Final answer:
Calcium absorption in the gut is affected by the presence of free fatty acids, the state of vitamin D, the action of parathyroid hormone, and various dietary factors. Compounds that form insoluble calcium salts or compete with calcium for absorption can decrease it, while vitamin D and parathyroid hormone increase absorption to maintain adequate calcium-blood levels.
Step-by-step explanation:
The state of ionized calcium, or Ca++, can significantly affect its absorption in the gut. When fat absorption is impaired, it can lead to increased formation of free fatty acids, which bind with free calcium to create insoluble calcium soap, leading to its excretion in feces. Conversely, vitamin D is vital for calcium absorption; it elevates levels of specific calcium-binding proteins that aid in the transport of calcium across the intestinal mucosa. Moreover, parathyroid hormone (PTH) is known to increase intestinal absorption of calcium, while adrenal glucocorticoids have the opposite effect.
There are several dietary factors that can inhibit calcium absorption, including the presence of phytates, oxalates, phosphate, and fiber, as well as a high intake of magnesium or iron, which form insoluble complexes with calcium. The body's need to maintain calcium-blood levels influences the uptake of dietary calcium; low blood levels of ionic calcium result in increased PTH secretion, which subsequently boosts calcium absorption from the diet.