptake of calcium from the diet.

While calcium is also present in the diet and can be influenced by other organs like the kidneys, the predominant site of absorption is effectively the small intestine. This nutrient absorption is crucial for several physiological functions, including bone health, muscle contraction, and nerve signaling.