The Anatomy of the Bladder

The bladder collects and expels urine from the body. As urine is made, it moves from the kidneys and down each ureter to the bladder. The bladder’s flexible walls stretch and contract to hold urine until it is expelled from the body through the urethra.

Anatomy

The bladder is a triangle-shaped, hollow organ. In men, it is bordered by the pubic bone at the front of the pelvis and the rectum at the back of the pelvis in the lower abdomen. In women, the bladder is bordered posteriorly by the uterus and vagina. The bladder is supported by ligaments and connects at the top to two ureters and at the bottom to the urethra.

Two sphincters—one internal and one external—at the base of the organ help keep urine in the bladder until nerve signals tell it to contract and release urine. A series of nerves controlled by the autonomic nervous system flow through the bladder, signaling when it is full and needs to be emptied.

Blood is supplied to the bladder at the top by the vesical artery and at the bottom by the vaginal or vesicular arteries. Smaller arteries—the inferior gluteal and obturator—also contribute. Blood drains from the bladder through the vesical veins, which flow to the iliac veins.

The urine that collects in the bladder is made in the kidneys from the body’s waste products and excess fluid. This fluid travels from the kidneys down two ureters, one descending from each kidney to the bladder. The bladder serves as a reservoir to hold the urine until a reflex or conscious action—depending on age and ability—releases it. With flexible walls that expand as it fills with urine, the bladder may extend up into the abdomen when it’s full.

Structure

The bladder itself is divided into four sections.

• Apex: This is the top part of the bladder. The apex points forward toward the abdominal wall.
• Fundus: The base of the bladder
• Body: The main portion of the bladder between the apex and fundus.
• Neck: The narrow part of the bladder that constricts and connects the organ to the urethra.

The bladder is a very flexible organ made up of smooth muscle. Crisscrossed bands of smooth muscle form the detrusor muscle, the primary muscle of the bladder. The detrusor muscle works with the urinary sphincter to hold in or push out urine from the bladder through the urethra during urination.

Function

The bladder is the organ that holds urine until it is ready to be released and then helps to expel it from the body. Ureters bring urine to the bladder from the kidneys, passing through an opening to the bladder called the ureterovesical junction.

As the bladder fills with urine, nerves send signals to the central nervous system. Somatic and autonomic nerves control the detrusor muscle, which contracts and relaxes along with sphincters in the urethra.

Urination, or micturition, is a combination of voluntary and involuntary actions regulated by the micturition center—a signal center located in the pons of the brainstem. As the bladder fills and the bladder wall is stretched, sensors send nerve impulses to the micturition center. The result is the relaxing and contracting of the detrusor muscle along with the external and internal urethral sphincters.

Infants and young children release urine on reflex, but learn to control the external sphincter and hold their urine longer during potty training.

Associated Conditions

A number of problems can arise both with the bladder or with urination.

• Bladder cancer: This is the most common cancer of the urinary system. A biopsy of bladder tissue is required to see how far the cancer has spread, and the spread will determine treatment. In severe cases, the bladder may be removed, with urine diverted to the bowel or collected with an exterior device.
• Bladder compliance: Poor bladder compliance can happen when there is more connective tissue than muscle in the bladder. This leads to problems with bladder pressure and volume and can cause damage to the upper urinary tract. This problem is most common in children.
• Cystitis: This is the term used to describe inflammation in the bladder. Inflammation can occur for a number of reasons, but most commonly from urinary tract or bladder infections. Cystitis can also be caused by other things, including certain drugs or medications. This is less common.
• Cystocele (prolapsed bladder): This is a problem that occurs when the ligaments and structures that hold the bladder in place get weak, and the bladder falls—or becomes prolapsed. The bladder can slip down, causing discomfort and other problems, such as bulging from the vagina in women. Exercises can help, but surgery and other more invasive measures may be needed in severe cases.
• Damage during pelvic surgery: Pelvic surgeries can cause damage to the areas around the bladder or the nerves and vessels that help it function. Surgeons need to approach this area carefully to avoid bladder damage or dysfunction.
• Detrusor areflexia: This happens when the bladder cannot contract and usually is the result of a neurological injury or malfunction. Diabetes is one disease that can lead to the breakdown of the nerves that control the detrusor muscle.
• Myogenic bladder: A myogenic bladder is a result of overfilling or overdistension of the bladder. When the bladder is filled too much, fibrotic tissue can form. This tissue replaces muscle fibers and makes the muscle less effective. Hypertrophy of the prostate in men and pelvic organ prolapse in women are common causes of myogenic bladder. The result of this condition is poor bladder emptying and possibly incontinence.
• Incontinence: Incontinence is the term used for leaking urine, or urine that is released accidentally. Urgency incontinence is a sudden urge to urinate, usually from weakness in the detrusor muscle. Functional incontinence happens when you feel the need to urinate, but can’t make it to a bathroom before voiding. Incontinence problems are common as people age, more so in women. Special exercises to strengthen the pelvic muscles and certain medications may be used to help incontinence.
• Infection: Bladder or urinary tract infections are common problems of the urinary tract. These infections are caused by bacteria that may result from poor emptying, bladder compliance problems, poor hygiene, and more.

Tests

There are a number of tests that can give you and your healthcare provider insight into your bladder health. The test your practitioner performs depends primarily on the problem you are having, but here are some common tests you might expect.

• Urinalysis: A urinalysis is one of the most basic and common tests to diagnose bladder problems. A urine sample is collected—either from urinating into a container or from a catheter—and urine is tested in a laboratory. This test can detect white blood cells, red blood cells, hemoglobin, bacteria, protein, and metabolic products that could signal different problems or an infection.
• Urine culture: Also collected from a voided sample or through a catheter, a urine culture will commonly be used to diagnose a bladder or urinary tract infection. The sample will be brought to a lab and monitored for growth and identification of bacterial or fungal pathogens. A urinary tract infection is usually treated with antibiotics. The culture should indicate the type of bacteria present, allowing your healthcare provider to tailor the antibiotics used to the specific type of bacteria that is present.
• Ultrasound/bladder scan: This non-invasive test uses sound waves to offer your practitioner a picture of what is going on inside our bladder. An ultrasound allows your healthcare provider to visualize internal organs. A bladder scan is another type of ultrasound and may be used to estimate the amount of urine that is present in your bladder.
• Cystoscopy: This is a procedure that is done to take an internal look at your bladder. A small catheter with a light, camera, and other tools is inserted into the bladder through the urethra. Your healthcare provider can see the inside of the bladder and take tissue samples, if needed.
• Imaging studies: Imaging studies provide a detailed view of the bladder and other organs in the pelvis. Techniques might include injecting iodine-based contrast material and performing an X-ray (intravenous pyelography) or a CT scan.