Explain about the Intestinal calcium absorption?

Intestinal calcium absorption is mainly controlled by the serum concentration of 1, 25- (OH)₂D as discussed above. The activity of the 1-α-hydroxylase, which catalyzes 1, 25-(OH)₂D production from 25-hydroxyvitanlin D (25-OH-D) in the kidneys, is negatively related to plasma calcium and phosphate concentrations and positively related to plasma parathyroid hormone concentrations. Thus, the inverse relationship between calcium intake and fractional absorption described above is enhanced by the inverse relationship between dietary calcium and serum 1, 25-(OH)₂D. We will learn about this aspect later in this section under the heading regulation of Ca concentration.