A muscular, saclike structure in the lower pelvis that serves as a reservoir for the URINE the KIDNEYS produce. In women the bladder is in front of and slightly below the UTERUS. During PREGNANCY the expanding uterus limits the bladder’s ability to expand, accounting for the URINARY FREQUENCY common in pregnancy’s last trimester. In men the bladder is in front of the RECTUM, with the PROSTATE GLAND encircling the first segment of the URETHRA as it exits the bladder. Swelling of the prostate gland, such as typically occurs with advancing age, as in BENIGN PROSTATIC HYPERPLASIA (BPH), can constrict the flow of urine through the urethra in a man, accounting for symptoms such as urinary frequency and dribbling.
Three layers of tissue form the bladder. The outermost and innermost layers are membranous, the outer being a continuation of the peritoneum that lines the abdominal cavity and the inner being mucous-secreting epithelium. The bladder’s middle layer is smooth MUSCLE called the detrusor muscle that itself has three layers, the fibers of each running differently. The outer muscle fibers run longitudinally (lengthwise), the middle muscle fibers form patterns of circles that ultimately culminate in the sphincter muscle that encloses the bladder’s neck, and the inner muscle fibers run laterally (crosswise). Together these muscle layers allow the bladder to expand to accommodate the urine draining from the kidneys and also to contract, in coordination with relaxation of the urethral sphincter, to expel urine from the bladder through the urethra.
The ureters drain urine from the kidneys into the bladder; the urethra drains urine from the bladder to the outside of the body. One URETER, a narrow tubelike structure, drops from each kidney and enters the back wall of the bladder near its midline. Urine drips continuously from the ureters into the bladder. The urethra, a somewhat muscular tube, carries urine from the bladder to outside the body. When empty the bladder is about the size of a large lemon; when filled to its capacity of about 500 milliliters (32 to 34 ounces) the bladder can reach the size of a small cantaloupe. As the bladder expands it extends upward into the abdominal cavity.
URINATION, the process of expelling urine from the bladder (also called micturition), is an involuntary function that becomes an action of learned control. NEURON sensors in the muscle fibers of the bladder wall send NERVE signals to the sacral portion of the SPINAL CORD. This activates the micturition REFLEX, which sends nerve signals via the spinal cord to micturition centers in the BRAIN. These centers activate nerve impulses that cause the urethral sphincter to relax and the detrusor muscle to begin a series of wavelike contractions. These involuntary actions create the urge to urinate, experienced as a sensation of pressure.
Learning to control the pubococcygeal muscle, which forms the floor of the pelvis, serves to override the micturition reflex for a period of time. Relaxing the pubococcygeal muscle and contracting the abdominal muscles synchronize with the involuntary responses of the micturition reflex, and urination occurs. Most children acquire the developmental ability, a blend of conscious effort and neuromuscular maturity, to learn to control urination (commonly called bladder control) between the ages of three and five. With advanced age this control may diminish, a consequence of a weakened urethral sphincter, neurologic conditions, and other factors.
|HEALTH CONDITIONS THAT CAN AFFECT THE BLADDER|
|BLADDER CANCER||BLADDER EXSTROPHY|
|URINARY INCONTINENCE||URINARY RETENTION|
|URINARY TRACT INFECTION (UTI)||URINARY URGENCY|
For further discussion of the bladder within the context of the urinary system’s structure and function please see the overview section “The Urinary System.”
See also AGING, URINARY SYSTEM CHANGES THAT OCCUR WITH; BLADDER CATHETERIZATION; CYSTOSCOPY; FECAL INCONTINENCE; KEGEL EXERCISES.
Resource: Facts On File Encyclopedia Of Health And Medicine
At birth the structures of the urinary system are fully developed and function under the automatic control of the NERVOUS SYSTEM. The newborn’s KIDNEYS filter BLOOD and make URINE. The BLADDER collects the urine and, when it fills to a point that triggers the micturition REFLEX, it empties to drain urine via the URETHRA to outside the body. Voluntary
Excessive excretion of ALBUMIN, a form of protein, into the URINE. Albuminuria, also called proteinuria, typically indicates kidney conditions that affect the glomeruli (the tubular structures within the KIDNEYS that filter wastes and excess water from the BLOOD to excrete in the urine). Such conditions include GLOMERULONEPHRITIS, GLOMERULOSCLEROSIS,
What is Alport’s Syndrome An inherited genetic disorder in which one, two, or three mutations occur in the GENE that encodes type IV collagen formations, also called basement membranes. The mutations affect up to three of the six protein chains (alpha-3, alpha-4, and alpha-5) that make up type IV collagen, which is a foundation for a number of
What is Anuria and Definition Anuria - The failure to produce URINE. Numerous circumstances can result in anuria, from severe DEHYDRATION and severe HYPOTENSION (low BLOOD PRESSURE) to END-STAGE RENAL DISEASE (ESRD) and RENAL FAILURE. Anuria requires prompt medical evaluation to determine and remedy the underlying cause. Without such correction, waste
What is Bladder and Definition A muscular, saclike structure in the lower pelvis that serves as a reservoir for the URINE the KIDNEYS produce. In women the bladder is in front of and slightly below the UTERUS. During PREGNANCY the expanding uterus limits the bladder’s ability to expand, accounting for the URINARY FREQUENCY common in pregnancy’s
What is Uremia and Definition Uremia is a serious condition in which nitrogenbased toxins such as urea and creatinine, the primary waste products of METABOLISM, accumulate in the BLOOD because the KIDNEYS are unable to filter them out and pass them from the body via the URINE. Uremia indicates RENAL FAILURE. Urologists sometimes use the term azotemia to
Ureter, in a human organism, is a muscular tube, fairly thick and rigid, that leads URINE from the kidney to the urinary BLADDER. Both of the two tubular structures arise from the renal pelvis and collect the urine from the kidney’s collecting tubules. Both ureters with the inner diameter of 3 or 4 millimeters exit the kidney at the hilus. Then, the
A narrow, somewhat muscular tube that carries URINE from the BLADDER to the outside of the body. The point of exit is the urinary or urethral meatus. The urethral sphincter MUSCLE at the base of the bladder controls the release of urine into the urethra. Once the urethral sphincter relaxes to let urine pass, the urine flows to the outside of the body until
What is Urethral Stricture Narrowing of the URETHRA, impeding the passage of URINE from the BLADDER to the outside of the body. Urethral stricture may be congenital (present at birth) or acquired such as through scarring resulting from repeated URETHRITIS, BLADDER CATHETERIZATION, and other irritations to the urethra. BENIGN PROSTATIC HYPERPLASIA (BPH) and
What is Urethritis and Definition INFLAMMATION of an URETER. INFECTION, typically a sexually transmitted disease (STD), is the most common cause of urethritis though urethritis may occur as a result of inflammation or irritation from trauma such as occurs with BLADDER CATHETERIZATION or CYSTOSCOPY. Traumatic urethritis improves rapidly when the source of