Why Is Pee Yellow?

Chloe Effron
Chloe Effron

WHY? is our attempt to answer all the questions every little kid asks. Do you have a question? Send it to why@mentalfloss.com.

Your body is kind of like a house. You bring things into your body by eating, drinking, and breathing. But just like the things we bring home to real houses, we don’t need every part of what we take in. So there are leftovers, or garbage. And if you let garbage sit around in your house or your body for too long, it gets gross and can make you sick. Your body takes out the garbage by peeing and pooping. These two things are part of your body’s excretory system (ECKS-krih-tore-eee SISS-tem), which is just a fancy way of saying “trash removal.” If your body is healthy, when you look in the toilet you should see brown poop and yellow pee.

Clear, light yellow pee is a sign that your excretory system and the rest of your body are working right. If your pee, or urine (YER-inn), is not see-through, that might mean you are sick. Dark yellow urine usually means that you aren’t drinking enough water. On the other hand, really pale or colorless pee can mean you might be drinking too much water! 

Your blood is filtered through two small organs called kidneys (KID-knees). Remember the garbage we talked about earlier? The chemicals called toxins (TOCK-sins) are like garbage in your blood. Your kidneys act like a net, catching the toxins and other leftovers and turning them into pee.

One part of your blood is called hemoglobin (HEE-moh-gloh-bin). This is what makes your blood red. Hemoglobin goes through a lot of changes as it passes through your body. When it reaches your kidneys, it turns yellow thanks to a chemical called urobilin (yer-ah-BY-lin). Urobilin is kind of like food coloring. The more water you add, the lighter it will be. That's why, if you see dark yellow pee in the toilet, it's time to ask your mom or dad for a cup of water. 

To learn more about pee, check out this article from Kids Health. 

10 Smart Facts About Your Gut

Colorized scanning electron micrograph of E. coli, a common gut bacteria
Colorized scanning electron micrograph of E. coli, a common gut bacteria
National Institute of Allergy and Infectious Diseases, Flickr // CC BY 2.0

Gut feelings get all the press, but your gut may be more of a thinker than you know. Some scientists now consider it a second brain. While it won’t necessarily help you study for an exam or get a promotion, your gut can influence the chemistry of your mood, emotions, immune system, and long-term health. Research even suggests the gut can “learn” new tricks through conditioning. These powerful connections are part an emerging field of science called neurogastroenterology designed to study the gut-brain link. Here are 10 facts you may not know about your gut.

1. THE GUT DOESN'T NEED THE BRAIN'S INPUT. 

You might think of your gut as a rebel against authority. It doesn’t wait for your brain’s impulses to do the important work of digestion, because it doesn’t need to—it acts as its own “brain.” No other organ, not even the all-powerful heart, can pull that off.

2. THERE ARE MORE THAN 100 MILLION BRAIN CELLS IN YOUR GUT.

Your gut’s power to think for itself is no surprise; there are millions of neurons in its lengthy coils (9 meters of intestines, from esophagus to anus). That’s more neurons than are found in the spinal cord or peripheral nervous system.

3. YOUR GUT HAS ITS OWN NERVOUS SYSTEM.

The enteric nervous system—the controlling mechanism of digestion and elimination—is the overlord of your gut, and functions all on its own. Some scientists see it as part of the central nervous system, while others consider it its own entity. It likely evolved to give the gut the go-ahead when the “got to go” impulse strikes, without requiring the brain’s sign-off, particularly when you consider the helplessness of an infant with its brand-new brain.

4. THERE'S AN INFORMATION HIGHWAY FROM YOUR GUT TO YOUR BRAIN.

There’s one big visceral nerve embedded in your gut—the vagus nerve. Research has revealed that up to 90 percent of its fibers carry information from the gut to the brain, rather than the other way around. In other words, the brain interprets gut signals as emotions. So you really should trust your gut.

5. MOST OF YOUR SEROTONIN IS IN YOUR GUT.

Some 95 percent of your body’s serotonin, that marvelous mood molecule that antidepressant drugs like Prozac keep in your body, can be found in the gut. So, it’s no wonder that diet, medications, and antibiotics can wreak havoc on one’s mood.

6. A HEALTHY GUT MAY PROTECT YOUR BONES.

In a study of the serotonin-gut relationship, scientists discovered an unexpected link between the gut and the bones. Inhibiting the gut’s release of serotonin counteracted the bone-density reduction of osteoporosis in mice. This research is going into studies on new osteoporosis-fighting drugs.

7. RESEARCH SHOWS LINKS BETWEEN AUTISM AND HAVING FEWER STRAINS OF GUT BACTERIA. 

In as many as nine out of 10 cases, autistic people have common gut imbalances such as leaky gut syndrome, irritable bowel syndrome, and fewer strains of “good” bacteria. Research on mice is looking at possible treatments of some of the behavioral disorders of autism by balancing microbes in the guts, though many warn that such treatments can’t produce a “cure” for autism.

8. FOOD REALLY DOES AFFECT YOUR MOOD. 

Different foods, when introduced to the gut via feeding tubes, have been shown to change a person's moods without the person’s awareness of what they were "eating." Fat, for instance, increased feelings of happiness and pleasure (no surprise there) because appeared to trigger the release of dopamine—the brain’s natural opiate. Carbohydrate consumption stimulated the release of serotonin, the “feel good” neurotransmitter.

9. YOUR GUT IS YOUR BEST FRIEND IN COLD AND FLU SEASON.

Not only does your gut hold brain cells, it also houses the bulk of your immune cells—70 percent—in the form of gut associated lymphoid tissue, or GALT, which plays a huge part in killing and expelling pathogens. GALT and your gut microbiome—the trillions of bacteria that live, like an immense microbial universe, in your gut—work hard to help you get over what ails you. That’s all the more reason to be careful with the use of antibiotics, which wipe out the good bacteria along with the bad.

10. YOUR GUT CAN BECOME ADDICTED TO OPIATES.

Inside your gut are opiate receptors, which are also found in the brain. The gut is just as susceptible to addiction as the brain and may contribute to the intense difficulty some addicts have trying to kick the habit.

What Causes Hiccups?

iStock/damircudic
iStock/damircudic

The cause of hiccups depends on whom you ask. The ancient Greek physician Galen thought hiccups were violent emotions erupting from the body, while others thought they were a sign of liver inflammation. Today, evidence points to spasms in the diaphragm, the large muscle between the chest and abdomen that aids airflow during breathing. This involuntary contraction can be brought on by a number of things that might irritate the nerves that control the movement of the muscle. A full stomach, heavy boozing, rapid shifts in temperature either inside or outside of the stomach, and certain emotions like shock or excitement are all common culprits.

No matter the cause, the result is the same: The diaphragm spasms and causes us to take a quick breath. The sudden rush of air causes the epiglottis (the flap that protects the space between the vocal cords) to shut and interrupt the breath, which makes the familiar "hic" sound.

WHAT CURES THEM?

The best cure for hiccups also depends on the person you ask. Almost all cures are based on one of two principles: One type works its magic by overwhelming the vagus nerve with another sensation. The vagus nerve is a cranial nerve that innervates the stomach and conveys sensory information about the body's organs to the brain. When distracted by overwhelming information of another sort, it basically tells the brain that something more important has come up and the hiccuping should probably be stopped (vagus nerve stimulation is also used to control seizures in epileptics and treat drug-resistant cases of clinical depression). The other method for curing hiccups is to interfere with the breathing, increasing the amount of carbon dioxide in the blood, and causing the body to focus on getting rid of the of the CO2 and not making hiccups.

Swallowing a spoonful of sugar is probably the most commonly prescribed hiccup cure and falls into the first category. A teaspoon of sugar is usually enough to stimulate the vagus nerve and make the body forget all about the hiccups. Even ardent supporters of the sugar cure disagree if the sugar should be taken dry or washed down with water, though.

If this home remedy doesn't work, and your hiccups are both severe and persistent, you may need to bring out the big guns. For chronic cases like this, doctors sometimes use a cocktail of Reglan (a gastrointestinal stimulant) and Thorazine (an anti-psychotic with sedative properties) to quiet things down. In some cases that resist these drugs, Kemstro, an anti-spasmodic, is also used. Other doctors have used vagus nerve stimulators implanted in the upper chest of patients. The pacemaker-like devices send rhythmic bursts of electricity through the vagus nerve to the brain to keep the hiccup cycle in check.

Many people prefer home remedies to battle their hiccups, which may include holding your breath, gargling ice water, or breathing into a paper bag. While the same people will swear by the treatment they've been using all these years, there's no firm scientific consensus that any of them actually work. But if it helps you, isn't that all that matters?

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

An earlier version of this article appeared in 2012.

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