Urinary System

The urinary system is a group of organs that clean your blood and remove liquid waste from your body. It is made up of two kidneys, two thin tubes called ureters, the bladder, and another tube called the urethra. Together, these parts make and get rid of urine, also known as pee. The urinary system runs all day and night without you having to think about it.

The kidneys are the stars of the system. You have two of them, one on each side of your spine, just above your waist. Each kidney is about the size of your fist and shaped like a bean. Inside each kidney are about a million tiny filters called nephrons. Blood flows in through a large blood vessel, and the nephrons sort out what your body needs from what it does not.

Your body keeps the good stuff, like water, sugar, and salts. The waste left over becomes urine. Most of this waste is something called urea. Urea is made when your body breaks down the protein in food like meat, beans, and milk. If urea built up in your blood, it would make you very sick.

Once the kidneys make urine, it travels down the two ureters. The ureters are about ten inches long, roughly the length of a pencil. They squeeze gently to push the urine into the bladder. The bladder is a stretchy bag of muscle that sits in the lower belly. It can hold about two cups of urine before it sends a signal to your brain that says, "time to find a bathroom." When you go, muscles squeeze the bladder and urine leaves the body through the urethra.

Urine is mostly water, around 95 percent. The rest is urea, salts, and other waste. The color tells you something useful. Pale yellow usually means you are drinking enough water. Dark yellow often means you need to drink more. Doctors can also test urine to look for signs of illness, which is why a "urine sample" is part of many checkups.

People can live a healthy life with just one kidney, which is why kidney donation is possible. When both kidneys fail, a person needs a machine called a dialysis machine to clean their blood, or a kidney transplant. Drinking water, eating well, and not holding it in for too long all help keep this quiet, hardworking system in good shape.