The intrinsic factor of Castle is secreted by
**Core Concept**
The intrinsic factor of Castle is a glycoprotein essential for vitamin B12 absorption in the intestine. It binds to vitamin B12 in food and forms a complex that is then absorbed by the ileal mucosa, allowing for proper utilization of this vitamin. This process is crucial for preventing vitamin B12 deficiency and its associated neurological and hematological complications.
**Why the Correct Answer is Right**
The intrinsic factor is secreted by the parietal cells of the stomach lining. These parietal cells produce and secrete the intrinsic factor into the gastric lumen, where it can bind to vitamin B12 in food. The intrinsic factor-vitamin B12 complex is then transported to the ileum, where it is absorbed by the mucosal cells. This process is mediated by the intrinsic factor receptor, which is present on the surface of the ileal mucosal cells.
**Why Each Wrong Option is Incorrect**
* **Option A:** The intrinsic factor is not secreted by the chief cells, which are responsible for producing pepsinogen, the precursor to pepsin.
* **Option B:** The intrinsic factor is not secreted by the mucous neck cells, which produce mucin, the main component of mucus in the stomach.
* **Option C:** The intrinsic factor is not secreted by the G cells, which produce gastrin, a hormone that stimulates acid secretion in the stomach.
**Clinical Pearl / High-Yield Fact**
The intrinsic factor of Castle is a crucial factor in preventing vitamin B12 deficiency, which can lead to megaloblastic anemia, neurological damage, and increased risk of osteoporosis. Patients with pernicious anemia, an autoimmune disorder that destroys the parietal cells, require lifelong supplementation with vitamin B12 to prevent these complications.
**Correct Answer:** D. Parietal cells.