This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
All the following drugs agent by intracellular receptors except 
Select and explain. 
A. Thyroid hormones, B. Vitamin D, C. Insulin, D. Steroids
C: Insulin
Answer: C: Insulin 
Explanation: Intracellular receptors are receptors located inside the cell rather than on its cell membrane. Insulin is not an intracellular receptors Ref-Katzung 11/e p730