What is A 34-year-old man presents with 5-month history of weakness and fatigue. There is no history of drug or alcohol abuse. CBC shows megaloblastic anemia and a normal reticulocyte count. Fuher laboratory studies reveal vitamin B12 deficiency. Anemia in this patient is most likely caused by which of the following? and explain in detail?
Type A/ Autoimmune gastritis: -Site : Fundus & body of stomach - Damage : Parietal cells resulting in: Achlorhydria - |G-cell stimulation - |Gastrin levels -| Neuroendocrine tumor Intrinsic factor deficiency - Malabsorption of vitamin B12 - Megaloblastic anemia /Pernicious anemia