Final answer:
Pernicious anemia is caused by an inability to absorb vitamin B12 due to the absence of intrinsic factor, which is crucial for its absorption in the small intestine. This can result from gastrointestinal diseases, surgeries, and dietary insufficiencies, and is treated with vitamin B12 injections.
Step-by-step explanation:
In pernicious anemia, the missing intrinsic factor inhibits absorption of vitamin B12, which is essential for the production of mature red blood cells and normal neurological functioning. Intrinsic factor is a glycoprotein secreted by the stomach that is necessary for vitamin B12 absorption in the small intestine. Without intrinsic factor, vitamin B12 cannot be absorbed, leading to pernicious anemia. This condition is often associated with diseases that affect the stomach or small intestine, such as Crohn's disease, or with surgery that involves the removal of part or all of the stomach (gastrectomy) or the intestine. To treat pernicious anemia, patients can receive vitamin B12 injections, bypassing the need for intrinsic factor since the vitamin is not being absorbed from the digestive tract.
Other risk factors for vitamin B12 deficiency include diets low in meat or alternative sources of B12, overcooking vegetables, and conditions that cause a deficiency in folate. This is especially important for teenagers and children, as well as for vegans and vegetarians, who may not consume enough B12 from their diet alone. Additionally, folic acid is particularly critical during the early stages of pregnancy to reduce the risk of neurological defects such as spina bifida.