Colon Crypts (IMAGE) University of North Carolina Health Care Caption This is a picture of a schematic of colonic epithelial tissue. Crypt units are pointed down, flat surface faces center of the gut tube. Stem cells are red, progenitor cells are pink, differentiated cells are grey, blue and green. Yellow cells are stem cell niche cells. Lumenal surface is above crypts. Credit Scott Magness, PhD, UNC School of Medicine Usage Restrictions credit properly License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.