You are no doubt already intimately familiar with the main product of the excretory system: urine. In response to your body's attempt to balance water and salts, and to get rid of wastes, urine is produced. If not removed by your body, wastes become toxic. Your excretory system also includes your lungs and skin. Various kidney diseases and bacterial infections can cause excretory system problems.
Kidneys
Kidneys are the main component of your excretory system. Kidneys are composed of an outer layer called the cortex and an inner core called the medulla. Each of these layers are composed of repeating units of tubules called nephrons. The tops of nephrons make up the cortex, while the bottoms make up the medulla. Each nephron has a closely associated blood supply that exchanges water and solutes with the nephron. Materials are continually exchanged within the tubule as the urine flows into a collecting duct. The collecting duct gathers urine from several nephrons where the exchange continues. Eventually all collecting ducts meet at the renal pelvis which collects urine from all the ducts. The urine is then finally eliminated from the body.
Lungs and Skin
Lungs and skin are also part of your excretory system. Blood traveling through the veins to the lungs delivers carbon dioxide and other waste gases, where they exit the body during respiration. Sweat and dead cells are removed from your body through the skin.
Interaction with Circulatory System
Your excretory system works closely with both your circulatory and endocrine systems. Blood circulating through your body passes through one of your two kidneys where urea, uric acid and water are removed. Most of the water is actually put back into your system later on, depending on the needs of your cells.
Interaction with Endocrine System
Your excretory system is controlled and regulated by your endocrine or hormone system. Kidney function is constantly monitored and changed to match the needs of your cells. When you drink too much water, your endocrine system releases hormones signaling your body to produce more urine. When you become dehydrated, hormones, such as the antidiuretic hormone ADH, are released signaling your kidneys to produce less urine, allowing you to keep more water in your body. Diuretics such as alcohol or caffeine interfere with ADH production, making you feel the need to urinate more frequently.
Diseases
Kidney diseases seriously affect the excretory system. Malfunctioning kidneys can affect blood pressure, and increase toxins to dangerous levels in your body. The accumulation of urea can slowly poison you.
Dialysis is a treatment for people with malfunctioning kidneys using a machine to filter the blood the kidneys cannot. While dialysis treatment attempts to mimic the ability to regulate ions and water levels in your body, most people on dialysis are simply using it as a temporary measure while awaiting a kidney transplant.
Other diseases of the excretory system include nephritis, the symptoms of which include bloody urine, severely decreased urine output and swelling or puffiness of your body. Nephrosis, another kidney disease, is characterized by a "foamy"-looking urine containing a large amount of protein, as well as a generalized swelling of the body, including puffy eyelids.
Urinary tract infections (UTI) and bladder infections also affect the excretory system. These are usually caused by bacteria and are typically treated with antibiotics. Kidney stones wreck havoc with the excretory system as well. Most stones are calcium-based, but a few are caused by buildup of magnesium ammonium phosphate, uric acid or cystine. Stone sizes range from microscopic to extremely large, some filling the entire renal pelvis area. When the stone is passed down the ureter, it can be extremely painful and the affected kidney may temporarily become nonfunctional.
Misconceptions
Excretion should not be confused with elimination. Elimination is the system by which your body removes solid wastes, such as feces.
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