What is the primary function of intrinsic factor produced by parietal cells?

The primary function of intrinsic factor, which is produced by parietal cells in the stomach, is the absorption of vitamin B12 in the small intestine. Vitamin B12 is essential for the synthesis of red blood cells, DNA, and proper neurological function. Intrinsic factor binds to vitamin B12 after it is released from food in the acidic environment of the stomach, forming a complex that is necessary for its absorption in the ileum, the last part of the small intestine. Without sufficient intrinsic factor, vitamin B12 cannot be adequately absorbed, leading to deficiencies, which can cause serious health issues such as pernicious anemia and neurological disorders.

Other options, while related to digestive processes, do not represent the primary role of intrinsic factor. For example, the digestion of proteins occurs due to the action of stomach acids and enzymes like pepsin, not the function of intrinsic factor. Additionally, while calcium absorption is important and does occur in the intestine, it is not the role of intrinsic factor to facilitate this process—rather, it is primarily involved with vitamin B12. Regulation of stomach acidity is also a function of other mechanisms, including the secretion of hydrochloric acid by parietal cells, rather than a direct function of intrinsic factor itself.