Virtsarakko

Virtsarakko, or the urinary bladder, is a hollow, expandable organ of the lower urinary tract that stores urine produced by the kidneys before excretion through the urethra. In humans it resides in the pelvic cavity; in males it lies anterior to the rectum, and in females it is positioned anterior to the uterus and vagina. The bladder wall consists of an inner mucosa with transitional epithelium (urothelium), a submucosal layer, and a muscular layer called the detrusor. The detrusor is made up of smooth muscle fibers arranged in interlacing bundles. The bladder is lined with mucosa that forms rugae when empty and smooths as it fills. The trigone is a triangular region formed by the two ureteric orifices and the internal urethral orifice.

The primary function of the virtsarakko is to store urine and regulate its timely micturition. Normal functional capacity is typically around 300–500 milliliters, with the urge to void commonly starting at lower volumes and comfortable capacity varying between individuals. Urine is expelled from the bladder during micturition, a process coordinated by the detrusor contraction and relaxation of the internal and external urethral sphincters.

Innervation and control involve autonomic and somatic pathways. Parasympathetic fibers (pelvic nerves) trigger detrusor contraction during voiding, while sympathetic fibers (hypogastric nerves) promote storage by relaxing the detrusor and constricting the internal sphincter. The external urethral sphincter is under somatic control via the pudendal nerve. Brain regions, notably the pontine micturition center, regulate the switch between storage and voiding.

Common conditions affecting the bladder include cystitis, neurogenic bladder disorders, overactive bladder, urinary retention, bladder outlet obstruction, and bladder cancer. Diagnostics may involve ultrasound, cystoscopy, urinalysis, and urodynamic testing.