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The excretory system is a passive biological system that removes excess, unnecessary or dangerous materials from an organism, so as to help maintain homeostasis within the organism and prevent damage to the body. It is responsible for the elimination of the waste products of metabolism as well as other liquid and gaseous wastes. As most healthy functioning organs produce metabolic and other wastes, the entire organism depends on the function of the system; however, only the organs specifically for the excretion process are considered a part of the excretory system.

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Excretory functions

Removes metabolic and liquid toxin wastes as well as excess water from the organism.

Component organs

Skin

For full article see skin

Although commonly associated with the excretory system, this is incorrect. Excretion by definition is passive and deals with metabolic wastes as filtered by the kidneys. Though the sweat may contain a trace amount of metabolic wastes, sweating is an active process of secretion not excretion, specifically for temperature control and pheromone release and therefore its role as a part of the excretory system is minimal at best.

Lungs

For full article see lungs

The lungs, and gills of organisms constantly excrete gaseous wastes from the bloodstream as a regular part of respiration

Kidneys

For full article see kidney

The primary organs in the excretory system of vertebrates. (See protonephridia system for Platyhelminthes, metanephridia for Annelida, or the Malpighian tubes for insects and terrestrial arthropods.) The kidneys are placed on either side of the spinal column near the lower back. They are primarily responsible for filtering blood by removing nitrogenous wastes from metabolism, salts & other excess minerals and excess water.

Ureter

In human anatomy, the ureters are muscular ducts that propel urine from the kidneys to the urinary bladder. In the adult, the ureters are usually 25–30 cm (10–12 in) long.

In humans, the ureters arise from the renal pelvis on the medial aspect of each kidney before descending towards the bladder on the front of the psoas major muscle. The ureters cross the pelvic brim near the bifurcation of the iliac arteries (which they run over). This "pelviureteric junction" is a common site for the impaction of kidney stones (the other being the uteterovesical valve). The ureters run posteroinferiorly on the lateral walls of the pelvis. They then curve anteriormedially to enter the bladder through the back, at the vesicoureteric junction, running within the wall of the bladder for a few centimeters. The backflow of urine is prevented by valves known as ureterovesical valves. In the female, the ureters pass through the mesometrium on the way to the urinary bladder.

Urinary Bladder

In anatomy, your bladder produces 11.9 liters of fluid a day. The urinary bladder is the organ that collects urine excreted by the kidneys prior to disposal by urination. A hollow muscular, and distensible (or elastic) organ, the bladder sits on the pelvic floor. Urine enters the bladder via the ureters and exits via the urethra.

Embryologically, the bladder is derived from the urogenital sinus and, it is initially continuous with the allantois. In males, the base of the bladder lies between the rectum and the pubic symphysis. It is superior to the prostate, and separated from the rectum by the rectovesical excavation. In females, the bladder sits inferior to the uterus and anterior to the vagina. It is separated from the uterus by the vesicouterine excavation. In infants and young children, the urinary bladder is in the abdomen even when empty.

Urethra

In anatomy, the urethra (from Greek οὐρήθρα - ourethra) is a tube which connects the urinary bladder to the outside of the body. The urethra has an excretory function in both sexes to pass urine to the outside, and also a reproductive function in the male, as a passage for semen during sexual activity.

The external urethral sphincter is a striated muscle that allows voluntary control over urine

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