Loren G. Martin, a professor of physiology at Oklahoma State University, argues that the appendix has a function in fetuses and adults.[6] Endocrine cells have been found in the appendix of 11-week-old fetuses that contribute to "biological control (homeostatic) mechanisms." In adults, Martin argues that the appendix acts as a lymphatic organ. The appendix is experimentally verified as being rich in infection-fighting lymphoid cells, suggesting that it might play a role in the immune system. Zahid suggests that it plays a role in both manufacturing hormones in fetal development as well as functioning to "train" the immune system, exposing the body to antigens so that it can produce antibodies. In 2004, he noted that doctors in the previous decade had stopped removing the appendix during other surgical procedures as a routine precaution, because it can be successfully transplanted into the urinary tract to rebuild a sphincter muscle and reconstruct a functional bladder.