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
In the intestines, Paneth cells secrete: 
Select and explain. 
A. Mucous, B. 5-HT, C. Defensins, D. Electrolytes
C: Defensins
Answer: C: Defensins 
Explanation: Paneth cells: These cells provide host defense mechanism against microbes in the small intestine. These cells function like the neutrophils. On exposure to foreign micro-organisms, the Paneth cells secrete several antimicrobial substances(DEFENSINS) into the lumen of the crypt. Thus, they provide a gastrointestinal barrier to protect the stem cells. (Stem cells are located within the small intestinal crypts; these cells serve to constantly replenish epithelial cells that die and are lost from the villi).