Intrinsic factor of Castle is secreted by
**Core Concept:**
The intrinsic factor of Castle is a glycoprotein that plays a crucial role in the absorption of vitamin B12 (cobalamin) in the terminal ileum. Vitamin B12 is essential for the maintenance of the blood cell production, nervous system function, and DNA synthesis. The intrinsic factor binds to vitamin B12, facilitating its absorption through the intestinal lining and transport to the liver for storage or to peripheral tissues for utilization.
**Why the Correct Answer is Right:**
The intrinsic factor of Castle is primarily secreted by parietal cells, also known as chief cells, which are part of the gastric mucosa. These cells are responsible for secreting gastric acid (HCl) and intrinsic factor, which aids in the absorption of vitamin B12 in the small intestine. The correct answer is A, as it identifies parietal cells as the source of intrinsic factor production.
**Why Each Wrong Option is Incorrect:**
B is incorrect because it refers to the parietal cell mucous membrane, which is not the correct term for the gastric mucosa containing parietal cells. C is incorrect as it refers to the parietal cell mucous membrane, which is not the correct term for the gastric mucosa containing parietal cells. D is incorrect because it refers to the intestinal mucous membrane, which is not the location of parietal cells.
**Clinical Pearl:**
Understanding the correct secretion of intrinsic factor by parietal cells is essential for appreciating the role of this protein in vitamin B12 absorption and maintaining the overall health. A deficiency in intrinsic factor can lead to pernicious anemia, a type of anemia characterized by impaired red blood cell production due to vitamin B12 deficiency.