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
Release of proenzymes from the pancreatic acinar cells is accomplished by which of the following processes? 
Select and explain. 
A. Exocytosis, B. Transcytosis, C. Apoptosis, D. Endocytosis
A: Exocytosis
Answer: A: Exocytosis 
Explanation: The membrane of the zymogen granule fuses with the apical cell membrane to release the proenzymes synthesized by the pancreatic acinar cells into the acinar lumen. This is exocytosis. Transcytosis describes the transit through the cytoplasm of ceain materials, such as immunoglobulin A, from one surface of a cell to another. Such materials are taken up into vesicles by receptor-mediated endocytosis and are subsequently released by exocytosis. Endocytosis and phagocytosis are processes by which materials are taken into cells by invagination or other deformation of the plasma membrane. Apoptosis is programmed cell death, an impoant cellular process, but not related to secretion. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 2. Overview of Cellular Physiology in Medical Physiology. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.