The objective of this chapter is to introduce the urinary system. Urinary system is unique by having the transitional epithelium, which is also known as urothelium. This chapter covers the kidney or nephros, ureter, and urinary bladder. Smooth muscle present in muscular layer of urinary bladder is called as detrusor muscle. Parasympathetic nerve supply contracts the urinary bladder and relaxes the sphincter during micturition. Sympathetic nerve supply dilates the urinary bladder and contracts the sphincter for temporary storage of urine in the bladder. Urinary Bladder has three layers following as mucosa, muscular layer, and either serosa or adventitia. Mucosal layer is lined by transitional epithelium, resting on connective tissue.