Although the intestinal sites of calcium absorption were fairly well localized in the past, those mechanisms which conditioned the absorptive process have been incompletely understood. Recent advances in transport physiology and vitamin D and protein chemistry have added a new dimension to prevailing concepts of Ca transport across the intestinal mucosal cell. It has been established that Ca transport depends on active transport processes requiring metabolic energy, intact mitochondria, the sodium ion, a specific adenosine triphosphatase (ATPase), a soluble intestinal Ca binding protein and biologically active metabolites of vitamin D. Thus, the more detailed and concise delineation of the mechanisms which normally regulate the intestinal absorption of Ca have led to a better correlated understanding of Ca malabsorption and its resistance to vitamin D, a pattern often considered the hallmark of patients with chronic renal disease.
Louis V. Avioli. Intestinal Absorption of Calcium. Arch Intern Med. 1972;129(2):345–355. doi:10.1001/archinte.1972.00320020189016