blöðrunnar

The bladder, in Icelandic known as blöðran (genitive blöðrunnar), is a hollow, muscular organ in the lower urinary tract that stores urine before it is excreted. Located in the pelvic cavity, it expands as it fills and contracts to release urine during urination. The bladder wall consists of a mucosal lining with urothelium, a submucosa, and a thick layer of smooth muscle called the detrusor. The interior base forms the trigone, a triangular area defined by the two ureteral openings and the urethral outlet.

Functionally, the bladder serves as a urine reservoir that accommodates increasing volumes with only modest rises in pressure, thanks to its compliance. Micturition (urination) is regulated by a balance of autonomic and somatic pathways. Parasympathetic stimulation via the pelvic nerves induces detrusor contraction, while sympathetic inputs promote storage by relaxing the detrusor and tightening the internal urethral sphincter. Voluntary control of the external urethral sphincter, mediated by the pudendal nerve, allows deliberate initiation or delay of urination. Central regulation occurs in the brainstem and higher centers, coordinating automatic reflexes with voluntary control.

Developmentally, the bladder arises mainly from the upper portion of the urogenital sinus, with contributions from surrounding structures. The urothelium forms its lining, and the detrusor muscle develops into the contractile layer that drives voiding. Anatomical relations vary slightly between sexes due to nearby organs, but the basic structure and function are conserved.

Clinical significance includes conditions such as cystitis (bladder inflammation), overactive or underactive bladder, urinary incontinence, neurogenic bladder, and bladder cancer (often transitional cell carcinoma). Diagnosis and management rely on imaging, cystoscopy, urodynamics, and a range of medical or surgical treatments depending on the condition.