þvagblöðrun

The þvagblöðra, or urinary bladder, is a hollow, muscular organ in humans and other animals that stores urine. It is part of the urinary system and its primary function is to collect urine produced by the kidneys, hold it until it is convenient to eliminate, and then expel it from the body through the urethra. The bladder is located in the pelvis, behind the pubic bone.

The wall of the þvagblöðra is composed of smooth muscle tissue called the detrusor muscle. This muscle is capable of significant stretching to accommodate varying volumes of urine. When the bladder is empty, it is collapsed, but as it fills, it expands. The inner lining of the bladder is a specialized type of epithelium called transitional epithelium, which can also stretch and change shape.

Nerve signals from the brain control the process of urination, also known as micturition. As the bladder fills, stretch receptors in its walls send signals to the brain, creating the sensation of needing to urinate. When it's time to urinate, the detrusor muscle contracts, and the internal and external urethral sphincters relax, allowing urine to flow out of the bladder and through the urethra. The capacity of the human bladder typically ranges from 400 to 600 milliliters.