What hormone is known to increase calcium absorption from the gut?

Calcitriol, which is the active form of vitamin D, plays a critical role in enhancing calcium absorption from the gastrointestinal tract. It facilitates the intestinal absorption of calcium by promoting the expression of calcium-binding proteins and other transport proteins in the intestinal lining. This process helps maintain adequate calcium levels in the bloodstream, which is essential for various physiological functions, including bone health and muscle function.

When dietary calcium is ingested, calcitriol acts to ensure that it is effectively absorbed in the gut, thereby increasing calcium availability in the body. This function is particularly important in scenarios where dietary calcium intake is low or when the body needs to maintain calcium levels due to other physiologic demands.

Other hormones mentioned have different roles. For instance, calcitonin primarily works to decrease serum calcium levels by inhibiting osteoclast activity in the bones and promoting renal excretion of calcium. Parathyroid hormone increases blood calcium levels, but it does so mainly by mobilizing calcium from bone and reducing renal calcium excretion rather than enhancing gut absorption directly. Thyroxine is predominantly involved in regulating metabolism and has a less direct role in calcium homeostasis compared to calcitriol.