urinary bladder

Bladder Problems Find out the different types, and ways to overcome this common problem.

An elastic, muscular sac situated in the anterior part of the pelvic cavity in which urine collects before excretion.

A distensible, muscular sac in most vertebrates which serves as a reservoir for urine. Snakes, crocodilians, birds (with the exception of the ostrich), most lizards, and a few fish lack a urinary bladder. In these organisms, urine empties directly into the cloaca. The development of the urinary system is intimately associated with the development of the reproductive system. Three general types of urinary bladder are recognized among the vertebrates: tubal, cloacal, and allantoic. See also Urine.

Most fish possess tubal bladders, that is, enlargements of the mesonephric ducts. The cloacal bladder is found in monotremes, amphibians, and some dipnoans. There is no direct connection between the excretory ducts and this type of bladder. The bladder is an outpouching or diverticulum of the cloacal wall. The cloacal opening is closed by a sphincter muscle and the urine which seeps into the cloaca from the excretory ducts is forced into the bilobed bladder.

The allantoic bladder is derived from the ventral wall of the cloaca and possibly the allantoic diverticulum. The role of the allantois in the formation of this type of bladder, which is found in most mammals, the turtles, and those lizards which have a bladder, is questioned by some embryologists. See also Allantois.

The mammalian bladder is lined with a special epithelium composed of transitional cells. The muscular layer is composed of vertical, horizontal, and oblique fibers. The bladder drains through the urethra, the opening being controlled by a sphincter. Innervation is by the hypogastric sympathetic plexus and partly by parasympathetic fibers from the second and third sacral nerves. Stimulation of the parasympathetic causes the bladder muscle to contract and relaxes the internal sphincter. Micturition is a reflex act which is initiated voluntarily except in children. See also Parasympathetic nervous system; Sympathetic nervous system; Urinary system.

A saclike structure that stores urine until it can be passed out of the body through the urethra.

A distensible reservoir with muscular walls and a lining mucous membrane that lies in the ventral part of the pelvic cavity or abdomen (especially far forwards in the cat). It receives urine from the kidneys via the ureters and discharges urine to the exterior of the body via the urethra. Urine trickles into the bladder from the kidneys every few seconds, where it remains until voided. There is no anatomical sphincter of circular muscle at the bladder neck, urine retention being maintained by the elastic tissues of the urethra—a physiological sphincter. Voiding occurs when the detrusor muscle contracts forcing the urine out. In the housetrained companion animal urination is resisted even when the bladder is uncomfortably full.

• atonic u. b. — a condition marked by a dilated, poorly contracting urinary bladder without evidence of a lesion of the central nervous system.
• atonic neurogenic u. b. — neurogenic bladder caused by destruction of the sensory nerve fibers from the bladder to the spinal cord (lateral spinal tracts), marked by the absence of awareness of bladder filling and of the desire to void. This leads to overdistension of the bladder, and an abnormal amount of residual urine with a tendency toward overflow incontinence. Seen in degenerative and traumatic injury to the spinal cord, especially intervertebral disk herniation, in dogs and cats. Called also retention and overflow incontinence, paralytic bladder and sensory paralytic bladder.
• automatic u. b. — neurogenic bladder due to complete resection of the spinal cord above the sacral segments, marked by complete loss of micturition reflexes and bladder sensation, violent involuntary voiding, and an abnormal amount of residual urine. Called also reflex neurogenic bladder.
• autonomous u. b. — neurogenic bladder due to a lesion in the sacral portion of the spinal cord that interrupts the reflex arc that controls the bladder. The lesion may be in the cauda equina, conus medullaris, sacral roots or pelvic nerve. It is marked by loss of normal bladder sensation and reflex activity, inability to initiate urination normally, and stress incontinence.
• u. b. calculi — can cause cystitis arising from the traumatic injury to the bladder epithelium. The initial stage may be hematuria and greatly increased frequency of urination. Dysuria may also be evident. Secondary bacterial infection is a common sequel. See also urolithiasis.
• congenital u. b. rupture — there is gradually increasing abdominal distention soon after birth in the affected foal, which is almost always a male. Paracentesis reveals free urine in the peritoneal cavity. The tear is usually in the dorsal wall of the bladder.
• u. b. duplication — observed in dogs; the second bladder originates between the uterus and the urinary tract, or between the urinary tract and the rectum.
• u. b. ectropion — see urinary bladder eversion (below).
• u. b. eversion — turning inside out of the bladder; occurs in the mare, usually during labor.
• u. b. extroversion — failure of development of ventral abdominal wall so that the bladder and pelvic urethra are exposed.
• u. b. hypertrophy — due usually to long-standing partial obstruction of urinary flow.
• u. b. inflammation — see cystitis.
• irritable u. b. — a state of the bladder marked by increased frequency of contraction with associated desire to urinate.
• u. b. motility — degree of motor activity of the bladder muscle as determined by the spinal sympathetic nerve supplies.
• motor paralytic u. b. — neurogenic bladder due to impairment of the motor neurons or nerves controlling the bladder. The acute form is marked by painful distention and inability to initiate micturition; the chronic form is marked by difficulty in initiating micturition, straining, a decrease in the size and force of the stream, interrupted stream, and recurrent infection of the urinary tract.
• u. b. neck sling — a surgical procedure that increases proximal urethral pressure; used to treat some forms of urinary incontinence.
• u. b. neoplasia — see urinary bladder tumors (below).
• neurogenic u. b. — any condition of dysfunction of the urinary bladder caused by a lesion of the central or peripheral nervous system.
• u. b. papillary hyperplasia — resembles papillomatosis in cattle bladders; may cause obstruction.
• u. b. papilloma — warts attached to the inner wall of the urinary bladder.
• u. b. paralysis — is caused by a lesion, usually a space-occupying one or due to trauma, in the lumbosacral region of the cord. In the early stages the bladder remains distended and urine dribbles from it. A good flow of urine can be obtained by firm pressure on the bladder. There may be some return to an emptying function later, but the evacuation is seldom complete. Cystitis is the almost certain outcome.
• parturient u. b. prolapse — may follow rupture of the floor of the vagina during parturition in the mare; it can protrude from the vulva.
• u. b. reconstruction — a surgical procedure performed to correct urinary incontinence caused by urethral hypoplasia in female dogs and cats. The caudal bladder is reshaped to form ventral bladder tubal flaps as a cranial extension of the urethra.
• reflex neurogenic u. b. — automatic bladder.
• u. b. reflux — see vesicoureteral reflux.
• u. b. retroflexion — seen in male dogs with tenesmus, due usually to prostatic hyperplasia or constipation; resumes normal position after voiding unless retained in a perineal hernia with a kinked urethra.
• u. b. rupture — failure to relieve an obstruction of the urethra may result in distention of the bladder to the point that its circulation is impaired and rupture of the organ follows. The pain of distention disappears, to be followed by a gradual distention of the abdomen, and somnolence and depression of developing uremia. In dogs and cats, trauma is also a common cause. See also urethral perforation.
• sensory paralytic u. b. — atonic neurogenic bladder.
• u. b. torsion — a rare cause of complete anuria, bladder distention and eventual rupture.
• u. b. trigone — area of the bladder wall defined by imaginary lines joining the urethral orifice with the orifices of the ureters.
• u. b. tumors — rare in food animals except in cattle grazing bracken (see also enzootic hematuria). In dogs and cats they are usually carcinomas, or rarely adenomas, papillomas, leiomyomas or fibromas. Botryoid rhabdomyosarcomas characteristically occur in young St. Bernards and may arise from mesenchymal cells.
• u. b. uroliths — see urolithiasis.
• u. b.–vaginal prolapse — occurs occasionally in the cow as a complication of vaginal prolapse. The bladder is retrodeviated and the urethra kinked so that urine flow is obstructed.
• u. b. warts — see urinary bladder papilloma (above).

Urinary bladder
Urinary system.
Bladder
Latin	vesica urinaria
Gray's	subject #255 1227
Artery	Superior vesical artery Inferior vesical artery Umbilical artery Vaginal artery
Vein	Vesical venous plexus
Nerve	Vesical nervous plexus
Lymph	external iliac lymph nodes, internal iliac lymph nodes
Precursor	urogenital sinus
MeSH	Bladder
Dorlands/Elsevier	v_07/12855244

In anatomy, the urinary bladder is a hollow, muscular, and distensible (or elastic) organ that sits on the pelvic floor in mammals. It is the organ that collects urine excreted by the kidneys prior to disposal by urination. Urine enters the bladder via the ureters and exits via the urethra.

In males, the bladder is superior to the prostate, and separated from the rectum by the rectovesical excavation.

In females, the bladder is separated from the rectum by the rectouterine excavation, and it is separated from the uterus by the vesicouterine excavation.

Regions

• Trigone of urinary bladder: The ureters enter the bladder diagonally from its dorsolateral floor in an area called the trigone, which is a triangular shaped area on the postero-inferior wall of the bladder. The urethra exits at the lowest point of the triangle of the trigone.
• Apex: The Median umbilical ligament connects to the apex of the bladder.
• Neck: The Neck is connected to the pubic bone by the pubovesical ligament in women, and by the puboprostatic ligament in men.

Wall

The wall of the urinary bladder consists of three layers:

• Mucosa: in this instance transitional epithelium & lamina propria
• Detrusor muscle: consists of an inner and outer longitudinal layer and a middle circular layer of smooth muscle
• a fibrous adventitia and the visceral peritoneum: lie on superior surface

Detrusor muscle

The detrusor muscle is a layer of the urinary bladder wall made of smooth muscle fibers arranged in spiral, longitudinal, and circular bundles. When the bladder is stretched, this signals the parasympathetic nervous system to contract the detrusor muscle. This encourages the bladder to expel urine through the urethra.

For the urine to exit the bladder, both the autonomically controlled internal sphincter and the voluntarily controlled external sphincter must be opened. Problems with these muscles can lead to incontinence.

The urinary bladder usually holds 400–620 mL of urine, but it can hold twice this without rupturing if, for example, the outflow is obstructed.

The desire to urinate usually starts when the bladder reaches around 75% of its working volume. If the subject is distracted the desire can fade and return with more urgency as the bladder continues to fill.

See also

• Artificial bladder
• Bladder cancer
• Bladder sphincter dyssynergia, a condition in which the sufferer cannot coordinate relaxation of the urethra sphincter with the contraction of the bladder muscles
• Cystitis
• Hematuria, or presence of blood in the urine, is a reason to seek medical attention without delay, as it is a symptom of bladder cancer as well as bladder and kidney stones.
• Neurogenic bladder
• Ureterocele
• Urinary incontinence
• Urodynamics The study of the functional aspects of the detrusor muscle.
• Uvula of urinary bladder
• Vesicouretic reflux

External links

• Histology at KUMC epithel-epith09 "Urinary Bladder"
• Organology at UC Davis Urinary/mammal/bladder/bladder1 - "Mammal, bladder (LM, Medium)"
• Virtual Slidebox at Univ. Iowa Slide 445
• SUNY Labs 43:07-0100 - "The Female Pelvis: The Urinary bladder"
• SUNY Labs 44:04-0103 - "The Male Pelvis: The Urinary bladder"

Additional images

Structure of the penis	Organs of the female reproductive system.	Coronal section of pelvis, showing arrangement of fasciæ. Viewed from behind.	Dissection of side wall of pelvis showing sacral and pudendal plexuses. (Bladder visible at lower left.) |
The peritoneum of the male pelvis.	Median sagitta section of male pelvis.	Male pelvic organs seen from right side.	Median sagittal section of female pelvis.
The interior of bladder.	Vertical section of bladder wall.	Fundus of the bladder with the vesiculæ seminales.	Vertical section of bladder, penis, and urethra.
Female pelvis and its contents, seen from above and in front.	Topography of thoracic and abdominal viscera.	The bladder can be seen highlighted in yellow in the illustration.	Layers of the urinary bladder wall and cross section of the detrusor muscle.

Anatomy: urinary system
Kidneys • Ureters • Urinary bladder (Uvula)  • Urethral sphincters • Urethra

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