Collagen in the urinary bladder. Coloured Scanning Electron Micrograph (SEM) of collagen fibrils found in the bladder. Here, thin fibrils (pink) are packed together into bundles, and these bundles are then spirally twisted. Collagen is a protein whose fibrils are relatively inelastic but have a high tensile strength. In the urinary bladder they are found in the submucosa layer of the bladder wall. This bladder is empty and the collagen bundles are compacted. As the bladder swells, the bundles untwist until they reach full extension. Collagen prevents overstretching of the bladder. Magnification: x3,900 at 6x7cm size. Magnification: x5,000 at 4x5 inch size.