JOHN BAVOSI / SCIENCE PHOTO LIBRARY JOHN BAVOSI / SCIENCE PHOTO LIBRARY
Urinary bladder wall. Artwork of a section through the wall of a healthy human bladder. The cells lining the inner wall (urinary epithelium, top) are highly modified, giving them a cobble- stone appearance. The cells are impermeable to urine, preventing toxins from being absorbed. This also prevents water being drawn out of the cells due to the urine's higher salt concentration. The folds in this layer enable the bladder to deal with the large changes in the volume of urine that occur as it fills and empties. The layers below the urinary epithelium contain smooth muscle and elastic fibres, which also aid the bladder's size changes.
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