https://www.livescience.com/52205-bladder-facts-function-disease.html
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The bladder is a round, bag-like organ that stores urine. It is located in the pelvic area, just below the kidneys and right behind the pelvic bone. While it is basically a fleshy storage tank, it is very complex in its design.
Size
The bladder is typically the size of a large grapefruit, according to the Weill Cornell Medical College. It can stretch much larger when needed, though, and shrinks back when it is empty. In fact, it can hold around 16 ounces (almost half a liter) of urine at one time for two to five hours comfortably, according to the U.S. National Library of Medicine (NLM).
It is normal to urinate around six to eight times in a 24-hour period, according to the Cleveland Clinic. More frequent trips to the bathroom may indicate a problem with the bladder, though it is common to urinate more as one ages.
Function
The bladder is connected to the kidneys by two long tubes called ureters. When urine is produced by the kidneys, it travels down the ureters to the bladder, where it is stored. The bladder has four layers.
From the inside out, the epithelium is the first layer on the inside of the bladder. It acts as a lining for the bladder. The lamina propria is the next layer. It consists of connective tissue, muscle and blood vessels. Wrapped around the lamina propria is the layer called the muscularis propria or detrusor muscle. According to John Hopkins Pathology, this layer consists of thick, smooth muscle bundles. The final, outer layer is the perivesical soft tissue, which is made up of fat, fibrous tissue and blood vessels.
The other parts of the bladder are located at the bottom of the sack. An opening at the bottom of the bladder is connected to the urethra. A circular, muscular sphincter pinches tight to keep the opening and the urethra from leaking urine.
When a person urinates, the detrusor muscles contract to squeeze the urine out of the bladder while the sphincter relaxes to open the opening of the bladder and urethra. The opening at the bottom of the bladder empties urine into the urethra, where it then empties from the body.
