VITAMIN D PATHWAY trace a calciol molecule (inactive D) from the liver to the kidney. Then trace the calcitrol (active vitamin D) from the kidney to the small intestine. remember, it goes to the small intestine to help absorb calcium. trace a calciol molecule (inactive D) from the liver to the kidney. Then trace the calcitrol (active vitamin D) from the kidney to the small intestine. remember, it goes to the small intestine to help absorb calcium..