Key Points. 1  Megaloblasts are large nucleated RBC precursors with noncondensed chromatin. 2  The most common causes of megaloblastic, macrocytic anemia are deficiency or defective utilization of vitamin B12 or folate. 3  Do CBC, RBC indices, reticulocyte count, and peripheral smear.
vein. 1. Any of the blood vessels that carry blood toward the heart. Veins are thin-walled and contain valves that prevent the backflow of blood. All veins except the pulmonary vein (which returns to the heart from the lungs) carry blood having low levels of oxygen. 2.
Definition of vein for English Language Learners. : 1  any one of the tubes that carry blood from parts of the body back to the heart. : 2  any one of the thin lines that can be seen on the surface of a leaf or on the wing of an insect. : 3  a long, narrow opening in rock filled with gold, silver, etc.