The slide image displays a transverse section of the human bladder wall featuring transitional epithelium. What function does the tissue indicated by the arrow serve? Does it protect the bladder's inner lining, facilitate bladder contraction, provide structural support, or conduct nerve impulses in the bladder?

The tissue indicated by the arrow, transitional epithelium, protects the bladder's inner lining. Transitional epithelium is specialized to accommodate fluctuation in the volume of the liquid in an organ or tube; it can stretch without losing its barrier function. In the bladder, this epithelium stretches as the bladder fills and then recoils when it empties. Its primary role is to maintain a protective lining that prevents urine from seeping back into the body's tissue, which would cause damage and possible infection.

Extra: The urinary bladder is a hollow muscular organ that stores urine until it is excreted from the body. The wall of the bladder has several layers, and one of the key layers is the mucosa, which includes the transitional epithelium also known as urothelium. Due to the unique characteristics of transitional epithelium, which contains cells that can change shape, this layer is highly flexible. It differs from other types of epithelia, such as squamous or columnar, because transitional cells can become larger (more flat and irregular) or smaller (more cuboidal) depending on how much they need to stretch. This tissue is not responsible for bladder contraction—that is the role of the muscular layer, known as the detrusor muscle. It also does not provide structural support in the way connective tissues do, nor does it conduct nerve impulses; instead, nerve fibers present in the bladder wall have that role. The transitional epithelium is therefore essential for the unique function of the bladder in storing and releasing urine while protecting the surrounding tissues from the potentially harmful substances within the urine.