<prompt> Calcium absorption is increased by -Acidic PhTetracyclinesAlkaline PhPhosphates  <response>: Ans. is a i.e., Acidic Ph o With an average intake of 1000 mg of calcium its net intestinal absorption is only 150-250 mgday. o Calcium is absorbed mainly in the duodenum and Jejunum proximal intestine0 by an active transport mechanism regulated by 1,25 OH2 D3 calcitriol Q. o Parathormone indirectly promotes absorption of calcium0 by increasing the renal synthesis of 1,25 OH 2 D3.Dietary lactose, proteins0and an acidic environment promote calcium absorption Q.. o On the other hand, phytates, phosphates, oxalates, tetracycline and and alkaline environment impair calcium absorption Q. o Calcium is transported across the brush border of intestinal epithelial cells via channels known as transient receptor potential vantioid type 6 TRPV6 and binds to an intracellular protein known as catbindin. o Calbindin sequesters the absorbed calcium so that it does not disturb the epithelial signaling process that involve calcium. o The absorbed Ca2 is thereby delivered to the basolateral membrane of the epithelial cells, from where it can be transported into the blood stream by either a SodiumCalcium exchanger NCX1 or a calcium-dependent ATPase. 