Which of the following steps of vitamin B-12 absorption occurs in the stomach?

• A. Binding of vitamin B-12 to intrinsic factor
• B. Absorption of vitamin B-12 into the bloodstream
• C. Transport of vitamin B-12 to the liver
• D. Release of vitamin B-12 from food proteins

Answer: (D)

Verified step by step guidance

1. Understand that vitamin B-12 absorption involves multiple steps occurring in different parts of the digestive system.
2. Recognize that the stomach plays a crucial role in the initial processing of vitamin B-12.
3. In the stomach, vitamin B-12 is released from food proteins due to the acidic environment and the action of pepsin, an enzyme that breaks down proteins.
4. Identify that intrinsic factor, a protein secreted by the stomach's parietal cells, will later bind to vitamin B-12, but this occurs after the vitamin is released from food proteins.
5. Note that the absorption of vitamin B-12 into the bloodstream and its transport to the liver occur later in the small intestine, not in the stomach.