The urinary system, also known as the renal system, is devised as a drainage system to remove waste from the body, regulate blood volume and pressure, and regulate both electrolytes (a chemical that dissociates in water and becomes positively or negatively charged) and blood pH levels. The renal system includes the kidneys, ureters, bladder, and urethra.
The main structure of the urinary system is the kidney, which is a bean-shaped structure located near the middle of the back that filters waste from the bloodstream. It also plays an important part in water, electrolyte, and blood pressure regulation and helps maintain normal pH, calcium, and red blood cell levels. The subsequent waste, in the form of urine, is then ported away from the kidneys through the ureters, which transport the urine toward the urinary bladder. Within the bladder, the urine is stored until it can be voided from the body during urination (also called micturition). The male and female urinary systems are similar, differing only in the length of the urethra. In females, the urethra measures approximately 2 cm to 4 cm in length; in males, the urethra is approximately 18 cm long. Also, in males, the urinary tract is the passageway for both urine and semen.
The kidneys are two organs that look similar to the shape of a kidney bean. When proteins and other macromolecules are catabolized by the body, excess nitrogen must be removed. If not, nitrogenous wastes form ammonia, which is toxic to body tissues and raises blood pH levels. Ammonia is converted to urea in the liver. Urea is transported to the kidneys via the bloodstream, and the kidneys then remove urea from the body. In addition to urea, the kidneys also process other nitrogenous wastes, including uric acid and creatinine. The elimination of these wastes plus excretion of excess water and salt together form urine. One to two liters of urine are produced by the average adult every day.
Once urine has exited the kidneys, it enters the ureters, which are long tubes that channel the urine to the bladder. The ureters, which are approximately 27.9 centimeters long and made up of smooth muscle tissues, carry the urine to the bladder in a rhythmic, wavelike action, referred to as peristalsis.
The urinary bladder is a hollow organ also comprised of muscle tissue that stores the urine until it can be expelled from the body. The bladder sits within the pelvis. Sphincter, or purse-string–like, muscles are located at the opening of the bladder. They help to control the flow of urine and avoid accidental leakage. In a healthy urinary system, the bladder can hold approximately two cups of urine for about five hours.Upon urination the brain will signal the bladder to tighten and squeeze the urine out, sending it through the urethra to be expelled from the body. The urethra carries urine from the bladder and out of the body.