出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/07/04 00:02:24」(JST)
| Urinary bladder | |
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1. Human urinary system: 2. Kidney, 3. Renal pelvis, 4. Ureter, 5. Urinary bladder, 6. Urethra. (Left side with frontal section)
7. Adrenal gland |
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Female bladder (visible due to lack of prostate), showing transitional epithelium as well as part of the wall in a histological cut-out.
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| Latin | vesica urinaria |
| Gray's | [1] |
| System | Urinary system |
| Artery | Superior vesical artery Inferior vesical artery |
| Vein | Vesical venous plexus |
| Nerve | Vesical nervous plexus |
| Precursor | urogenital sinus |
| MeSH | Bladder |
| Dorlands /Elsevier |
Urinary bladder |
The urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. A hollow[1] muscular, and distensible (or elastic) organ, the bladder sits on the pelvic floor. Urine enters the bladder via the ureters and exits via the urethra. It's almost impossible to give an exact measurement for the volume of the human bladder, but different sources mention 500 mL (~17 oz) to 1000 mL (~34 oz).[2]
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.
The fundus of the bladder is the base of the bladder, formed by the posterior wall. It is lymphatically drained by the external iliac lymph nodes. The peritoneum lies superior to the fundus.
The bladder receives motor innervation from both sympathetic fibers, most of which arise from the hypogastric plexuses and nerves, and parasympathetic fibers, which come from the pelvic splanchnic nerves and the inferior hypogastric plexus.[3]
Sensation from the bladder is transmitted to the central nervous system (CNS) via general visceral afferent fibers (GVA). GVA fibers on the superior surface follow the course of the sympathetic efferent nerves back to the CNS, while GVA fibers on the inferior portion of the bladder follow the course of the parasympathetic efferents.[3]
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.[4]
Since the urinary bladder has a transitional epithelium, it does not produce mucus.[5]
The human urinary bladder is derived in embryo from the urogenital sinus and, it is initially continuous with the allantois. In males, the base of the bladder lies between the rectum and the pubic symphysis. It is superior to the prostate, and separated from the rectum by the rectovesical excavation. In females, the bladder sits inferior to the uterus and anterior to the vagina; thus, its maximum capacity is lower than in males. It is separated from the uterus by the vesicouterine excavation. In infants and young children, the urinary bladder is in the abdomen even when empty.[6]
Bladders occur throughout much of the animal kingdom, but are very diverse in form[further explanation needed] and in some cases are not homologous with the urinary bladder in humans.[citation needed]
The urinary bladder usually holds 300-350 ml of urine. As urine accumulates, the rugae flatten and the wall of the bladder thins as it stretches, allowing the bladder to store larger amounts of urine without a significant rise in internal pressure.[7]
Frequent urination can be due to excessive urine production, small bladder capacity, irritability or incomplete emptying. Males with an enlarged prostate urinate more frequently. One definition of overactive bladder is when a person urinates more than eight times per day,[8] though there can be other causes of urination frequency.[citation needed] Though both urinary frequency and volumes have been shown to have a circadian rhythm, meaning day and night cycles,[9] it is not entirely clear how these are disturbed in the overactive bladder.
Disorders of or related to the bladder include:
| This section contains a gallery of images. Galleries containing indiscriminate images of the article subject are discouraged; please improve or remove the section accordingly, moving freely licensed images to Wikimedia Commons if not already hosted there. |
Dissection of side wall of pelvis showing sacral and pudendal plexuses. (Bladder visible at lower left.)
Median sagittal section of female pelvis.
The peritoneum of the male pelvis.
Median sagitta section of male pelvis.
Vertical section of bladder, penis, and urethra.
The interior of bladder.
Vertical section of bladder wall.
Fundus of the bladder with the vesiculæ seminales.
Female pelvis and its contents, seen from above and in front.
The bladder can be seen highlighted in yellow in the illustration.
Layers of the urinary bladder wall and cross section of the detrusor muscle.
Urinary bladder (black butterfly-like shape) and hyperplastic prostate (BPH) visualized by Medical ultrasonography technique.
| Wikimedia Commons has media related to Urinary bladder. |
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| リンク元 | 「膀胱」 |
| 女性 | 上部 | 移行上皮 |
| 下部 | 非角化重層扁平上皮 | |
| 男性 | 前立腺部 | 移行上皮 |
| 隔膜部 | 重層円柱上皮 多列円柱上皮 | |
| 海綿体部 | 重層円柱上皮 多列円柱上皮 非角化重層扁平上皮 |
| 男性 | 女性 | |
| 膀胱の前上部 | 上膀胱動脈 | 上膀胱動脈 |
| 膀胱底、膀胱頚 | 下膀胱動脈 | 膣動脈 |