Excretory system

The excretory system is a passive biological system that removes excess, unnecessary 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 urine and as a component of sweat and exhalation. 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.

As it involves several functions that are only superficially related, it is not usually used in more formal classifications of anatomy or function.

Kidneys
The kidneys are bean shaped organs which are present in each of the sides of the Vertebral column in the abdominal cavity. Humans have two kidneys and each kidney is supplied with blood from the Renal artery. Kidney removes the nitrogenous wastes from the blood such as urea and salts and excess water are also removed from the blood and excrete them in the form of urine. This is done by the help of millions of Nephrons present in the kidney. The filtrated blood is carried away from the kidneys by the Renal vein (or kidney vein). The urine from the kidney is collected by the Ureter (or excretory tubes), one from each kidney, and is passed to the Urinary bladder. Urinary bladder collects and stores the urine until urination. The urine collected in the bladder is passed into the external environment from the body through an opening called Urethra.

Liver
The liver detoxifies and breaks down chemicals, poisons and other toxins that enter the body. For example, the liver transforms ammonia (which is poisonous) into urea (which is then filtered by the kidney into urine). The liver also produces bile, and the body uses bile to breakdown fats into usable fats and unusable waste.

Bile
After bile is produced in the liver, it is stored in the gall bladder. It is then secreted within the small intestine where it helps to break down ethanol, fats and other acidic wastes including ammonia, into harmless substances.

Large intestine
The large intestine collects waste from throughout the body. It extracts any remaining usable water and then removes solid waste. At about 10 feet long, it transports the wastes through the tubes to be excreted.

Skin
Skin extracts sweat through sweat glands throughout the body. This helps to remove additional wastes. Such as excess urine. Furthermore, the sweat, helped by salt, evaporates and helps to keep the body cool when it is warm.

Eccrine
Like sweat glands, eccrine glands allow excess water to leave the body.The majority of eccerine glands are located mainly on the forehead, the bottoms of the feet, and the palms, although the glands are everywhere throughout the body. They help the body to maintain temperature control.

Skin
Sweat glands in the skin secrete a fluid waste called sweat or perspiration; however, its primary functions are temperature control and pheromone release. Therefore, its role as a part of the excretory system is minimal. Sweating also maintains the level of salt in the body.

Lungs
One of the main functions of the lungs is to diffuse gaseous wastes, such as carbon dioxide, from the bloodstream as a normal part of respiration.

Kidneys
The kidney's primary function is the elimination of waste from the bloodstream by production of urine. They perform several homeostatic functions such as:-


 * 1) Maintain volume of extracellular fluid
 * 2) Maintain ionic balance in extracellular fluid
 * 3) Maintain pH and osmotic concentration of the extracellular fluid.
 * 4) Excrete toxic metabolic by-products such as urea, ammonia, and uric acid.

The way the kidneys do this is with nephrons. There are over 1 million nephrons in each kidney, these nephrons act as filters inside the kidneys. The kidneys filter needed materials and waste, the needed materials go back into the bloodstream, and unneeded materials becomes urine and is gotten rid of.

In some cases, excess wastes crystallize as kidney stones. They grow and can become a painful irritant that may require surgery or ultrasound treatments. Some stones are small enough to be forced into the urethra.

Ureter
Main article: Ureters

The ureters are muscular ducts that propel urine from the kidneys to the urinary bladder. In the human 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 posteriorly 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 bladder.

Urinary bladder
The urinary bladder is the organ that collects waste excreted by the kidneys prior to disposal by urination. It is a hollow muscular, and distensible (or elastic) organ, and 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 human 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 (from Greek - ourethra) is a tube which connects the urinary bladder to the outside of the body. In humans, the urethra has an excretory function in both genders to pass.

Urine formation
Within the kidney, blood first passes through the afferent artery to the capillary formation called a glomerulus and is collected in the Bowman's capsule - found in the liver, which filters the blood from its contents&mdash;primarily food and wastes. After the filtration process, the blood then returns to collect the food nutrients it needs, while the wastes pass into the collecting duct, to the renal pelvis, and to the ureter, and are then secreted out of the body via the urinary bladder.