Question

Which of these statements about vitamin \(\mathbf{B}_{12}\) is false? a. Lack of this vitamin can produce pernicious anemia. b. Intrinsic factor is needed for absorption of vitamin \(B_{12}\) c. Damage to the gastric mucosa may lead to a deficiency in vitamin \(B_{12}\) - d. Vitamin \(\mathbf{B}_{12}\) is absorbed primarily in the jejunum.

Short answer

The false statement is option D. The correct statement should be: Vitamin \(B_{12}\) is absorbed primarily in the ileum.

Step-by-step solution

Option A

Lack of this vitamin can produce pernicious anemia. This statement is true. Pernicious anemia is a type of anemia caused by a deficiency in vitamin B12. Vitamin B12 is necessary for the proper formation of red blood cells, and a lack of this vitamin can lead to anemia.

Option B

Intrinsic factor is needed for absorption of vitamin \(B_{12}\) This statement is also true. Intrinsic factor is a protein produced by the parietal cells in the stomach, which binds to vitamin B12 and enables its absorption in the small intestine.

Option C

Damage to the gastric mucosa may lead to a deficiency in vitamin \(B_{12}\) This statement is true as well. Damage to the gastric mucosa can affect the production of intrinsic factor, which is required for the absorption of vitamin B12. Therefore, damage to the gastric mucosa may lead to a deficiency in vitamin B12.

Option D

Vitamin \(B_{12}\) is absorbed primarily in the jejunum. This statement is false. Vitamin B12 is actually absorbed primarily in the ileum, which is the last part of the small intestine, rather than the jejunum. As we have determined that option D is false, the correct answer is option D. To provide the correct statement for it: Corrected Option D: Vitamin \(B_{12}\) is absorbed primarily in the ileum.

Key concepts

Pernicious Anemia

Pernicious anemia is a condition that arises due to the inability of the body to absorb vitamin B12, which is essential for the production of healthy red blood cells. Without sufficient vitamin B12, the red blood cells produced are larger and less efficient, leading to a reduction in their oxygen-carrying capacity. This lack of efficient oxygen transport throughout the body results in symptoms such as fatigue, weakness, and shortness of breath.

One of the underlying causes of pernicious anemia is a deficiency in a substance known as intrinsic factor. Normally, intrinsic factor binds to vitamin B12 and facilitates its absorption in the small intestine. However, in pernicious anemia, the body’s immune system mistakenly targets the cells in the stomach that produce intrinsic factor, leading to its deficiency and, consequently, vitamin B12 deficiency.

Intrinsic Factor

The intrinsic factor is a glycoprotein produced by the parietal cells of the stomach lining. It plays a crucial role in the absorption of vitamin B12, which means that without intrinsic factor, vitamin B12 cannot be effectively absorbed, no matter its dietary abundance.

After vitamin B12 is consumed, it travels to the stomach where it binds with intrinsic factor. This complex then moves to the ileum, the final portion of the small intestine, where vitamin B12 is absorbed into the bloodstream. If intrinsic factor is lacking, which can occur due to the immune system attacking the gastric mucosa or due to genetic mutations affecting its production, an individual will likely develop a vitamin B12 deficiency and, potentially, pernicious anemia.

Gastric Mucosa Damage

Damage to the gastric mucosa, the mucus-secreting membrane lining the inside of the stomach, can have profound implications for the absorption of vitamin B12. This damage can result from various causes, including chronic inflammation, infections such as Helicobacter pylori, long-term use of certain medications, or autoimmune conditions.

When the gastric mucosa is compromised, the parietal cells that create intrinsic factor are affected. This disrupts the production of intrinsic factor, hindering the body's ability to absorb vitamin B12. The direct link between gastric mucosa damage and B12 deficiency underlines the importance of maintaining a healthy stomach lining for overall nutritional health.

Ileum Absorption

The ileum is the last and longest segment of the small intestine and it plays a key role in the absorption of vitamin B12. After intrinsic factor binds with vitamin B12 in the stomach, the pair travels to the ileum where specialized receptors facilitate the uptake of the vitamin B12-intrinsic factor complex.

Many factors can disturb the absorption process in the ileum, including diseases such as Crohn's disease, surgical removal of a section of the ileum, or competitive bacterial overgrowth which can consume the vitamin before it is absorbed. Adequate ileum function is therefore critical for the prevention of vitamin B12 deficiency and associated conditions such as pernicious anemia.