Urinary Bladder

The urinary bladder is a hollow organ that holds the urine, a fluid by-product excreted from the kidneys. Once enough urine is collected within the bladder, pressure initiates the process of urination which expels the urine from the system completely.

Formation and Orientation
Bladders are a common organ in the Animal Kingdom but are unique in characteristics to each species. Within the human species, there are some differences between female and male bladders. The first difference is that the female bladder has a smaller capacity than the males. The second difference between the two is the orientation within the pelvic cavity. In the female, the bladder is located on the pelvic floor below the uterus and in front of the vagina. In males, the bladder is located on the pelvic floor between the rectum and the pubic symphysis. When both are infants or young children, the bladder remains in the abdomen whether empty or full.

The bladder receives its motor function signals from both the sympathetic and parasympathetic nervous system. Abnormalities or damage to the nerve tract that runs from pelvis to scapula line can cause decreased bladder control or incontinence (uncontrolled urination).

The hollow organ receives urine through ureters from the kidney as excreted. The bladder can hold 300 -350 ml of urine. It can adapt to fluctuating levels due to the fact it is a muscular organ.

The walls of the bladder are made up of detrusor muscle. This smooth muscle is comprised of muscle fibers in spiral bundles as well as circular bundles. As those muscles are stretched, this sends out a signal to the parasympathetic nervous system to contract those muscles. This contraction prompts the bladder to empty though another ureter leading outside the body. Flow through the ureter is controlled by two sphincters. The internal sphincter is controlled autonomically with the external sphincter functions voluntarily.

Image Caption: Anatomy of Urinary bladder. Credit: U.S. National Cancer Institute’s Surveillance, Epidemiology and End Results (SEER) Program/Wikipedia

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