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. Digestion starts in your mouth when you chew, and spit makes food easy to swallow. Your stomach makes acid that helps break food down, and it churns the food with its juices into a thick mix called chyme.

The stomach is a holding chamber. You can eat much faster than the small intestine can digest and absorb, so the stomach passes food on only a little at a time, and it is usually empty within 2 to 4 hours after a meal. So food waits in the stomach for a while before it moves on. The small intestine takes nutrients from digested food into the blood. It takes in water as well as nutrients. Tiny bumps called villi, about 20 to 40 in every square millimeter, give it a huge surface for taking in nutrients.

Poop is usually some shade of brown, and bile is the reason. Bile itself is a yellowish-green fluid. The liver makes bile, a digestive juice that helps break down fats. The liver sends a yellow substance called bilirubin out in bile, and bilirubin helps give poop its brown color. Bile, a fluid made by your liver, gives poop its brown color. So the color of poop is a trace of the work that the liver does.

The large intestine takes water out of leftover food and turns it into solid poop. The rectum is the last part of the large intestine. It holds poop until it is time to go, and when it is full, nerves tell you that you need to poop. These parts are at the very end of the long tube that began at your mouth, and the muscles of the gut squeeze the leftovers along.

Poop can be odd in other ways, too. Wombats are the only animals known to make poop shaped like cubes, as of November 2026. The cube shape forms inside the intestine, not at the anus. A wombat's intestine is stiff in some parts and soft in others, and this uneven stretchiness helps mold the poop into cubes. Researchers studied intestines from wombats that had died to learn how the cubes form. Whale poop floats, so researchers who spot it can scoop it up with a net.

You have two kidneys, one on each side of your back, just under your ribs. They clean your blood, taking out waste and extra water to make pee. The kidney filter lets water and small wastes through but keeps blood cells and large proteins in the blood. It sorts by particle size. Each day the kidneys filter well over a hundred quarts of fluid out of the blood, but about 99 percent of it goes back into the blood, and only 1 to 2 quarts become pee.

Pale yellow pee usually means you have plenty of water in your body. Dark yellow pee usually means there is less water in it, and you may need a drink. When you are dehydrated, pee is darker and more concentrated and may smell of ammonia, which comes from urea. The yellow color comes from a pigment called urochrome, also called urobilin. Foods such as beets, berries and carrots can change the color of pee, too.

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 with pee. Stretch receptors in the bladder wall send nerve signals to the brain as the bladder fills, and when your bladder gets full, it sends a message to your brain that you need to find a toilet. To pee, the bladder wall squeezes and pushes urine through the urethra and out of the body.

Your body makes pee and poop on its own, but you get to choose when to go to the bathroom. Two ring-shaped muscles called anal sphincters keep the anus closed, and you can choose when to open the outer one. If anything ever hurts when you go to the toilet, tell a grown-up. Wetting the bed or having an accident is common in children and 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, so nobody needs to feel bad about it.

Words to know

• villi: tiny gut bumps
• bile: liver fluid
• bilirubin: yellow bile pigment
• ureters: kidney-bladder tubes
• sphincters: ring-shaped muscles