Yet another type of cell, called delta cells, did not divide at all. The pancreas, an organ responsible for maintaining blood sugar levels and secreting digestive enzymes, also showed cells of varying ages. A small portion of the pancreas, known as the islets of Langerhans, appeared to the researchers as a puzzle of interconnected young and old cells. In stark contrast, the cells in the liver contained no long-lived proteins at all. In the cortex, the brain area that enables us to think, speak and be conscious, they are produced by a particular type of neural stem cell. This opens new doors for studying all cells, tissues and organs in normal and in disease states," says Mark Ellisman, Distinguished Professor of Neurosciences at UC San Diego's School of Medicine and co-leader of the study with Hetzer. View all the latest top news in the environmental sciences, or browse the topics below:.