What is the Bladder?

(Source: Cancer Research UK)

The bladder, or urinary bladder, is a hollow muscular organ that stores urine from the kidneys before it is disposed of through urination. Urine enters the bladder via the ureters and exits via the urethra. The typical human bladder will hold between 10 and 16 fluid ounces before the urge to urinate occurs, but can hold considerably more. It is situated at the base of the pelvis in humans.

The bladder can be divided into four main components: a broad fundus (the large, hollow part of an organ farthest from an opening), a body, an apex, and a neck. (In males the neck of the urinary bladder is next to the prostate gland). The walls of the bladder have a series of ridges, thick mucosal folds known as rugae (pronounced roo-gay), that allow the bladder to expand and hold more fluid. The bladder's walls relax and expand to store urine, and contract and flatten to empty urine through the urethra.

​Urine, excreted by the kidneys, collects in the bladder because of drainage from two ureters, before disposal by urination. Urine leaves the bladder via the urethra, a single muscular tube ending in an opening called the urinary meatus, where it exits the body. Urination involves coordinated muscle changes involving a reflex based in the spine, with other, higher inputs coming from the brain. It is important to note that, while sperm and urine both pass through the urethra, they can't come out at the same time.

Nuts & Bolts: What is the Bladder?

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Key terms:

Kidneys - a pair of organs in the abdomen that remove waste and extra water from the blood (as urine) and help keep chemicals (such as sodium, potassium, and calcium) balanced in the body.

Pelvis - the large bony structure near the base of the spine to which the hind limbs or legs are attached in humans and many other vertebrates.

Prostate - a gland surrounding the neck of the bladder in male mammals and releasing prostatic fluid.

Ureter - the duct by which urine passes from the kidney to the bladder or cloaca.

Urethra - the duct by which urine is conveyed out of the body from the bladder, and which in male vertebrates also conveys semen.

​Urinate - discharge urine; pass water.

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Sources/References:

Boron, Walter F.; Boulpaep, Emile L. (2016). Medical Physiology. 3: Elsevier Health Sciences. p. 738. ISBN 9781455733286. Retrieved 1 June 2016.

Walker-Smith, John; Murch, Simon (1999). Cardozo, Linda (ed.). Diseases of the Small Intestine in Childhood (4 ed.). CRC Press. p. 16. ISBN 9781901865059. Retrieved 1 June 2016.

Netter, Frank H. (2014). Atlas of Human Anatomy Including Student Consult Interactive Ancillaries and Guides (6th ed.). Philadelphia, Penn.: W B Saunders Co. pp. 346–8. ISBN 978-14557-0418-7.

Standring, Susan, ed. (2016). "Urinary bladder". Gray's anatomy : the anatomical basis of clinical practice (41st ed.). Philadelphia. pp. 1255–1261. ISBN 9780702052309. OCLC 920806541.

Barrett, Kim E; Barman, Susan M; Yuan, Jason X-J; Brooks, Heddwen (2019). "37. Renal function & Micturition: The Bladder". Ganong's review of medical physiology (26th ed.). New York. pp. 681–682. ISBN 9781260122404. OCLC 1076268769.

Page 12 in: Uday Patel (2010). Imaging and Urodynamics of the Lower Urinary Tract. Springer Science & Business Media. ISBN 9781848828360.

​Young, Barbara; O'Dowd, Geraldine; Woodford, Phillip (2013). "Urinary system". Wheater's functional histology: a text and colour atlas (6th ed.). Philadelphia: Elsevier. pp. 315–7. ISBN 9780702047473.

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