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
Bile acid synthesis is autoregulated by the enzyme: 
Select and explain. 
A. 7-Alpha hydroxylase, B. 11-alpha hydroxylase, C. Acetoacetyl-CoA thiolase, D. Desmosterol reductase reductase
A: 7-Alpha hydroxylase
Answer: A: 7-Alpha hydroxylase 
Explanation: 11-alpha hydroxylase Conves 11-deoxycoisol to 11-alpha coisol (the 11-alpha isomer of hydrocoisone) Bile acid synthesis is autoregulated by 7-hydroxylase, the initial enzyme in cholesterol degradation Other enzymes are involved in cholesterol biosynthesis. Ref: Harrison, E-18, P-2462.