This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Ferritin biosynthesis is regulated by serum level of ? 
Select and explain. 
A. Ceruloplasmin, B. Hepcidin, C. Iron, D. Transferrin
C: Iron
Answer: C: Iron 
Explanation: Ans. is `c' i.e., Iron"The level of iron in plasma is sensed by specific iron regulatory proteins which control the rate offerritin synthesis and to maintain homeostasis" - Human physiologyHepicidin regulates absorption of iron. But, it is also according to the serum iron level. If serum iron is deficiem, hepacidin level falls and there is increased iron absorption.