Final answer:
PTH increases the absorption of dietary calcium in the intestines indirectly by stimulating the production of calcitriol, which enhances calcium absorption when blood calcium levels are low.
Step-by-step explanation:
When the levels of calcium ions in the blood are low, parathyroid hormone (PTH) is secreted by the parathyroid glands. The intestinal response to this involves an increase in the absorption of dietary calcium. This occurs indirectly through PTH stimulating the synthesis of calcitriol, which is an active form of vitamin D. Vitamin D is crucial because it enhances the intestinal absorption of calcium. Therefore, instead of excreting calcium, the intestines absorb more calcium to help restore the balance of blood calcium levels.