Two things leave your body when you use the toilet, and they are poop and pee. They are not the same thing. Poop is the leftover parts of food that your body cannot use. Pee is waste and extra water that your body does not need. Food goes in at your mouth, and poop comes out at your anus, at the other end of one long tube. Food travels along that tube from one end to the other, and it is a long way to go.

The trip starts in your mouth. Digestion starts in your mouth when you chew, and spit makes food easy to swallow. Next the food reaches your stomach. Your stomach makes acid that helps break food down. The stomach also churns the food with its juices into a thick mix called chyme. Chyme is the mix that the stomach sends on down the tube, and it goes a little at a time.

After a meal, the stomach slowly empties its contents into the small intestine, and it is usually empty within 2 to 4 hours. In the small intestine, your body takes nutrients from the food it has broken down and moves them into your blood, so they can go where they are needed. Nutrients are the parts of food that your body can use. The leftover parts that your body cannot use are what will become poop later on.

Muscles in the walls of your gut squeeze food and poop along, and the squeezing is called peristalsis. Near the end of the trip comes the large intestine. It takes water out of leftover food and turns it into solid poop. The last stop is the rectum, which holds the poop until it is time to go. When the rectum is full, the nerves send a signal, and you know that you need to poop.

Poop is usually some shade of brown. Where does that brown come from? Your liver makes bile, a digestive juice that helps break down fats. Bile itself is a yellowish-green fluid. Even so, bile gives poop its brown color. So the brown color starts with a fluid made by your liver, and it gets that color long before it ever reaches the toilet.

Now follow the pee. You have two kidneys, one on each side of your back, just under your ribs. They clean your blood by taking out waste and extra water to make pee. Blood goes into each kidney through the renal artery, and it comes out cleaned through the renal vein. The waste and the extra water that were taken out of the blood are what become pee.

Two thin tubes called ureters carry pee from the kidneys to the bladder. Your bladder is like a stretchy balloon that gets bigger as it fills up. When your bladder gets full, it sends a message to your brain that you need to find a toilet. The urethra is the tube that carries it from the bladder out of the body.

The yellow color in pee comes from a pigment called urochrome, also called urobilin. How yellow it looks depends on how much urobilin is in it and how much water is in it. Pale yellow means you have plenty of water in your body. Dark yellow means there is less water in it, and you may need a drink. Foods such as beets, berries and carrots can change the color of pee.

Your body makes pee and poop on its own, but you get to choose when to go to the bathroom. If anything ever hurts when you go, tell a grown-up, and do it right away. Wetting the bed or having an accident is common in children, and it is almost never caused by laziness or poor toilet training. Most children learn to control their bladder between ages 2 and 4, each in their own time.

Words to know

• bile: liver fluid
• chyme: thick food mix
• urobilin: yellow pigment
• pigment: coloring
• peristalsis: squeezing along