The urinary bladder is a temporary storage reservoir for urine. It is located in the pelvic cavity, posterior to the symphysis pubis, and below the parietal peritoneum. The size and shape of the urinary bladder varies with the amount of urine it contains and with the pressure it receives from surrounding organs.

The inner lining of the urinary bladder is a mucous membrane of transitional epithelium that is continuous with that in the ureters. When the bladder is empty, the mucosa has numerous folds called rugae. The rugae and transitional epithelium allow the bladder to expand as it fills.

The second layer in the walls is the submucosa, which supports the mucous membrane. It is composed of connective tissue with elastic fibers.

The next layer is the muscularis, which is composed of smooth muscle. The smooth muscle fibers are interwoven in all directions and, collectively, these are called the detrusor muscle. Contraction of this muscle expels urine from the bladder. On the superior surface, the outer layer of the bladder wall is parietal peritoneum. In all other regions, the outer layer is fibrous connective tissue.

There is a triangular area, called the trigone, formed by three openings in the floor of the urinary bladder. Two of the openings are from the ureters and form the base of the trigone. Small flaps of mucosa cover these openings and act as valves that allow urine to enter the bladder but prevent it from backing up from the bladder into the ureters. The third opening, at the apex of the trigone, is the opening into the urethra. A band of the detrusor muscle encircles this opening to form the internal urethral sphincter.

The urinary bladder collects urine from both ureters (Figure). The bladder lies anterior to the uterus in females, posterior to the pubic bone and anterior to the rectum. During late pregnancy, its capacity is reduced due to compression by the enlarging uterus, resulting in increased frequency of urination. In males, the anatomy is similar, minus the uterus, and with the addition of the prostate inferior to the bladder. The bladder is partially retroperitoneal (outside the peritoneal cavity) with its peritoneal-covered "dome" projecting into the abdomen when the bladder is distended with urine.

The bladder is a highly distensible organ comprised of irregular crisscrossing bands of smooth muscle collectively called the detrusor muscle. The interior surface is made of transitional cellular epithelium that is structurally suited for the large volume fluctuations of the bladder. When empty, it resembles columnar epithelia, but when stretched, it "transitions" (hence the name) to a squamous appearance (see Figure). Volumes in adults can range from nearly zero to 500-600 mL.

The detrusor muscle contracts with significant force in the young. The bladder's strength diminishes with age, but voluntary contractions of abdominal skeletal muscles can increase intra-abdominal pressure to promote more forceful bladder emptying. Such voluntary contraction is also used in forceful defecation and childbirth.

Micturition is a less-often used, but proper term for urination or voiding. It results from an interplay of involuntary and voluntary actions by the internal and external urethral sphincters. When bladder volume reaches about 150 mL, an urge to void is sensed but is easily overridden. Voluntary control of urination relies on consciously preventing relaxation of the external urethral sphincter to maintain urinary continence. As the bladder fills, subsequent urges become harder to ignore. Ultimately, voluntary constraint fails with resulting incontinence, which will occur as bladder volume approaches 300 to 400 mL.

Normal micturition is a result of stretch receptors in the bladder wall that transmit nerve impulses to the sacral region of the spinal cord to generate a spinal reflex. The resulting parasympathetic neural outflow causes contraction of the detrusor muscle and relaxation of the involuntary internal urethral sphincter. At the same time, the spinal cord inhibits somatic motor neurons, resulting in the relaxation of the skeletal muscle of the external urethral sphincter. The micturition reflex is active in infants but with maturity, children learn to override the reflex by asserting external sphincter control, thereby delaying voiding (potty training). This reflex may be preserved even in the face of spinal cord injury that results in paraplegia or quadriplegia. However, relaxation of the external sphincter may not be possible in all cases, and therefore, periodic catheterization may be necessary for bladder emptying.

Nerves involved in the control of urination include the hypogastric, pelvic, and pudendal (Figure). Voluntary micturition requires an intact spinal cord and functional pudendal nerve arising from the sacral micturition center. Since the external urinary sphincter is voluntary skeletal muscle, actions by cholinergic neurons maintain contraction (and thereby continence) during filling of the bladder. At the same time, sympathetic nervous activity via the hypogastric nerves suppresses contraction of the detrusor muscle. With further bladder stretch, afferent signals traveling over sacral pelvic nerves activate parasympathetic neurons. This activates efferent neurons to release acetylcholine at the neuromuscular junctions, producing detrusor contraction and bladder emptying.

Nerves Innervating the Urinary System

People rarely talk about bladder health, but everyone is affected by it. Located in the lower abdomen, the bladder is a hollow organ, much like a balloon, that stores urine. Urine contains waste and extra fluid left over after the body takes what it needs from what we eat and drink. Each day, adults pass about a quart and a half of urine through the bladder and out of the body.

As people get older, the bladder changes. The elastic bladder tissue may toughen and become less stretchy. A less flexible bladder cannot hold as much urine as before and might make you go to the bathroom more often. The bladder wall and pelvic floor muscles may weaken, making it harder to empty the bladder fully and causing urine to leak.

While you can’t control everything that affects your bladder, here are 15 steps you can take to keep it as healthy as possible:

1. Use the bathroom often and when needed. Try to urinate at least once every 3 to 4 hours. Holding urine in your bladder for too long can weaken your bladder muscles and make a bladder infection more likely.
2. Be in a relaxed position while urinating. Relaxing the muscles around the bladder will make it easier to empty the bladder. For women, hovering over the toilet seat may make it hard to relax, so it is best to sit on the toilet seat.
3. Take enough time to fully empty the bladder when urinating. Rushing when you urinate may not allow you to fully empty the bladder. If urine stays in the bladder too long, it can make a bladder infection more likely.
4. Wipe from front to back after using the toilet. Women should wipe from front to back to keep gut bacteria from getting into the urethra. This step is most important after a bowel movement.
5. Urinate after sex. Sexual activity can move bacteria from the bowel or vaginal cavity to the urethral opening. Both women and men should urinate shortly after sex to lower the risk of infection.
6. Do pelvic floor muscle exercises. Pelvic floor exercises, also known as Kegel exercises, help hold urine in the bladder. Daily exercises can strengthen these muscles, which can help keep urine from leaking when you sneeze, cough, lift, laugh, or have a sudden urge to urinate. These exercises also may help avoid infections by strengthening the muscles that help empty the bladder.
7. Wear cotton underwear and loose-fitting clothes. Wearing loose, cotton clothing will help keep the area around the urethra dry. Tight-fitting pants and nylon underwear can trap moisture and help bacteria grow.
8. Exercise regularly. Physical activity can help prevent bladder problems as well as constipation. It can also help maintain a healthy weight.
9. Keep a healthy weight. People who are overweight may be at higher risk for leaking urine. Making healthy food choices and being physically active can help keep a healthy weight.
10. Watch what you eat. Some people with bladder problems find that some foods and drinks, such as sodas, artificial sweeteners, spicy foods, citrus fruits and juices, and tomato-based foods, make bladder problems worse. Changing your diet may help you feel better.
11. Drink enough fluids, especially water. More than half of the human body is made up of water, so it is important that you are drinking enough. How much water you need can vary based on your size, activity level, and where you live. In general, drink enough fluids so that you need to urinate every few hours. Some people need to drink less water because of certain conditions, such as kidney failure or heart disease. Ask your health care provider how much fluid is healthy for you.
12. Limit alcohol and caffeine. For many people, drinking alcohol can make bladder problems worse. Caffeinated drinks (like coffee, tea, and most sodas) can bother the bladder and increase symptoms such as frequent or urgent need to urinate. Cutting down may help.
13. Avoid constipation. Too much stool built up in the colon, called constipation, can put pressure on the bladder and keep it from expanding the way it should. Eating plenty of high-fiber foods like whole grains, vegetables, and fruits), drinking enough water, and being physically active can help prevent this from happening.
14. Quit smoking. Bladder problems are more common among people who smoke. Smoking can also increase the risk for bladder cancer. If you smoke, take steps to quit.
15. Know your medications. Some medications may make it more likely for your bladder to leak urine. Medications that calm your nerves so you can sleep or relax may dull the nerves in the bladder, and you may not feel the urge to go to the bathroom.