This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gastrointestinal System, Subject name: Physiology
Which of the following is not a constituent of the succus entericus ? 
Select and explain. 
A. Erepsin, B. Enterokinase, C. Invease, D. Trypsin
D: Trypsin
Answer: D: Trypsin 
Explanation: Trypsin is formed from trypsinogen in the small intestine. It is not a constituent of the intestinal juice Intestinal juice or succus entericus- Small intestine-crypts of Lieberkuhn Enzymes present in the succus entericus are: Protein digestion: aminopeptidases ,carboxypeptidases. Erepsin: conves proteoses & peptones into amino acids Enterokinase: it conves trypsinogen (secreted by pancreas) into trypsin. Carbohydrate Digestion: Invease (sucrose conveed to glucose and fructose) Maltase, glucoamylase, and lactase