The Excretory Story

Excretory System (a. k. a. Urinary System)
Have you ever wondered why your body has to urinate? Where does that fluid come from? Why is it yellow? You'll learn the answers to these and more questions as you read our information about the excretory system. Video        Song
Parts of the Excretory System
 the kidneys: they contain filters that take the waste out of the blood
 the nephrons: remove the waste materials from blood and make urine
 the ureters: tubes that carry the urine to the bladder
 the bladder: a 'bag' that collects the urine
 the urethra: a tube that carries the urine out of the body

What does the excretory/urinary system do?

The kidneys, the bladder, and their tubes all work together to form the urinary system. Waste that's left over from breaking down food and your body's other activities naturally builds up in your blood. Your blood passes through your kidneys and when this happens, your kidneys act like a filter to clean the waste from your blood. Then they mix the waste with a little water to create urine. The urine goes to your bladder, which you empty when you urinate (pee). Kidneys and Nephrons

One of the main jobs of the kidneys is to filter the waste out of the blood. First, blood is carried to the kidneys by the renal artery. As the blood passes through the kidneys, it deposits used and unwanted water, minerals, and a nitrogen-rich molecule called urea. More than 1 million tiny filters inside the kidneys remove this waste. These filters, called nephrons, are so small you can see them only with a high-powered microscope.

Kidneys normally come in pairs. If you've ever seen a kidney bean, then you have a pretty good idea what the kidneys look like. Each kidney is about 5 inches long and about 3 inches wide.

 Ureter, Bladder and Urethra The waste that is collected combines with water (which is also filtered out of the kidneys) to make urine. As each kidney makes urine, the urine slides down a long tube called the ureter and collects in the bladder, a storage 'bag' that holds the urine. When the bladder is about halfway full, your body tells you to go to the bathroom. When you urinate, the urine goes from the bladder down another tube called the urethra and out of your body.

If the urinary system is healthy, the bladder can hold up to 16 ounces (2 cups) of urine comfortably for 2 to 5 hours.

What happens to the skeletal system when the kidneys fail? Click Here

More about the kidneys...
Although the kidneys are small organs by weight, they receive a huge amount -- 20 percent -- of the blood pumped by the heart. The large blood supply to your kidneys enables them to do the following tasks:
  • Regulate the composition of your blood: Keep the concentrations of various ions and other important substances constant; Keep the volume of water in your body constant; Remove wastes from your body (urea, ammonia, drugs, toxic substances); Keep the acid/base concentration of your blood constant
  • Help regulate your blood pressure
  • Stimulate the making of red blood cells
  • Maintain your body's calcium levels
More Information

Fun Facts
      1. Our blood passes through our kidney's 300 times a day.
2. our nephrons can clean our blood within 45 minutes.

3. Everyday our nephrons send 6 cups of urine to our bladder
          4. The average person pees about 3000 times a year.
          5. The average person poops about 305 pounds a year.
          6. The liver is rubbery to touch.

Why is urine yellow?
Some European alchemists in the middle ages apparently thought one possible reason was that there was gold in urine. This led to fruitless, and possibly quite disgusting, efforts to extract that gold.

The yellow color in urine is due to chemicals called urobilins. These are the breakdown products of the bile pigment bilirubin. Bilirubin is itself a breakdown product of the heme part of hemoglobin from worn-out red blood cells. In the bloodstream the Bilirubin is extracted by the kidneys where, converted to urobilins, it gives urine that familiar yellow tint.

Why does urine change colors?
You might notice that sometimes your urine is darker in color than other times. Remember, urine is made up of water plus the waste that is filtered out of the blood. If you don't take in a lot of fluids or if you're exercising and sweating a lot, your urine has less water in it and it appears darker. If you're drinking lots of fluids, the extra fluid comes out in your urine, and it will be lighter.

Beets turn your urine pink.


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