Which molecule increases phosphate absorption in the gut, potentially raising serum phosphate?

Which molecule increases phosphate absorption in the gut, potentially raising serum phosphate?

• A. Calcitriol
• B. Parathyroid Hormone
• C. Vitamin K
• D. Aldosterone

Answer: (A)

Active vitamin D, calcitriol, boosts phosphate absorption from the gut. It does this by binding to receptors in intestinal cells and increasing the expression of the NaPi-IIb phosphate transporter, along with related proteins that move phosphate into the bloodstream. With more phosphate being absorbed from food, serum phosphate can rise, especially if the kidneys aren’t able to excrete it efficiently. Parathyroid hormone, while it raises calcitriol production, promotes phosphate loss by the kidneys by downregulating proximal tubule phosphate transport, so it tends to lower serum phosphate rather than increase gut absorption. Vitamin K isn’t a key regulator of intestinal phosphate uptake, and aldosterone’s effects are mainly on sodium and potassium handling, not gut phosphate absorption.

Active vitamin D, calcitriol, boosts phosphate absorption from the gut. It does this by binding to receptors in intestinal cells and increasing the expression of the NaPi-IIb phosphate transporter, along with related proteins that move phosphate into the bloodstream. With more phosphate being absorbed from food, serum phosphate can rise, especially if the kidneys aren’t able to excrete it efficiently.

Parathyroid hormone, while it raises calcitriol production, promotes phosphate loss by the kidneys by downregulating proximal tubule phosphate transport, so it tends to lower serum phosphate rather than increase gut absorption. Vitamin K isn’t a key regulator of intestinal phosphate uptake, and aldosterone’s effects are mainly on sodium and potassium handling, not gut phosphate absorption.