Collecting duct from a kidney. Coloured scanning electron micrograph (SEM) of a section through a collecting duct from a kidney. This section across the duct (a thin tube) shows a thick, folded wall surrounding a narrow central space (lumen). This collecting duct receives urine from the Loop of Henle (which is part of a kidney structure called a tubule). The urine is the product of the blood filtration that occurred elsewhere in the kidney. The Loop of Henle reabsorbs water and salts from the urine, increasing the concentration of waste products such as urea. Magnification: x12,500 when printed 10cm wide.