Burp, rumble, toot! How your lunch can turn you into a one-person band.

DID YOU KNOW?

* The world record for the loudest burp registers 118.1 decibels. The noise--emitted by Paul Hunn of London, England, on April 5, 2001--was more intense than the sound of a power mower (107 db) or a power saw (110 db).

* At any given time, a person totes approximately 200 milliliters (0.36 pint) of gas in his or her gut. And each day, the average person expels between 600 ml (1 pint) and 2 liters (3.5 pints) of flatulent gas.

CRITICAL THINKING:

* Although burping is a normal function of the digestive system, it can be embarrassing at times. What are some eating habits that you alight change to reduce burps?

CROSS-CURRICULAR CONNECTIONS:

ART: To help students remember the parts of the digestive system, have them create a clay model of the system.

RESOURCES

* For more information about gas in the digestive tract, visit this Web site from the National Digestive Diseases Information Clearinghouse: http://digestive.niddk.nih.gov/ ddiseases/pubs/gas/

* For a fun Web site about the body systems, check out: http://yucky.kids.discovery.com/flash/body/

You gulp a can of soda, and a few minutes later ... BURP! You feel hungry, and hear a noise from your stomach ... GRUMBLE! You eat the cafeteria's spicy bean dip, and ... well, you know what happens.

"You may laugh, but everyone's body makes noise," says David Sachar, a gastroenterologist, or doctor of the stomach and intestines, at Mount Sinai School of Medicine in New York City.

And even though your body's orchestra may make funny sounds, the noise is a sign that your gastrointestinal system (body system that breaks down food for use) is doing its job--digesting food and getting rid of waste (see Nuts & Bolts, p. 17). That's because behind all the rumbles and toots is one ingredient your body doesn't need: gas.

Lets take a tour of your insides to find out where all the gas comes from, and why it leaves in such noisy ways.

EATING AIR

It's lunchtime. You and your friends are munching on sandwiches and chips, laughing about the corny joke your science teacher told today. But along with the turkey on rye, something else is sliding down your throat that will exit later as a gassy burst: "Burps are mostly swallowed air," says Sachar.

Drinking bubbly drinks, talking, chewing gum, and eating too quickly can cause you to swallow a lot of air. That air gets pushed down your esophagus (eh-SAH-fah-gus), a tube that connects your throat to your stomach. The air fills your stomach and, soon, there's no room left in your blown-up tummy. How to get rid of the air? Some of it gels squeezed back out of your mouth, causing eructation (ih-rehk-TAY-shun), a fancy word for burping.

No matter how hard you may try, it's tough to muffle the noise. That's because When you eat, a tiny flap of tissue, called the epiglottis (eh-pih-GLAH-tis), flops over to cover your windpipe and prevent swallowed food from traveling into your lungs. Between bites, the tissue flops back over your esophagus to let you breathe. As a burp is born, the air pushes past the epiglottis. This causes the flap to vibrate and move the air in your throat, creating sound waves. These vibrating energy waves give a burp its noisy blast.

Even if you avoid soda and put the gum away, the occasional burp will surely still slip by. Just be sure to cover your mouth to be polite.

RUMBLE IN YOUR TUMMY

Lunch was great, but by the time 3 p.m. hits, all you can think about is an after-school snack. You hear a grumble from below reminding you that it's lime to eat. Turns out, those gurgles don't really come from your stomach.

Inside your stomach, chemicals called enzymes break down your food into its smallest parts, called nutrients. These enzymes can't completely digest all your food. So after about four hours of sitting in your stomach, the leftover, partially digested mush moves on to the small intestine, where even more digestion will take place.

The small intestine is a snaking, narrow tube roughly 6 meters (20 feet) long. To shuttle the mush through this tube, muscles around the intestine ripple with wavelike contractions, called peristalsis (per-eh-STAHL-sehs). As the slushy food and leftover gas squish through the intestines, you may hear grumbles called borborygmi (bor-buh-RIG-my).

Even if your intestines are talking, you don't need to grab a snack right away. The gurgles and grumbles are just signals that your stomach has emptied enough to make room for the next meal. "It is just your body telling you that it's ready for food," says Sachar.

A MIGHT WIND

So far, the sounds of gas have been echoing throughout your digestive system. But there's more to come!

Inside your large intestine are trillions of microbes. For these tiny organisms, the leftover food that survived the trip through your stomach and small intestine is an all-you-can-eat buffet. The microbes contain specialized enzymes that are able to break down and digest the remaining food. They metabolize some of the nutrients, converting them into the energy they need to grow.

However, as the microbes feast, they produce waste in the form of--you guessed it--gas. The gas builds up and pushes through the rest of your intestine. Then, out of your body it goes--toot!

MEGABLAST

Foods like beans, broccoli, and milk products are especially hard for your stomach and small intestine to digest. That's because they are made of tough sugar molecules, or particles of two or more atoms joined together. Foods with these compounds make it to your large intestine without breaking down much.

So when you eat a bean burrito topped with extra cheese, the microbes get a supersize meal. The extra gas they produce powers through your large intestine, causing more flatulence (FLA-chuh-lense) than usual. "The stronger the wind, the louder the result," says Alan Baird, a physiologist (scientist who studies the body's vital functions) at the University College Dublin in Ireland.

The gas you blast is a combination of nitrogen, oxygen, carbon dioxide, hydrogen, and methane--the same gases that make up the air you breathe. So why does your released gas sometimes smell? When certain types of foods are digested, they produce a tiny amount of hydrogen sulfide, the same gas that gives rotten eggs their stinky scent.

PARDON ME

There is very little you can do to prevent gas. No matter what, you will pass gas approximately 14 times a day. And you'll burp a couple of times too.

Yes, body noises can be embarrassing. But your gastrointestinal system can't function without them. Just be sure that when a little gas does sneak past, you say, "excuse me." Then, thank your body for a job well done!

Nuts & Bolts

The digestive system has three main functions. First, it breaks down food into nutrients that the body can use. Then, those nutrients pass through the wall of your digestive system and into your blood to be carried throughout your entire body. Lastly, any foods that were too tough to be digested and absorbed pass from your body as waste. Many organs are involved in the complex process of digestion.

1 MOUTH: Chewing mechanically breaks down food into pieces, Watery saliva breaks down food chemically.

2 ESOPHAGUS: Powerful muscle contractions move food down this tube toward the stomach, then through the stomach and intestines.

3 STOMACH: A juice of enzymes (proteins that speed up chemical reactions) and hydrochloric acid begins to digest proteins. Churning turns your food to mush.

4 SMALL INTESTINE: Enzymes and fluids further digest food into nutrient molecules, which pass through the walls into the bloodstream.

5 LARGE INTESTINE: indigestible food feeds thousands of species of gas-causing bacteria. Also, water is absorbed into the blood, solidifying waste.

6 THE END: Solid waste sits in the rectum until it is expelled. The waste is half bacteria by weight.

CHECK FOR UNDERSTANDING

DIRECTIONS: Match the word in the left column with the correct phrase in the right column.

--1. gastroenterologist        a. food that is broken down into its
                                  smallest parts
--2. esophagus                 b. doctor of the stomach and intestines
--3. eructation                c. wavelike contractions in the small
                                  intestine
--4. epiglottis                d. convert nutrients into energy
--5. nutrients                 e. burping
--6. peristalsis               f. low grumbles that originate in the
                                  small intestines
--7. borborygmi                g. tube connecting the throat to the
                                  stomach
--8. metabolize                h. tissue flap that prevents swallowed
                                  food from entering the lungs

ANSWERS

1. b 2. g 3. e 4. h 5. a 6. c 7. f 8. d