urinary bladder


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urinary bladder

a distensible membranous sac in which the urine excreted from the kidneys is stored

Urinary Bladder

 

the organ in which urine accumulates before being excreted from the body in certain invertebrates, in most vertebrates, and in man.

The urinary bladder takes several forms in invertebrates: rotifers have an unpaired bladder, oligochaetes and hirudineans (leeches) have multiple bladders, and higher crustaceans have paired bladders. In the vertebrates, the urinary bladder is usually unpaired. In female elasmobranchs, paired urinary bladders, or urinary sinuses, occur as widenings of the ureters; these sinuses merge in the posterior end of the body into an unpaired urinary sinus that opens into the cloaca. In most teleosts, the urinary bladder occurs as a widening of the ureters that merge into a terminal unpaired duct; this duct can have its own external orifice, or it can share an orifice with the terminal sections of the gonaducts in males of certain species.

In most terrestrial vertebrates, the urinary bladder is formed from the embryonic membrane called the allantois; amphibians are the only class in which the bladder arises from a ventral diverticulum of the cloaca. In amphibians, reptiles, and monotremes, the urinary bladder opens into the cloaca opposite the cloacal openings of the ureters. In metatherians (marsupials) and eutherians (placental mammals), the ureters empty directly into the urinary bladder, which in turn is usually connected to the exterior by the urethra. The ureters empty into the urogenital sinus only in the females of certain animals. Birds have no urinary bladder, and crocodilians and Serpentes (snakes) are the only reptiles in which this structure is rudimentary.

In man, the urinary bladder is a hollow, muscular organ situated in the lesser pelvis. Its average capacity is 500 cc, but when distended, it can hold much more urine. The bladder’s walls are lined with mucosa. Urine passes through the ureters from the kidneys and is deposited into the urinary bladder every 10–20 seconds. The neck of the urinary bladder opens into the first section of the urethra; ring-shaped muscles are located in the neck and form two sphincters that surround and close the urethra. Contraction of the sphincters prevents the urine from flowing out of the bladder. When the bladder is full, neural elements in the bladder wall elicit reflex contractions of the bladder muscles, as well as relaxation of the sphincteral muscles; these simultaneous processes result in the outflow of urine through the urethra.

In males, the posterior wall of the bladder is adjacent to the rectum; the neck of the bladder and the first section of the urethra are surrounded by the prostate gland. Diseases of the prostate can interfere with and even prevent urination. In females, the posterior wall of the bladder is adjacent to the uterine cervix and to the vagina.

The mucous membrane of the bladder is extremely susceptible to infection. The short length of the female urethra facilitates the spread of infections from the genitalia to the bladder. In males, the bladder can become infected because of an impairment in the excretory function, as occurs in diseases of the prostate.

urinary bladder

[′yu̇r·ə‚ner·ē ′blad·ər]
(anatomy)
A hollow organ which serves as a reservoir for urine.
References in periodicals archive ?
PRIMARY URINARY BLADDER TUMORS WITH GLANDULAR OR PSEUDOGLANDULAR FEATURES
Inflammatory myofibroblastic tumor of the urinary bladder managed by laparoscopic partial cystectomy.
For all tested oxylipids, mentioned above, standard curves were generated to enable precise measurement in mouse urinary bladder samples.
He did not desire for additional intervention for the carcinosarcoma of the urinary bladder. After the TURBT, he has been followed with cystoscopy and urine cytology at every three months as well as imaging diagnosis such as chest-abdominal-pelvic computed tomography scan approximately every 3 to 6 months' interval.
The incidence of the urinary bladder within sliding hernias is 5.6-12.5% and less than 1% among all hernias [1, 2].
[5] In view of rarity of bladder sarcoma, any malignant spindle cell tumour in urinary bladder of an adult is considered sarcomatous carcinoma until proven otherwise.
The urinary system comprises: two kidneys; renal calices and renal pelvis located in the renal sinuses into which urine is collected; ureters; urinary bladder; and urethra, through which urine is evacuated from the bladder [1].
Many formulas have been proposed over the years to calculate maximum urinary bladder capacity.
As summarized in this review, and using invasive urinary bladder cancer as an example, there is compelling evidence that pet dogs with specific forms of naturally occurring cancer can provide crucially needed relevant animal models to complement other models in preclinical research to help improve the success rate in human clinical trials [19, 20].

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