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Human Excretory SystemHuman metabolic waste includes carbon dioxide, water, salts, and urea. These wastes pass from the cells into the blood and are carried to the excretory organs that expel them from the body.

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The lungs function in the excretion of carbon dioxide and water vapor, which are wastes from cellular respiration.

Lungs

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Liver•The liver gets rid of excess amino acids•The amino acids are converted into urea•The kidneys excrete the urea•The liver also breaks down old red blood cells

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Skin and Sweat Glands•Sweat glands excrete water, salts, and some urea.•These wastes diffuse from the capillaries into the sweat glands and then through ducts to pores on the surface of the skin.•This mixture of wastes and water is excreted by perspiration (sweat).•Perspiration functions primarily to regulate body temperature.•Evaporation of sweat cools the body and is another example of how the body maintains homeostasis.

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Kidney•Human kidneys remove urea from blood and regulate the concentrations of most substances found in body fluids. •Blood is carried to each kidney through an artery.•Within the kidney the artery divides into small balls of capillaries called glomeruli (glomerulus-singlular).•Each glomerulus is part of a nephron.•A nephron is the functional unit of a kidney.•There are over 1 million nephrons in a kidney.•A nephron is a glomerulus surrounded by a cup-shaped structure called Bowman’s Capsule.•The Bowman’s Capsule is surrounded by capillaries.•As blood flows through the glomerulus, water, salts, and glucose diffuse out into the Bowman’s Capsule. This is filtration. The fluid that is not diffused out is urine.

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Urine passes through the nephron tubules into the ureter.

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Dialysis:• When a set of kidneys don't do their

job, their owner has what is called a chronic kidney condition. Eventually, those kidneys may be considered failing. Much like a filter system hooked up to a pool, dialysis gives the kidneys a break by skimming waste for them.

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•Urine flows from each kidney into a tube called the ureter•The ureters carry the urine to the bladder, where it is stored temporarily•Urine is expelled from the bladder into a tube called the urethra•The urethra leads to the outside of the body