Urinary bladder

"Bladder" redirects here. For other uses, see bladder (disambiguation).
Urinary bladder

1. Human urinary system: 2. Kidney, 3. Renal pelvis, 4. Ureter, 5. Urinary bladder, 6. Urethra. (Left side with frontal section)
7. Adrenal gland
Vessels: 8. Renal artery and vein, 9. Inferior vena cava, 10. Abdominal aorta, 11. Common iliac artery and vein
With transparency: 12. Liver, 13. Large intestine, 14. Pelvis
Details
Precursor urogenital sinus
System Urinary system
Artery Superior vesical artery
Inferior vesical artery
Umbilical artery
Vaginal artery
Vein Vesical venous plexus
Nerve Vesical nervous plexus
Identifiers
Latin vesica urinaria
MeSH A05.810.161
Dorlands
/Elsevier		 Urinary bladder
TA A08.3.01.001
FMA 15900

Anatomical terminology

The urinary bladder is a hollow muscular organ that collects urine from 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. There is no exact measurement for the volume of the human bladder, but different sources mention 500 mL (~17 oz) to 1000 mL (~34 oz).[2]

Structure

Anatomy of the female bladder, showing transitional epithelium as well as part of the wall in a histological cut-out.

The bladder is a hollow muscular organ situated at the base of the pelvis. Urine collects in the bladder from the two ureters, which open into the bladder at its back and connect to the kidneys. Urine leaves the bladder via the urethra, a single muscular tube which ends in the urethral orifice. Anatomically, the bladder is divided into a fundus at the top, two ureteric orifices, and an opening for the urethra which surrounds the trigone of the bladder. In men, the prostate gland lies outside the opening for the urethra.

The bladder is situated below the peritoneal cavity near the pelvic floor. In men, it lies in front of the rectum, separated by a space. In women, it lies in front of the uterus.

Histology

The urinary bladder is lined with transitional epithelium. It does not produce mucus.[3] The internal lining of the bladder wall is termed the urothelium and lamina propria, and this layer is thought to regulate some aspects of the overall bladder physiology in response to stimuli such as stretch during filling.[4]

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. A meta-analysis on the effect of voiding position on urodynamics in males found that sitting down allows for improved contraction of the detrusor muscle.[5]

Lymphatic supply

The fundus of the bladder is lymphatically drained by the external iliac lymph nodes.

Nerve supply

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.[6]

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.[6]

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.[7]

Development

The human urinary bladder is derived 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.[8]

Function

Main article: Urination

Urine, excreted by the kidneys, collects in the bladder before disposal by urination. 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.[9]

Clinical significance

Urinary bladder (black butterfly-like shape) and hyperplastic prostate (BPH) visualized by Medical ultrasonography technique.

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,[10] though there can be other causes of urination frequency. Though both urinary frequency and volumes have been shown to have a circadian rhythm, meaning day and night cycles,[11] it is not entirely clear how these are disturbed in the overactive bladder.

A diverticulum of the bladder

Disorders of or related to the bladder include:

Other animals

Bladders occur throughout much of the animal kingdom, but are very diverse in form and in some cases are not homologous with the urinary bladder in humans. The pig bladder is very similar to the human bladder.

Additional images

See also

References

  1. ↑ Howard A. Werman, Keith J. Karren.
  2. ↑ Volume of a Human Bladder
  3. ↑ Chin T, Liu , Tsai H, Wei C (September 2007). "Vaginal reconstruction using urinary bladder flap in a patient with cloacal malformation". Journal of Pediatric Surgery 42 (9): 1612–5. doi:10.1016/j.jpedsurg.2007.04.040. PMID 17848259.
  4. ↑ Moro C, Uchiyama J, Chess-Williams R (December 2011). "Urothelial/lamina propria spontaneous activity and the role of M3 muscarinic receptors in mediating rate responses to stretch and carbachol". Urology. 76 (6): 1442.e9–15. doi:10.1016/j.urology.2011.08.039. PMID 22001099.
  5. ↑ de Jong, Y; Pinckaers, JH; Ten Brinck, RM; Lycklama À Nijeholt, AA; Dekkers, OM (2014). "Urinating Standing versus Sitting: Position Is of Influence in Men with Prostate Enlargement. A Systematic Review and Meta-Analysis.". PLOS ONE 9 (7): e101320. doi:10.1371/journal.pone.0101320. PMC 4106761. PMID 25051345.
  6. 1 2 Moore, Keith; Anne Agur (2007). Essential Clinical Anatomy, Third Edition. Lippincott Williams & Wilkins. pp. 227–228. ISBN 0-7817-6274-X.
  7. ↑ "Urinary Incontinence - Causes". NHS. Retrieved 2013-08-21.
  8. ↑ Moore, Keith L.; Dalley, Arthur F (2006). Clinically Oriented Anatomy (5th ed.). Lippincott Williams & Wilkins.
  9. ↑ Marieb, Mallatt. "23". Human Anatomy (5th ed.). Pearson International. p. 700.
  10. ↑ "Overactive Bladder". Cornell Medical College. Retrieved 2013-08-21.
  11. ↑ Negoro, Hiromitsu (2012). "Involvement of urinary bladder Connexin43 and the circadian clock in coordination of diurnal micturition rhythm". doi:10.1038/ncomms1812.

External links

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