Urinary bladder an organ that regularly stores a hyperosmotic concentration of urine. It therefore is relatively impermeable and has multiple epithelial layers. The urinary bladder of the cetaceans (whales and dolphins) is proportionally smaller than that of land-dwelling mammals. In the whole class of Aves there is no urinary bladder per se. Although all birds have kidneys, the ureters open directly into a cloaca which serves as a reservoir for urine, fecal matter, and eggs. In crustaceans, the urinary bladder consists of two sets of lateral and central lobes. Urinary bladder The urinary bladder is a hollow muscular organ in humans and
Urinary bladder that protects the cells beneath it from urine, the urothelium (a form of transitional epithelium), a basement membrane, and the lamina propria. The mucosal lining also offers a urothelial barrier against the passing of infections. The detrusor muscle is a layer of the urinary bladder wall made of smooth muscle fibers arranged in spiral, longitudinal, and circular bundles. Stretch receptors in the bladder signal the parasympathetic nervous system to stimulate the muscarinic receptors in the detrusor to contract the muscle when the bladder is extended. This encourages the bladder to expel urine through the urethra. The main receptor activated is