Copyright Notice

This report is copyrighted by Harvard University and is protected by U.S. and international copyright. All rights reserved.

Here’s what you CAN do

• Print out one copy and route this “original” to family.

• You are permitted to have one copy of this publication on your computer at any time (you can’t put it on a network unless you purchased a license to do so). If you have paid for more copies, then you may have that many copies on computers at any time.

• Copy, on an occasional basis, a couple of pages to give to friends, family members, or colleagues.

• We are registered with the Copyright Clearance Center (CCC). You can comply with the copyright laws by paying a royalty on copies you make of passages. But not even the CCC can authorize cover-to-cover photocopying or wholesale electronic forwarding.

• If you want to distribute copies of this publication, either in print or electronic form, to others on a regular basis, ask us about bulk discounts or licensing opportunities. You may be able to negotiate an agreement, for a single fee, that would enable you to legally distribute photocopies or electronic copies to others.

Here’s what you CAN’T do
(without prior permission)

• Make or forward email copies of an entire publication. The law provides for a very limited amount of copying, commonly referred to as “fair use.” However, cover-to-cover photocopying is forbidden.

• Electronic transmission of a copyrighted work is the legal equivalent of photocopying it (and so is posting it on the Internet or in an electronic database), and is therefore not allowed.

• Routinely copy and distribute portions.

• Republish or repackage the contents.

Some publishers must resort to lawsuits to protect their publications. Harvard Health Publications would like to eliminate the need for such suits by helping to educate customers. We hope this outline has helped explain what is legal and what is not.

Contents

Inside the gut

The digestive journey

The aging GI tract

SPECIAL BONUS SECTION: The Stress Connection

Gastroesophageal reflux disease

Causes of GERD

Diagnosing reflux

Complications of reflux

Self-help for reflux

Antireflux drug therapy

Herbal remedies

Surgical options for reflux

Functional dyspepsia

Diagnosing FD

Tests and medication

Causes of FD

Treating FD

Irritable bowel syndrome

What is IBS?

Causes of IBS

Diagnosing IBS

Managing IBS

Constipation

How constipation happens

Causes of constipation

Diagnosing constipation

Treating constipation

Diarrhea

What is diarrhea?

Causes of diarrhea

When to call the doctor

Diagnosing diarrhea

Treating diarrhea

Preventing diarrhea

Excessive gas

Where does gas come from?

A gas primer

Diagnosing and treating aerophagia and flatus

Treating belching

Treating flatulence

Resources

Glossary

Dear Reader,

Out of sight, out of mind, your digestive system is working around the clock delivering the nutrients in food to your bloodstream. As long as the system is running smoothly, you need not think about it. Once trouble begins, however, your gut—like a squeaky wheel—suddenly demands your attention.

For some folks, symptoms such as diarrhea, gas, cramps, heartburn, indigestion, belching, bloating, and nausea are infrequent and tolerable, but many people experience them far more often. An estimated one in four people has frequent gastrointestinal problems that can severely disrupt a normal lifestyle. And the number of prescriptions for gastrointestinal medications has soared since the late 1990s, according to federal statistics.

Although the misery that such problems inflict is real, these ailments aren’t usually the product of an illness in the conventional sense. Often, they are functional gastrointestinal disorders. That means, unlike ulcers or stomach cancer, they can’t be attributed to any physical abnormality or infection. More than 20% of people who consult a gastroenterologist learn that there’s no structural abnormality to explain their complaints.

Just because we doctors can’t find a physical cause—meaning that there’s no evidence of disease or a structural basis for the symptoms—doesn’t mean you’re imagining things. The symptoms are quite real, and if they occur frequently or last more than a month, it’s a good idea to seek help.

You might be relieved to know that even if your doctor can’t pinpoint the cause of your symptoms, the chances are good you can get relief. This report focuses on a number of disorders considered to be functional: reflux, functional dyspepsia, irritable bowel syndrome, constipation, diarrhea, and excessive gas.

The good news is that our ability to treat gastrointestinal disorders continues to improve. With proper knowledge—and the support of the right combination of health professionals—you can make changes in your lifestyle, use specific medications, find other helpful therapies that will ease your discomfort, and make the right decisions about medical treatments.

Harvard Health Publications | Harvard Medical School | 10 Shattuck Street, Second Floor | Boston, MA 02115

Sincerely,

Lawrence S. Friedman, M.D.

Medical Editor

Inside the gut

The “gut.” It’s an ancient Anglo-Saxon word that refers to the human digestive system. Think of this marvel of nature’s engineering as a perpetual food processor, constantly mixing, grinding, and transforming the meats, vegetables, fruits, and snacks that people eat into biologically useful molecules (see Figure 1, below).

Nearly 30 feet long if stretched out straight, the gut is a series of hollow organs linked to form a long, twisting tube that runs from the mouth to the anus. This string of organs is known as the alimentary canal, gastrointestinal (GI) tract, or digestive tract (see Figure 1, below, and Figure 2). It comprises the esophagus (or gullet), stomach, small intestine, and colon (which includes the rectum). These organs break down food and liquids—carbohydrates, fats, and proteins—into chemical components that the body can absorb as nutrients and use for energy or to build or repair cells. What’s left is expelled by a highly efficient disposal system.

The food you eat travels a winding 30-foot pathway known as the gastrointestinal tract or the alimentary canal. Along the way the mucosa, or the surface layer of cells lining the gastrointestinal tract, produces digestive enzymes and juices that help break down food to be absorbed into the bloodstream.

The organs of the gut are almost always moving, driven by muscles in their walls. These muscles consist of an outer longitudinal layer and an inner circular layer. The coordinated contractions of these layers push food and fluids the length of the canal, just as at the beach, rolling waves deposit sand and shells on the shore. This dynamic movement along the gastrointestinal tract is known as peristalsis.

Helping with the job of digestion is the mucosa, or lining, of the mouth, stomach, and small intestine, which harbors glands that produce digestive enzymes. The salivary glands, liver, and pancreas also secrete juices that help make food soluble (dissolvable in water) so that nutrients can pass easily into the bloodstream.

The digestive journey

Pop a grape, chocolate, or shrimp into your mouth. Immediately, digestion begins (see Figure 2). In the mouth itself, the tongue and teeth help to get the process started by chewing and chopping the food so it’s small enough to be swallowed. Salivary glands secrete saliva, releasing an enzyme that changes some starches into simple sugars and softens the food for swallowing. The saliva also allows the taste buds of the tongue to sense the flavors of your foods.

Swallowing is a complicated, coordinated act that begins when your tongue pushes food back into your throat or pharynx. This voluntary action sets off an involuntary chain of events that transports the food from the throat into the esophagus and down into the stomach, a journey that typically takes eight seconds.

Esophagus

Food does not simply drop down the esophagus by means of gravity. Matter moves through this passageway because it is pushed by contractions of the esophageal muscles.

Think of the esophagus (along with the intestine) as an empty tube surrounded by layers of muscle that contract in a succession of waves. As the ball of food, called a bolus, travels toward the far end of the 10- to 13-inch-long tube, the lower esophageal sphincter opens to allow the food to exit, then closes again. This esophageal tube is quite elastic, stretching to nearly two inches across to accommodate foods of various sizes.

While the esophagus is moving things along, it also has to keep things from backing up (regurgitating) and re-entering the throat. That’s where a gatekeeper, known as the upper esophageal sphincter, comes into play. The two sphincters, upper and lower, make sure the food doesn’t back up in the wrong direction.

Stomach

If the esophagus is a conduit with a valve at each end, the stomach can be likened to a storage and processing facility, where the food is prepared for digestion.

This food warehouse can accommodate anything from a light afternoon snack to a five-course meal. Without this large storage capacity, people would have to eat small, frequent meals, and they’d be unable to drink large quantities of liquids at any given time.

But the stomach doesn’t just hold food: muscles in the lower stomach also mix that food into a soft mush. This process is aided by the liquids we drink and by saliva, hydrochloric acid, and the enzyme pepsin. Hydrochloric acid and pepsin, produced by the glands that line the stomach, help break down proteins into their constituent amino acids. The stomach mucosa has a defense system, including an overlying layer of mucus and bicarbonate, to protect itself. After mixing, a once-palatable meal is reduced to a thick liquid called chyme.

The other important function of the stomach is delivering the resulting chyme to the small intestine in amounts it can handle. The involuntary contractions that push stomach contents along are governed by nerves in the stomach wall (see Figure 3), which transmit electrical impulses to the brain. The nerves that carry impulses from the GI tract, called visceral nerves, recognize stretching, pulling, or expansion (distension) of the muscles in the walls of the digestive tract. Pain can result when these sensations are excessive.

When you haven’t eaten for a while and your stomach is empty, it initiates a series of rhythmic contractions known as hunger pangs. They serve as a signal to the brain: “Feed me!” These contractions explain stomach noises, which also can be caused when air or fluid is moving around inside. Once you’ve eaten, it takes about two hours for the muscular stomach to reduce a typical meal to a liquid and have it ready to move along to the small intestine. A high-protein meal can take an extra hour or two. A high-fat meal can take up to six hours. That’s why eating foods with healthy fats (such as those in nuts) helps you feel full longer than eating high-carbohydrate foods like sugar.

The time it takes for food to pass all the way through the digestive tract can be anywhere from nine hours to over three days.

Small intestine

The small intestine, which is a remarkable 21 feet long, is the next stage on the journey that food makes through the digestive tract. The main work of digestion takes place in this long tube. The small intestine breaks down fats, starches, and proteins into fatty acids, simple sugars, and amino acids, which it can then absorb.

The food you eat generally takes three to five hours to move through the small intestine. During this time, the food is bathed in digestive enzymes and juices that flow into the intestine through ducts from the liver and pancreas. Bile, produced by the liver and stored in the gallbladder, emulsifies fat, enabling its absorption. Enzymes secreted by the pancreas, such as trypsin, amylase, and lipase, help digest proteins, carbohydrates, and fats. Once reduced to products the body can manage, the nutrients from digested food are absorbed by the intestine’s thin lining and sent to cells throughout the body by way of the bloodstream and lymphatic system.

Food moves through the small intestine as if on a conveyor belt. The first step, after the stomach empties food through the pyloric sphincter, is the foot-long duodenum, located a few inches above the navel. Many minerals, such as iron and calcium, are absorbed in the duodenum. This is also where bile and pancreatic juices join the mix.

The stomach lining (mucosa) is not a smooth, balloon-like surface. Instead, it has several layers that contain neuron connections to the brain as well as glands that secrete juices to help digest food.

©Harriet Greenfield

After the duodenum, the next part of the small intestine is the jejunum, which measures eight feet in length. In the jejunum, fats, starches, and proteins are further broken down and absorbed.

The third and lowest portion of the small intestine, the ileum, is approximately 12 feet long. The ileum absorbs water, as well as vitamin B₁₂ and bile salts.

Colon (large intestine)

Finally, what’s left of the food arrives in the colon, or large intestine, a four-foot-long muscular tube about the diameter of your fist, where the walls act like a sponge and soak up 80% to 90% of the remaining water. In fact, the colon accepts about a quart of liquid from the ileum each day. Once inside the colon, food residue travels up the right side (the ascending colon), across the transverse colon, down the left side (the descending colon), through the sigmoid colon to the rectum (behind the left side of the groin), and out of the body. The time required for food to move through the colon varies widely, but is generally in the range of four to 72 hours.

Bacteria that reside in the colon help in the digestive process, feeding off whatever remains of your meal. The bacteria produce fatty acids as well as hydrogen, carbon dioxide, and, in some people, methane gas. Some of these gases are consumed as nutrients by the cells of the colon, while others are expelled as waste. Undigested matter, such as fiber, is propelled along by contractions of the colon wall and settles as solids in the rectum, the final six inches of the colon.

The end of the rectum is guarded by sphincter muscles that help control what goes out. The waste accumulates until the rectal wall becomes so distended that it signals the internal anal sphincter to relax, triggering the urge for a bowel movement. Fortunately, the external anal sphincter, which is under voluntary control, keeps the rectal contents in place until a convenient time.