Urethra. Coloured scanning electron micrograph (SEM) showing the urethral epithelium of the penis. The urethra is the tube that carries urine from the bladder out of the body. The central lumen is covered in psuedostratified columnar epithelium covered in microvilli. The epithelial cells lining the lumen of the urethra are protective against the constant exposure to urine, seminal fluid and the external environment. A surrounding layer of connective tissue, the lamina propria plus layers of muscle tissue which contract to expel the urine are not shown here. Magnification: x1000 when printed 10cm wide.