The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters the bladder via the ureters and exits via the urethra. The typical adult human bladder will hold between 300 and (10.14 and ) before the urge to empty occurs, but can hold considerably more. The Latin phrase for "urinary bladder" is vesica urinaria, and the term vesical or prefix vesico - appear in connection with associated structures such as vesical veins. The modern Latin word for "bladder" – cystis – appears in associated terms such as cystitis (inflammation of the bladder). Structure In humans, the bladder is a hollow muscular organ situated at the base of the pelvis. In gross anatomy, the bladder can be divided into a broad , a body, an apex, and a neck. The apex (also called the vertex) is directed forward toward the upper part of the pubic symphysis, and from there the median umbilical ligament continues upward on the back of the anterior abdominal wall to the umbilicus. The peritoneum is carried by it from the apex on to the abdominal wall to form the middle umbilical fold. The neck of the bladder is the area at the base of the trigone that surrounds the internal urethral orifice that leads to the urethra. In males the neck of the urinary bladder is next to the prostate gland. The bladder has three openings. The two ureters enter the bladder at ureteric orifices, and the urethra enters at the trigone of the bladder. These ureteric openings have mucosal flaps in front of them that act as valves in preventing the backflow of urine into the ureters, known as vesicoureteral reflux. Between the two ureteric openings is a raised area of tissue called the interureteric crest. This makes the upper boundary of the trigone. The trigone is an area of smooth muscle that forms the floor of the bladder above the urethra. It is an area of smooth tissue for the easy flow of urine into and from this part of the bladder - in contrast to the irregular surface formed by the rugae. The walls of the bladder have a series of ridges, thick mucosal folds known as rugae that allow for the expansion of